EPISODE: 024 - APPROVED DOCUMENT H - DRAINAGE AND WASTE DISPOSAL

BYTNAR - TALKS

EPISODE 024 - APPROVED DOCUMENT H - DRAINAGE AND WASTE DISPOSAL

This episode is for people who want to know more about Approved Document Part H – Drainage and Waste Disposal.

You should like this episode if you ask yourself questions like:

• What are the key requirements for foul water drainage systems according to Requirement H1 in Approved Document H?

• How can blockages, leaks, and foul air ingress be prevented in a building's drainage system?

• What standards and guidelines apply to wastewater treatment systems and cesspools as specified in Requirement H2?

• How should rainwater drainage systems be designed and maintained to comply with Requirement H3?

• What are the best practices for rainwater management, including the use of soakaways, watercourses, and sewer discharge?

• What considerations are necessary when building over existing sewers to avoid affecting drainage systems (Requirement H4)?

• Why is it important to have separate systems for surface and foul water drainage, and how should these be designed as per Requirement H5?

• What are the rules for combining surface and foul water drainage, and how should this be agreed with the local authority?

• How should solid waste storage be planned to be vermin-proof, weather-resistant, and hygienic in compliance with Requirement H6?

  
  

LET'S TALK ABOUT YOUR PROJECT

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This is Bytnar Talks: The Engineer Takes on Construction, Episode 24.

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 the 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 H – Drainage and Waste Disposal[Music]

Hi, and welcome to Bytnar Talks, your favorite podcast on all matters of architecture, engineering, and construction.

It is Saturday, the 13th of July, 2024, and I'm back with you for the 24th episode, sharing information on Approved Document H: Drainage and Waste Disposal. As ever, before I begin covering the material of this episode, let's have a look at what was covered last week.

In the last episode, I talked about Approved Document G: Sanitation, Hot Water Safety, and Water Efficiency. Every single time, I like to reiterate that the primary responsibility for compliance with building regulations lies with the building owner, followed by those involved in the initiation, design, and execution of the work — including principal designers and contractors.

On domestic projects, this will mainly be the principal designers and contractors though, as we cannot expect the homeowner to know all the nitty-gritty about the Building Safety Act and other regulations. But we should — all parties must be competent, and the building owner must enable proper coordination.

Generally, and in light of Regulation 8, emphasis is put on health and safety. But here, Requirement G2 deals with another subject — water conservation. Exemptions from building regulations are detailed in Schedule 2 and Regulation 9 of the Building Regulations.

Key coverage points of the last episode:

• Requirement G1 deals with a reliable supply of wholesome cold water with adequate flow and pressure, avoiding waste and contamination. It allows for alternatives like rainwater or greywater to be used in the property, if properly installed and designed.

• Requirement G2 focuses on water efficiency, setting a standard of 125 L per person per day for the property — or a bit less (110 L per person per day) under optional requirements, often as a condition of planning approval. This requires calculations for total net water use using either the whole building performance method or the limitation-on-fittings approach.

• G3 addresses hot water supply, ensuring safe heating and delivery. Systems must have safety measures including thermostats and relief valves. Larger hot water containers — systems over 500 L or 45 kW — require design by qualified engineers and notification to Building Control if unvented.

• G4 stipulates adequate sanitary conveniences with hand-washing facilities, considering the building type and use. Houses and flats need at least one water closet with a nearby wash basin, separated from food preparation areas and located at the story of entry to the building.

• G5 requires a bathroom with a fixed bath or shower and a wash basin in houses and flats, with compliant water discharge. And if you don’t know which side your hot water tap should be on — it’s the left. Once and for all. So if your plumber says otherwise, well, he might have made a mistake — direct him back to G5 of this Approved Document.

• G6 mandates a sink in food preparation areas, with discharge through proper systems. As ever, additional hand-washing facilities may be required in regulated food hygiene areas.

All installations must adhere to approved standards, ensuring safety, efficiency, and compliance in any water system within a building.

In this episode, I will move on to Approved Document H and the considerations of drainage and waste disposal. So without further ado, let’s dive into this not-so-palatable Approved Document.

[Music]

Approved DocumentsI will first read you the text of the actual regulation, and then we'll go section by section, dealing with what's required.

The document contains guidance for the discharge of Requirement H in Parts H1 to H6. So, let's get into the nitty-gritty of this approved document, shall we?

Starting with the text of the legislation — and this one is pretty long, longer than the trip to a bathroom, that's for sure — so brace yourself, ’cause here we go.

Foul Water Drainage — Requirement H1.1

An adequate system of drainage shall be provided to carry foul water from appliances within the building to one of the following, listed in order of priority:

a. A public sewer; or, where that is not reasonably practicable,b. A private sewer communicating with a public sewer; or, where that is not reasonably practicable,c. Either a septic tank which has an appropriate form of secondary treatment, or another wastewater treatment system; or, where that is not reasonably practicable,d. A cesspool.

