NHBC Chapter 6.1–6.10

Superstructure Inspection Checklist

Masonry superstructure checks — cavity width, wall ties, DPC, lintels and bearings, cavity trays, movement joints, party wall fire stopping and restraint straps.

22 checks · Reviewed 20 August 2026 by the ProPlot site team · How we write these guides

In short

The superstructure inspection covers the masonry shell as it rises. The inspector checks cavity width and cleanliness, wall tie type, spacing and embedment, DPC position and continuity, lintels and their bearings, cavity trays and weep holes, insulation fit, and fire stopping and cavity barriers at compartment lines.

Use it on site

Cavity wall at the superstructure visit: tie type, spacing and fall to the outer leaf, insulation held tight to the inner leaf, and a cavity tray with weeps over the opening. ProPlot original drawing, prepared from the Building Regulations Approved Documents and British Standards. Indicative only — build to the approved drawings for the plot.

Superstructure is where a warranty inspector spends the most time, because a masonry shell hides more than any other stage. Wall ties, cavity trays, lintel bearings and insulation continuity all end up behind a finished face, and a defect found at handover means taking brickwork down. Most providers inspect at least once during the superstructure — often at first lift and again at wall plate.

The inspector is checking three things at once: structure, weathertightness and fire. Structure means tie centres and type, lintel specification and bearing, restraint straps to gables and floors, and the bond and coursing of the masonry itself. Weathertightness means DPC height, cavity tray and stop end details over every opening, weep holes, and a cavity kept clear of mortar droppings. Fire means the separating wall carried tight to the underside of the roof with the cavity barriers and stopping actually installed rather than intended.

The list below follows the order a bricklayer builds in, so you can walk the scaffold with it. Photograph cavity trays, ties and insulation before the next lift goes on — concealed-work photographs are the cheapest insurance on the site.

What happens at this visit

When it happens

During the masonry lifts and again once the wall plate is strapped down, before the roof structure closes off access to the cavity and the party wall head.

Who inspects

Warranty provider inspector, building control, and on timber-frame or steel-frame hybrids the frame supplier's own erection check.

If it fails

Superstructure failures are the most disruptive to fix. Missing ties or trays mean cutting out and rebuilding sections of the outer leaf, usually with the scaffold already struck and the roof on.

How this visit is booked and recorded

Inspection type: Key Stage Inspection. Bay windows, render, cavity trays and dummy chimneys typically trigger additional Risk Based Inspections at the same stage.
Notice required: Minimum 24 hours’ notice. On a masonry plot the useful window is while the cavity is still open and before scaffold lifts hide the work.
What it signs off: Feeds the Buildmark record, the Part A structural checks and, with the pre-plaster visit, the fabric evidence for Part L.

What the inspector will ask for

Approved elevations, sections and cavity tray details
Wall tie specification and cavity width confirmation
Lintel schedule with bearing lengths
Insulation product data and installer instructions
Mortar mix designation for the exposure zone

Photograph these moments in time

Wall ties at the correct centres, with the drip pointing down
Cavity trays and weep holes at every interruption
Lintel bearings before they are built over
Full-fill or partial-fill insulation with the residual cavity clear
Restraint straps to gables and separating walls

Concealed work cannot be re-photographed later. Take these before the element is covered and file them against the plot.

Reportable Item hotspots at this stage

A Reportable Item (RI) is a defect the inspector records against the plot. NHBC weigh each one by its Damage Potential, and the score feeds your site's Construction Quality Review. These are the ones raised most often here:

Cavity trays missing or not stopped at the ends
Wall ties at the wrong centres or sloping inwards
Mortar droppings bridging the cavity

How Reportable Items and Quality Common Scoring work

The numbers for this stage

The measurable values most often argued about at the superstructure visit, each traced to an openly published source. Take a tape to the ones that apply before you book.

