EPISODE: 028 - APPROVED DOCUMENT L - CONSERVATION OF FUEL AND POWER - VOLUME 2 - BUILDING OTHER THAN DWELLINGS
- Piotr Bytnar BEng (Hons) MSc CEng MIStructE
- Nov 5, 2024
- 35 min read
Updated: Jun 25
BYTNAR - TALKS
EPISODE 028 - APPROVED DOCUMENT L - CONSERVATION OF FUEL AND POWER - VOLUME 2 - BUILDING OTHER THAN DWELLINGS
This episode is for people who want to know more about Approved Document Part L – Conservation of Fuel and Power – Volume 2 – Buildings Other Than Dwellings.
You should like this episode if you ask yourself questions like:
What are the requirements for calculating target primary energy and emission rates for non-domestic buildings under Approved Document L?
How do I ensure accurate as-built energy performance calculations for a building with multiple fuel sources?
What is the mandatory assessment process for high-efficiency alternative systems, and what should the feasibility report include?
What are the U-value limits and airtightness standards for fabric performance to minimize heat gains and losses in commercial buildings?
What are the efficiency standards for building services, and how should systems be sized and controlled for energy conservation?
What energy efficiency guidelines apply to heating, ventilation, and Combined Heat and Power (CHP) systems in large non-residential buildings?
How are air permeability tests conducted for non-domestic buildings, and what standards and exemptions apply?
What is the purpose of a Building Log Book for energy-efficient operations, and what must be included for buildings over 1000m²?
What are the requirements for consequential improvements in energy performance when extending or renovating large non-domestic buildings?
This is Bytnar Talks: The Engineer Takes on Construction, Episode 28.
Hi, I’m Piotr Bytnar. Each day I help my clients plan and design building projects through Bytnar Limited, a consulting Chartered Structural Engineers practice.
My biggest passion—and the cornerstone on which I’ve built my business—is finding clever solutions for construction projects. I am a Chartered Structural Engineer and a budding software developer, so you can rest assured that I will strive to talk about best practices and the use of new technologies in the industry.
If you're embarking on a construction project, or are involved in planning, designing, and building the world around us, you’ll find this podcast useful.
Approved Document L: Conservation of Fuel and Power, Volume 2 – Buildings Other Than Dwellings
Hi, and welcome to Bytnar Talks, your favorite podcast on all matters of architecture, engineering, and construction.
It is Thursday, the 5th of September, 2024—so, yet another fortnightly release of the episode—but I’m here, back with you, with the 28th episode and information on Approved Document L: Conservation of Fuel and Power, Volume 2 – Buildings Other Than Dwellings.
The last episode was the longest of them all so far, so I’ll try to keep this one a bit slimmer.
It has been another busy week, and the weather out there is sort of heading for the worse. Seems like the British summer started to shift toward September—which was nice last year—but it doesn’t seem to be the case this year.
As ever, before I go into covering the material for this episode, let’s have a look at what was covered last week.
In the last episode, I talked about the first volume of Approved Document L: Conservation of Fuel and Power, dealing with dwellings. These are contained within Part L requirements and 19 additional regulations, covered in 12 sections of the document.
Section One describes the process for calculating the total energy performance of new dwellings using the Standard Assessment Procedure (SAP), with key metrics including target primary energy rate, emission rate, and fabric energy efficiency rate. For buildings with multiple dwellings, these targets may be averaged based on floor area.
Section Two deals with the calculation of actual energy performance metrics, which must be compared to the target values described in Section One—as designed, and then again after construction. These calculations are documented in the BREL report and submitted to Building Control, with considerations for fabric efficiency and low-carbon technologies.
Section Three requires a feasibility analysis of high-efficiency alternative systems—such as renewable energy and heat pumps—before construction begins. This analysis must be documented and made available for inspection, regardless of whether the systems are implemented or not.
Section Four specifies limitations on heat gains and losses. It emphasizes U-values and continuous insulation to prevent thermal bridging at the joints of thermal element planes. It sets minimum U-values for new and existing dwellings, with strict standards for renovations, ensuring airtightness and proper insulation.
Section Five mandates that new and replacement building services meet minimum efficiency standards and be correctly sized, with a focus on low-temperature heating systems and appropriate controls. Existing buildings must also adhere to these standards to prevent energy waste.
Section Six outlines performance standards for heating, cooling, ventilation, and energy generation systems—requiring high efficiency, appropriate controls, and proper sizing. It also covers district heating, underfloor heating, and on-site electricity generation to ensure overall energy efficiency of the building.
Section Seven mandates pressure testing for new dwellings to ensure compliance with air leakage regulations. Certified professionals must conduct this test, with results submitted to Building Control and energy metrics recalculated based on the outcomes.
Section Eight requires the commissioning of fixed building services and on-site electricity generation systems. A detailed commissioning plan must be submitted to Building Control. Compliance must be confirmed within up to 30 days when we talk about the person who’s registered under the approved person scheme—or 5 days if we deal with building notice or with full plans approval. We need to ensure the systems operate properly and meet the standards.
Section Nine requires that building owners receive clear, detailed information on the operation and maintenance of fixed services and on-site electricity generation systems. Upon completion, new buildings also need a BREL report and an Energy Performance Certificate, with updates required for significant changes in existing buildings.
Section 10 mandates that new or replacement thermal elements in existing dwellings meet specified performance standards, particularly for major renovations or replacements. Extensions and integrated conservatories must also adhere to this criteria, ensuring energy efficiency is maintained.
Section 11 stipulates that buildings undergoing a material change of use, renovation, or energy status change must comply with relevant energy efficiency and thermal performance standards. Major renovations must meet updated criteria, with SAP procedures used for assessing energy use in multiple dwellings.
Section 12 requires that work on existing buildings over 1,000 m² involving extensions, implementation of new services, or increased service capacity comply with Part L requirements, provided it is feasible. Renewable energy installations are exempt, with further guidance in Volume Two of the approved document.
In this episode, I will move to Approved Document L: Conservation of Fuel and Power, Volume 2 – Buildings Other Than Dwellings. So, without further ado, let's dive straight into it.
