NHBC’s Good Craftsmanship Guide for Brickwork and Blockwork in New Build Homes is an essential guide that highlights the key problems frequently encountered during NHBC’s inspections of homes under construction and provides practical guidance on how to avoid these issues. All photographs included in the guide depict real defects observed on building sites, offering a realistic perspective on common construction challenges.

The guide, based on the NHBC Standards, is intended for use by NHBC registered builders and inspection staff. It is  structured to cover a wide range of critical areas in brickwork and blockwork construction, ensuring that the highest standards of craftsmanship are upheld. Below, you will find a summary of the guide’s advice, section by section, helping you to understand the main points and recommendations for each aspect of construction.

For those who wish to delve deeper into the specifics, a link to download the full guide in PDF format is available at the bottom of this page. We encourage all builders, inspectors, and construction professionals to utilise this resource to enhance the quality and durability of their building projects.

Substructure

The substructure section focuses on preventing rising damp by ensuring proper damp-proof course (DPC) placement. It is crucial to position the DPC at least 150mm above the external ground or paving level and stop cavity fill at least 225mm below the base DPC. Correct DPC installation includes ensuring it is of the correct width and does not project into the cavity, which could trap mortar and debris. Additionally, DPC should lap with the damp-proof membrane (DPM) of the floor slab to provide continuous protection against moisture ingress. Following these guidelines helps to maintain the integrity of the substructure and prevent common moisture-related issues.

Cavities

Cavity construction requires careful attention to prevent water crossing and maintain structural integrity. Cavities should be uniform and at least 50mm wide, with mortar struck off all joints as work progresses to avoid mortar droppings. Keeping cavities clear of debris is essential, and using battens helps in this regard. The height difference between the two leaves of a cavity wall under construction should not exceed six standard block courses. Proper scaffolding and working heights are important to prevent overreaching and ensure even construction. Adhering to these practices ensures effective water management and structural stability within cavity walls.

Wall Ties

Proper use of wall ties is essential for structural integrity and preventing water ingress. Wall ties must be as specified and of the correct type, ensuring they are bedded a minimum of 50mm into each leaf of the cavity wall. They should be kept clean and level or slightly sloping outward, with drips facing downwards in the centre of the cavity. Correct spacing is vital, with ties placed at appropriate intervals in walls, reveals, and movement joints. For supporting partial fill insulation boards, ties might need to be spaced closer together. Following these guidelines helps ensure walls are securely tied and resistant to moisture penetration .

Mortar

The mortar section emphasises the importance of maintaining consistent mix proportions to ensure adequate strength and durability of the mortar used in brickwork and blockwork. It is essential to keep mixers and plant clean, and store materials correctly to avoid contamination. The mortar mix should be appropriate for the bricks or blocks being used, their location in the building, and the exposure of the area. Variations in the mix can lead to low strength and poor durability, which can compromise the integrity of the structure. Additionally, it is advised not to use masonry cement as if it were ordinary Portland cement (OPC); following the manufacturer’s recommendations for the correct proportions is crucial.

The guide advises against using unauthorised additives such as washing up liquid, as these can adversely affect the mortar’s properties. When using plasticisers or other additives, it is important to adhere to the manufacturer’s instructions. Retarded mortars should be protected and stored correctly before use and must be used within the supplier’s or manufacturer’s time limit. It is also crucial not to retemper mortar that has started to set. Proper application involves laying bricks and blocks on a full bed of mortar and filling perpend joints solidly. Recessed joints should be avoided when using full-fill cavity insulation​​.

Thermal Insulation

Proper installation of thermal insulation is vital to avoid water crossing the cavity and thermal bridging, which can lead to cold spots. The guide advises following the manufacturer’s instructions for built-in insulation and ensuring that the bottom row of boards or batts is supported using ties. Insulation should be installed throughout the entire wall area, including below the damp-proof course (DPC), with staggered joints and closely butted boards to prevent gaps. It is essential to fit insulation tightly against lintels, cavity trays, and cavity closures, and maintain a minimum 50mm clear cavity between partial cavity fill and the external leaf.