Critical dimensions that apply at the superstructure inspection
What	Value	Type
Air temperature limits for laying masonryMasonry and render work in cold weather.Check hessian or frost blankets are on the work at the end of the shift, not folded on the scaffold.	Stop at 3 °C and falling; do not restart below 1 °C rising	Minimum
Background ventilator equivalent areaDwelling with background ventilators, including window replacement workCheck the ventilator equivalent area printed on the product data against the window schedule room by room — not the physical slot size.	8000 mm² equivalent area to habitable rooms; 4000 mm² to kitchens, utility rooms and bathrooms	Minimum
Cavity drainage and DPC extensionCavities in external walls must extend at least 150mm below the damp-proof course (DPC) level to allow for proper drainage and collection of moistureCheck that the cavity extends sufficiently below the DPC and that weep holes are correctly spaced, unobstructed, and clear of mortar.	150 mm	Minimum
Cavity tray upstand heightCavity tray over an opening, abutment or cavity interruptionPhotograph each tray before the next lift covers it. Confirm the tray rises at least 150 mm, is continuous, and has stop ends and weep holes at each end.	150 mm	Minimum
Cavity wall tie horizontal spacing (full-fill insulation)For cavity walls incorporating full-fill insulation, wall ties must be placed at maximum 900mm horizontal centresVerify that horizontal tie spacing for full-fill insulated cavities does not exceed 900mm.	900 mm	Maximum
Chimney wall thickness and constructionThe minimum wall thickness for block, brick, or stone chimneys, excluding flue lining, is typically 100mmCheck the thickness of chimney walls, ensuring 100mm minimum for general construction, and 200mm for compartment walls, and verify factory-made flues are installed per manufacturer's instructions.	100 mm	Minimum
Concrete Placement Conditions and TechniqueConcrete should not be placed if its temperature at the point of use is below 5°C, as fresh concrete is vulnerable to frost damageCheck concrete temperature before placement, confirm no standing water in the pour area, and observe that concrete is placed continuously and directly to minimise handling and segregation.	5 °C	Exact
Coursing and Jointing in Rubble Stone MasonryFor squared or random rubble stone masonry, it is essential to incorporate coursing at regular intervals not exceeding 450mm to maintain structural integrity and a consistent appearanceCheck that rubble masonry is regularly coursed within 450mm vertically and that wall ties are correctly specified and installed for the wider joint widths.	450 mm	Maximum
Lintel end bearing lengthMasonry openings — confirm against the lintel manufacturer's schedule for the specific span and loadMeasure the bearing at both ends before the opening is closed up, and check the bearing masonry is solid, level and fully bedded.	100 mm for spans up to 1200 mm; 150 mm for longer spans	Minimum
Lowest fixing position for strapsFor any structural strap, the lowest fixing into the masonry or supporting structure must be positioned no more than 150mm from the bottom of the strapMeasure the distance from the bottom of the strap to the centre of its lowest fixing.	150 mm	Maximum
Nominal mortar joint thicknessBrick and block masonry laid to a gauge rod.Check the gauge rod against the course heights at each lift; drifting joints show up badly on a long elevation.	10 mm nominal	Exact
Residual clear cavity width with partial fill insulationMasonry cavity wall with partial fill insulation boardCheck the residual cavity at each lift with a gauge, and confirm retaining clips hold the boards tight to the inner leaf.	50 mm	Minimum
Temperature limits and protection for masonryBrickwork and blockwork should generally not be laid when the air temperature is below 3°C and falling; work can resume when temperatures rise to 1°C with an expectation of exceeding 3°CVerify air temperatures are suitable for masonry work, materials are unfrozen, and new masonry is adequately protected by covers and insulation.	3 °C	Exact
Wall tie embedment and slopeWall ties are critical for connecting masonry leaves and must be long enough to achieve proper embedment into both leaves, typically a minimum of 50mm in the mortar bedEnsure wall ties are of the correct length, embedded at least 50mm into mortar beds in both leaves, and installed sloping outwards.	50 mm	Minimum
Wall tie embedment into each masonry leafCavity walls built with ties to a suitable length for the cavity width.Check the tie length against the cavity width before the leaf is closed up, and look along the course for ties sloping the wrong way.	50 mm	Minimum
Wall tie spacing at reveals and movement jointsWithin 225 mm of an unbonded vertical edge — reveals, movement joints, wall endsCheck every reveal on each lift. Ties should be visible in the perp adjacent to the closer before insulation and cavity closers are fitted.	Additional ties at 300 mm vertical centres within 225 mm of the opening	Maximum
Wall tie spacing in a standard cavity wallMasonry cavity wall, cavity width up to 100 mm, wall height up to 15 mCount ties per square metre on each lift before the cavity is closed. Check ties are level or fall slightly to the outer leaf and that drip features point downwards.	900 mm horizontally, 450 mm vertically (2.5 ties per square metre)	Maximum
Weep hole spacing above a cavity trayOver lintels, cavity trays and at the base of the cavityCount weep holes over each opening as the outer leaf is built. They must sit in the course immediately above the tray, not one or two courses higher.	900 mm maximum centres, with at least two weep holes over every opening	Maximum

Browse the full critical dimensions library

The superstructure checklist

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Cavity and wall ties

Check cavity width is maintained at minimum 50mm (or as designed) and clear of mortar droppings (NHBC 6.1)
NHBC 6.1
Verify wall ties installed at correct centres (900mm × 450mm max) and slope outwards to outer leaf (NHBC 6.1)
NHBC 6.1
Check scaffold ties have not damaged cavity insulation or cavity trays (NHBC 6.1)
NHBC 6.1
Verify insulation boards are tight-butted, clipped and continuous with no gaps at corners (AD L1A)
AD L1A

Damp proofing and openings

Confirm DPC is continuous, correctly lapped and at minimum 150mm above finished ground level (AD C)
AD C
Inspect lintels for correct specification, adequate bearing (min 150mm) and correct orientation (NHBC 6.5)
NHBC 6.5
Check cavity trays are dressed correctly with stop ends and weep holes at max 900mm centres (NHBC 6.1)
NHBC 6.1
Check window and door reveals — DPC, insulation returns and cavity closers correctly installed (NHBC 6.1)
NHBC 6.1
Confirm render carrier board, mesh and bellcast bead installed correctly where specified (NHBC 6.11)
NHBC 6.11

Masonry workmanship

Verify blockwork bond pattern is correct with perpends filled and coursing level (NHBC 6.1)
NHBC 6.1
Check coursing gauge is consistent and within tolerance (±3mm per course) (NHBC 6.1)
NHBC 6.1
Confirm movement joints are positioned per design and filled with compressible filler + sealant (NHBC 6.1)
NHBC 6.1
Confirm correct mortar designation is used and protected from frost and rapid drying (BS EN 1996)
BS EN 1996

Restraint, structure and floors

Check wall plate straps are fitted at correct centres (max 2m) and properly embedded (AD A)
AD A
Confirm head restraint straps fitted to gable walls at correct centres (AD A)
AD A
Verify first floor joist hangers are correct specification and fully engaged into masonry (NHBC 6.4)
NHBC 6.4
Verify that any steel beams or columns have correct fire protection and bearing plates (AD B)
AD B
Confirm balcony / bay window construction matches structural engineer details (NHBC 6.9)
NHBC 6.9

Fire, sound and services

Verify party wall construction matches Robust Details or approved drawing for sound separation (AD E)
AD E
Confirm fire stopping at party wall / separating wall junction with roof is complete and continuous (AD B)
AD B
Verify meter box positions and service penetrations are correctly sealed and fire-stopped (AD B)
AD B
Check subfloor ventilation (suspended floors) or radon sump pipework is correctly installed (AD C)
AD C

Above and beyond: protecting the fabric as it goes up

Brickwork and blockwork are on show for sixty years. Most of the finish problems come from what happened to the wall between lifts, not from the laying. No inspector will fail the visit on these — they are the difference between a plot that passes and a plot that hands over clean.

