If you’re a new homeowner experiencing issues with your timber framed property, understanding the technical standards that guided its construction can be invaluable. The NHBC (National House Building Council) Standards serve as the industry benchmark for quality and performance in new home construction across the UK, providing guidance to builders on meeting technical requirements related to warranty coverage.
Chapter 6.2 of the NHBC Standards specifically addresses external timber framed walls in new build homes. This comprehensive technical guidance applies to timber framed homes up to seven storeys high, substantially timber framed properties, and timber wall panels. The chapter establishes clear requirements that builders must follow to ensure these structures are constructed safely, durably, and in compliance with building regulations.
Timber frame construction has become increasingly popular in the UK housing market due to its sustainability credentials, efficient build times, and excellent thermal performance. However, the proper design and construction of timber frame walls is critical to prevent issues such as moisture ingress, structural movement, fire safety concerns, and inadequate insulation performance.
Key Areas Covered in Chapter 6.2
Load-bearing Walls
The standards provide detailed requirements for load-bearing timber framed walls, which must be constructed to support and transfer loads to foundations safely and without undue movement. This includes specifications for timber elements, joints between panels, positioning of sole plates, and packing under sole plates.
Structural timber components must be of suitable strength class and properly graded according to British and European standards. Individual timber studs should have a minimum width of 38mm and maximum spacing of 600mm, unless additional support is provided for wall boards and fixings.
Protection from Moisture
One of the most critical aspects of timber frame construction is protecting the structure from moisture. The chapter outlines requirements for cavity construction, drainage, ventilation, and the proper installation of DPCs (damp-proof courses) and cavity trays.
A drained and vented cavity should be provided between the cladding and sheathing to reduce the risk of rain penetration. For masonry cladding, a minimum 50mm nominal cavity width is required, while other types of cladding have varying requirements.
Differential Movement
Timber naturally shrinks as it dries out, causing the overall height of a timber frame to reduce over time. The standards provide detailed guidance on accommodating differential movement between the timber frame and other building elements such as masonry cladding, door and window openings, balconies, and service entries.
Movement joints should be designed to safely accommodate the expected movement, with an additional allowance for any compressible filler materials. In the absence of project-specific calculations, the standards provide a table of recommended gap sizes to accommodate differential movement based on the number of storeys.
Fire Resistance
The standards specify requirements for controlling and resisting the spread of fire and smoke through timber walls and panels. This includes guidance on cavity barriers, fire-stopping, services, and ensuring adequate fire resistance of the wall or panel in accordance with Building Regulations.
Breather Membranes and Air Barriers
The chapter details the requirements for breather membranes, which protect the sheathing and frame from moisture while allowing water vapour from within the frame to pass into the cavity. Similarly, air and vapour control layers must be correctly installed to restrict the passage of air and water vapour from within the home into the timber frame.
Insulation
Insulation must be correctly installed to provide suitable thermal performance. The standards provide guidance on different insulation types and installation methods, whether placed within the stud void, on the external/cavity face of the frame, or on the inside face of the frame.
Snagging Inspections for Timber Framed Homes
New Build Inspections, a professional snagging company mentioned in your provided documents, specialises in identifying defects in new build homes, including those with timber frame construction. They recommend having a snagging inspection before you move in or as soon as possible afterwards, ideally within the first two years when cosmetic issues are covered by your warranty.
Professional inspectors with experience in timber frame construction can identify issues that may not be immediately apparent to the untrained eye, including problems with:
- Moisture protection measures
- Movement allowances around openings and interfaces
- Ventilation of cavities
- Quality and fixing of external cladding
- Insulation installation
- Fire safety measures
If you’re experiencing issues with your timber framed home, it’s advisable to seek help from professionals who understand the NHBC Standards and can identify whether your home complies with them. Companies like New Build Inspections can provide an independent assessment and help you communicate with your developer about any remedial work required.
Remember that new homes typically come with a 10-year warranty, with the first two years covering issues with finishes and other non-structural elements. More serious structural issues are covered for the full warranty period. Having a professional snagging inspection can help ensure that problems are identified and addressed within the appropriate warranty timeframe.
Further Details
6.2.1 Compliance
This subchapter establishes the fundamental requirement that external timber framed walls must comply with the NHBC Technical Requirements. It states that walls constructed according to the guidance in Chapter 6.2 will generally be acceptable and refers to additional chapters for internal walls and upper floors within timber frame buildings. Importantly, it notes that timber frame components that cannot be inspected on site (such as closed panels or fully fitted volumetric units) should be subject to review by NHBC through their Accepts service.
