UK Nationwide Professional Snagging Inspections | Getting the Quality You Deserve

NHBC Releases Technical Extra Issue 17

The National House Building Council (NHBC) has released Issue 17 of their Technical Extra publication, providing important updates and guidance for the house-building industry. The comprehensive document covers several key areas affecting construction standards and building regulations.

Key Updates on Windows and Doors

A recent NHBC survey has revealed that 15% of all defect-related contacts they receive relate to windows and doors, with ironmongery issues being the most significant concern. Ironmongery defects account for approximately 50% of these complaints, with the majority of problems relating to handles, locks, and hinges. The survey identified that many of these issues occur in areas of high usage, such as bedrooms, suggesting potential problems with either incorrect fitting or manufacturing standards.

Customer satisfaction surveys have highlighted that these problems often affect multiple units within developments, with homeowners frequently reporting difficulties in opening and closing windows, and cases where every window has needed adjustment or hinge replacement. To address these issues, NHBC Standards Chapter 6.7 provides specific recommendations for ironmongery installation, including detailed requirements for various door types. For example, external doors should have 1½ pairs of 100mm hinges, while internal doors typically require 1 pair of 75mm hinges. The guidance emphasizes the importance of proper fitting, with locks being appropriately sized for mortices and ensuring proper alignment of keyholes.

Changes to Air Tightness Testing

The NHBC has announced significant changes to air leakage testing with the British Institute of Non-Destructive Testing (BINDT) Registration Scheme being replaced by a new comprehensive ATTMA-branded Scheme from 1 January 2015. This new scheme represents a collaboration between BINDT and ATTMA to create a more harmonised approach to testing standards. A key change is that the scheme now defines its members as companies to ensure ‘corporate accountability’, while still maintaining individual certification for testing staff.

The new system introduces three distinct certification levels for testers: Level 1 for testing dwellings and simple buildings up to 4000m³ in volume, Level 2 for testing all but very large, complex and high-rise buildings, and Level 3 for ‘experts’ in air-tightness testing. To ensure transparency and verification, all ATTMA testers now carry ID cards stating their credentials, backed up by an online register at www.attma.org where their certification levels can be verified. The scheme includes a full-time Scheme Manager who will both police and support members, while also acting as a technical expert to assist Building Control Bodies and builders with complex projects or dispute resolution.

Ventilation Requirements

The NHBC has highlighted important considerations regarding ventilation in homes that achieve better airtightness than originally designed for. According to Approved Document F (2010), homes using background ventilators and intermittent extract fans (System 1) or passive stack ventilation (System 2) require increased total ventilator areas in specific circumstances: when the design air permeability is tighter than 5m³/(h.m²) at 50 Pa, or when the as-built air permeability is tighter than 3m³/(h.m²) at 50 Pa.

This guidance has become particularly relevant as builders have become more proficient at delivering airtight dwellings, with an increasing proportion of homes over-achieving their airtightness targets. The NHBC emphasizes that where a dwelling achieves better airtightness than designed, it may require additional ventilation measures to ensure adequate air quality. For example, if a home was designed with an air permeability leakier than 5m³/(h.m²) but achieves better than 3m³/(h.m²) when tested, it will need additional background ventilation. The guidance stresses that this issue shouldn’t be ignored, given the established links between airtightness, indoor air quality, and occupant health.

Window Safety Guidelines

The NHBC has issued updated guidance on safety measures for windows with low-level cills, particularly focusing on the protection against falls. The guidance addresses an increasing trend in home design where deeper windows and French windows with low-level cills are being incorporated, which can create potential safety risks, especially for children. According to research cited in the guidance, 50% of four-year-old children can step up 410mm, and 3% can step up 550mm, making any cill height lower than 600mm potentially climbable by children.

For French windows, the guidance specifies a minimum guard height of 1100mm measured from finished floor level, with specific requirements for upstands. Where cill heights are between 300mm and 600mm above floor level, the guidance requires a non-climbable barrier height of minimum 700mm above the cill, as these heights are considered readily climbable by children. For cill heights between 600mm and 800mm, compliance can be achieved with barrier rails maintaining an overall guard height of 800mm above floor level. The guidance also addresses scenarios where fixed glazing is used in combination with openable windows, providing specific requirements for guarding arrangements in these cases. Importantly, the document highlights potential conflicts between guarding requirements and means of escape requirements, offering solutions for situations where these conflicts arise.

Autoclaved Aerated Concrete (AAC)

The NHBC has provided important guidance regarding the use of autoclaved aerated concrete (AAC) masonry units, particularly focusing on the differences between European and UK manufacturing and testing procedures. While European-manufactured AAC blocks may appear similar in size and strength to UK-manufactured equivalents, the testing procedures on the continent have traditionally been different, which has important implications for construction projects.