In this episode, I’ll talk about the statutory guidance contained within Approved Document L: Conservation of Fuel and Power, Volume 2 – Buildings Other Than Dwellings.
The requirements in Part L are short and sweet—only two—but they are fairly expanded by 17 different additional regulations, including Regulation 6, some regulations from Part 6 of the Building Regulations, as well as Part 8 and Part 9.
These are basically the same requirements as with dwellings, with slight differences. For example, there are no Regulations 26A, or 27A included—so aspects concerned solely with dwellings are excluded.
This episode will follow the structure of the approved document, from Section 0 to Section 12, and will include all the additional regulations along the way, as laid down in the document. But I will not return to reading you the text of the legislation—as that was already done in the previous episode.
I strongly recommend you listen to that episode, as the philosophy and layout of the approach is very similar, and I trust it will help consolidate your knowledge about these requirements.
Let’s get into the nitty-gritty of this approved document.
All right guys, let us start with Section 0, which simply introduces us to the document—stating what is included within it and its application.
It overlaps heavily with Volume One, but we will find differences, like information on different provisions for the shell and core (first-fit) commercial buildings, and then afterwards, considering second-fit as work on the existing building.
Modular builds will be treated as a new building, and if this technology is used for extension work, the building may need an upgrade.
In general:
Work on new buildings is covered in Sections 1 to 9
Work on existing buildings is covered in Sections 4 to 6, and 10 to 12
Some buildings are exempt, such as:
Places of worship
Temporary buildings used for less than two years
Low-energy demand buildings
Industrial sites
Workshops
Non-residential agricultural buildings
Standalone buildings of up to 50 m² useful floor area (also called gross floor area)
Carports, covered yards, and covered ways
Some conservatories and porches are also exempt, and the same rules apply as in the previous volume of this document.
Similar provisions, as previously, are given to open extensions of buildings at the ground level and in an area of less than 30 m², as well as to live/work units and mixed-use units.
Exemptions are also given to:
Historic buildings
Monuments
Listed buildings
Buildings in conservation areas
The upgrade of such buildings should apply within reasonable intervention criteria, so they need to be judged on their particular merits.
The guidance contained within this document needs to be approached holistically, along with other aspects of the building regulations—things like:
Ventilation
Transfer of moisture
Condensation
Noise transfer
Airtightness, and so on.
Moving to Section 1, which covers calculations of:
Target Primary Energy Rate
Target Emission Rate
These two energy rates apply to a so-called notional building, which is of the same size and volume as the proposed building, but using standardized fabric and services specifications. We can find the full properties in the National Calculation methodology modeling guide, available at www.uk-ncm.org.uk.
The Target Primary Energy Rate is stated in kilowatt-hours per square metre per year (kWh/m²/year), and the Target Emission Rate is measured in kilograms of CO₂ per square metre per year (kgCO₂/m²/year).
The calculation should be made using the Simplified Building Energy Model—the so-called SBEM—or another approved software tool, in line with the current policy version. These software tools, like listed, can be found on the Department for Levelling Up, Housing and Communities (DLUHC) website. A version of the approved methodology or guidance on which one to use can be found in the National Calculation Methodology (NCM) modeling guide.
Now, these rates will be compared with the outcomes of the "as-designed" and "as-built" calculations, just as was the case with dwellings. Nothing really changes here—we set the targets, we design to meet them, and then we check whether what we’ve built meets them. Simple as that.
Section Two
Section Two deals with the calculation of the building's Primary Energy Rate and Building Emission Rate, which are to be compared against the target values. As before, we should use the same tools for the calculation, and do it both at the design stage and once the building is as built.
The as-built calculations should take into consideration what was actually installed on site, including the measured air permeability of the building.
Both the target, design, and as-built rates—together with the specification—need to be communicated to Building Control. This will usually follow the output of approved software using the BRUKL report standard (Building Regulations UK Part L report).
Now, taking into consideration the source of fuel, the calculations for Primary Energy may become slightly more complicated when systems can be fired by two fuels—like biomass and gas, or biomass and fossil fuel, or others.
In the first case, we need to use a weighted average of CO₂ emissions, based on the usage ratio.
In the second case, similarly—unless the appliance is in a Smoke Control Area, in which case the anthracite figure needs to be used.
For other combinations, the higher CO₂ emission case should be applied.
Using district or community heat networks will require us to establish primary energy factors and CO₂ emission factors suitable to that network. The National Calculation Methodology Guide provides relevant information for this.
The calculation should:
Take into account the entire system;
Consider the annual average performance;
Factor in heat recovery, all plant losses, combined heat and power (CHP), or heat dumping.
The calculations should use the first 12 months of operation as a baseline for any future increases or decreases in system capacity.
CHP or Tri-generation schemes should use factors from the National Calculation Methodology Guide (e.g. Table 32). In the case of tri-generation, the energy used should be attributed proportionally to its actual use—i.e., what is used to supply heat or to remove it in district networks.
The calculation should reflect the energy source that will be used until the end of 2027, so that any future changes can be anticipated. When the change comes, it must be operationally and legally sound—meaning it must have planning permission, where required, and be contractually secured.
Building Control will need to see proof of this.
All of this must be accompanied by a report from a suitably qualified person, showing how the factors were derived.
The document provides an equation for the calculation of the primary energy factor, which is essentially:
(Energy input – energy generated by the system) ÷ useful heat (in kWh)
A similar equation applies for the CO₂ emission factor, but using CO₂ emissions instead of system efficiency.
We can reduce the design rates for energy and emissions if we intend to use enhanced management and control features for the heating system.
This follows from the increased efficiency of a well-controlled system:
We do not waste heat when it’s not needed;
We improve system operation by matching output to actual demand.
This makes the system more efficient.
The adjustment factors allowed are:
1% for achieving a power factor between 0.90 and 0.95
2.5% when exceeding 0.95
5% with a total control system
Finally, the document informs us that only following the minimum fabric element standards will not be enough to meet the Target Primary Energy Rate or the Target Emission Rate—and that the approach will need to be combined with efficient building services and low- and zero-carbon technologies.
