Waterproofing for New Builds: Building Regulations and Best Practices ![Loading Syla Damp Proofing](https://syladamproofing.co.uk/img/logo/logo.svg) [ contact@syladamproofing.co.uk ](mailto:contact@syladamproofing.co.uk) Mon–Fri 8am–6pm · Sat 9am–2pm [Book a free damp survey](https://syladamproofing.co.uk/request-a-damp-survey) [ 07399 539 436](tel:07399539436) | [ 020 3051 3196](tel:02030513196) [ ![](https://syladamproofing.co.uk/img/icons/bar_icon.svg) ](javascript:void(0)) [![Syla Damp Proofing — back to homepage](https://syladamproofing.co.uk/img/logo/logo.svg)](https://syladamproofing.co.uk) - [Home](https://syladamproofing.co.uk) - [Our Services](https://syladamproofing.co.uk/services) - [Resources](https://syladamproofing.co.uk/blog) - [Our Work](https://syladamproofing.co.uk/gallery) - [About Us](https://syladamproofing.co.uk/about-us) - [Contact Us](https://syladamproofing.co.uk/contact-us) - [Get In Touch](https://syladamproofing.co.uk/contact-us) [![Syla Damp Proofing — back to homepage](https://syladamproofing.co.uk/img/logo/logo.svg)](https://syladamproofing.co.uk) - [](https://facebook.com) - [](https://instagram.com) - [ ](https://www.mybuilder.com/profile/syla_damproofing) [![Syla Damp Proofing — back to homepage](https://syladamproofing.co.uk/img/logo/logo.svg)](https://syladamproofing.co.uk) #### Office Address Flat 35, The View Staines Road West, Sunbury-on-Thames, TW16 7FF #### Phone & Mobile Number [020 3051 3196](tel:02030513196) [07399539436](tel:07399539436) #### Email Address [](https://www.facebook.com/syladamproofing) [ ](https://www.instagram.com/syla_damp_proofing_) [ ](https://www.mybuilder.com/profile/syla_damproofing) [ ](https://www.checkatrade.com/give-feedback/1097677?utm_source=members_area&utm_medium=link&utm_campaign=review_reminder&utm_content=ttr_id) ![Syla Damp Proofing](https://syladamproofing.co.uk/img/logo/logo.svg) Syla Damp Proofing +44 20 3051 3196 contact@syladamproofing.co.uk https://syladamproofing.co.uk ![Syla Damp Proofing](https://syladamproofing.co.uk/img/logo/logo.svg) Blog Waterproofing for New Builds: Building Regulations and Best Practices ===================================================================== Damp problems in newly built properties are more common than you would expect. What BS 8102 and the Building Regulations require, and how to get it right first time. +44 20 3051 3196 4.9 (47 reviews) Waterproofing for New Builds: Building Regulations and Best Practices ===================================================================== [Home](https://syladamproofing.co.uk) / Waterproofing for New Builds: Building Regulations and Best Practices BlogWaterproofing for New Builds: Building Regulations and Best Practices --------------------------------------------------------------------- 10 May 2026 Waterproofing a new build correctly from the start is far cheaper and more effective than retrofitting it later. Yet damp problems in newly constructed properties are surprisingly common — often because waterproofing was treated as an afterthought rather than designed into the build from the foundations up. Whether you are a developer, architect, or self-builder working on a London project, understanding the regulatory requirements and current best practices for waterproofing will protect the building and avoid costly remedial work within the first few years. Why New Builds Still Get Damp ----------------------------- It is a common assumption that damp is a problem exclusive to older properties. In reality, new builds face their own set of waterproofing challenges: - **Construction moisture** — a typical new build contains thousands of litres of water in its concrete, mortar, plaster, and screed. If the building is sealed and occupied before this moisture has dried out, it becomes trapped and manifests as condensation, mould, or damp patches. - **Tight building envelopes** — modern energy efficiency standards require high levels of airtightness, which reduces natural ventilation and increases the risk of condensation if mechanical ventilation is not properly specified. - **Below-ground construction** — basements and lower ground floors are increasingly common in London new builds, and these require specialist waterproofing design that goes well beyond a simple membrane. - **Programme pressure** — compressed construction programmes can lead to shortcuts in waterproofing detailing, particularly at junctions, penetrations, and transitions between different waterproofing systems. Building Regulations: What the Law Requires ------------------------------------------- ### Approved Document C: Site Preparation and Resistance to Moisture **Approved Document C** of the Building Regulations sets out the requirements for protecting buildings against moisture from the ground and from weather. The key provisions for new builds are: **Walls (Section 5)** - External walls must resist the passage of moisture to the inner face - Cavity walls must include a damp proof course (DPC) at least 150mm above external ground level - Cavity trays must be installed above openings and at any point where moisture could bridge the cavity - Solid walls must incorporate a moisture barrier or be constructed of materials that resist moisture penetration **Floors (Section 4)** - Ground floors must incorporate a damp proof membrane (DPM) - The DPM must be continuous with the DPC in the walls to form an unbroken moisture barrier - Concrete ground floors typically use a 1200-gauge polyethylene DPM, lapped and taped at joints **Below-Ground Structures (Section 3)** - Basements and other below-ground habitable spaces must be waterproofed to resist groundwater and surface water pressure - The regulations reference **BS 8102:2009** (Code of Practice for Protection of Below Ground Structures Against Water from the Ground) as the standard for basement waterproofing design ### BS 8102:2009 — The Basement Waterproofing Standard BS 8102 defines three types of waterproofing protection for below-ground structures: TypeSystemHow It Works**Type A**Barrier protectionA waterproof membrane (tanking) applied to the structure — externally, internally, or sandwiched within the construction**Type B**Structurally integral protectionThe structure itself is designed to be waterproof, using waterproof concrete (e.g., reinforced concrete designed to BS EN 1992-3)**Type C**Drained protectionA cavity drain membrane system manages any water that penetrates the structure, directing it to a sump and pump for removalFor habitable basements, BS 8102 recommends using **at least two types** in combination — for example, Type B waterproof concrete with a Type C cavity drain membrane as a secondary defence. This dual approach provides redundancy: if one system fails or is breached, the other continues to protect the space. For a deeper guide to basement waterproofing methods, see our [basement waterproofing vs tanking guide](/blog/basement-waterproofing-vs-basement-tanking). ### NHBC Standards For new homes registered with the **National House-Building Council (NHBC)**, Chapter 5.4 of the NHBC Standards sets additional requirements for below-ground waterproofing. These standards require: - A waterproofing design prepared by a specialist - Selection of a system appropriate to the assessed water table and ground conditions - Independent inspection of waterproofing installation at key stages - A minimum design life of 60 years for the waterproofing system Best Practices for New Build Waterproofing ------------------------------------------ ### 1. Design Waterproofing Early Waterproofing should be considered at **RIBA Stage 2 (Concept Design)** or earlier — not left to the contractor to figure out on site. Early design allows the waterproofing strategy to influence structural decisions, drainage layout, and service penetration locations. ### 2. Commission a Waterproofing Design Specialist For any project with a basement or below-ground habitable space, appoint a specialist waterproofing designer. They will assess ground conditions, water table levels, and drainage capacity, and specify a system that meets BS 8102 and NHBC requirements. This is a regulatory expectation, not an optional extra. ### 3. Get the DPC and DPM Details Right The most common waterproofing failures in new builds occur at **junctions** — where the DPC meets the DPM, where the floor meets the wall, and where services penetrate the moisture barrier. Ensure: - The DPM laps up behind the DPC to form a continuous barrier - All service penetrations through the DPM are sealed with proprietary collars or mastic - Cavity trays are installed at every point where moisture could bridge from the outer to inner leaf ### 4. Allow for Drying Out A new build needs time to release construction moisture. Best practice includes: - **Ventilating** the building during and after the wet trades (plastering, screeding) using temporary dehumidifiers or natural ventilation - **Not decorating** internal walls for at least one full heating season to allow moisture to escape - **Specifying breathable finishes** initially — lime plaster or clay paint allows moisture to evaporate through the surface, whereas vinyl wallpaper or impermeable paint traps it ### 5. Specify Adequate Mechanical Ventilation Modern airtight new builds **must** have mechanical ventilation to manage indoor moisture levels. The standard approach is a **Mechanical Ventilation with Heat Recovery (MVHR)** system, which extracts moist air from wet rooms and supplies fresh, filtered air to living spaces while recovering heat. Without MVHR or equivalent, condensation problems are virtually guaranteed in a building that meets current airtightness standards. ### 6. External Drainage and Landscaping Ensure the external ground levels, drainage, and landscaping work **with** the waterproofing, not against it: - Finished ground