EPISODE: 020 - APPROVED DOCUMENT C - SITE PREPARATION AND RESISTANCE TO CONTAMINATES AND MOISTURE

BYTNAR - TALKS

EPISODE 020 - APPROVED DOCUMENT C - SITE PREPARATION AND RESISTANCE TO CONTAMINATES AND MOISTURE

This episode is for people who want to know more about Approved Document Part C – Site Preparation and Resistance to Contaminates and Moisure.

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

• What are the key requirements of Approved Document C for site preparation and resistance to contaminants and moisture?

• How do Building Regulations address construction in flood-prone or contaminated areas?

• What legislation applies to contaminated land in the UK, including The Contaminated Land Regulations 2006?

• How do you ensure a building site is free from hazardous materials like asbestos, radon, or sulphates?

• What are the methods for evaluating building sites for contaminants and moisture issues?

• Where can I find guidance on impact assessments and remediation for contaminated sites, like BRE DIGEST or NHBC publications?

• What are the different types of risk assessment procedures for managing site contamination?

• How can subsoil drainage be implemented to protect buildings from groundwater damage?

• What construction methods help prevent ground moisture transfer in floors, walls, and roofs?

LET'S TALK ABOUT YOUR PROJECT

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This is Bytnar Talks: The Engineer Takes on Construction – Episode 20

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 C: Site Preparation and Resistance to Contaminants and Moisture

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

It is Thursday, the lucky 13th of June 2024, and I’m back with you with the 20th episode—and information on site preparation and resistance to contaminants and moisture.

Yes, you heard it right—it’s the 20th episode, so that would mean Bytnar Talks is now at the top of the podcasters of podcasts in the world!Not because we have the best quality or talk about the things that everyone wants to listen to, but because we persevere—and that’s the 20th episode.And I think we still deliver—a lot, lot more.

Anyway, let’s get back to the merits of this podcast, and let’s recap what I talked to you about in the last episode, where I finalized the discussion on Approved Document B, Volume Two: Fire Safety in Buildings Other Than Dwellings.

I mentioned Fire Requirement B3, which mandates that buildings be designed to:

• Maintain structural stability during an event of fire, and

• Resist fire spread between shared walls,

  
  

  …focusing on compartmentation and fire suppression systems.

Loadbearing elements such as roofs, floors, and walls must meet detailed fire resistance standards outlined in Appendix B, with single-storey buildings generally exempt—unless they support compartment structures.

However, there are caveats, provisos, and stipulations to everything.So, raised storage areas in single-storey buildings may require additional protection, as they may change the character of the building and turn it into a multi-storey.

I told you that sprinklers are generally required for buildings with top storeys over 30 m above ground level, to enhance fire suppression.

Cavity barriers are necessary to prevent fire spread through concealed spaces, with specific guidelines for large hidden spaces.

Open-sided car parks may rely on natural ventilation, while closed-sided car parks need enhanced fire resistance and mechanical ventilation, in compliance with standards like BS 1366, BS 12101, or BS 7346.

External walls and roofs must resist fire spread, considering the building’s height, use, and position, with Regulation 7 enforcing appropriate materials and workmanship.

Adequate access for fire appliances and firefighters is crucial, with specific guidelines for:

• Vehicle access,

• Fire mains, and

• Hydrants,

  
  

  …with special consideration for buildings lacking fire mains or with extensive perimeters.

Finally, I discussed Regulation 38, which requires the provision of relevant fire safety information to the responsible person upon the completion or occupation of the building.

This information should include:

• Design and construction details,

• As well as information necessary for the safe operation and maintenance of the building—

  
  

  …particularly for those under the Regulatory Reform (Fire Safety) Order 2005,

  
  

  which, in simple terms, means nearly all buildings except single dwellings and single flats.

In This Episode

We now move on to Approved Document C and the consideration for the discharge of site preparation and resistance to contaminants and moisture requirements.

So without further ado, let’s dive into the text of Approved Document C. 🎵

As mentioned, in this episode I will talk about the statutory guidance contained within Approved Document C: Site Preparation and Resistance to Contaminants and Moisture.

I will start by reading you the actual requirement as put in the Building Regulations, which breaks the consideration into two parts:

• Part C1 – deals with preparation of the site and resistance to contaminants

• Part C2 – deals with resistance to moisture

The guidance is then further divided into Sections 0 to 6, along with some general commentary—and I cannot wait to tell you all about it. So let us not waste any more time on fussing about and dive into it straight away, shall we?

So here we go:

Part C – Site Preparation and Resistance to Contaminants and Moisture

Requirements – C1

Point 1:The ground to be covered by the building shall be reasonably free from any material that might damage the building or affect its stability, including vegetable matter, topsoil, and pre-existing foundations.