Special considerations for the calculations of rates should be given to:
Modular and portable buildings with a service life of over two years
Swimming pools
Shell and core developments
Industrial sites
Workshops and non-residential agricultural buildings
Buildings with low energy demand
Modular and Portable Buildings
Let’s start with modular and portable buildings — the ones that are in operation for more than two years.The building regulations consider the placement of a module on a new site as the construction of a new building, and distinguish between:
Modules placed on one site, and
Those that move from site to site
The stationary ones should comply with the energy efficiency requirements. However, if at least 70% of the elements were manufactured prior to the implementation of this consideration, the factors can be extended by up to 68% for elements manufactured before the 6th of April 2006.
When it comes to portable buildings or modules that move between sites, these also need to comply with the energy efficiency requirements.The calculations should be made once the building is constructed for the first time.
For allocations where buildings then stay on site for less than two years, that initial calculation will suffice, but the target emission rate should still take into account the use of electric resistance heating, following the National Building Specification.
The same 70% rule for shell construction also applies here.However, in this case, the extension factor can be as high as 103% for elements manufactured before 6th April 2006.
Swimming Pools
Swimming pool basins are treated similarly to dwellings.We need to consider the fabric of the pool enclosure, including the area of the pool in our calculations.
Shell and Core Developments
Shell and core developments, on the other hand, must prove that they will meet the target once the building is fully fitted out.Only the design-stage rates apply here.
The design should specify:
What systems are being installed, or
What systems ought to be installed at the time of fit-out
At the time of completion, we should assume to what extent the space will be conditioned, and that assumption needs to be carried forward.The incoming occupier will then be required to abide by this assumption to demonstrate compliance — whether that be with heat management or lighting.
A new energy certificate will be required for the fit-out work in areas. Building logbook should be completed with the first fit-out work information.
Industrial Sites
When we assess industrial sites, the National Calculation Methodology (NCM) modeling guide may fail to recognize the feasibility of the project — in which case, we may need to resort to in-depth evaluation.
Buildings with Low Energy Demand
Buildings with low energy demand are considered if they need to be heated, but not to the level of typical buildings or not entirely.Rates still need to be calculated — but to different standards, which can be found in the NCM modeling guide.
In such buildings:
Each service still needs to meet energy efficiency standards
Services must be appropriately insulated
The opaque building fabric cannot be worse than 0.7 W/m²K
Partitioned or zoned heating should meet normal standards
When such buildings change use to a building of normal energy demand, they may need improvement.
Similarly, when a shell and core building of low energy use is fitted out to be of normal energy use, normal standards will apply.
Section Three
Section Three, similar to dwellings, again considers high-efficiency alternative systems.We should assess the technical, environmental, and economic feasibility of such systems and compile it into a report, which must be made available for viewing by Building Control.
Section Four
Section Four deals with the fabric performance regarding heat gains and losses.
BRE Report 443 is used for the assessment of elements. In the case of windows, the glazing and frame are considered together and treated as a controlled fitting.
When it comes to windows, the document gives us options:
We either go into detailed assessment, or
Treat the window as standard, and take size limits on board.
For windows in similar settings to dwellings, the limits are:
1.23 m width ±25%
1.48 m height ±25%
We then either:
Treat it as a particular window configuration, or
Use standard configurations, which relate to framing.
The standard window configuration will not apply to commercial windows.
Alternatively, we can approach the matter using the Hot Box method to BS EN ISO 12567.
When we deal with doors, we follow similar conditions, but the sizes differ slightly. Doors are categorized as under 3.6 m² and over 3.6 m², with standard sizes being 1.23 m × 2.18 m or 2 m × 2.18 m, and again a ±25% variation is allowed on each dimension.
The Hot Box method or using the actual size and configuration is acceptable. Also, be aware that different limits apply depending on the plane of the element — elements placed horizontally need to carry a better U-value.
Generally, all new elements, including those in extensions or replacements in existing buildings, need to follow the set U-value limits. If we are dealing with elements that we cannot change, we may need to add secondary elements to improve performance. The central pane of the component should not be worse than 1.2 W/m²K.
Some of the U-value limits are as follows:
Roofs (flat): 0.18 W/m²K
Roofs (otherwise): 0.16 W/m²K
Walls: 0.26 W/m²K
Floors: 0.18 W/m²K
Swimming pool basins: 0.25 W/m²K
All these values assume an air permeability of less than 8 m³/h/m².
Renovated elements will have slightly different limits, and the condition of the repair will also determine whether or not we need to upgrade the thermal element.
Similarly, for elements that are part of a formal exposure, adapted, or converted spaces, the change also depends on factors of reasonability — like a 15-year payback time, and technical or functional feasibility.
Generally speaking, elements should not lose more than 0.7 W of energy per m² per 1 Kelvin degree difference, and less when considering horizontal elements.
Limiting Factors for Improvements
The threshold and improvement U-values are:
Threshold:
0.35 W/m²K for roofs
0.70 W/m²K for walls and floors
Improvement values:
0.16 W/m²K for ceiling-level roof insulation
0.18 W/m²K for floors
0.25 W/m²K for walls
0.55 W/m²K for cavity wall insulation
0.30 W/m²K for external or internal wall insulation
It is important to:
Maintain continuity of the insulation and
Avoid breaks in it throughout — especially to prevent thermal bridging.
Thermal bridging can be:
Assessed detail by detail using BRE 497 methodology, or
Estimated using typical values from BRE Information Paper 1/06, increased by:
0.04 W/m·K, or
50%, whichever is greater.
In any case, the performance of the detail should exceed the minimums set in the information paper.
Building Control should be satisfied if:
All this is done by a competent person,
It is demonstrated that the detail can be achieved on site, and
There is a robust methodology in place to check if it has been implemented correctly.
When we renovate or replace thermal elements, we must:
Ensure a suitable signed report is produced to account for the change,
Confirm that suitable design details and building techniques have been specified, and
Ensure that the elements provide adequate protection from surface condensation, as identified in BRE Publication 497 and Information Paper 1/06.
We are reminded by the document to:
Mind the airtightness of the building, and
Maintain a good seal with newly installed or replaced elements.
We should also be mindful of solar gain — and for new buildings, this is covered in Approved Document O, about which an episode is coming.