levels must be at least **150mm below the DPC line** - Surface water drainage must direct water **away** from the building - Raised planters, paving, and paths must not bridge the DPC or block weep holes - Land drains or French drains may be needed on sloping sites to intercept groundwater before it reaches the foundations Common Mistakes to Avoid ------------------------ - **Bridging the DPC with render or paving** — one of the most frequent causes of damp in new builds. External render must stop above the DPC, and paving must not be laid above it. - **Omitting cavity trays** — particularly above windows, doors, and where lean-to roofs meet cavity walls. A missing cavity tray allows rainwater to track across the cavity and saturate the inner leaf. - **Relying on a single waterproofing system for basements** — BS 8102 recommends dual protection for habitable spaces. A single membrane or a single type of waterproof concrete provides no redundancy. - **Sealing the building before it has dried out** — rushing to decorate and occupy traps construction moisture inside the building envelope. New Build Waterproofing in London --------------------------------- London presents specific challenges for new build waterproofing: - **High water tables** in areas near the Thames, particularly in Southwark, Lambeth, and Tower Hamlets, require robust below-ground waterproofing with sump and pump systems - **Clay soils** across much of south and west London swell and shrink with seasonal moisture changes, placing additional stress on below-ground waterproofing membranes - **Basement extensions** are extremely common in London new builds and conversions, pushing waterproofing requirements well beyond standard above-ground construction We work with homeowners, self-builders, and their architects on London projects, specifying and installing waterproofing systems that meet current regulations and provide long-term protection. Next Steps ---------- If you are planning a new build or conversion project in London and need waterproofing advice, we can help — from specifying the right system at design stage through to installation. - [Request a consultation](/contact-us) - [View our basement waterproofing services](/services/basement-waterproofing) - [Read our complete guide to cellar waterproofing](/blog/complete-guide-to-cellar-waterproofing-in-london) - [Learn about basement waterproofing vs tanking](/blog/basement-waterproofing-vs-basement-tanking) - [Contact us](/contact-us) ##### Share This Post: - [ ](https://twitter.com/intent/tweet?url=https%3A%2F%2Fsyladamproofing.co.uk%2Fblog%2Fwaterproofing-for-new-builds-building-regulations-and-best-practices&text=Waterproofing+for+New+Builds%3A+Building+Regulations+and+Best+Practices "Share on X (Twitter)") - [ ](https://www.facebook.com/sharer/sharer.php?u=https%3A%2F%2Fsyladamproofing.co.uk%2Fblog%2Fwaterproofing-for-new-builds-building-regulations-and-best-practices "Share on Facebook") - [ ](https://www.linkedin.com/sharing/share-offsite/?url=https%3A%2F%2Fsyladamproofing.co.uk%2Fblog%2Fwaterproofing-for-new-builds-building-regulations-and-best-practices "Share on LinkedIn") - [ ](mailto:?subject=Waterproofing+for+New+Builds%3A+Building+Regulations+and+Best+Practices&body=https%3A%2F%2Fsyladamproofing.co.uk%2Fblog%2Fwaterproofing-for-new-builds-building-regulations-and-best-practices "Share via email") More ArticlesRecent blog posts ----------------- 10 May 2026### [Can You Claim on Insurance for Damp Damage?](https://syladamproofing.co.uk/blog/can-you-claim-on-insurance-for-damp-damage) Whether your insurer covers damp damage comes down to one thing: was the cause sudden or gradual? What is covered, what is excluded, and how to give your claim the best chance. [Read More ![](https://syladamproofing.co.uk/img/icons/right_arrow.svg)](https://syladamproofing.co.uk/blog/can-you-claim-on-insurance-for-damp-damage) 10 May 2026### [Condensation vs Damp: How to Tell the Difference and What to Do](https://syladamproofing.co.uk/blog/condensation-vs-damp-how-to-tell-the-difference) Condensation is the most common cause of moisture in UK homes, and the most commonly mistaken for rising damp. How to tell them apart and what each one actually needs. [Read More ![](https://syladamproofing.co.uk/img/icons/right_arrow.svg)](https://syladamproofing.co.uk/blog/condensation-vs-damp-how-to-tell-the-difference) 10 May 2026### [How to Choose a Waterproofing Contractor: 7 Questions to Ask](https://syladamproofing.co.uk/blog/how-to-choose-a-waterproofing-contractor) Seven questions every London homeowner should ask before hiring a waterproofing contractor, covering PCA membership, surveyor qualifications, systems, and guarantees. [Read More ![](https://syladamproofing.co.uk/img/icons/right_arrow.svg)](https://syladamproofing.co.uk/blog/how-to-choose-a-waterproofing-contractor) Worried about damp? 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