It is important to keep partial cavity fill securely in place using the correct clips for the type of tie and ensuring that horizontal joints in partial cavity fill insulation coincide with wall ties. The top edge of insulation should be kept clear of mortar droppings to maintain its effectiveness. These practices help ensure the thermal efficiency of the building and prevent issues such as cold spots and moisture ingress, which can compromise the building’s thermal performance and structural integrity​.

Openings

The section on openings addresses the need to prevent water ingress and ensure the proper fitting of frames. Openings should be built to the correct size and be square, with brickwork closely butted against the frame if built in situ. It is critical to provide vertical DPCs at jambs, either as separate components or integrated into proprietary cavity closers, and to install these DPCs in one continuous length to prevent water crossing the cavity. In areas of very severe exposure, using ‘check’ reveals can provide additional protection by extending the vertical DPCs up to the lintel and turning them back towards the inner leaf.

To ensure frames are securely fixed within openings, they must be level and plumb, with adequate blocking or packing at fixing points. Proper DPC placement under jointed and permeable sills is crucial, with DPCs turned up at the back and ends of the sill to prevent water ingress. Bay and bow windows require additional support to prevent sagging and bowing, and they should be linked to DPCs at reveals to maintain the integrity of the installation. These measures help maintain the structural and moisture resistance performance of the openings​.

Lintels

The lintels section underscores the necessity of providing adequate structural support over openings. Lintels must extend beyond the opening at each end by at least 100mm for simple lintels and 150mm for lintels combined with a cavity tray, depending on the span. They should be bedded on mortar to ensure stability. Additionally, padstones should be provided where required by the design, and masonry should not overhang the edge of a lintel by more than 25mm to prevent structural issues. For steel lintels, it is critical to build the inner and outer leaves up together to avoid twisting the flange, with a maximum height difference of 225mm.

The guide recommends that lintels be properly bedded to distribute loads evenly and prevent structural failure. Ensuring lintels are correctly installed helps to avoid potential problems such as cracking and sagging. Proper support and alignment are crucial for the longevity and stability of the structure, particularly in load-bearing applications where the integrity of the opening must be maintained.

Cavity Trays

The cavity trays section highlights the importance of preventing water from crossing the cavity and compromising the building’s structure. Cavity trays should be provided where required by the design, such as over lintels, roof abutments, air bricks, and meter boxes. They should be installed in one continuous length and extend at least 25mm beyond the cavity closers, covering the ends of lintels. Properly shaped cavity trays with a total rise of at least 140mm help to redirect water away from the cavity. Additionally, stop ends and weep holes at a maximum of 450mm intervals (with at least two per opening) ensure effective water drainage.

For areas of severe exposure, particularly in Scotland, Northern Ireland, the Isle of Man, and areas with very severe driving rain, separate damp-proof protection over all lintels is recommended. Cavity trays should also be provided over full-fill insulation unless the insulation extends to the top of the wall. At roof abutments, cavity trays must link with flashing, with the lowest tray having two stop ends and a weep hole to facilitate water drainage. These measures are crucial in maintaining the integrity of the cavity wall and preventing water ingress.

Bonding

The bonding section focuses on ensuring the stability and appearance of walls by maintaining a regular bonding pattern. Proper setting out of work is essential to minimise cutting bricks and blocks, which helps to maintain the structural integrity of the wall. Maintaining a consistent bond pattern, especially around openings, prevents the need for excessive cutting and helps distribute loads evenly. It is crucial not to mix materials of different types within the same wall, as this can lead to differential movement and instability.

Bonding external walls to partitions and separating walls is essential for stability. This can be achieved by toothing alternate courses where blocks of the same type are used or using wall ties or expanded metal (at maximum 300mm centres) to bond dissimilar materials. When joists are built into masonry, it is important to fully fill between joists without excessive mortar joints. These practices help ensure the walls are robust and capable of withstanding various loads and movements without compromising structural integrity.