Point 2

In this part, foul water means wastewater which comprises or includes:

• a. Waste from a sanitary convenience, bidet, or appliance used for washing receptacles for foul waste; or

• b. Water which has been used for food preparation, cooking, or washing.

Requirement H1 does not apply to the diversion of water which has been used for personal washing or for the washing of clothes, linen, or other articles to collection systems for reuse.

Requirement H2 — Wastewater Treatment Systems and Cesspools

Point 1:Any septic tank and its form of secondary treatment, or the wastewater treatment system or cesspool, shall be so sited and constructed that:

• a. It is not prejudicial to the health of any person;

• b. It will not contaminate any watercourse, underground water, or water supply;

• c. There are adequate means of access for emptying and maintenance; and

• d. Where relevant, it will function to a sufficient standard for the protection of health in the event of a power failure.

Point 2:Any settling tank or holding tank which is part of a wastewater treatment system or cesspool shall be:

• a. Of adequate capacity;

• b. So constructed that it is impermeable to liquids; and

• c. Adequately ventilated.

Point 3:Where a foul water drainage system from a building discharges to a septic tank, wastewater treatment system, or cesspool, a durable notice shall be affixed in a suitable place in the building containing information on any continuing maintenance required to avoid risks to health.

Requirement H3 — Rainwater Drainage

Point 1:Adequate provision shall be made for rainwater to be carried from the roof of the building.

Point 2:Paved areas around the building shall be so constructed as to be adequately drained.

Point 3:Rainwater from a system provided pursuant to sub-paragraphs 1 or 2 shall drainage to one of the following, listed in order of priority:

• a. An adequate soakaway or other adequate infiltration system; or, where that is not reasonably practicable,

• b. A watercourse; or, where that is not reasonably practicable,

• c. A sewer.

Requirement H3.2 applies only to paved areas:

• a. Which provide access to the building, pursuant to Requirement M1 (Access to and Use of Buildings), Requirement M2 (Access to Extensions to Buildings or Dwellings), or Requirement M4(1) (Access to and Use of Dwellings);

• b. Which provide access to or from a place of storage, pursuant to Requirement H6.2 (Solid Waste Storage);

• c. In any passage giving access to the building where this is intended to be used in common by the occupiers of one or more buildings.

Requirement H3.3 does not apply to the gathering of rainwater for reuse.

Requirement H4 — Building Over Sewers

Point 1:The erection or extension of a building, or work involving the underpinning of a building, shall be carried out in a way that is not detrimental to the building or building extension, or to the continued maintenance of the drain, sewer, or disposal main.

Point 2:In this paragraph, disposal main means any pipe, tunnel, or conduit used for the conveyance of effluent to or from a sewage disposal works, which is not a public sewer.

Point 3:In this paragraph and paragraph H5, map of sewers means any records kept by a sewerage undertaker under Section 199 of the Water Industry Act 1991.

Requirement H4 applies only to work carried out:

• a. Over a drain, sewer, or disposal main which is shown on a map of sewers; or

• b. On any site or in such a manner as may result in interference with the use of, or obstruction of the access of any person to, any drain, sewer, or disposal main which is shown on any map of sewers.

Requirement H5 — Separate Systems of Drainage

Any system for discharging water to a sewer, which is provided pursuant to paragraph H3, shall be separate from that provided for the conveyance of foul water from the building.

Requirement H5 applies only to:

• A system provided in connection with the erection or extension of a building where it is reasonably practicable for the system to discharge directly or indirectly to a sewer for the separate conveyance of surface water, which is shown on a map of sewers,

• or is under construction either by the sewerage undertaker or by some other person, where the sewer is the subject of an agreement to make a declaration of vesting pursuant to Section 104 of the Water Industry Act 1991.

Requirement H6 — Solid Waste Storage

1. Adequate provision shall be made for storage of solid waste.2. Adequate means of access shall be provided:

• a. For people in the building to the place of storage; and

• b. From the place of storage to a collection point where one has been specified by the waste collection authority under:

  • Section 46 (household waste), or

  • Section 47 (commercial waste) of the Environmental Protection Act 1990,

— or to a street where no collection point has been specified.

So this is it — are you still here? Excellent.

Let’s move on to what does all that mean to the Secretary of State?

Like with all the other requirements following Regulation 8, nothing more needs to be done than assuring reasonable standards of health and safety in all requirements that deal with such issues.

However, paragraph H2 is excluded, as it deals with the prevention of contamination of water.

It really goes without saying — but I will repeat it anyhow — the quality of workmanship should follow current standards and due consideration should be given for the health and safety of people laying the drains or working in confined spaces. This matter should be fully addressed before the work commences or during the work.