For now, we should keep it to a reasonable level, to give that air-con unit a fair chance.
The consideration is for the usable space — the space we generally operate in and which is air-conditioned.In such cases, solar gain (considered from April to September) should be no greater than the relevant reference system, using the solar energy transmittance, so-called g-values, as calculated according to BS EN 410.
The limit values are:
0.48 for:
Side-lit spaces
East-facing façades
Side and top lighting up to 6 m height
0.42 for:
Roof location, and
Zone height over 6 m
The glazing area taken into consideration is:
Full width up to 1 m height for vertical elements
Up to 10% of the roof area for roof glazing
Building Services and Thermal Gains/Losses
Building services may also add considerable heat gains and losses.
Hot water pipes should always be insulated, unless we want that heat in the room.
Insulation should follow BS 5422, which for low heat pipes in hot water space heating systems, means:
Between 15 mm to 55 mm thickness, for pipes of 10 mm to 100 mm diameter
For coating with thermal conductivity between 0.025 to 0.04 W/m·K
Slightly less insulation is allowed for hot water services
Temperature limits are:
Up to 95°C for heating, and
60°C for hot water
Cooling pipes should also be insulated, unless the cooling load related to distribution pipes is less than 1%, meaning there will be minimal losses from such piping. The insulation should follow BS 5422 heat gain limits and the HVAC guidance of the manufacturer to mitigate condensation.
Heating or cooling air ductwork should also be insulated, with insulation thickness according to calculations made to BS EN ISO 12241. The document states certain specifications for ducts, using assumptions like the size of the vertical sidewall, the nature of the surrounding air, its temperature, and the thermal conductivity limit of the insulation material.
We are told to use:
21 mm insulation for heating ducting, and
36 mm insulation for cooling and dual-purpose ducting.
Hot water storage vessels: Heat loss should be limited to approved levels, and energy consumption controlled to BS EN 12897. According to the document, the rate should be within 2.1 to 5.2 kWh per 24 hours for storage vessels between 22 and 2,000 L.
Section Five: Minimum Building Services Efficiencies and Controls
Services should be efficient, and that is covered in Section Five, which deals with minimum building services efficiencies and controls.
The efficiency claimed should be tested to the appropriate standard and certified by a notified body.
Replacement fixed building services should be at least as good as the existing system, and no worse than the value given in Section Six.
If the replacement service uses a different fuel, we need to assess its CO₂ emissions and primary energy demand. In both cases, the levels should be no worse than the existing system.
Replacement of renewable technology should be like-for-like in terms of output.
Every new heating appliance should be controlled in terms of:
Timing of operation
Temperature, and
Where possible, have weather compensation installed.
We should also consider possible future connection to a district heat network system.
Sizing new and replacement space heating systems should follow appropriate heat loss calculations for the building. These should be based on BS EN 12831-1 and CIBSE Guide B1, ensuring that systems are not significantly oversized.
When a wet heating system is newly installed or fully replaced (including pipework, appliances, and emitters), it should be sized for a 55°C or less flow temperature, or as low as is practical for a given heat source and the building.
Naturally, control of the system is important. Zoning of the heating system and its control can fine-tune the operation.
Zones should be considered based on:
Solar exposure,
Pattern of use, and
Type of use.
Significantly different areas should be made into zones.
Control of timing and temperature should be independent for each zone. Heating and cooling of a given zone at the same time should be prevented by system design. Heating should also have weather compensation where possible, and systems should switch off when not needed.
The system for heating and provision of domestic hot water should be:
Cleaned and flushed out, and
Treated to inhibit scale and corrosion.
The scaling of the feed water may also be necessary to prolong the service life of the system.
All rooms where we need or are able to control temperature should be provided with thermostatic control.
Buildings of low heat demand (under 10 W/m²) and buffer zones in buildings with high thermal mass may not need to be controlled in this way. In cases where it's better to control zones rather than rooms, do so — this is considered for open spaces or adjacent rooms of similar use.
Heat recovery from exhaust air may also be controlled, if technically and economically feasible.
The control of the room or zone thermal condition will be by:
A thermostat in the room, and
Control of each emitter (e.g., fan coil or radiator)
This is known as thermostatic control of the room or zone. Alternatively, individual network heating or cooling emitter control should be used.
Sub-meters should be installed in new buildings with new heating system installations or extensions. The sub-meter should inform us about the use of the particular fuel with 90% accuracy for this purpose.
CIBSE TM39 gives recommendations on how to achieve this.
The information provided by the meter should be:
Good enough to inform us of use and performance,
Allowing comparison with the design-stage energy forecast, and
Should allow for the separation of tenants and the accounting for renewables.
If the building is over 1,000 m², the whole meter reading and data collection should be automatic.
Now we move to Section Six, which gives us specific guidance on the efficiency of systems.
We are straight-up informed about the Ecodesign for Energy-Related Products Regulations 2010 and its requirements, and that we should pay attention to it just as we do to this legislation.
The equipment specified for a given building and its use should be selected to optimize its use in the given circumstance—and that’s the gist of the whole thing.
Now, we go system-by-system, by type:
Boilers
These are considered part of a wet central heating system, fired by commercial boilers using natural gas, LPG, oil, or biomass.
That is it.
The efficiency requirements will be slightly different depending on whether the system is installed in a new building or an existing one.
For new buildings, a single boiler up to 2 megawatts output should be 93% efficient.
The same applies to multiple boilers.
If the boiler output exceeds 2 megawatts, the efficiency can drop to 88%, as it can for a single boiler in a multiple boiler scenario.
The efficiency is considered seasonal and based on the gross calorific value of Natural gas. Systems in existing buildings can be slightly less efficient:
As low as 84% for a single boiler over 2 MW, and
91% for small boilers and multiple boiler systems.
Other fuel type efficiencies should meet or exceed the standard set for new buildings.
We are also informed that whenever possible, we should think about retrofitting non-condensing boilers with a flue condensing kit—that is, whenever feasible.
Seasonal Efficiency Calculations
The way we arrive at seasonal efficiency for single boilers and multiple boiler systems with identical boilers is by the following equation:
Use the boiler’s gross efficiency at:
30% load, and
100% load,
Then weight them in a proportion of 81% to 19%, respectively.
This equation applies to single boilers and multiple boilers supplying low-temperature hot water of output up to 400 kW.
For boilers over 400 kW, we should use the manufacturer's declared efficiencies.
For more varied systems, the calculation is a bit more involved but relatively simple, following the same principle of:
Combining efficiency at different load levels, and
Weighting based on proportional output contribution.
If the boilers vary in their output and efficiency, we should weight their involvement by the percentage of their output in the building's operation.
Boiler Controls
Boilers over 100 kW output should have:
Optimum start and stop control, with
Either night setback or frost protection outside occupied periods, and
Either a stage (high/low) firing facility in the boiler or
Multiple boilers with sequential control to provide partial-load performance.
When gas-fired and multi-stage oil-fired boilers exceed 500 kW output, they should have fully modulating burner controls.
Biomass Boilers
Tested to BS EN 12809
Efficiency should be no lower than:
65% for gravity-fed systems under 20.5 kW output
75% for automatic pellet or wood chip systems
Gas and Oil-Fired Warm Air Heaters
Depending on how they deliver heat, they should be at least 91% efficient.
They are regulated by the following standards:
BS EN 621 – Non-domestic gas-fired forced convection air heaters for space heating not exceeding a net heat input of 300 kW without a fan to assist transportation of combustion air and all combustion products.
BS EN 1020 – Non-domestic forced convection gas-fired air heaters for space heating not exceeding 300 kW, incorporating a fan to assist transportation of combustion air or combustion products (withdrawn).
BS EN 525 – Non-domestic direct gas-fired forced convection air heaters for space heating, not exceeding 300 kW.
BS EN 13842 – Oil-fired forced convection air heaters, stationary and transportable, for space heating.
Whew—that was quite a series of Kalashnikov standards… one by one, in automatic rounds!
Gas and Oil-Fired Radiant Heaters
If flued, they should be tested to BS EN 1020 or BS EN 13842.
The efficiency is considered using the net calorific value, and should:
Exclude fans, and
Account for the radiant heater and piping within the building envelope.
Efficiencies, depending on appliance type, are generally:
86–91% thermal efficiency, and
Over 55% radiant heat generation efficiency
Electric Space Heating Systems
These are considered to be 100% efficient. For Boiler systems should have flow temperature control and be capable of modulating the power input to the primary water depending on space heating conditions, timing, and temperature demand control.
Heating controls must be split into zones for buildings over 150 m².
For electric warm air heating, we need to consider:
Timing and temperature demand control, as well as
Zoning
Radiant heaters should have automatic zone or occupancy presence detection.
Panel heaters should have timing and temperature demand controls.
Storage heaters should also be controlled by required input, in line with the internal temperature, but with manual override.
Combined Heat and Power Systems (CHPs)
So-called CHPs, with capacity between 5 kW and 5 MW, used in commercial applications, are covered here.Smaller installations should follow Volume One recommendations for dwellings.
Such CHPs under annual operation should have:
A minimum CHPQA Quality Index of 105, and
A power efficiency greater than 20%
The plant should be metered to measure:
Electricity generated, and
Fuel supply to the CHP
Control should ensure it operates as the lead heat generator.
Dedicated Domestic Hot Water Heaters
These efficiency standards apply to:
The heat generator, and
Any integral storage vessels, but not:
Secondary pipework,
Fans,
Pumps,
Diverter valves,
Solenoids,
Actuators, or
Supplementary storage vessels
The system should be appropriately sized, based on BS EN 12831-3.
The efficiency standards are generally:
Over 91%, and
Over 92% for LPG-fuelled types
Whether combustion-heated or electrically-heated, domestic hot water systems should be controlled by:
Time,
Temperature,
Flow control, and
Emergency shut-off (among other controls)
Comfort Cooling
These recommendations do not apply to:
Evaporative, or
Desiccant cooling systems
Each cooling unit should meet its seasonal energy efficiency ratio (SEER), which will depend on:
The type of unit, and
Its power rating
The cooling system specification should be based on heat gain calculations per CIBSE Guide A, and should not be significantly oversized—meaning:
Not larger than 120% of the designed cooling load
Like all systems, cooling should be:
Controlled, and
Divided depending on the needs of each space
Control of the cooling system should comply with BS EN 15232 B/C.
We are provided with a formula for the calculation of SEER, depending on:
Load conditions and
Efficiency ratios at 25%, 50%, 75%, and 100% load
SEER should be determined using BS EN 14825.
There are different variations for chillers, depending on:
Known or unknown parameters
Multiple chillers in a plant
Systems with free cooling or heat recovery
Variable refrigerant flow
Absorption chillers using CHPs, or
District cooling schemes
Heating and Cooling Systems: Circulators and Water Pumps
On variable volume systems, variable glandless circulators should be used in closed-loop systems.
If the water pump motor is rated at more than 750 watts, it should be controlled by a variable speed controller.
Heat Pumps
Air-to-air heat pumps up to 12 kW output should have either:
A seasonal coefficient of performance (SCOP) for a medium temperature range, of at least D, according to BS EN 14825, or
A coefficient of performance (COP) of:
Not less than 2.5 for space heating
2.0 for hot water heating
0.5 for absorption-type heat pumps, and
1.0 for gas engine heat pumps
Any outdoor fan should be controlled, and all heat sources should be incorporated into a single control mechanism.
Mechanical Ventilation
There are many factors to consider here.The bottom line is that we need to:
Satisfy the needs of the building and its occupation
Do it in a reasonable and controllable way
And not use energy when it is not needed
Several standards are referred to, including:
BESA DW/144 – Specification for sheet metal ductwork
BS EN 1507 – Ventilation for buildings, metal air ducts, rectangular section, requirements for strength and leakage
BS EN 12237 – Ventilation for buildings, ductwork strength and leakage of circular metal ducts
BS EN 13403 – Ventilation for buildings, non-metallic ducts made from insulation duct boards
BS EN 1886 – Ventilation for buildings, air handling units, mechanical performance
BS EN 16798-3 – Energy performance of buildings, ventilation for non-residential buildings, performance requirements for ventilation and room-conditioning systems modules M5-1 through M5-4
BS EN 1850 — Fan coil unit performance: determination of specific fan power — provides the test method.
To establish limits on the Specific Fan Power (SFP) for a given scenario.
SFP is measured in watts per litre per second (W/L·s).We need to refer to the table provided in the document, where we will find different values for new and existing buildings.
The SFP value at 25% of the design flow rate should not be higher than that at 100%.
Fans that are rated over 1,100 watts should be fitted with variable speed drives.
Ductwork needs to be reasonably airtight, as should air handling units, which should comply with Class L2 to BS EN 1886, and so on.
Heat recovery should be used whenever possible.
Lighting
In short, lighting needs to be sufficient for the space and activity.Design should be based on the CIBSE SLL Handbook or a similar design guide.
General lighting should have an efficacy of 95 lumens per watt, or follow the LENI method (Lighting Energy Numeric Indicator).
For display lighting, the standard is 80 lumens per watt, or up to 0.3 W/m² power use — or again, follow the LENI method.
For high excitation purity light sources, we go down to 65 lumens per watt.
Lighting energy usage should be metered, either by:
Separating it into material circuits,
A meter coupled into the lighting system controller, or
Through a lighting management system.
We are directed to BRE Digest 498 for more information on lighting control.
We are told to control lighting wherever possible, including:
Switching off when a space is not occupied or is well-lit during the day, and
Separating display lighting on a dedicated circuit.
Building Automation and Control Systems (BACS)
These systems need to be installed when a building’s heating or air-conditioning effective rated output exceeds 290 kW.(Though it is prudent to have controls even on smaller systems.)
At a minimum, manual switches should be provided to turn off appliances when not needed.
Effective rated output includes:
All components that use energy to condition the space, but
Excludes heating for:
Emergencies
Frost protection
Domestic water
Industrial processes
We must account for the heat network delivery and capacity of appliances, when appropriate, and consider the final stage of the building’s use.
The BACS specification should comply with BS EN ISO 16484, and should:
Continuously monitor,
Log,
Analyze, and
Allow for adjustment of energy use.
It should:
Automatically detect losses,
Benchmark performance, and
Inform the responsible person about opportunities for improvement.
It must be capable of integrating all building systems under one control, regardless of the type, manufacturer, or model of system or appliance.
We are told that Class A control systems, as per BS EN 15232, meet the requirements.But as ever, this should always be appropriate to the building's expected use and service specification.
On-Site Electricity Generation and Storage
Such systems should be appropriately sized to meet demand.When replaced, they should not be smaller than what is needed.
The system should be fully automatically controlled.
District Heat Networks and Community Heating
In such cases, the heat source should comply with minimum standards, and should not emit more than 0.35 kg of CO₂ per kilowatt of heat delivered to a new building.This must be checked against the building’s emission rate.
Section Seven: Permeability and Pressure Testing
The minimum standard for permeability is 8 m³/h/m² at 50 Pascals.We need to prove our building is sealed well enough to meet or exceed this target.
We must prove to Building Control that the test was conducted properly using:
Well-calibrated equipment, and
Qualified personnel
Calibration must be:
UKAS-accredited,
Done every 12 months, or at least every 24 months, and
In accordance with CIBSE TM23.
The person conducting the test must also be:
Trained, and
Registered to test the specific class of building.
Certain buildings do not need testing if specific conditions are met, such as:
Buildings under 500 m² total useful floor area, if:
The air permeability used to calculate the Building Primary Energy Rate and Building Emission Rate is assumed at 15 m³/h/m², or
The building is factory-made modular construction under 500 m²
is to be used for more than 2 years in general, and modules are linked using standard details, the base data for this particular unit should have been established in C2 previously.
So you can do it, but with caveats:
For large extensions, if it is not practical to seal it off from the main building, we may need to treat it as a complex building.
In the case of complex buildings, where testing may not be practical, we need to justify why that is and how we intend to achieve a continuous air barrier in our building.
The justification strategy for the air barrier may suffice for Building Control purposes.
TM23 publication is the point of guidance, and we should not try to push the claimed air permeability to values lower than 5 m³/h/m² at 50 Pascals.
For compartmented buildings, it may be sufficient to test a representative area only.
The Building Emission Rate and Primary Energy Rate must still meet the target and be recalculated after testing to confirm this is the case.
If the building fails the test, we must improve it, and a record of all tests must be submitted to Building Control.
The procedure for testing is approved and contained within CIBSE’s TM23 publication.
Section Eight: Commissioning
We are told that fixed building services need commissioning to ensure they are fit for purpose, meaning:
Fuel and power are not wasted
Energy generation is reasonable for the circumstances
This means testing and adjusting the system to meet actual needs.
For large and complex projects, a commissioning manager should be appointed.Their skill set and knowledge should align with CIBSE’s Commissioning Code M requirements.
If we install a system subject to Energy Efficiency requirements, a commissioning plan must be prepared that addresses:
The systems to be tested
The tests to complete
A schedule of commissioning
Defined roles and responsibilities
Documentation requirements
Building Control will need to receive:
The commissioning plan,
The target energy and emission rates, and
Will monitor the commissioning as the build progresses.
Commissioning should follow:
CIBSE’s Commissioning Code M,
Or a combination of specific CIBSE commissioning codes, and/or
BSRIA commissioning guides relevant to the services installed
Including the procedure for leakage testing of ductwork
A notice of completion must be submitted to Building Control and the building owner, confirming:
That the commissioning plan was followed
That all systems have been inspected in appropriate sequence
That systems meet a reasonable standard
That performance is as intended, or
Comments on any shortcomings, where systems do not perform as expected
The notification period is 5 days after completion, or up to 30 days if the person commissioning the work is registered under the Competent Person Scheme.
Ductwork Leakage Testing
If the system is served by fans with a design flow rate over 1 m³/s, a leakage test should be carried out following the Building Engineering Services Association (BESA) documents:
DW/143, and
DW/142
If we test at least 10% of low-pressure ductwork to DW/143, we can calculate an improvement on building energy rates, in line with the National Calculation Methodology modeling guide.
The document recognizes:
BESA’s Specialist Ductwork Group (OADCA / ATCAS) — The Association of Ductwork Contractors and Allied Services — as a competent organisation
So their members will be considered competent too
Leakage limits are specified, and if the ductwork fails, it must be improved and retested.
Limits vary depending on the class of ductwork, from:
Low to high pressure, Classes A to D,
With maximum positive/negative pressures,
And maximum air velocities expressed in litres per second per m²
Section Nine: Handover and Information Requirements
This section tells us what information must be provided.
We refer to the building logbook, which should follow CIBSE TM31 publication.This is where the operating and maintenance instructions should be recorded — and handed over to the building owner.
This logbook can relate to:
Maintenance manuals, or
The Health and Safety File
We are directed to seek further guidance in BSRIA BG 26/2011 publication.
The information provided should allow for the energy-efficient operation of the building.This includes details about:
The building itself,
Fixed building services,
On-site electricity generation, and
The maintenance requirements of the fixed building services and on-site electricity generation, as well as a copy of the complete commissioning records.
Large buildings—meaning those over 1,000 m²—will need a detailed assessment (or forecast, if you like) of their energy use per fuel, determined using a combination of:
Design calculations,
Energy benchmarks, and
Energy forecasting methodology, such as CIBSE TM54, or other building modelling or spreadsheet tools.
SBEM output is considered not compliant with forecasting estimates.
The logbook should also contain:
The target and building energy and emission rates, and
The information for the Building Automation and Control System, when installed.
For work on existing buildings, the existing or new logbook should also contain the following:
Information on the thermal elements but existing,
Controlled fittings but existing (such as windows, doors, rooflights),
And any newly installed energy meters,
The efficiency of new services across the entire system.
For a new system, we will need to quantify the change by either:
Assessment to generate the Energy Performance Certificate,
Ecodesign labelling and documentation as appropriate,
A documented assessment (representative of the complete system) by the manufacturer or by other equivalent assessment methods,
All conducted by a qualified person.
Technical information should be given to the owner when changing elements of the system, such as a boiler or emitter.
The information following the fit-out should also be provided in the logbook, as should any work that extends the capacity of the system by more than 25% or fundamentally alters its parameters.
Section 10: New Elements in Existing Buildings (Including Extensions)
In general, new elements should be up to current expectations, unless:
They do not form part of the thermal envelope of the building, and
Do not rely on the building's heating system.
We are directed to:
Section 4,
Paragraphs 4.5, 4.6, and
Table 4.1, for limits of fabric performance.
Proof of the window energy rating may come from a certification scheme that follows a recognised calculation and quality assurance procedure.
Enlargements of openings should also remain within limits to avoid triggering the requirement for general improvement to compensate for that opening.
These limits are:
20% of the area of the roof for rooflights
30% for exposed walls in residential buildings
40% in assembly, offices, and shops
50% in industrial buildings
For windows and doors, these limits also apply to extensions.
If we extend a building that is over 1,000 m², we need to consider consequential improvements.
If the extension is:
Larger than 100 m², and
Greater than 25% of the useful floor area of the building,
…it must be considered a new build.
The openings in the extension must follow the same limits described above for enlargements.
However, access doors, display windows, smoke vents, and similar glazing can exceed these limits as required for their purpose.
We can also use:
The U-values for comparison with the extension value that complies with requirements to prove compliance, or
Use calculation tools to assess the existing building plus a notional extension, and compare it with the actual proposal.
Conservations and porches are treated in the same way as in domestic counterparts.
Section 11: Work to Fabric Elements in Existing Buildings
This section gives us guidance when we:
Renovate existing thermal elements,
Make a material change of use of the building, or
Make changes that constitute a change in energy status.
If we add or replace elements, we should follow the directions of Section 10.
By renovation of the thermal element, we mean:
The addition or replacement of a layer externally or internally,
Replacement of the waterproof membrane on a flat roof, or
Providing cavity wall insulation
Now, if we improve more than 50% of the surface area of the element, we should upgrade the entire element to the appropriate limits in Table 4.2, Column B.
Similarly, if at least 25% of the building envelope is being renovated, we must upgrade it.
In the case of a material change of use, we need to consider:
The change in energy used due to its new operation, and
How it similarly impacts other aspects of building performance.
The considerations are simple:Whenever energy use changes, we must upgrade that part of the building to maintain or rather improve its energy performance.
The assessment then generally follows the procedure of:
Establishing the existing U-value of the element,
Comparing it with the required limits, and
Applying the specification needed to reach the target, when necessary.
These values are included in Section Four.
U-values for windows and doors in such cases are limited to:
3.8 W/m²·K for rooflights, and
3.3 W/m²·K otherwise.
New and replacement elements shall be treated as such—meeting standards for new and replaced elements.
The total area of openings in newly created buildings should not exceed 25% of the total floor area, unless it can be otherwise proven that the building can still meet the required energy performance despite a higher percentage of openings.
Section 12: Consequential Improvement
This section discusses improvements to large buildings.
Consequential improvement may be necessary when we deal with a building that is:
Over 1,000 m² of useful floor area, and we:
Wish to extend it,
Provide fixed building services within it for the first time, or
Increase the capacity of the building systems—not from renewable technologies.
Improving the building’s energy performance as part of the principal works is considered a consequential improvement.
However, if we improve the building because we justify an extension of poorer quality, then this is not considered consequential improvement.
So, when we:
Extend a building over 1,000 m², or
The habitable area is being increased,
We need to think about consequential improvements for at least the extent identified in Appendix D of the Approved Document.
Table D1 shows what is considered:
Technically,
Functionally, and
Economically feasible in typical circumstances.
We are also met with a minimum spend requirement, which is:
At least 10% of the cost of the principal works.
That number needs to be established by a Chartered Quantity Surveyor or other qualified person, and form part of the Building Control submission.
Now, when we:
Install a fixed system, or
Extend an existing one, increasing the capacity per m²,
We should follow the same principle as for extensions:
Upgrade to the standards in Table D1,
Spend at least 10% of the value of the principal works, and
Report that value to Building Control.
The service area should be improved to these standards regardless of the cost of the principal works.
There is also important information contained in the Appendices, such as:
Key temperature settings,
The Lighting Energy Numeric Indicator (LENI) method of calculation,
Guidance on the appropriate level of energy use per m²/year for lighting systems,
BRUKL report requirements,
Further standards for consequential improvement of heating systems when required, and
How to establish the seasonal efficiency of the existing heating system when parameters are unknown.
So that’s it, folks — Approved Document L: Conservation of Fuel and Power, Volume Two – Buildings Other Than Dwellings.
Let’s sum it up, section by section:
Section Zero – Introduction
Highlights the overlap with Volume One, noting the differences in provisions for:
Various building types, and
Stages like shell and core, modular builds, second fit-out.
It also details exemptions for certain buildings and stresses the holistic approach to integrating this document with other building regulations.
Section One – Target Calculations
Focuses on calculating the:
Target Primary Energy Rate, and
Target Emission Rate
…for a notional building, using standard specifications.
The calculations, performed using approved software like SBEM, must be compared with the as-designed and as-built rates, with results communicated to Building Control.
Section Two – Actual Performance Calculations
Covers calculating the building’s Primary Energy Rate and Emission Rate, emphasizing:
The importance of accurate as-built calculations, especially when multiple fuel sources are involved.
The section also addresses:
Special considerations for district heating systems, and
Potential adjustments for enhanced system management.
Section Three – High-Efficiency Alternatives
This section tells us that we need to assess high-efficiency alternative systems for our buildings, and produce a report on their:
Technical,
Environmental, and
Economic feasibility for Building Control review.
Section Four – Fabric Performance
Covers fabric performance in relation to:
Heat gains and losses, outlining
Specific U-value limits for different building elements.
The section also addresses:
The importance of thermal bridging,
Airtightness, and
Controlling solar gains in new buildings.
Particular attention to service insulation and heat loss prevention.
Section Five
This section establishes the minimum efficiency standards for Building Services, requiring compliance with specific regulations and testing for both new and replacement systems.
We are informed to ensure:
Proper sizing,
Effective control, and
Ongoing maintenance of heating systems,
Including the use of meters for accurate energy monitoring and reporting.
Section Six
This section outlines the energy efficiency requirements for various building systems, including:
Boilers,
Heaters,
Heat pumps,
Mechanical ventilation.
Efficiency standards vary depending on:
Fuel type, and
System capacity.
There are also additional guidelines for:
Control systems, and
Specific technologies like Combined Heat and Power as well as lighting.
Section Seven
Section Seven focuses entirely on air permeability standards, which are set at:
8 m³ per hour per m² at 50 Pascals.
It provides specific guidelines on testing procedures and exemptions.
Testing must be conducted by:
Qualified personnel,
Using calibrated equipment.
Extensions and complex buildings have tailored requirements, and all results must be reported to Building Control.
Section Eight
Deals with fixed Building Services, which must be commissioned to ensure energy-efficient operation.
A commissioning plan is required for all systems subject to energy efficiency standards, and all commissioning activities must align with:
CIBSE's Commissioning Code M.
A notification of completion must be submitted to Building Control, detailing:
The commissioning outcomes, and
Any deviations from expected performance.
Section Nine
Tells us that we must inform people about what has been done to the building.
A Building Log Book, following CIBSE TM31, must be provided. It should include:
Details about energy-efficient operation,
Maintenance requirements, and
Commissioning records.
Large buildings, meaning over 1,000 m², require:
Forecasts of energy use, per fuel type.
Updates to the log book are necessary when systems are modified, ensuring all changes are documented for continued compliance.
Section Ten
Deals with new elements in existing buildings.
New elements must meet current energy performance standards, unless exempt.
Extensions over 100 m² may need to be treated as new builds.
Specific limits apply to glazing and other components.
Compliance can be demonstrated through:
Area-weighted U-values, or
Approved calculation tools.
Section Eleven
Covers fabric elements in existing buildings.
Renovations or material changes that affect energy use must improve thermal performance to meet specific U-values.
Significant renovations (e.g., more than 50% of an element’s surface area) require upgrades to the entire element.
Section Twelve – Consequential Improvements
Applies to buildings over 1,000 m² undergoing:
Extension, or
Significant system upgrades.
In such cases, consequential improvements are required to enhance the overall energy performance.
These improvements must be:
Technically,
Functionally, and
Economically feasible.
A minimum spend of 10% of the principal works' cost is required. This figure must be established by a Chartered Quantity Surveyor or qualified person, and included in the Building Control submission.
In the next episode, we will move to Approved Document M: Access to and Use of Buildings – Volume One: Dwellings.
I hope you enjoyed this episode and that the considerations of the Approved Document L – Conservation of Fuel and Power, Volume 2: Buildings Other Than Dwellings are clear for you now.
If you have any questions, reach out to me on LinkedIn or send me an email — I'm more than happy to help you out.
At Bytnar, we deal with:
Planning,
Designing, and
Managing your projects.
We are always glad to facilitate a free initial consultation to steer you in the right direction.
Visit www.bytnar.co.uk and reach out to us.
Whether your question is:
“Can you help with my project?”, or
“What should I do?” —
We will be able to give you a piece of non-obligatory advice.
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Investigate the reasons, and
Provide you with a strategy, design, and specifications for repair.
Thank you again for listening.
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See you next week!
🛠️ Bytnar Designs – The World Around You👋 Toodloo!
Piotr Bytnar BEng (Hons) MSc CEng MIStructE
Chartered Structural Engineer who deals with the Architecture of buildings. His Master's Studies led him to an in-depth understanding of risk and contract arrangements in construction as well as specialist knowledge in soil mechanics.
He and his team help homeowners and property developers to design and deliver construction projects reducing waste in time and the cost. He believes that the construction project is an iterative process that can be well managed and it is best managed if all the aspects of the project definition and management are dealt with in-house or coordinated by one organisation. His team works to all stages of RIBA and ISTRUCTE stages of work and enables contractors to deliver projects on-site providing risk evaluations, methodologies for execution of works and temporary works designs.
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