A key difference lies in the testing methodology. In the UK, AAC masonry units have traditionally been tested as whole blocks with maximum dimensions of 650mm length and height not exceeding the length or six times the width. However, across Europe, AAC masonry units may be much larger, with allowable lengths up to 1500mm and heights up to 1000mm. This size difference has led to different testing approaches, with European standards introducing the concept of testing cube specimens for larger units that cannot fit into standard compression testing machines. The NHBC emphasizes that these differences in testing regimes – including variations in size, surface preparation, and moisture conditioning – can significantly affect compression test results. When designing masonry to BS EN 1996-1-1, the manufacturer’s declared unit mean compressive strength must be converted to a normalised mean compressive strength to account for these variations in testing methods.

Steelwork Fabrication Standards

The NHBC has provided important guidance on CE marking requirements for fabricated structural steelwork, following significant changes in regulation. As of 1 July 2014, the harmonised standard for fabricated structural steelwork, BS EN 1090-1, came into force, making it a legal requirement for manufacturers of fabricated products to CE mark their products according to this standard. This requirement extends to all fabricated structural steelwork used in domestic buildings, marking a significant change in quality assurance requirements.

The standard introduces a new concept called ‘Execution Class’, which is used by designers and specifiers to define quality and assurance controls for the fabrication process. There are four Execution Classes (EXC1 to EXC4), with EXC1 being the lowest for structures where consequences of failure are low, and EXC4 being the highest for structures where consequences of failures are high. The majority of buildings fall under Execution Class EXC2, as they typically come under Consequence Class CC2 and Service Category SC1. To comply with these requirements, steelwork contractors must have their Factory Production Control (FPC) system assessed by a notified body, who will issue both an FPC certificate and a Welding Certificate, allowing them to CE mark their fabricated steelwork. The NHBC notes that all British Constructional Steelwork Association (BCSA) Member steelwork contractors have achieved the necessary certification for appropriate Execution Classes.

Pre-start Meetings and Risk Guides

The NHBC has highlighted the importance of pre-start meetings between site teams and NHBC building inspectors for every new site notification. These meetings serve as a crucial opportunity to review plans and drawings for the development and to discuss essential aspects such as ground conditions, foundation proposals, construction types, and proposed materials. The meetings are designed to facilitate early identification of risks and issues, which has been shown to help builders construct compliant homes more effectively.

At these meetings, building inspectors provide advice on any known risks associated with exposure and proposed construction types or materials, while also outlining NHBC inspection requirements for the site. They specifically focus on identifying potential risk areas such as balconies, basements, parapet walls, or render applications, providing appropriate guidance for each. Additionally, the NHBC has announced they will be producing a series of risk guides in the coming months, focusing on elements of construction with significant post-occupation claims potential or high frequency of reportable items during construction. These guides will be discussed with the site team during pre-start meetings, with copies left on site for reference, helping to ensure correct construction practices are followed in accordance with NHBC Standards.

Fire Protection for Dummy Chimneys

The NHBC has issued important guidance regarding fire protection where proprietary dummy chimneys are installed over party walls. The guidance addresses a significant safety concern, as these dummy chimneys typically have hollow cores and most have open bases, which could potentially compromise fire safety between properties if not properly protected.

Fire protection at the junction of a separating wall to a pitched roof is usually achieved through mineral quilt filling any gaps between the wall, roof underlay and roof covering across the full width of the wall. When a dummy chimney is positioned over a party wall, it’s essential that this fire protection is not compromised. The NHBC guidance specifies that the dummy chimney should be provided with a fire resistant base to maintain the required fire protection. Any gaps between the base of the chimney and the top of the separating wall must be filled with non-combustible material, similar to the fire stopping provided between the party wall and roof covering. The guidance also emphasizes that while most dummy chimney manufacturers can provide chimneys with fire resistant bases, these are not typically provided as standard and must be specifically requested when ordering.

Robust Details Launches Animated Training Videos

Robust Details Limited has announced the launch of an innovative series of animated training videos designed to improve construction standards and close the performance gap in building. This initiative follows 10 years of experience in inspecting and monitoring the performance of separating walls and floors in registered plots, during which they’ve observed that proper adherence to Robust Details specifications consistently delivers the expected performance.

Drawing on their extensive field experience, the animations detail the build process for Robust Details separating walls and floors, with a particular focus on best practices and common pitfalls. The videos feature an ‘invisible man’ operative demonstrating correct installation techniques, accompanied by text highlights for critical considerations and voice-over narration explaining the importance of each step. Beyond the main wall and floor type animations, supplementary mini-animations cover specific aspects such as building timber joists into masonry separating walls and treating soil and vent pipes where they penetrate separating floors. These videos are accessible on most devices, including PCs, tablets, and smartphones, making them ideal for both toolbox talks and on-site reference. The initiative is particularly timely given the current construction industry upturn and the need to train new site staff in Robust Details requirements effectively.