Point 2:Reasonable precautions shall be taken to avoid danger to health and safety caused by contaminants on or in the ground covered or to be covered by the building and any land associated with the building.

Point 3:Adequate subsoil drainage shall be provided, if it is needed, to avoid:

• (a) the passage of ground moisture to the interior of the building

• (b) damage to the building, including damage through the transport of water-borne contaminants to the foundations of the building

Point 4:For the purposes of this requirement, contaminants means any substance which is, or may become, harmful to persons or buildings—including substances which are corrosive, explosive, flammable, radioactive, or toxic.

Requirement C2 – Resistance to Moisture

The walls, floors, and roofs of the building shall adequately protect the building and the people who use it from harmful effects caused by:

• (a) ground moisture

• (b) precipitation, including wind-driven spray

• (c) interstitial and surface condensation

• (d) spillage of water from or associated with sanitary fittings or fixed appliances

It could not be simpler to abide by the requirement—just as long as we make sure there will be no damage to the structure or the health and well-being of the occupants, the requirement can be considered fulfilled.

It needs to be noted, though, that the building may require upgrading when it undergoes material change of use, even if it is a historical building, and historical fabric may need upgrading or relocation for later reinstatement.

Section 0 – General Considerations

Section 0 deals with general considerations, such as performance.

If you are in the construction game, you are well aware of things that can damage your building—things like sulfates, or the Japanese knotweed, and many, many more can harm you as you go about living in your property.

Eating arsenic-infused kale from your patio garden may prove not so healthy after all.Living in damp and moldy rooms is also not for the faint-hearted and sitting in the rain air whilst enjoying your favorite movie and unknowingly developing cancer in your lungs is something you should be protected from.

There are many ways in which the structure and well-being of the occupants in and around the building can be undermined, and the guidance highlights the responsibility of designers, builders, and contractors to ensure that the requirements of the Building Regulations are fulfilled.

The guidance points out that special consideration may be needed in flood-prone areas.Flooding, for whatever reason, may be problematic.Some sites may be affected by contaminants and may need extended consideration of other legislation, such as:

• The Contaminated Land (England) Regulations 2006

• The Environmental Protection Act 1990

• The Town and Country Planning Acts

There are also obligations put on us when we discover contamination on our land, and it includes:

• The provision of information to appropriate agencies, and

• Gaining appropriate authorizations for the works we are about to do.

And that leads us nicely to Section 1, which talks about:

Clearance or Treatment of Unsuitable Materials

In this section, you will quickly find out there is a process to all that building professionals do—and that no consideration starts without gathering proper information first.

This process is familiar to all surveys undertaken by engineers out there, and it contains:

• Planning stage

• Desk study

• Walkover survey

• Sampling and testing

Many of us think only about the sampling and testing stage, but this is the last part and cannot be done well if the previous steps are not in place and undertaken by a competent person with well-won experience.

Naturally, vegetation, roots, and turfs can be problematic for the bearing capacity and behaviour of structures. Trees in the near vicinity of structures have the potential to cause damage, especially when the soil consists of shrinkable clays.

The guidance references several publications to abide by when assessing such impact or providing a solution. It names BRE Digest 240, 241, and 298. It’s references NHBC Chapter 4.2. You can appreciate the map prepared by the guide, showing the typical distribution of shrinkable soil and where to expect less sulfate in the ground.

Roots can cause problems in the underground drainage as well, and building on brownfield sites or on fill brings about certain additional risks that also need identification during the investigation work, to inform the appropriate approach to the design and specifications for the building.

Section 2 – Resistance to Contaminants

This section deals with:

• Biodegradable waste in landfills

• Pesticides

• Fuel and oil spills

• Preservatives

• Munitions

• Decaying biological matter,

  
  

  …and many, many more potential sources that can be part of your site.

Identification of typical contaminants by the industry can be found in the EFRA/Department of the Environment profiling of industries guide, a rudimentary list of which is contained within the table in the Approved Document.

The natural geology may also suggest contamination with naturally occurring heavy metals or gases, for which further guidance can be found in the Environment Agency publications about land quality in England and Wales.

To address solid and liquid contaminants, we first need to assess the risk.

In essence, for a risk to exist, there must be:

1. A source of contamination

2. A pathway (such as air, soil, or water)

3. A receptor (such as a building, building services, or people in or around the building)

Remove any one of these three elements, and the risk is eliminated.

But first—you need to identify the hazard, don’t you?

DEFRA and the Environment Agency procedures, published in CLR 11 (now withdrawn but still referenced by the Approved Document), set out the stages of the procedure.

The approach is divided into three tiers:

• Tier 1 – Preliminary Risk Assessment

• Tier 2 – Generic Quantitative Risk Assessment

• Tier 3 – Detailed Quantitative Risk Assessment

As with all assessments, we start light, before we go into it all guns blazing—which in this case would be the Tier 3 approach.

Before deciding on the appropriate course of action, we need to:

• Identify possible hazards

• Assess the site

• Estimate and evaluate the risks

The scale and detail of the surveys will depend on the extent of the development part of the site, and the possible receptors of any particular hazard.

If we need to deal with the contamination, we can either:

• Treat it

• Contain it, or

• Remove it

Each strategy will have its limits and cost consequences, so needs to be approached carefully.

CIRIA publications, NHBC materials, and Environment Agency guidance are the places to go for further detail.

Special mention is given to hydrocarbons permeating polyethene water pipes, with reference to the guidance contained within the Water Research Report FR0448.

Gases can be a big issue—such as:

• Methane

• Carbon dioxide

• Volatile organic compounds,

  
  

  …and other gases from landfills, mines, organic deposits, and hydrocarbon spills.

These need to be taken into serious consideration.

Often, the only solution for isolating the receptor from the gas is through the use of:

• Membranes

• Ventilated spaces—to allow the gas to dissipate outdoors and not find its way into the building

Similarly, radon protection measures may be required, and can include radon protection membranes over naturally or mechanically ventilated sumps.

Section 6 – Subsoil Drainage

This section mentions considerations of gravity soil drainage when the site is susceptible to higher water tables, but not necessarily flooding as well as many other considerations for sites that do flood.

To address matters like:

• Surging of sewage, or

• When building over subsoil drainage,

  
  

  …due consideration must be given to either:

• Rerouting, and/or

• Provision of access points for cleaning and maintenance

Subsoil drainage should be considered if the building is located where groundwater transports contaminants and its job is to drive that water away from the building and its services.

Section 4 – Floors

And that is the start of Requirement C2.

The requirements are rather simple:

• The floor cannot transfer moisture from the ground to the top surface.

• It must not promote condensation, or be subject to interstitial condensation.

This means that somewhere in the buildup of the floor, you will need to provide:

• A vapor barrier

• Insulation, and

• A continuous DPM (damp-proof membrane)

This may be relaxed in storage spaces.

There are some minimum requirements for ground-bearing slabs, such as: a minimum 100 mm thick dense concrete slab, with an under-slab membrane of 0.3 mm thick, or otherwise called 1200 gauge—whatever nomenclature you like to use.

It should be laid over well-compacted hardcore and a layer of blinding.The purpose of blinding is to remove any sharp edges from the hardcore that could penetrate the membrane.

DPM over the slab can be the same polythene as for the under-slab application, but it can also be three layers of cold-applied bitumen solution, or a similar moisture- and vapour-resistant material.

More involved consideration may be needed for slabs subject to water pressure.

The suspended timber ground floor needs to be isolated from ground moisture by a damp-proof course, and must have a ventilated space underneath, with ventilation slots on opposite sides of the building of minimum 1500 mm² per metre run of external wall, or 500 mm² per m² of floor area, whichever is greater.

The ground beneath should be:

• Levelled,

• Drained, and

• Covered to resist moisture and the growth of plants.

Sometimes, the ground needs to be treated to kill any unwanted vegetation under the suspended floor.

Stopping that moisture and vegetation can also be achieved by:

• Pouring 100 mm of lean mix concrete over compacted hardcore, or

• Laying a damp-proof membrane under 50 mm of either sand or mixed concrete blinding.

Some consideration should be given to the boarding of the floor, which needs to be durable for its intended use. For example, in kitchens or toilets, it should be more resistant to spills than in other parts of the building.

All the BS standards need to be followed.

Similar considerations are applicable to suspended concrete floors.

In both timber and concrete suspended floors, heave may be an issue and may influence the amount of ventilated space underneath the floor.But it generally starts with 150 mm of clear space, or 75 mm under the wall plates.

When it comes to internal or surface condensation, the document makes reference to other approved sources such as:

• BRE Report 262, and

• Information Paper IP17/SL1,

  
  

  but gives a minimum U-value of 0.7 W/m²K.

Section 5 – Walls

Like floors, walls need to be constructed to stop:

• Moisture from the ground,

• Moisture from the outside, and

• Vapour and surface condensation.

When we talk dampness from the ground, we should think of an appropriate damp-proof course (DPC), made from engineering brick, slate, bitumen, or polyethylene. Generally, if the wall abuts the ground, the DPC should be 150 mm above ground level.

In the case of cavity walls, you either:

• Have a cavity that gathers water at the base (some 225 mm or three courses of brick below the damp-proof course),

  
  

  or

• There should be a cavity tray that directs water toward the external leaf,

  
  

  …which should include weep holes—provided every 900 mm (or every four bricks),

  
  

  but at least two weep holes per tray, and an end stop over openings.

When it comes to precipitation, the choices are three:

1. A thick enough solid wall,

2. A cavity wall, or

3. Cladding

If the exposure to driven rain is very severe, cladding is the right choice for the protection of solid walls.

Otherwise, the wall can be:

• Rendered, or

• Left bare

Anyhow, tops of walls, tops and bottoms of openings, and abutments with roofs should be properly addressed to stop moisture ingress.

Walls can be insulated in a plethora of ways:

• Externally,

• Within the cavity, or

• Internally

In all cases, moisture passage from the outside to inside (and vice versa) should be considered, and the appropriate composition specified.

Some details on the insulation of masonry walls, in line with exposure to driven rain zones, are provided within the guidance.

Cladding should be:

• Robust, and

• Fit for function

It can be:

• Impervious, like metal or glass

• Weather-resistant, like natural stone, clay, or wood

• Moisture-resistant, like products lapped at joints, or jointless, or sealed at joints

In any case, it needs to perform its function.

Particular attention should be given to the sealing of doors and windows, especially in parts of the country that suffer extreme exposure to driven rain, as well as in circumstances where level thresholds are expected to facilitate uninhibited access to the building.

Condensation issues will generally be addressed if the wall achieves a maximum U-value of 0.7 W/m²K.Interstitial condensation considerations are covered in:

• BS 5250, and

• BS EN ISO 13788

Section 6 – Roofs

Section 6 deals with roofs, but it basically reiterates the expectations previously given for framed and clad walls. The limit for condensation, however, is set at nearly half of that for floors and walls and it is 0.35 W/m²K.

So this is it, folks—Approved Document C: Site Preparation and Resistance to Contaminants and Moisture.

Let's Sum It Up:

Requirement C1

Mandates that building sites be free from harmful materials.Precautions must be taken to avoid health and safety hazards from contaminants like corrosives, explosives, radioactive material, or toxic substances.

Requirement C2

Ensures that the building’s walls, floors, and roof protect against:

• Ground moisture

• Precipitation, and

• Condensation

Section 0 – General Considerations

Tells us that designers and contractors must ensure compliance with Building Regulations—with special consideration given to flood-prone or contaminated areas.

Relevant additional legislation includes:

• The Contaminated Land (England) Regulations 2006

• Equivalent provisions for Wales

• Different regulations for Scotland and Ireland

• The Environmental Protection Act 1990

Section 1 – Clearance or Treatment of Unsuitable Material

Emphasizes thorough evaluation of site conditions and planning of investigation,starting with:

• Desk study,

• Walkover survey,

• Sampling and testing

Guidance references include:

• BRE Digests,

• NHBC publications

  
  

  …for impact assessments and providing solutions.

Section 2 – Resistance to Contaminants

Mentions common contaminants, including:

• Biodegradable waste

• Pesticides

• Hydrocarbons

And outlines the risk assessment procedure:

1. Preliminary Risk Assessment

2. Generic Quantitative Risk Assessment

3. Detailed Quantitative Risk Assessment

Options for dealing with contamination:

• Treatment

• Containment, or

• Removal

With guidance from:

• CIRIA,

• NHBC,

• The Environment Agency

Section 3 – Subsoil Drainage

Covers:

• Gravity soil drainage, especially in flood-prone zones

• Provisions for routing or accessing existing subsoil drainage

• Ensures water is directed away from the building and its services

Section 4 – Floors

Floors must:

• Prevent ground moisture transfer

• Avoid condensation

• Incorporate:

  • A vapour barrier,

  • Insulation, and

  • A damp-proof membrane

Ground-bearing slabs should be at least 100 mm thick, with appropriate polythene sheets as damp-proof membranes.

Suspended floors require:

• Ventilation of void space, and

• Isolation from ground moisture

Section 5 – Walls

Walls must:

• Prevent moisture ingress from both ground and outside

• Mitigate condensation

Use of:

• Appropriate DPCs (damp-proof courses),

• Cavity trays,

  
  

  …may be necessary.

Wall construction options:

• Solid walls

• Cavity walls

• Framed and clad walls,

  
  

  …with insulation considerations specific to each.

Section 6 – Roofs

Roofs must meet similar moisture and condensation resistance standards as walls and floors.In essence, they reiterate previous expectations for framed and clad elements.

In gist, these requirements and sections provide general guidelines to ensure buildings are:

• Safe

• Resistant to contaminants and moisture

• Protective of the structure, services, and occupants

In the Next Episode

We’ll move to Approved Document D: Toxic Substances, to talk about cavity insulation,and then move into Approved Document E: Resistance to the Passage of Sounds

I hope you enjoyed this episode and that the considerations of Approved Document C: Site Preparation and Resistance to Contaminants and Moisture now make simple sense to you.

The Building Control Approved Document guidance is pretty simple once you understand why and what is required.

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,

…and 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 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

• Investigate structural problems,

  
  

  …and provide you with an appropriate strategy, design, and specifications for 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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