Cover the wall head at the end of every shift
Rain into an unfinished wall causes efflorescence, saturated insulation and lime staining that no amount of cleaning fixes.
When: Every day, and before any forecast rain.
Cover party wall and separating wall insulation before you leave it
Wet acoustic insulation loses performance and takes weeks to dry, and it is a certain sound test problem.
When: End of shift, every shift.
Keep the cavity clean and clear the base
Mortar snots bridging the cavity is the classic penetrating damp callback and it is invisible once the wall is up.
When: Lift by lift, with a cavity board.
Protect formed reveals, corners and cills as soon as they are built
Chipped arrises and stained cills are handover snags that require a brick to be cut out.
When: Immediately after building, until the scaffold comes down.
Keep the scaffold boards clear of the wall face
Boards tight to new brickwork drip dirty water down the elevation and leave a tide line the customer will see.
When: At every lift.
Clean down as you go rather than at the end
Fresh mortar comes off with a brush. Set mortar needs acid, and acid burns the brick face.
When: Same day.

Full inspection point register

291 inspection points that apply at the superstructure stage, each written in our own words from openly published guidance, with how to check it on site and what counts as acceptable. Use the checklist above on the day and this register when you need to settle a detail.

Acceptable appearance of external walls
How to check
Visually inspect all external wall finishes for consistency, alignment, and absence of significant defects, noting any variations in texture or colour.
Acceptable when
External walls must achieve an acceptable finished appearance, which encompasses various cladding types such as fair-faced masonry, render, timber, and rainscreen systems. The quality of installation and the aesthetic integration of these materials are critical for the overall visual impact and durability of the building envelope.
Acceptable lintel materials
How to check
Check that lintel materials match the specification and that timber lintels, if used, are in appropriate, protected locations not supporting masonry.
Acceptable when
Commonly accepted materials for structural lintels include concrete, steel, and reinforced brickwork, which offer appropriate strength and durability for supporting masonry. Timber lintels are generally not suitable unless they are fully protected from weather and do not support rigid or brittle materials like masonry.
Accounting for differential movement in structures
How to check
Review structural drawings and specifications to confirm that provisions for differential movement have been incorporated in the design.
Acceptable when
When designing and constructing building elements, it is crucial to account for potential differential movements that can occur over time. These include casting and fabrication tolerances, creep, thermal expansion/contraction, deflection under load, foundation settlement, and variations in storey height.
Achieving Desired Masonry Appearance
How to check
Ensure a site reference panel has been built and agreed upon to benchmark the acceptable standard for masonry appearance and workmanship.
Acceptable when
The final appearance of a masonry wall is a result of the materials used, the quality of workmanship, and accurate setting out. To establish an agreed benchmark for quality, a site reference panel should be constructed, demonstrating the acceptable standard of finish and product consistency.
Acoustic and Fire Performance for Flat Roofs Over Occupied Spaces
How to check
Confirm that the design specifies appropriate acoustic and fire-rated materials and constructions where the element is above another dwelling.
Acceptable when
Flat roofs, terraces, and balconies situated above habitable spaces must incorporate adequate acoustic insulation to meet Building Regulations. Furthermore, these constructions must satisfy the fire protection requirements specified within the Building Regulations, particularly concerning material reaction to fire and separation.
Acoustic flanking in external walls
How to check
Check that the inner leaf material matches the acoustic specification and that junctions between external and separating walls are properly sealed.
Acceptable when
External walls adjacent to separating walls between dwellings must be designed to mitigate flanking sound transmission. This includes ensuring adequate density of the inner leaf, sealing air paths at junctions, appropriate spacing of external wall openings, and avoiding structural elements bridging across separating walls.
Anchoring of LSF against lateral and uplift forces
How to check
Verify that all specified anchors, including bolt-down brackets, are correctly installed and securely fixed to resist wind uplift and lateral loads on the LSF structure.
Acceptable when
Light Steel Frame (LSF) structures must be securely anchored to the substructure to resist both lateral movement and uplift forces. The anchoring system, including specific components like bolt-down brackets, must be installed in accordance with the structural design.
Artstone protection during construction
How to check
Verify that artstone is adequately covered and protected from impact or staining, and that garage pillars extend to the foundation.
Acceptable when
Decorative masonry units, such as artstone, should be protected from damage throughout the construction process. Structural elements like garage pillars must be built from the foundation up, rather than being initiated solely from the ground slab, to ensure stability and proper load transfer.
Backfilling around flue liners
How to check
Check that flue joints are clean internally and that the void around the liner is filled with insulating concrete or a suitable alternative, not ordinary concrete.
Acceptable when
All flue liner joints must be fully filled, with any surplus material cleared from the interior of the flue as it is constructed to maintain a smooth passage. The void between the flue liner and the surrounding masonry should be filled with weak insulating concrete or another specified material in accordance with manufacturer recommendations, ensuring adequate protection.
Balcony & Terrace Drainage Outlet Design
How to check
Verify that discharge outlets are designed and installed to direct water away from the building and other balconies, especially on multi-storey structures.
Acceptable when
Drainage designs for balconies and terraces should adhere to guidelines such as BS 8579, ensuring outlets provide sufficient clearance and capacity to throw rainwater clear of the building facade. For stacked balconies, specific measures are needed to prevent water from cascading onto lower balconies or the building below.
Balcony structural timber use and durability
How to check
Verify that primary structural elements of balconies are not constructed from timber where durability and load-bearing requirements prohibit its use.
Acceptable when
Balcony structural elements, including those supporting timber components, should be designed for a service life of at least 60 years. Structural timber is generally restricted in external balcony applications, particularly for critical load-bearing elements such as gallows brackets, posts, columns, cantilevered joists, or guardrails, to ensure long-term durability and structural integrity.
Basis for differential movement calculations
How to check
Ensure that any required calculations for differential movement in timber frames have been carried out by a competent person and comply with BS EN 1995-1-1.
Acceptable when
When project-specific calculations are required to determine differential movement, particularly for timber frame structures, these calculations must adhere to relevant European standards. For timber structures, the calculations are typically based on BS EN 1995-1-1.
Bay window cavity tray and flashing
How to check
Ensure cavity trays are correctly installed, rise adequately across the cavity, link with lead flashing, and include weep vents.
Acceptable when
At bay window heads, preformed cavity trays are installed across the cavity to collect and discharge water to the exterior via weep vents, often with an enhanced rise in severe exposure areas. These cavity trays must link effectively with external lead flashings, which are typically tucked into a raked and pointed mortar joint to ensure a weather-tight seal.
Bay window head structural support and flashing
How to check
Verify the correct installation of the combined lintel, the lead flashing upstand, and its secure sealing into the external wall.
Acceptable when
Combined insulated steel lintels are typically used to support masonry over bay window openings, providing both structural support and thermal performance. A lead flashing, with a minimum upstand, is usually incorporated above the lintel and sealed into the external wall to prevent water ingress, often integrated with a GRP upstand.
Breathable membranes and water-resistant insulation
How to check
Verify that breathable membranes are correctly installed and lapped, or that water-resistant insulation boards have all joints and penetrations properly taped with manufacturer-recommended tape.
Acceptable when
External walls typically incorporate a breathable membrane behind the external cladding to provide weather protection and allow water vapour to escape. Alternatively, water-resistant insulation boards with appropriately taped joints may fulfil this function, provided the tape is specified by the manufacturer and is breathable.
Breather membrane function and installation
How to check
Visually inspect that the breather membrane is correctly positioned on the external side of the insulation and appears continuous and undamaged.
Acceptable when
Breather membranes, also known as breathable membranes, are installed on the cold side of the insulation in external wall constructions. Their primary function is to protect the underlying sheathing and frame from external moisture, such as wind-driven rain, while simultaneously allowing water vapour from inside the structure to pass outwards, preventing condensation within the wall cavity.
Breather membrane performance and lapping
How to check
Check that breather membranes are correctly lapped to shed water, with vertical joints staggered and secured, and that the product specified meets the required water resistance and vapour permeability.
Acceptable when
Breather membranes must possess specific vapour permeability properties, allowing moisture vapour to escape, and be sufficiently water-resistant to prevent external water ingress, typically meeting Class W1 or W2 standards. Correct lapping, with upper layers overlapping lower ones, is essential to ensure that any water draining down the membrane is shed outwards.
Breather membrane requirements
How to check
Check that the breather membrane is installed with the correct face outwards, all overlaps are secured, and it is free from tears or damage.
Acceptable when
Breather membranes are installed on the external face of a structure to protect the sheathing and frame from external moisture while allowing water vapour to escape from within the wall. They must possess specific properties, including high vapour permeability (less than 0.6 MNs/g), resistance to water penetration (at least Class W2 to BS EN 13859-2), and self-extinguishing characteristics for fire safety.
Brick Laying and Cutting Practice
How to check
Confirm that frogged bricks are laid correctly with frogs filled, and that any cut bricks are neat, accurately sized, and not made with a trowel.
Acceptable when
Frogged bricks, especially those with a single frog, should be laid with the frog facing upwards and fully filled with mortar to ensure a solid bed. When bricks require cutting to achieve bond, they should be cut cleanly and accurately using appropriate tools, avoiding the use of a trowel for facing brickwork, and standard work sizes such as halves or three-quarters should be utilised where possible.
Brick selection for frost resistance
How to check
Verify that specified bricks and mortar types align with the manufacturer's guidance and the intended exposure conditions.
Acceptable when
The selection of bricks for external use must consider their frost resistance classification to ensure suitability for the local environmental conditions and the specific application within the building. Manufacturers' recommendations regarding brick type, mortar choice, and joint finishes are crucial for achieving durable brickwork.
Brick selection for soluble salts
How to check
Confirm that bricks specified for persistently wet or damp locations are classified as having low soluble salts.
Acceptable when
In environments where brickwork will be persistently wet, it is essential to specify bricks that have a low soluble salt content to mitigate the risk of efflorescence and potential long-term damage. Manufacturers provide data on soluble salt classifications, which should guide selection for such conditions.
Brick Specifications
How to check
Check that brick deliveries clearly state compliance with the appropriate BS EN 771 part.
Acceptable when
Bricks employed in construction must adhere to the relevant British Standards based on their material composition. Clay bricks must comply with BS EN 771-1, calcium silicate bricks with BS EN 771-2, and concrete bricks with BS EN 771-3.
Brick types for severe frost exposure
How to check
Verify that all external masonry materials used in severe frost zones meet the required frost resistance classifications or strength specifications.
Acceptable when
In areas designated with severe frost exposure, specific brick types are required to withstand harsh conditions. Acceptable options include clay facing bricks classified as F2,S2 or F2,S1, and concrete bricks with a minimum compressive strength of 20N/mm². Additionally, certain aircrete blocks with render or concrete blocks meeting density or strength criteria may be suitable.
Cavity barrier continuity
How to check
Verify that cavity barriers extend to the required depths and are tightly fitted into the cavity, ensuring no gaps around DPCs or cavity trays.
Acceptable when
Vertical cavity barriers must extend below the damp proof course (DPC) where required, and their continuity must be meticulously maintained, especially where cavity trays are present. The installed barrier must compress to fill the cavity fully, necessitating a consistent cavity width for effective performance.
Cavity barriers behind cladding
How to check
Confirm cavity barriers are present and correctly positioned at all edges and junctions of concealed spaces behind external cladding.
Acceptable when
When external cladding creates a concealed cavity against a masonry substrate, firestopping cavity barriers are essential. They must be installed at all cavity edges, including around openings, at eaves and verges, and at junctions with compartment floors and walls to prevent fire spread.
Cavity closer installation in masonry
How to check