6.2.2 Provision of Information
This section emphasises the importance of clear, detailed documentation for timber frame construction. It requires designs and specifications to be produced in an understandable format, with all relevant information distributed to appropriate personnel. Key documents include complete drawings, materials specifications, cavity barrier positions, fixing schedules, and manufacturers’ recommendations. For walls where plasterboard provides racking resistance, the design must clearly identify these walls and specify the type and spacing of fixings required.
6.2.3 Design Checking and Certification
This subchapter mandates that the design of timber frame superstructures must be adequately checked by qualified professionals. Homes with timber frame superstructures require certification confirming that the design has been reviewed by an NHBC-approved timber frame certifier—typically a qualified civil or structural engineer with at least three years of timber frame construction experience. Alternatively, frames manufactured by Gold level members of the Structural Timber Association Assure scheme (who use Silver/Gold level designers and engineers) are acceptable without additional certification. Designs for buildings of four storeys or more with solid timber floor joists must be submitted to NHBC.
6.2.4 Load-bearing Walls
This comprehensive section details requirements for load-bearing timber frame walls, which must safely support and transfer loads to foundations without undue movement. It covers specifications for timber elements (including strength classes, dimensions, and spacing), joints between panels, positioning of sole plates, packing methods, fixing techniques, and erection tolerances. Specific guidance is provided for timber studs, lintels, cripple studs, multiple studs for point loads, and the proper support of prefabricated chimneys, ensuring structural integrity throughout the timber frame system.
6.2.5 Fixing the Frame
This subchapter focuses on the crucial connection between the timber frame and the substructure. It provides guidance on shotfiring techniques into masonry (requiring minimum crushing strength blocks) and anchoring methods to ensure the frame can resist both lateral and vertical forces. The section specifies requirements for holding-down devices, which must be durable and manufactured from appropriate materials—either austenitic stainless steel or galvanized mild steel with specified minimum coating weights. For sole plate anchors within the internal envelope, galvanized mild steel with minimum coating Z275 is acceptable.
6.2.6 Nails and Staples
This subchapter establishes requirements for the durability and suitability of mechanical fixings in timber frame construction. It specifies that nails used for fixing sheathing or timber must be either austenitic stainless steel, galvanised, or sherardised to provide adequate corrosion resistance. Similarly, staples used for fixing breather membranes must be made of austenitic stainless steel or an alternative material with comparable strength and corrosion resistance properties. This ensures that these critical connections maintain their integrity over time, preventing premature failure that could compromise the structural performance or weather resistance of the timber frame.
6.2.7 Sheathing
This section addresses the requirements for sheathing materials, which must be durable and capable of providing structural resistance to racking forces. It lists acceptable materials including specific grades of plywood, oriented strand board, moisture-resistant chipboard, medium board, and impregnated soft board that comply with relevant British and European standards. Proprietary sheathing materials must be assessed according to Technical Requirement R3. The subchapter also notes that plasterboard may contribute to racking resistance when used in accordance with PD 6693-1, though certain limitations apply for non-separating walls and when plasterboard is combined with wood-based sheathing on the same wall diaphragm.
6.2.8 Differential Movement
This extensive subchapter addresses the critical issue of differential movement between timber frame walls and other building elements as timber dries out and shrinks. It provides detailed guidance on accommodating movement at interfaces with masonry cladding, openings, eaves, verges, services, balconies, and other elements. The guidance includes a comprehensive table of recommended gap sizes based on the number of storeys and joist types, with illustrations of specific details for various junctions. Movement joints must be designed to safely accommodate expected movement, provide additional allowance for compressible fillers, ensure weather resistance, and include cover strips for larger gaps. This section is crucial for preventing cracking, distortion, and weather penetration issues as the building ages.
6.2.9 Fire Resistance
This subchapter outlines requirements for controlling and resisting the spread of fire and smoke in timber walls and panels. It covers three key areas: cavity barriers and fire-stopping, services, and fire resistance of the wall or panel. The section specifies that cavity barriers must be installed according to Building Regulations and protected by DPCs arranged to shed moisture away from the sheathing. It restricts services in separating walls and addresses the fire resistance requirements for timber frame walls in accordance with Building Regulations. The subchapter also references guidance on fire prevention during construction from the Fire Protection Association and the Structural Timber Association, emphasizing the importance of comprehensive fire safety measures throughout the building’s lifecycle.
