If you’re purchasing a new build home featuring curtain walling or modern cladding systems, you’re investing in a property with sophisticated external envelope technology. These systems are increasingly common in contemporary developments, particularly in apartment buildings and mixed-use schemes. Whilst they offer excellent thermal performance and striking aesthetics, they also require careful specification, installation, and inspection to ensure they perform as intended.
The NHBC (National House Building Council) has established comprehensive standards in Chapter 6.9 specifically for curtain walling and cladding systems. These standards exist to protect homebuyers by ensuring these critical building elements provide adequate weather resistance, thermal efficiency, fire safety, and long-term durability. Understanding what these standards require can help you appreciate what your developer should be delivering and what to look for during your snagging inspection.
Before diving into the standards, it’s helpful to understand what we’re actually talking about. Curtain walling refers to non-load bearing façade systems, typically comprising a framework with glazed panels that hang on the building’s structure like a “curtain” rather than supporting any weight themselves. You’ll often see curtain walling on modern apartment buildings with extensive glazing and sleek, contemporary appearances.
Cladding systems, by contrast, are the external skin applied to a building’s structural walls. The NHBC standards cover several types, including rainscreen cladding (with a ventilated cavity behind panels), insulated render systems (where insulation is fixed to the wall and then rendered), and brick slip cladding (using thin brick sections attached to a carrier system). Each type has its own specific requirements and potential issues to watch for.
These systems differ fundamentally from traditional brick and block construction, which is why the NHBC dedicates an entire chapter to their specific requirements. When properly designed and installed, they provide excellent performance. When corners are cut or installation is poor, however, problems can emerge that range from minor aesthetic issues to serious water penetration or thermal performance failures.
Why These Standards Matter to Homebuyers
You might wonder why you need to understand technical construction standards when you’re simply buying a home. The answer is straightforward: knowledge is power. Understanding what standards your developer must meet helps you recognise when something isn’t right and gives you the confidence to challenge defects rather than accepting assurances that “it’s meant to be like that.”
The NHBC standards establish clear requirements that your developer has committed to meet. These cover everything from the types of materials that can be used and how they must be fixed, through to testing requirements that verify the system actually works. When a professional snagging inspection identifies defects, these standards provide the objective criteria that demonstrate work falls short of acceptable quality.
Water penetration is perhaps the most serious risk with curtain walling and cladding systems. Unlike traditional masonry construction where water resistance comes from the sheer thickness and mass of the wall, these modern systems rely on careful detailing, proper sealing, and effective drainage to keep weather out. A missing seal, blocked drainage path, or poorly detailed interface can allow water into the building structure, potentially causing significant damage.
Thermal performance is another critical consideration. These systems place insulation on the exterior of the building structure, which is generally beneficial, but only if the insulation is properly specified, installed without gaps, and protected by appropriate vapour control layers. Poor thermal performance doesn’t just mean higher heating bills; it can also lead to condensation, cold spots, and mould growth that affect both your comfort and health.
Fire safety has understandably received heightened attention following high-profile building fires. The NHBC standards require proper fire-stopping, appropriate material selection, and cavity barriers to prevent fire spreading through the external wall system. For buildings over 18 metres, particularly stringent requirements apply.
Key Requirements Every Homebuyer Should Understand
The NHBC standards establish requirements across numerous aspects of curtain walling and cladding systems. Whilst the full technical detail runs to many pages, several key principles are worth understanding as a homebuyer.
Firstly, systems must have proper certification from independent technical approval bodies such as the British Board of Agrément, Building Research Establishment, or similar organisations. This isn’t simply the manufacturer claiming their product is suitable; it requires independent verification that the system has been tested and found to perform adequately. Your developer should be able to provide evidence of this certification if asked.
Weather resistance depends on multiple layers of protection. Curtain walling systems typically incorporate external and internal seals with drained and ventilated cavities between them, acknowledging that the external seal might not be perfect under extreme conditions. Rainscreen cladding systems work on the principle of pressure equalisation, where the cavity behind the panels is compartmented so that pressure differences don’t drive water through the joints. Insulated render and brick slip systems rely on the integrity of the rendered or brick slip finish, with proper detailing at vulnerable locations like window openings and interfaces.
The standards specify minimum cavity widths for rainscreen cladding (typically 50mm for open-jointed panels or 38mm for baffled joints) to ensure adequate drainage and ventilation. They require specific fixing types and spacing, particularly noting that non-combustible fixings must be provided at specified intervals for fire safety. They establish requirements for thermal breaks in metal frames to prevent cold bridging, and they mandate vapour control layers on the warm side of insulation to manage condensation risk.
Testing is a crucial element of quality assurance. Curtain walling systems should undergo both off-site testing of prototype installations (to verify the design works) and on-site testing of the actual installed system (to verify the installation is correct). This testing typically involves directing water at the façade under pressure and checking for any penetration beyond the drainage cavity. At least five percent of the completed curtain walling should be tested, with emphasis on vulnerable areas.
Installation quality matters enormously. The standards require that systems be installed by operatives who are competent and have received training specific to the system being installed. Generic construction skills aren’t sufficient for these specialised systems. Installation must be completed within reasonable tolerances, ensuring panels are plumb, level, and properly aligned, with consistent joint widths and neat finishing.
What Can Be Identified During a Snagging Inspection
A professional snagging inspection provides valuable protection when purchasing a new build home with curtain walling or cladding systems. Whilst inspectors cannot verify every aspect of compliance with NHBC standards without access to documentation and hidden elements, they can identify numerous visible defects that indicate quality issues.
Installation defects are often readily apparent to an experienced inspector. Panels that aren’t plumb or level, inconsistent joint widths, misaligned components, and poor finishing around edges and trims all indicate that installation tolerances haven’t been achieved. These aren’t merely aesthetic concerns; they can also affect weathertightness and long-term durability.
Weather sealing is a critical area where snagging inspections provide particular value. Missing sealants, gaps in sealant runs, sealant pulling away from substrates, and inadequate depth or width of sealant joints are common defects that can lead to water penetration. Interfaces between the curtain walling or cladding and other building elements (windows, doors, roofs, balconies) are especially vulnerable and deserve careful attention.
Visible damage to components should be identified and rectified before completion. This might include scratched or damaged glazing, dented or marked cladding panels, damaged protective coatings, or components showing signs of impact or poor handling. Insulated glass units with failed seals (condensation between panes) represent a particular concern, as they’ll need replacement.
For insulated render systems, inspectors can check for cracks in the render, poor finishing, colour inconsistencies, inadequate or poorly fitted trims, and areas where reinforcement mesh is visible. For brick slip cladding, they can identify poor coursing, excessive cutting of slips in visible locations, poor jointing, lippage (uneven surfaces), and misaligned corners.
Opening windows and doors in curtain walling should be tested to ensure they operate smoothly, hang square, close securely, and have adequate sealing. Drainage openings at the base of cladding systems should be clear and unobstructed. Ventilation screens should be present and properly fitted to exclude birds and animals whilst allowing necessary ventilation.
What Cannot Be Verified Without Documentation
It’s equally important to understand the limitations of visual snagging inspections. Many critical aspects of curtain walling and cladding systems are hidden within the construction or require documentation to verify.
Structural adequacy, load calculations, and fixing capacities cannot be verified visually. Inspectors cannot determine whether fixings have the correct embedment depth, are installed to proper torque settings, or have adequate load capacity without destructive testing. They must rely on the developer’s quality control processes and NHBC oversight.
Hidden elements such as cavity barriers, fire-stopping, damp proof membranes behind cladding, and vapour control layers are not visible once construction is complete. These critical elements should be verified by NHBC inspectors during construction, but homebuyers don’t typically have access at that stage.
System certification and testing documentation cannot be verified without access to the relevant paperwork. Whilst inspectors can observe the system and identify obvious defects, they cannot confirm that proper off-site testing was completed, that on-site testing achieved satisfactory results, or that the system has appropriate certification for its application.
Thermal performance and condensation risk require specialist assessment using thermal modelling and calculations. Visual inspection cannot determine whether thermal bridging has been properly controlled or whether condensation risk analyses were carried out. These issues may only become apparent after you’ve lived in the property through a winter season.
This doesn’t diminish the value of professional snagging inspections; it simply acknowledges their scope. The aspects that can be visually assessed provide important indicators of overall construction quality. Visible defects often correlate with hidden problems. A builder who takes care over the finish you can see is more likely to have taken care over the elements you cannot see.
Taking Action: Your Next Steps
If you’re purchasing a new build home with curtain walling or cladding systems, investing in a professional snagging inspection is one of the most valuable steps you can take to protect your investment. At New Build Inspections, our qualified inspectors have extensive experience with modern façade systems and understand the NHBC standards that govern their installation.
We’ve prepared a comprehensive guide to NHBC Standards Chapter 6.9 that explains in detail what requirements apply to curtain walling and cladding systems, what can go wrong, and what you should look for. The guide covers everything from the fundamentals of how these systems work through to specific requirements for weather resistance, thermal performance, fire safety, and installation quality.
Whether you’re purchasing an apartment in a development with glazed curtain walling, a house with contemporary rainscreen cladding, or a property featuring insulated render or brick slip systems, understanding these standards empowers you to ensure your home meets the quality you deserve.
Read our full guide to NHBC Standards Chapter 6.9 for curtain walling and cladding on our knowledgebase, where you’ll find detailed explanations of each requirement, what professional inspections can identify, and how your NHBC warranty protects you if defects emerge.
And when you’re ready to book your snagging inspection, our team is here to help ensure your new home is thoroughly checked by independent professionals who understand exactly what standards your developer should be meeting. Contact New Build Inspections today to arrange your inspection and gain the peace of mind that comes from knowing your home has been properly scrutinised before you complete.
Your new home represents a significant investment. Make sure it’s built to the standards you’re entitled to expect.