Now, off to Requirement H1, which deals with foul water drainage.

In Section 1 of the document, we will find out what the expectations are for the system.

The Secretary of State is happy the requirement is met as long as:

• The outfall of the water is addressed properly;

• The system is so designed to minimize blockages, leaks, and flooding, and can be cleared of blockages;

• The ingress of foul air into the building is prevented;

• The system has sufficient capacity, which will depend on the size of the pipes used and the gradient.

The document provides the minimum requirements. The reading of the document deals with domestic buildings and small non-domestic buildings. Appendix A of Approved Document H deals with larger buildings, but for complex situations outside the scope of this document, we are referenced to use the guidance of British Standard European Norm 12056.

The information here provided assumes that periodically there will be at least five litres of water flushed through the system.

The document requires all discharge points to be fitted with a serviceable trap to prevent foul air from entering the house. The retained water seal should be at least 25 mm, but it is generally higher in line with the document and increases in value with the diameter of the trap.

So, for toilets — or rather, trap diameters of 65 mm and over — the water seal is 50 mm, and below that, it’s 75 mm.

There are some exemptions and easing of the requirement if there is another trap along the way, like a gulley.

There are limitations on the location of the branch pipe discharges in terms of discharging into open hoppers — otherwise, discharge into another branch pipe, gully, stack, or drain is perfectly okay.

In the case of direct drain connections, such needs to be from ground floor appliances, and the water closet floor cannot be higher than 1.3 m above the invert level of the drain.

Branch pipes should not cause a cross-flow to happen. Connection of branch pipes to stacks on opposite sides at the same level is prohibited, and the minimum offset dimension is given in the document.

The offsets are taken by the centre line of all drainage runs and are between 110 to 250 mm, depending on the branch pipe diameter and the stack diameter.

Solid waste branch pipe manifolds can be used instead.

It should be noted that a branch pipe connecting at the lowest point needs to be at least 450 mm above the invert level of the drain at the bend tail. For buildings under three storeys in height 7500 mm up to five storeys. For taller buildings, or where the minimum cannot be achieved, the discharge should be either direct—through its own stack—or to a gully. Interestingly, similar provision must be put on the discharge from first-floor appliances in buildings over 20 storeys in height.

Branch pipes can discharge to the soil-vent stack, and the condensate from a boiler may also discharge through sanitary pipework—but must be “washed over” by discharges from other appliances, owing to the lower pH of condensate which can otherwise corrode plastic or metal pipes. This means you can either connect condensate directly into an internal stack or downstream of a sink.

The size, length, gradient, connection angle, and number of appliances connected to a single branch pipe are all covered in the document. They ensure that the water seal is never broken by suction in a vented branch—this happens when a whole column of water rushes through a pipe, creating a void that sucks the seal dry. Vented branches can serve longer runs, but problems with sedimentation or noisy runoff may arise.

Ventilation must be provided no more than 750 mm downstream of any trap, and at a level higher than any potential flood level. If the ventilation discharges outdoors, it must extend at least 900 mm above any opening within a 3 m radius.

When it comes to stacks, all should discharge to a drain with the largest possible bend radius—but no less than 200 mm at the centre-line. Offsets, in other words, bends in the wet portion of stacks are discouraged. If needed:

• In buildings up to three storeys, any branch connection must be at least 750 mm away from the offset.

• In taller buildings, the offset may need ventilation at its top and bottom.

Stacks in taller buildings should be kept inside the structure wherever possible, ventilated, and of the correct diameter. Soil stacks are allowed if you observe:

1. The maximum toilet connection height (from the drain tail).

2. The maximum height of the highest branch centre-line to the drain or connection centre-line—2 m.

The termination of the ventilation stack must be 900 mm above any opening within a 3 m radius and protected with a termination cage. The stack must be serviceable and have rodding eyes (rodding access) where necessary.

Many different materials can be used for discharge piping, but the choice must be well conceived and installation properly executed. All piping should withstand an airtightness test simulating 38 mm water gauge pressure for at least 3 minutes. All traps must maintain a 25 mm water seal.

Section 2: External Drainage

Section 2 covers drainage outside the building but before it reaches its final destination—whether a public sewer, cesspool, or wastewater treatment system.

• House drainage can be separate (foul water and rainwater) or combined.

• Foul drainage should connect to the public sewer whenever possible, and when it is within 30 m of a small development.

• We should rely on gravity where feasible, though pumping may sometimes be required.

• Larger developments may need to run drains some distance to the water undertaker’s system, possibly through private land. In such cases, the developer may requisition a sewer from the undertaker, who has the power to construct sewers over private land.

• If possible, connection should be made to any existing private sewer that itself connects to the public system.

• In all cases, three weeks’ prior notice of the intent to connect must be given to the local undertaker.