6.2.10 Protection from Moisture
This critical section details requirements for protecting timber structures from moisture, which is essential for preventing decay and maintaining structural integrity. It covers cavity construction specifications (with minimum cavity widths ranging from 15mm to 50mm depending on cladding type), drainage and ventilation requirements, and the correct installation of DPCs and cavity trays. The subchapter specifies that cavities must be vented to allow limited air movement, kept clean and free of obstructions, and capable of draining freely. For masonry cladding, ventilation equivalent to open brick perpend joints every 1.2m is required. The section also includes specific details for protecting the lowest timber elements, which should generally be at least 150mm above finished ground level.
6.2.11 Timber Preservation
This concise subchapter addresses the requirements for protecting timber against fungal decay and insect attack. It stipulates that all timber and timber products used in the construction must either possess adequate natural durability or be treated with appropriate preservatives. The section specifically identifies elements requiring protection, including timber framing members (studs, rails, sole plates), external timber cladding, and engineered timber components such as I-section or metal-web studs. The preservation treatments must conform to the standards outlined in Chapter 3.3 regarding timber preservation for natural solid timber, ensuring long-term durability and structural integrity of the timber frame.
6.2.12 Air and Vapour Control Layers
This subchapter details the requirements for air and vapour control layers (AVCLs), which are essential for restricting the passage of air and water vapour from within the home into the timber frame. It specifies that a high-resistance AVCL should be provided unless a condensation risk analysis demonstrates it’s unnecessary. The section provides comprehensive installation guidance, including proper fixing methods, positioning relative to insulation, lapping requirements, and sealing techniques around openings and service penetrations. For standard applications, a minimum 500 gauge (125 micron) polyethylene sheet or vapour control plasterboard is required, with joints properly sealed and positioned over structural elements. Special considerations for floor zone airtightness membranes are also addressed.
6.2.13 Breather Membranes
This section outlines the requirements for breather membranes, which play the dual role of protecting the sheathing and frame from external moisture while allowing water vapour from within the frame to escape into the cavity. The subchapter specifies performance criteria including vapour resistance (less than 0.6MNs/g or 0.12 Sd) and water resistance (at least Class W2, with Class W1 required in areas of severe exposure). Installation requirements include proper lapping (minimum 100mm on horizontal joints and 150mm on vertical joints), fixing methods, and positioning to protect the lowest timber and shed water away from the structure. Damaged membranes must be repaired or replaced before cladding installation to maintain the weather resistance of the wall system.
6.2.14 Wall Ties and Fixings
This subchapter focuses on the critical connections between the cladding and timber frame. It requires wall ties and fixings to comply with BS 845-1 and be capable of accommodating anticipated differential movement. The section specifies that ties must be made of austenitic stainless steel, fixed directly to the studs (not the sheathing) using manufacturer-supplied fixings, and kept clean from mortar droppings. Precise spacing requirements are provided: maximum 600mm horizontally and 450mm vertically, with closer spacing (maximum 300mm vertically and within 225mm horizontally) at jambs of openings, movement joints, and the top of walls. Ties should be inclined away from the sheathing to maintain drainage pathways even after differential movement occurs.
6.2.15 Insulation
This subchapter addresses the correct installation and performance requirements for insulation in timber frame walls. It specifies acceptable insulation types, including breathable materials like mineral wool (rock or glass) or alternatives assessed under Technical Requirement R3. The section emphasizes complete coverage within stud voids, with no gaps at corners, junctions, or around services. For external/cavity face insulation, specific requirements include maintaining a clear cavity between insulation and cladding, proper breather membrane installation, suitable wall tie systems, and appropriate cavity barrier arrangements. For internal face insulation (either as insulated plasterboard or a separate continuous layer), the fire resistance of the wall must comply with the standards in Clause 6.2.9 and be supported by appropriate evidence.
6.2.16 Further Information
This final subchapter provides references to additional guidance documents that complement the NHBC standards for timber frame construction. It lists resources from the Structural Timber Association, including guidance on fire safety in structural timber buildings, cavity barriers and fire stopping, and construction tolerances for timber frame wall panels. Other referenced materials include the Institution of Gas Engineers & Managers’ guide to gas installations in timber framed buildings, the STA guide to differential movement in platform timber frame, and BRE Report BR 262 on avoiding risks related to thermal insulation. These resources offer deeper technical insight for professionals seeking to understand specific aspects of timber frame construction in greater detail.