Movement Joints

The section on movement joints stresses the importance of installing them correctly to prevent excessive cracking in masonry walls. Movement joints should be provided in the outer leaf of walls, with the width and spacing depending on the material used. For example, clay brickwork requires 16mm wide joints at intervals of 12m (or a maximum of 15m), while calcium silicate brickwork needs 10mm wide joints every 7.5 to 9m. Concrete block and brick should have 10mm wide joints every 6m. For parapet walls, the spacing should be half of these dimensions, and the first joint from a return should not exceed half the standard interval.

Movement joints must be properly sealed with materials such as flexible cellular polyethylene, cellular polyurethane, or foam rubber, and the sealant should be at least 10mm deep to ensure a strong bond. Ties should be installed on each side of movement joints, spaced vertically at 300mm intervals or every block course, and horizontally within 150mm of the joint. Using the correct filler material and ensuring proper placement helps maintain the structural integrity and appearance of the wall, preventing unsightly and potentially damaging cracks​​.

Separating Walls

The guide highlights the necessity of constructing separating walls to ensure proper sound insulation and fire resistance. It is essential to use blocks of the correct type and thickness as specified in the design, avoiding cracked or damaged blocks. Only approved ties, such as butterfly ties, should be used to maintain a clear cavity width. Blocks should be fully bedded with all perpend joints filled solidly to avoid gaps that can compromise sound and fire performance. Where separating walls join external walls, they should be toothed or tied with appropriate materials to ensure stability.

Flexible cavity closers should be installed at the junctions of separating and external cavity walls to prevent cold bridging. The top of separating walls must be accurately cut and finished, stopping about 25mm below the top of adjacent roof trusses to allow for firestopping. Fire barriers should be installed in boxed eaves and between battens above and below the underlay. These measures help ensure that separating walls effectively block sound transmission and contain fire, contributing to the overall safety and comfort of the building​​.

Appearance

The appearance section emphasises maintaining consistent mortar mix and colour to avoid unsightly brickwork and colour variations. Variations in sand can significantly impact the colour, so bricks should be mixed from different batches unless they have been pre-blended. Ensuring materials are stored correctly, away from site traffic, and protected from rain and mud splashes is crucial. Handling materials carefully during construction and avoiding the use of chipped or fractured bricks for facework helps maintain a high-quality finish.

Using a gauge rod marked with the heights of openings ensures courses are kept at the correct height, maintaining level and plumb work according to the design bond. Protecting new work from rain and frost, keeping the workplace clean to reduce mortar splashes, and brushing off mortar smears after they have initially set are essential practices. These steps help to produce a visually appealing and structurally sound finished product, enhancing the overall quality and durability of the brickwork.

Cold Weather Working

The section on cold weather working addresses the potential for frost damage to brickwork and blockwork. To prevent this, it is crucial to cover materials such as sand, aggregates, and cement to keep them from becoming saturated and subsequently damaged by frost. Bricks and blocks should also be protected similarly. The guide advises against laying brickwork or blockwork when the air temperature is below or likely to fall below 2°C. If the temperature drops below this threshold, new work should be protected from frost to prevent damage. This includes using covers that provide a still air space to insulate the wall from frost.

Any work that has been damaged by frost must be taken down and rebuilt to ensure structural integrity. Following these guidelines helps maintain the quality and durability of the brickwork during cold weather conditions, ensuring that the masonry remains strong and free from frost-induced damage​.

Additional Guidance for Timber Frame

The section on additional guidance for timber frame construction highlights specific issues related to brickwork and blockwork used as cladding for timber frame homes. One of the main concerns is moisture damage to the timber frame, which can be mitigated by repairing any damage to the breather membrane promptly. It is also essential to fix ties to the studs, not the sheathing, using the specified fixings in the design. These ties should be spaced according to the design, typically not more than 600mm horizontally and 450mm vertically, with closer spacing at jambs of openings.

The guide stresses the importance of allowing for the movement of the timber frame at various points, such as the eaves, sills, heads, and jambs of openings. This involves ensuring that there is adequate clearance and using flexible sealant at points of movement to accommodate the frame’s natural shrinkage and expansion. Installing cavity barriers in accordance with the design is also crucial for fire safety and moisture control. These additional measures help ensure the stability, safety, and longevity of timber frame constructions when clad with brickwork or blockwork​.