• Where connection to the public sewer is impossible, a cesspool or wastewater treatment system may be required.

Combined rainwater drainage is designed to surcharge and may flood your property—especially at low-lying sites or where basements sit below drain levels. To mitigate possible foul flooding, in low-risk areas a non-return valve should be considered. Foul water can discharge through a gulley below house level, or you can pump the drainage from flood-prone areas—or the entire house—out.

The non-return valve should be a double-check type, capable of being locked manually by the occupants should know of its location and how to operate it. The drainage unaffected by a surcharge should bypass the protective measures on discharge by gravity.

The layout of the drain system should be simple, as straight as possible, ventilated, and maintainable, with access points provided where blockages cannot be cleared otherwise. Connections to other runs should be made obliquely or in the direction of the flow using prefabricated components—no duct-type "magic," please.

Any change of gradient will require an access point. Access points will also be required close to a bend or at the bend location.

The drain itself, for example in a commercial hot food kitchen, should be fitted with a grease separator or otherwise be capable of removing grease. Measures controlling rodent movements may also be necessary in the system.

Drainage can run under the building if it is laid in at least 100 mm of granular, flexible material and should not be subject to the forces exerted by the house on the ground, or affected by settlement or movement of the house.

Wherever pipes go through structures, use rocker pipes on both sides of the structure, with flexible joints, and provide at least 50 mm of space around the pipe so that the building can move without breaking the pipe. Naturally, all such perforations need to be sealed.

If the drainage needs to go lower than the foundation formation level and is within a metre of it, it should be concreted up to the level of the foundation's formation. Otherwise, to a level below the foundation formation of the distance minus 150 mm.

Basically, as you move away from the foundation—but do not go past the 45° angle minus 150 mm—you will not need to concrete in your pipes.

If we need to account for loading on pipes for whatever reason, we are guided to seek help elsewhere.

There are no special provisions for the depth of pipe cover, but whatever the depth, the pipe needs to be protected. It also needs to be at a certain gradient to service the load it’s being subjected to—between 1 in 10 and 1 in 150, but usually kept between 1 in 40 and 1 in 80.So per every metre, the drop is either 25 mm or 12.5 mm—you know, inch and a half, inch, in old money.

The size of the sewer should be at least 100 mm for up to 10 dwellings, and 150 mm and above for larger developments. For drainage other than foul water, the pipe can be as small as 75 mm.However, if the system is combined, we also need to account for rainfall in the sizing of the pipe.

Whenever we need to use a pumping installation, we are referenced to:

• BS EN 12050 – Wastewater lifting plants for buildings and sites: Principles of construction and testing

• BS EN 12056 – Gravity drainage system inside buildings

• BS EN 752 – Drain and sewer systems outside buildings

When we use pumping, the chamber receiving the effluent must be capable of holding 24 hours of inflow, at a minimum of 150 L per person per day. This follows the typical water usage cap and then some.

All types of pipes can be used underground—including the all-time favorite vitrified clay, but also concrete, grey iron, ductile iron, as well as the flexible types made of plastic.

These should be flexibly jointed and must not protrude into the flow of sewage.

The bedding and backfilling will depend on the depth of excavation, size, and strength of the pipe.Local undertakers generally concrete their installations, but we can go lighter on ours.Concrete installations will require a movement joint with a compressible board formed at junctions.

The bedding and backfilling material for pipes should prevent pressure points on the pipe that could break it—so uniform material with no vegetation, stones larger than 40 mm, lumps of clay over 100 mm, or frozen material is generally considered good enough.

In most cases however, you’ll often find this laid on some type of granular material, either single-size or graded, from 5 mm to 40 mm depending on the diameter of the pipe—10 mm for 100 mm pipes, to maximum dimension for pipes over 600 mm in diameter.

The minimum and maximum ground cover for different sizes and types of pipes, in various situations, is given in the document—starting with a minimum of 600 mm for fields, and 1.2 m otherwise for rigid pipes, and slightly lower at 0.9 m for thermoplastic.

Pipes shallower installations will require a bridging slab over them with a layer of compressible material between the pipe and the slab.

To maintain and service drains, access points must be introduced into the system, and the guidance interprets the reasonable spacing and placement of such. Rodding eyes, access fittings, inspection chambers, and manholes are typical points that could allow rodding. The guidance considers rodding in the direction of flow only.

The placement of such access needs to be considered at:

• the head of the drain run,

• at a bend,

• at a change of gradient,

• a change of pipe size, and

• a junction (if it can be rodded from one side only).

The type and spacing of these access features is guided by the document and depends on the depth of the invert level and the size of the pipe.Spacing of the access points ranges between 12 m and 200 m, depending on the type of access used — from 12 m from the start of the drain to 200 m between man-entry size drains and sewers.

The material used for the formation of access points should follow the material used for the pipes themselves.

The junctions of pipes in the inspection chamber should follow the direction of flow.

Covers to access features should be:

• appropriate for the location,

• airtight,

• durable, and

• may need to be lockable.

The guidance also requires metal steps in deep manholes. However, current practice prefers steps to be brought in with the plumber due to the corrosion risk of fixed steps and the surprise fall hazard for personnel.

The work of laying pipes, connections, and forming inspection chambers or manholes should be of the appropriate quality.

If piling takes place close to the pipes, the pipes may need to be exposed temporarily, and piling should not take place too close to pipes—meaning a minimum of two times the pipe diameter between the pipe and the nearest pile.

Drainage Testing

Gravity drain and private sewer systems should be tested following construction.

We are allowed to choose between a water test or an air test.

Air Test (for pipes up to 300 mm diameter):

• The system is loaded with a pressure of 110 mm on the water gauge for 5 minutes,

• Then an additional 100 mm of pressure is applied for 7 minutes,

• The maximum pressure drop permitted is 25 mm of water.

Water Test:

• The system is filled with water to a maximum of 5 m above the lowest invert level, but at least 1 m over the highest invert level.

• The system is then left for one hour to prime,

• It is then topped up to be within 100 mm of the required level,

• The system passes the test if the loss per square metre of surface area does not exceed:

  • 0.15 L for pipes only,

  • 0.2 L for pipes and manholes,

  • 0.5 L for manholes only.

The guidance further references alternatives such as:

• BS EN 1091 – Vacuum sewer systems outside buildings, and

• BS EN 1671 – Pressure sewer systems outside buildings.

Both standards are now withdrawn.

Although there are no Building Regulations requirements to maintain the drains, the local authority and undertakers have far-reaching rights that may include:

• inspection of your drainage system,

• orders for repair,

• sealing of old drainage, or

• its removal.

Similarly, for repair and alteration to drains, a one-day notice must be given to the local authority, unless it’s an emergency.

Adoption of Sewers

Another important thing to keep in mind is the adoption of sewers.

Under the Water Industry Act 1991, Section 104 agreements allow for:

• adoption of a sewer or sewer disposal works at a future date.

• You build the infrastructure for the undertaker to take care of.

• Certain standards of work need to be met — but these are generally available and can be agreed upon with the undertaker.

Single dwellings do not fall under this consideration.

If you are blocked from connecting your development to the building sewer due to third-party land, the requisition of sewage under Section 98 from the undertaker may be the only way to connect.

Under Section 102, existing drainage may be adopted if it meets the criteria, and the adoption may proceed either from:

• the developer’s inquiry, or

• the undertaker’s own volition.

Section 106 gives the right for connection to a public sewer with a 21-day notice, upon agreeing on the technical details of such connection.

Section 107 gives the right to the undertaker to carry out the work or to supervise the developer’s work.

Section 112 means the undertaker can request the manner in which the sewerage is constructed for the general system of drainage, and reimburse the developer for the extra cost.

Drainage may also be adopted by the Highway Authority under the Highways Act 1980.It is possible, at their discretion, that highway drainage becomes part of the building surface water drainage.

Now, moving on to Requirement H2, which deals with wastewater treatment systems and cesspools.

The Secretary of State is satisfied if:

• the systems are of the right capacity to do the job, and be sited so not to cause nuisance or health hazards, pollute controlled waters or water sources, or be in flood-prone areas. They should have enough ventilation, not allow groundwater ingress, or allow groundwater to overload the system. Information on maintenance should be available in all service buildings.

The first course of action prior to the specification of the wastewater treatment system is the permission of the Environment Agency, typically as part of the planning permission process.

The guidance makes reference to BS 6297, Code of Practice for the Design and Installation of Drainage Fields for Use in Wastewater Treatment, for the detailed design of these systems.

Septic tanks, or septic tanks with secondary treatment in drainage fields, mounds, or wetlands, are typical solutions for one to several dwellings. The basic idea is for the solids to settle in the tank, the water to soak into the ground, and bacteria to decompose in the aerated soil.

Package treatment works do what they say on the tin—same as septic tanks with secondary treatment but in a compacted version, allowing direct discharge to watercourses, and are more economical for larger developments.

Cesspools are just storage vessels for sewage, so they will generally not be permitted unless no other solution is feasible.

Now, septic tanks need to be positioned at least 7 m away from any habitable parts of buildings and must be readily available for emptying—meaning not farther than 30 m from the vehicle access for septic tanks with an invert level not deeper than 3 m, the tank needs to have at least 2.7 cubic meters of capacity under the inlet for four users, with an additional 180 L per person.

Tanks can either come from the manufacturer, or they can be constructed using engineering brick with a 1:3 cement-to-sand ratio mortar, or 150 mm of thick concrete at least 25 N/mm² strength.

Ventilation, further requirements for the avoidance of settlement or scum disturbance, controlling the amount of inflow, and access for testing of inflow and outflow—as well as for emptying—must be considered.

The access for emptying should be secured and durable.The information about the type of sewage treatment and maintenance requirements should be fixed within the building.

A drainage field should be:

• at least 10 m away from the watercourse or permeable drains;

• 50 m away from points of groundwater abstraction or Zone 1 groundwater protection zones;

• a minimum of 15 m from any building;

• and away from other drainage features.

Further expectations are put on the location and quality of the ground conditions and its capacity to absorb water. Therefore, a percolation test will be required—at least three times, in at least two trial holes.

The design generally follows the spread of effluent through perforated pipes over a bed of granular material similarly, with a mound system. To calculate the floor area of the drainage field, we need to:

Multiply the number of people using the system by the percolation value (in seconds per mm) and divide by four.

Reed beds are also a possibility for secondary or tertiary treatment systems and are of two types:

• Horizontal flow, where water spreads in a plane;

• Vertical flow, allowing water to permeate evenly through the layer of the reed bed.

The document refers to BRE Good Building Guide No. 42 for the design and construction of reed bed treatment systems.

In areas affected by nutrient neutrality regulations, reed beds may be one of the only viable treatment alternatives for development.

According to the document, package treatment works should comply with BS 7781, though this standard is now withdrawn.

The discharge from such a plant should be:

• at least 10 m away from watercourses or buildings;

• and should be able to function during power outages for at least 6 hours.

Cesspools

Cesspool requirements are similar to septic tanks, but the capacity needs to be much greater:

• At least 18 cubic meters for two users, with an additional 6.8 cubic meters for each additional person.

Greywater and Rainwater Reuse

Greywater and rainwater storage tanks for reuse within the house should be:

• contained and isolated from groundwater ingress;

• protected from backflow of sewage into the tank via the outflow.

As with previous requirements, local authorities and undertakers have overreaching rights to:

• ensure the systems are safe,

• are well maintained, and

• that our waterways are not polluted.

It is, however, an entirely different matter whether they are using these rights or not.

Requirement H3 — Rainwater Drainage

For the Secretary of State, it is enough to carry the water properly away from all the roofs and paved areas, making sure the system can be cleared of blockages, and so it does not damage the foundations of buildings or structures.

The preference of the outflow is given in this order: soakaway, then watercourses, then sewers.

The sizing of the rainwater system will depend on:

• the area of the drained surface, and

• the anticipated rainfall,

and can follow either the prescription of the Approved Document or align with BS EN 12056 – Gravity Drainage Systems Inside Buildings.

Flat areas will be treated as tributary area as is, but inclined planes will have a factor applied to the plan area that takes into consideration driving rain.

• For a 30° pitched roof, the factor will be 1.29 of the plain area;

• For a 45° roof, the factor is 1.5;

• And for a 60° roof, the factor is 1.85.

Walls are treated as 50% of the elevation area, and walls are considered any planes inclined more than 70°.

The sizing of rainwater goods then follows assumptions:

• Level gutters of half-round profile;

• Maximum run length at one outlet of no more than 50 times the water depth.

Gutter sizes start at 75 mm (with a 50 mm outlet) for an effective drained area of 6 m², and go up to 150 mm half-round gutters with an 89 mm outlet, servicing an effective area of 103 m².

Flow rates range between 0.38 to 2.16 L/s, depending on the configuration.

Rainfall intensity can be taken from maps—for example, Kent sits around 0.02 L/s/m², which is less than half a teaspoon per second.

Rainwater pipes can discharge to another gutter or surface, but ideally to a drain or a gully. If it drains onto a roof or pavement, a shoe should divert the water away from the building.

If the discharge is more than 25 m², the water should be distributed to avoid a waterfall due to an overflowing gutter on the lower roof.

Syphonic roof drainage should be considered using auxiliary standards, with special care taken due to:

• Possible downstream surcharge, and

• Time delay for the siphoning action,

• Possibly requiring an overflow arrangement.

The guidance references the use of High Hydraulic Research Ltd Report SR 463 as an aid and directs users to BS EN 12056 for more information.

If a drop system is allowed, due consideration should be given to the effect of falling water.Harvesting systems, when introduced, should be clearly marked.

Materials used in rainwater goods should be suitable, watertight, and firmly supported, but allowed to expand and contract due to temperature changes.

Pavement Drainage

For pavement drainage up to 4,000 m², we are directed to the following guidance:

• Rainfall intensity considered is lower than that for roofs, and in Kent is around 0.016 L/s/m²—around a third of a teaspoon per second.

• Maps give values for different parts of the country.

Surfaces should be:

• graded toward outfalls and away from buildings,

• with a minimum gradient of 1 in 60, and

• a maximum of 1 in 40 across a path.

Where possible, the paved area should drain freely to pervious areas. It is encouraged that pervious paving is used wherever practical.

The design of such paving will follow similar considerations to soakaways. If the ground beneath the paving is impervious, then a granular layer or a crate system can be used as an attenuation tank.

For more detail, the guidance refers to:

• CIRIA Report C522 – Sustainable Urban Drainage Systems: Design Manual for England and Wales.

Where Soakage Is Not Possible

If water cannot soak into the ground, drainage should incorporate gullies with appropriate catch pits for silt, and positioned to accommodate pavement settlement.

Guidance recommends gullies be placed 5 mm below pavement level.

The pavement drainage criteria within the document apply to areas larger than 2 hectares (i.e., 20,000 m²).

Where practicable, outlets should lead to:

• a soakaway,

• a watercourse,

• or a sewer.

Connection to a combined sewer should be the last resort.

In any case, the capacity of the system needs to match the combined flow rate.

The capacity charge is given in the document, relevant to:

• the size of the pipe, and

• its gradient.

Contaminated runoff will require separate drainage, and runoff from petrol stations and car parks should be provided with oil interceptors.

Further references for infiltration drainage design include:

• CIRIA Report C609 – Infiltration Drainage: Manual of Good Practice,

• BS EN 752, and

• BRE Digest 365 – Soakaway Design.

For small-area runoff, simple directions are given.

In addition, the use of swales, infiltration basins, filter drains, and detention ponds are all encouraged.

Requirement H4 — Building Over Sewers

The Requirement H4 deals with building over sewers. In the gist, to satisfy the requirement in the eyes of the Secretary of State, the proposed work—both during construction and as completed—cannot damage the existing drainage system or obstruct access to its inspection points.

The structure should be built so as not to obstruct future replacement works, usually meaning at least 500 mm away from the walls in case of shallow drains.

Moreover, the building should not be susceptible to drainage failures, which in practice often means bringing the depth of the foundation formation level to that of the drainage system.

This requirement is valid for building work within 3 m of the centreline of the drainage. Drainage is identified on the undertaker's asset maps, but often, when it comes to lateral disposal mains, these are not shown on maps. However, the provisions of this guidance will still be valid, and gaining the local undertaker’s approval for the proposed work is necessary.

The local undertaker will likely need to confirm the condition of the existing sewer—for reasons of possible need for replacement—and to ensure that the works do not damage the drains.

The guidance draws our attention to fine granular soils, which may settle due to the washing away of fine grains into the sewer in case of damage to the drains and groundwater infiltration, which can carry these particles away. We are also reminded of the possible collapse of drains and the impact this may have on our buildings.

Internal inspection chambers for more than one property are a no-no, as access for maintenance needs to be readily available. An alternative external provision, approved by the drainage owner (typically a local undertaker), would be the way forward.

A satisfactory diversion possibility needs to be allowed—one that permits reconstruction of the sewer without affecting the building. The Secretary of State states 3 m away from the building to be the right distance, and requires mechanical excavator access for drains below 1.5 m deep that could reasonably be excavated using such machines.

The guidance limits the length of the build-over sewer to 6 m, however, other agreements can be reached with the owner of the system.

Another 3 m limit exists for buildings nearby or over drainage systems that are more than 3 m deep or greater than 225 mm in diameter. As always, speak to the asset owner, as other agreements can be arranged.

During works near or over the drain line, every effort should be made to minimise the impact on the drain. Piling cannot be done closer than two times the pile diameter to the drain. If piling takes place within a metre of the drainage system, it should be exposed.

Settlement of the building should be addressed in the drainage construction, allowing for differential movements. Excavation for drain trenches should not undermine existing foundations. If the drain is deep enough—according to guidance, 2 m to the invert level—then the foundation should form a lintel over the drain with a 1.5 m span either side of the drain, and be designed so that no load is transmitted onto the drain or sewer.

Requirement H5 — Separate Systems of Drainage

There’s not much here to convey, really. The foul or greywater should not mix with rainwater.

For one, the sewage treatment works does not need that extra water from rain. And poop floating on our streets due to flooding is not an ideal scenario.

Rainwater can either be soaked into the ground locally or discharged to local waterways instead.

When there is work taking place to split combined systems, the new development drainage system should be separate and allow for future connection to a separate system.

To deal with contaminated runoff, an agreement with the local undertaker needs to be made first.

Requirement H6 — Solid Waste Storage

In the Secretary of State’s opinion, as long as the storage is safe, not prejudicial to amenities, and agreed with the collection authority in terms of size and placement, the requirement is satisfied.

A few general points to consider here:

• Storage space for waste containers needs to be provided.

• Containers of 250 L (i.e., 0.25 m³) per dwelling per week are suggested

• For domestic developments up to four storeys access to two separate movable containers, in line with local requirements, needs to be provided.

• For separate storage areas per dwelling, an area of 1.2 m × 1.2 m should be sufficient.

Communal storage areas will require consultation with the local waste collection authority.

In high-rise domestic buildings up to four storeys can have separate storage areas, and the rest can have a chute-fed system in place or another suitable arrangement.

The distance the householder has to travel to get to the storage area should not exceed 30 m horizontally, and for waste collectors, 25 m for containers up to 250 L.

Up to three steps on the way to the collection point are allowed, and the slope should not exceed 1 in 12.

External storage areas should be located away from windows and ventilators, preferably in shade and under shelter.

The NHBC Foundation Report NF60 provides some fair guidance.

Storage enclosures should:

• allow 150 mm movement around the container,

• be ventilated top and bottom,

• be on a paved surface,

• and high enough to open the lid for filling — minimum 2 m high for communal storage and they should also be protected from vermin,

• Areas should be washable and capable of receiving pooled effluent with a trap to prevent drying out and odour during dry periods.

Storage rooms should be separated for recyclable waste.

Storage chutes should:

• be ventilated,

• have at least 450 mm diameter,

• include closed access fittings at each storey,

• and their internal surface should be smooth and non-absorbent.

We are also told that BS 5906, Code of Practice for Waste Management in Buildings, is valid as an alternative approach. To compliance with the requirement usually means consultations with the local waste collection authority to establish their requirements — and to remain on the right side of the Environmental Protection Act 1990, especially in more complex or hazardous waste situations.

So, do it right, and segregate your waste as required — whether you are a homeowner or running a commercial gig.

🎵 [Music]

So, this is it folks — Approved Document H: Drainage and Waste Disposal.Let’s sum it up:

The Secretary of State expects that standards for health and safety are reasonably met.This responsibility excludes Paragraph H2, which pertains to water contamination prevention.

In Summary:

• Requirement H1 – Foul Water Drainage:

  
  

  Design must ensure proper capacity, minimize blockages, prevent leaks and flooding, and stop foul air ingress into buildings.

  
  

  Systems must pass an airtightness test simulating at least 38 mm water gauge pressure for 3 minutes minimum.

• Requirement H2 – Wastewater Treatment Systems and Cesspools:

  
  

  Systems must be of right capacity and in appropriate locations to avoid nuisance, health hazards, and pollution.

  
  

  They must have adequate ventilation, prevent groundwater ingress, and follow Environment Agency guidance and relevant British Standards.

  
  

  Maintenance requirements must be clear, and systems should be monitored and maintained to prevent contamination.

• Requirement H3 – Rainwater Drainage:

  
  

  Systems must carry rainwater away from roofs and paved areas.

  
  

  Outflows should go to soakaways, then watercourses, then sewers.

  
  

  Correct sizing is based on surface area, rainfall, and infiltration rates.

  
  

  The system should be simple, maintainable, and allow access for clearing blockages.

• Requirement H4 – Building Over Sewers:

  
  

  New works must not affect existing drainage systems, restrict access, or undermine building stability.

  
  

  An agreement with the system owner (usually the local undertaker) is required.

• Requirement H5 – Separate Systems of Drainage:

  
  

  Foul water and surface water must be kept separate.

  
  

  Rain should not burden the sewage treatment system.

  
  

  New developments must provide separate systems, and local approval is needed for combined systems.

• Requirement H6 – Solid Waste Storage:

  
  

  Buildings must provide adequate facilities for waste storage before collection.

  
  

  Prevent health hazards, ensure hygiene, and make spaces accessible to occupants and collectors.

  
  

  Waste areas must be vermin-proof, weather-resistant, well ventilated, and easily cleanable.

In the next episode, we will move on to Approved Document J: Combustion Appliances and Fuel Storage System.

I hope you enjoyed this episode, and that the consideration of Approved Document H: Drainage and Waste Disposal now makes more sense to you. It’s been a long one, but I decided not to split this into parts—I think, in this case, it's better to have it all in one place.

If you have any questions, reach out to me on LinkedIn or send me an email—I am more than happy to help you out.

At Bytnar, we deal with planning, designing, and managing your projects, and we are always glad to offer 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 me with my project?” or “What should I do?”

—we will be able to give you a piece of non-obligatory advice.

At Bytnar, we help our clients design and execute their dream homes or investments.If your building is falling apart, we can also help investigate the causes and provide a strategy, design, and specification for the repair.

Thank you again for listening.Please voice your opinions—I'm waiting for you on LinkedIn, and I want to hear from you.

See you next week, and remember:Bytnar Designs the World Around You.

Toodloo!

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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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