NHBC Foundation Research Updates

The NHBC Foundation has announced several significant research publications and ongoing projects aimed at supporting the house-building industry. Of particular note is their recently published research “Improving the prospects for small house builders and developers” (NF57), which reveals serious barriers to growth for small house builders in the UK. The study shows that between 2008 and 2013, the number of small house builders halved from approximately 5,500 to just over 2,700, with their contribution to annual output similarly declining from 40,000 to around 20,000 homes.

The Foundation has also released two new guides to help house builders and designers understand Part L 2013 requirements: one focusing on masonry construction (NF58) and another on timber frame construction (NF59). Looking ahead, the Foundation is working on several research projects including studies on bin storage in new housing developments, recruitment of young talent into the house-building industry, the evolution of housing through the decades, and Housing Associations’ experiences with sustainable technologies. They’re also developing a comprehensive guide to specifying lighting in new homes, aimed at helping housing developers reduce installation costs while providing better lighting solutions that comply with current Building Regulations.

Weep Holes and Weep Vents Requirements

The NHBC has provided important clarification regarding the provision of weep holes and vents in masonry walls, emphasizing their critical role in preventing water damage. The guidance explains that weep holes are essential for safely discharging any water that may enter a cavity wall to the outer face of the building. These are required at several key locations: at the base of cavity walls, at intervals along continuous cavity trays, at stepped cavity trays, and at cavity trays over openings.

The guidance specifies that in its simplest form, a weep hole can be an open brick perpend joint, though proprietary weep holes with baffles to prevent wind-driven rain or large insect ingress are also acceptable. For effective operation, the cavity end of any weep hole must be at least the size of a brick perpend joint (approximately 65mm x 10mm) and kept clear of mortar droppings, particularly where there is a cavity tray directly behind. While the outer face of a proprietary weep hole may have a smaller opening, it must still be large enough to discharge water safely and avoid being blocked by mortar. Special attention is required for extendable weep holes to ensure they protrude sufficiently beyond the wall face. The guidance also addresses specific requirements for masonry cladding to timber framed walls, where the weep hole becomes a ‘weep vent’ and must maintain its full size throughout its length to ensure proper cavity ventilation.

Technical News Updates

The NHBC has highlighted several important technical updates that require immediate industry attention. A critical deadline is approaching regarding Part L 2013 (England) transitional provisions. Builders who submitted sites to NHBC ahead of the Part L 2013 implementation must ensure they have recorded a commencement on site before 6 April 2015 to qualify for transitional provisions. To meet these requirements, an initial notice, building notice, or full plans submission must have been served before 6 April 2014. The NHBC clarifies that commencement of work typically includes activities such as excavation for foundations, digging for raft foundations, or specific drainage work, but does not include preliminary work such as site clearance or general servicing works.

Additionally, significant changes have been announced regarding BS 5534 implementation – the code of practice for slating and tiling for pitched roofs and vertical cladding. While sites could be working to both old and new versions of BS 5534 until the end of February 2015, the NHBC has set a final backstop date of 1 July 2015, after which all roofs must comply with the revised BS 5534:2014 requirements. The transition guidance specifies that roofing work already quoted and contracted can be completed under the old version, while new contracts should adopt the revised standards. This approach aims to ensure a smooth transition while encouraging early adoption of the new requirements.

Information and Support Services

The NHBC has announced several important initiatives and events to support the house-building industry. A key highlight is the Building for tomorrow 2015 event series, which will be held across multiple locations from February to April. These essential events are designed to help industry professionals stay current with challenges facing the sector. With increasing pressure on resources and the need to maintain quality and customer satisfaction, the events will feature presentations from industry experts covering technological advances in materials, changing technical requirements, and NHBC’s experiences from site.

Significant changes to online services have also been announced, with the NHBC Extranet being replaced by the new NHBC Portal. This upgrade follows extensive customer feedback and offers improved functionality including 24/7 access to key site information. The new portal allows users to submit new sites via an intelligent Site Notification and Initial Notice form, provide detailed plot information, receive instant Warranty and Building Control quotes, and monitor outstanding technical conditions and reportable items.

Technical training opportunities have also been expanded, with the NHBC offering several new courses. These include a half-day Part L1a 2013 training course, a free two-hour seminar on Construction (Design and Management) regulations in partnership with the HBF, and upcoming training on the new NHBC Standards Chapter 5.4 ‘Waterproofing of basements and other below ground structures’. Additionally, in partnership with BSRIA, the NHBC is offering a complete post-completion air-leakage testing service in England and Wales, providing fast response times and expert remedial advice if needed.

Share: