EPISODE: 012 - APPROVED DOCUMENT A - STRUCTURES - PART 1

BYTNAR - TALKS

EPISODE 012 - APPROVED DOCUMENT A - STRUCTURES - PART 1

This episode is for people who want to know more about Approved Document Part A - Structure.

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

• What are the key structural safety requirements outlined in Approved Document A of the Building Regulations?

• How does Approved Document A address loading requirements for traditional construction?

• What measures are recommended in Approved Document A for managing ground movement, like soil subsidence?

• What are the guidelines for the stability of timber and masonry structures in the Building Regulations?

• How should connections between walls, roofs, and floors be designed according to Approved Document A?

• What are the specifications for wall cladding and roof coverings to ensure structural integrity?

• How should builders ensure that roof fixings withstand wind loads and environmental stress?

• What are the regulations for addressing disproportionate collapse in existing buildings under Approved Document A?

• How does Approved Document A assist architects and engineers in selecting suitable materials for construction?

LET'S TALK ABOUT YOUR PROJECT

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This is Bytnar Talks: The Engineer Takes on Construction – Episode 12

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.

And 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 Documents – Structure, Part One

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Hi there, and welcome back to Bytnar Talks—your favourite podcast on all matters of architecture, engineering, and construction.

It is Thursday, the 11th of August 2024, and I’m back with you for the 12th episode, bringing you further information on the Approved Documents.

It’s been a busy week!We helped people achieve their planning permissions and full plan approvals for building control.We visited some dangerous structures to assess their condition.I even shot some pigeon clay as part of a local Kent networking group, closed new clients, and managed to do it all while preparing this podcast for you.

What would my childhood hero say?Who doesn’t love it when the plan comes together?

Last week, in Episode 11, I took you on a journey through all the Approved Documents and how it all comes together.

There are 18 requirements, covered by 17 Approved Documents—as Requirement N hides within Approved Document K. There’s also an additional document that deals with materials and workmanship.

Now, I will move us into more detail within the first requirement: Structure.

All right, let us unpack it all a bit.So, without further ado, let’s dive into the structural requirements of the Approved Document.

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The purpose of this material is to give you a general appreciation of the requirements placed on you by the Approved Documents.

The Approved Documents form the primary source of information prepared by the Secretary of State describing how the Building Regulations requirements can be discharged.

They form guidance for Registered Building Control Approvers to discharge their duties. So, the first thing they’ll do is take your project and dissect it point by point, ticking all the necessary boxes identified within the document.

In this episode, I will talk about the first consideration within the Schedule of Requirements identified in the Building Regulations 2010, which is:

Structure

There are three considerations brought up by the regulator:

1. A1 – Loading

2. A2 – Ground Movement

3. A3 – Disproportionate Collapse

In the main part of this episode, I’ll talk about the first two aspects—Loading and Ground Movement—and I’ll leave Disproportionate Collapse for its own episode, which will form Part Two of the Approved Document A – Structure.

I’ll begin by telling you how the document is structured, and then we’ll go section by section, giving you simple reasons behind the text, with my commentary.

All right, let’s get on to it.

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The Approved Document A is put in place to give a practical approach to the meaning of the Building Regulation Requirement A.

I will read it for you now so you can appreciate how broad it is.

Regulation A1 – Loading

Paragraph 1:The building shall be constructed so that the combined dead, imposed, and wind loads are sustained and transmitted by it to the ground:

(a) Safely; and(b) Without causing such deflection or deformation of any part of the building, or such movement of the ground, as will impair the stability of any part of another building.

Paragraph 2:In assessing whether a building complies with sub-paragraph 1, regard shall be had to the imposed and wind loads to which it is likely to be subjected in the ordinary course of its use, for the purpose for which it is intended.

Regulation A2 – Ground Movement

The building shall be constructed so that ground movement, caused by:

(a) Swelling, shrinkage, or freezing of the subsoil; or(b) Landslip or subsidence (other than subsidence arising from shrinkage)—

—insofar as the risk can be reasonably foreseen, will not impair the stability of any part of the building.

So here we have it.

You can appreciate that this is quite general—and possibly too broad to make much sense to anyone without some context or technical insight. What I mean by that is—I may have a different approach than yours, and you may have a different approach than mine.

To me, the requirement regarding loading is simple:

The structure must be safe on its own—in ordinary circumstances—and cannot unduly impact any other structure.

And the requirement regarding ground movement simply states:

The building needs to be placed on sound enough ground so that any movement will not impair the building’s stability.

Simples.

So, as long as the building is safe and stable and does not impact neighbouring buildings, it is compliant to the letter of the law.

But what does that actually mean?

No one knows.And no one assigns their judgement to it—at least, not the regulator.

As detailed and prescriptive as the Approved Documents may appear, they begin with the clear statement that:

There is no obligation to adopt them, if we want to discharge the requirements in another way.

Neither the regulator nor the Registered Building Control Approver will be liable for the use—or insistence—on any particular solution from that document.

Unfortunately, the approvers have the power of veto, and the only way they can judge a proposal is often by reference to the Approved Documents only.

So, the Principal Designer will, in most cases, be restrained to the use of these documents.

Let us now look at what this document is actually about.

The Approved Document addresses the requirement of structural safety by listing other documents that are also approved and applicable. The latest revision of those documents should always be taken into consideration—and that forms Section 1.

It allows us—chartered structural engineers—to use this information and draw on years of knowledge and experience to specify any needed project out there, starting from:

• Small projects, like those described in the Approved Document,

• Up to hospitals,

• Offices,

• Mixed-use high-rises,

• Tunnels,

• And bridges—just to name a few.

The Approved Document then moves on to giving directions for sizing of elements in traditional buildings to carry load and wind. That’s found in Section 2.

Section 3 deals with wall cladding, andSection 4 deals with roof coverings.

All these sections address Requirements A1 and A2 of the regulations, as mentioned earlier.Requirement A3—Disproportionate Collapse—will be discussed in the next episode, as I believe it requires due consideration and more attention.

There are 23 diagrams and 10 tables that accompany the text of this document and assist you in understanding and discharging the requirements.

It should be noted that the old British Standards are no longer approved where substituted by Eurocode alternatives.

However, in practice, I have not seen an officer who would not approve the use of old standards—if they are presented well.

I have received documentation that bases its design on standards going back half a century, and these were approved.

I’m interested to see if this will change now with the onset of the Building Safety Act and the requirement of competence.

Anyhow, the list of approved standards can be found in the document, and it is prudent to refer to these standards when forming the argumentation for your design decisions.

The list contained within Section 1 covers:

• Ways to approach structural analysis and design

• Typical loadings and actions to which a structure may be subjected

• All typical and codified design circumstances covered by Eurocodes, their National Annexes, and supplementary documents

• Guidance on interpretation for general application

This section also references documentation requirements posed by localised ground movement, including:

• Landslip

• Mining instability

• Filled ground

As well as the approach to the appraisal of existing buildings for material change of use.

Moving into Section 2, we are divided fairly clearly into aspects A, B, C, D, and E.

It should be noted that Requirement A tells us what to look into when considering aspects B and C—but in general, all aspects B to E can be treated independently of one another.

Section 2A1

States that the scope of this Approved Document is limited to low-rise residential buildings only, and it should be read in conjunction with paragraphs B and C.

Traditionally, in Britain, buildings are made of masonry walls—be it solid or cavity—and timber floors and roofs. Engineered products are now also widely available.

Subparagraph 2B2

Limits the overall size and proportions of the building and gives restrictions on layouts and cell sizes, requiring walls to connect to each other either:

• By bonding, or

• By means of mechanical connection

• mechanical fixings

and requires roofs and floors to provide lateral support capable of transferring loads to buttressing elements of the building.

So, when you think about a floor or roof, don’t just think about it in its traditional function—either carrying you and your gear in the case of a floor, or carrying roof tiles and snow in the case of a roof. You also need to consider that these horizontal planes—these floors and roofs—must connect to walls in both directions to stabilize those walls. Otherwise, the walls wouldn’t be that stable and could collapse.

Aspect B: Timber

This section directs us to TRADA tables, as the span tables have been removed in one of the revisions of the Approved Documents some years ago.

Although an engineer can easily calculate the required size and strength, the document also highlights the necessity of treating timber when it is susceptible to attack by house longhorn beetle, which is commonly found in the Southeast of our country. These dry and sunny areas are the regions where infestations are more likely.

These little creatures thrive on dry substructure made from coniferous trees or, more broadly, dry softwood.

Aspect C: Masonry

The Approved Document follows an approved approach here, but it is very broad, and variations are possible when proven by calculation or experience.

The limit of application for this guidance is considered to be for buildings of:

• Height not exceeding 15 m,

• No more than three storeys,

• And also applies to small single-storey non-residential buildings like annexes, garages, and outbuildings.

The limit on height may be more stringent, depending on the location, wind exposure, and orography (terrain) of the area.

The proportion of the least width to the height of the building cannot exceed 2:1, according to the document. That means:

The smallest side of the building will determine its maximum height.

Similarly, with annexes, if the annex protrudes away from the main building more than two times its width, the height of the annex cannot be more than two times the smaller width.

This is in place to make sure the building is stocky—or in other words, so that floors and roofs can translate wind loads to buttressing elements.

This principle is also evident in the floor area limits, which are:

• 70 m² for floors enclosed on all sides by walls

• 50 m² for floors with one open side

You will also note that:

• Walls are limited to 12 m runs or 12 m height between supporting elements

• There are limits on imposed loads, and if you intend to use the space with more onerous expectations, some localized strengthening will be required

Material Thickness Requirements

There are similar limits on:

• The material selection for walls

• The minimum thickness, which should not be less than 1/16 of the wall height

• And if the wall is made of uncoursed rubble, it should be at least 1/12 of the height

So, divide the wall height by 16 or 12, and you have the minimum thickness required.

There are further requirements, diagrams, and tables that can guide you in:

• Selection of appropriate materials

• Thickness

• Size and layout of your building

• As well as the number and position of wall ties if you choose a cavity wall system

Material Strength and Mortar

The rules for material strength and wall selection vary with:

• Building size

• Wall position

The specification for mortar does consider safety, but not performance, so it may be prudent to choose different mortar strengths in your building to:

• Mitigate the appearance of cracks

• Allow for future extensions

There’s a limit on the span of floors:

• 6 metres from centre to centre of bearings

• Which gives you around 5.9 metres between the faces of the walls

Guess what? When combined with the limit on wall length, this gives us the maximum floor area for a compartment: 70 m².

A similar proportion is applied to retaining walls, which must not retain more than 1 metre of soil height, and must extend for the entire storey height to provide enough vertical load to resist the horizontal push from the soil.

There is also a limit to the foundation load of 7 tonnes per metre run.

You will find rules on:

• Buttressing walls,

• Piers,

• Chimneys,

• Openings in walls,

• Chases and recesses

Unfortunately, masonry is weak in bending, so removal of parts of panels or buttressing weakens the wall, and may lead to the circumstance where the wall is weaker than the window or door you put into it, and the actual door or window ends up strengthening the wall—which, by the way, is not an ideal or reasonable thing to do.

As mentioned previously, the walls and roof need to provide lateral support on all sides to the structure and generally be mechanically fixed to the walls. Whether it is your external wall, party wall, or internal wall, you need to make sure they are tying the walls together at least every 2m centres.

However, some relaxation of these requirements is possible if there is enough contact between the wall and the floor, and the building is no more than two storeys high.

You should also remember to strap the roof down to the wall at the eaves at similar distances to avoid the roof lifting up. If the roof is of sufficient pitch and weight, this requirement may be omitted.

It is good to emphasise the fact that if there are wall or floor openings interrupting the lateral or vertical restraint, there should be provisions in place to address this, and enough restraint provided in suitable locations.

The mentioned rules are relaxed slightly when it comes to small non-residential buildings. It’s good to note that the wall build-up should be at least 130kg/m².

If the outbuilding, annexe, or garage is smaller than 10m², it doesn’t have to meet these requirements. But anything over that floor area should have enough mass not to behave like a kite.

The building shouldn’t be bigger than 36m², with a maximum wall size of 9m, and a height of 3m to 4.5m max:

• 3m for a flat roof

• 4.5m for a pitched roof

Walls should be tied to the roof horizontally and vertically, and ties should be provided wherever needed.

Aspect D: Masonry Chimneys

Similar to party walls, chimneys are referenced not to be higher than 4.5 times their smaller dimension, if constructed in traditional masonry of at least 1.5 tonnes per cubic metre density.

This provision is in place to resist the overturning action of wind by relying on gravity load—so here we are:

You need mass so the chimney stack does not collapse.

Mass Concrete Foundations

When mass concrete foundations are concerned, they need to be placed on uniform ground to mitigate differential settlement—the damage that can appear as the building settles unevenly.

The mass concrete strip foundation should not be less than 150mm deep—meaning it should be at least 150mm thick—and have a strength of 10N/mm², which corresponds to GEN 1 concrete.

However, the designation also needs to take into account durability, too.So, in clayish or typical British conditions, you often need to account for sulfates in the ground, and the foundation will very often require FND designation (Foundation Concrete, Designated).

There are more expectations relating to:

• Foundation width

• Formation depth

• Stepping of footings

The foundation width generally assumes:

• No higher ground pressure than 100kN/m² in granular soil

• And 50–75kN/m² in cohesive soil

The requirement for the foundation is usually governed more by projection requirements than by bearing pressure.

It is generally considered normal for a building to settle 25mm during construction or sometime after completion—which may take longer than 10 years.

All building control officers these days will ask you to identify trees nearby. We’re receiving requests for up to a 30m radius, regardless of the soil type.

This is due to NHBC guidance. NHBC stands for the National House Building Council, and in their Guidance Document 4.2 – Building Near Trees, they go in-depth with their expectations.

It basically boils down to two solutions:

1. If you build near trees in soil affected by water content variation,

2. You will either have to follow NHBC guidance, or

3. Have the foundations engineered.

From my personal experience, I see how damaging to the planet this approach is.People pour tons of concrete into the ground and use polystyrene to mitigate the impact—on sites where there are trees within the limits of the guidance, even though their influence does not extend to the full perimeter of the site.

This renders the guidance not just impractical, but harmful.It can be observed easily by looking at existing buildings around those trees—even those closer to them than your proposed works.

It is quite damaging for the planet and quite damaging for the pockets of clients—for people who want to build buildings—but maybe not for the contractors, compressive material producers, and certainly not for NHBC as a warranty provider.

In general, we are used to specifying the depth of foundations from around half a meter deep—45 cm below ground level—down to 1 metre. But following NHBC guidance, this may well go to 2 to 2.5 metres deep, or it will require a raft or piled-and-beam foundation.

Off to Section Three – Wall Cladding

This section treats wall cladding, which needs to be structurally sound, so it does not detach and harm anyone.

It also needs to be:

• Durable

• Resistant to weather

• Fire-resistant

• Resistant to the passage of sound

But hey—one thing at a time.

The cladding design, and the design of its fixings, needs to account for:

• All applied loads

• Thermal and moisture-related behavior

Fixings should be at least as durable as the cladding itself and must be designed, developed, and tested—either by the specifier of the bespoke solution or by the manufacturer of the off-the-shelf solution.

And finally, Section Four – Roof Coverings

Similar to Section Three, this one deals with roof coverings.

A roof must do a good job—it should neither fly away during inclement weather, nor collapse when accessed by repair personnel.

Some concessions are allowed in areas not accessed for maintenance, such as for roof lights—but that doesn’t mean it’s not dangerous.

It can also be risky to increase the weight of the existing roof by more than 15%, which often happens when:

• Converting attic space

• Adding insulation and ceiling boarding

• Installing photovoltaic panels on the top of the roof

In such cases, an engineering assessment will be required.

If the increase in weight is more than 15% of the existing weight, the structural system may need to be reassessed or upgraded.

On the other hand, removing the original weight from the roof—e.g., removing heavy tiles or ceiling layers—can result in the roof lifting off and possibly flying into the neighbour’s garden.

So to avoid such a predicament, it may be necessary to strap that roof down to the walls.

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Now, let's summarise that a little bit, shall we?

So yeah, Approved Document A provides guidance on ensuring the structural safety and stability of a building and its compliance with Building Regulation Requirement A.

It covers aspects such as:

• Loading

• Ground movement

• Stability of different building elements

• With emphasis on traditional construction

Considerations are given for materials like timber and masonry.

The document emphasises the importance of ensuring that a building can withstand various loads—including:

• Dead loads

• Imposed loads

• Wind loads

…without compromising the safety or stability of that building—or buildings nearby.

It also addresses ground movement caused by:

• Swelling

• Shrinkage

• Subsidence

—to prevent adverse effects on building stability, or, more likely, to avoid insurance claims against NHBC.

Different sections of the document focus on:

• Stability

• Timber elements

• Masonry

• Chimneys

• Foundations

For instance, it provides guidance on:

• Selecting suitable materials

• Ensuring proper connections between walls, roofs, and floors

Requirements for:

• Wall cladding

• Roof coverings

…are also mentioned, highlighting the need for:

• Structural integrity

• Durability

• Resistance to external forces

Fixings for cladding and roofing must be:

• Appropriately designed

• Able to withstand applied loads and environmental conditions

Additionally, the document addresses considerations for existing buildings undergoing a material change of use, and provides guidance on addressing disproportionate collapse—about which Part Two will be released next week.

So here we have it—Approved Document A serves as a comprehensive resource for:

• Architects

• Engineers

• Builders

…to ensure that buildings meet regulatory standards for safety and stability, especially for small and traditional buildings.

However, structural engineers can go on and design much, much more, using other approved standards and guidance.

🎵 [Music] 🎵

This is the end.

I'm glad you stayed all the way till now.I hope this episode helped you understand the expectations of Approved Document A—and that you now know how to use that document.

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.

You can book a non-obligatory consultation on our website:👉 www.bytnar.co.uk 👈

Ask a specific question—whether it’s:

• "Can you help with my project?"

• Or "What should I do next?"

We will help you find the right direction.

At Bytnar, we help our clients design and execute their dream homes or investments.

I’ll now take some time to dive into the topic of disproportionate collapse, to deliver some simple answers for you next week.

For now, have a great weekend, and a successful week ahead!

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