Confirm that cavity closers are installed progressively, correctly spanning the cavity and built into both inner and outer masonry leaves.
Acceptable when
Cavity closers, used at openings such as windows and doors, must be fully integrated into both leaves of the superstructure as construction progresses. They typically provide structural support and thermal breaks.
Cavity closer installation sequence
How to check
Verify that cavity closers are installed concurrently with the surrounding wall construction at all opening perimeters.
Acceptable when
Cavity closers are essential components for closing the cavity around openings, preventing cold bridging and moisture penetration. They must be installed progressively as the surrounding masonry or timber frame superstructure is constructed, ensuring a continuous thermal and moisture barrier.
Cavity closers at separating elements
How to check
Check that rigid insulation terminates at separating walls/floors and that a suitable flexible cavity closer is installed and tightly abutted.
Acceptable when
Rigid insulation should not be continuous across the ends of separating walls or floors. Instead, a flexible mineral wool cavity closer must be installed in line with these elements to maintain fire and acoustic performance, with the rigid insulation tightly butted against the closer.
Cavity Drainage and Cleanliness
How to check
Confirm that cavities extend below the DPC, are clean and unobstructed, and have provisions for drainage.
Acceptable when
External wall cavities must extend below the DPC level to allow for proper drainage and must be kept clear of obstructions to prevent water build-up. Adequate ventilation is also necessary to maintain a dry cavity environment.
Cavity Drainage and Ventilation for Timber Frames
How to check
Verify that the cavity between the timber frame and cladding has appropriate provisions for drainage and ventilation.
Acceptable when
Cavities between timber frame walls and external cladding, such as masonry, require both drainage and ventilation. This ensures that any moisture ingress can escape and that the cavity remains dry.
Cavity insulation around openings
How to check
Check that all cavity insulation is neatly cut and tightly abuts cavity closers, lintels, and cavity trays without gaps.
Acceptable when
Cavity insulation must be accurately cut to fit around all cavity closers, lintels, and cavity trays. Precise cuts and tight butting of the insulation against these elements are essential to maintain thermal performance and prevent cold spots within the building envelope.
Cavity insulation detailing for performance
How to check
Observe that insulation is installed according to approved details, ensuring fibres are correctly aligned and boards are accurately cut and fitted around obstructions.
Acceptable when
Proper detailing of cavity insulation is crucial for effective thermal performance and moisture control. This includes ensuring that insulation fibres in full fill systems run parallel to the wall to prevent cold bridging, and that partial fill insulation boards are cut precisely to fit around components like wall ties, avoiding uninsulated gaps.
Cavity insulation readiness
How to check
Verify that all cavity preparation work is complete and the cavity is clean before insulation installation begins.
Acceptable when
Before installing injected or blown cavity wall insulation, the building must be in a suitable state to receive the material. This typically means the external envelope is complete and weather-tight, with all necessary cavity barriers, fire stops, and structural elements in place, and the cavity clear of debris.
Cavity protection for reduced cavity at flue blocks
How to check
Verify that a vertical DPM and non-combustible insulation are correctly installed to protect flue blocks where the cavity is reduced.
Acceptable when
Where the cavity width is necessarily reduced around a flue block, the flue block must be protected. This protection typically involves a vertical damp-proof membrane (DPM) supported by a layer of non-combustible insulation, installed according to the manufacturer's specifications.
Cavity tie embedment
How to check
Verify that cavity wall ties are bedded into the mortar by at least 50mm in both inner and outer leaves.
Acceptable when
Cavity wall ties must be adequately embedded into the mortar beds of both leaves of masonry to ensure structural integrity and effective transfer of loads. A minimum embedment depth is critical for proper performance and preventing dislodgement.
Cavity Tray Design and Installation
How to check
Confirm cavity trays are installed over all openings, have adequate upstands and overlaps, and are specified as appropriate materials that are not LDPE.
Acceptable when
Cavity trays must be installed at all interruptions in the cavity, such as over openings, and designed to collect and discharge water to the exterior. They must be durable, have a minimum upstand and provide sufficient vertical protection to effectively manage moisture. Materials like low-density polyethylene (LDPE) to BS 6515 are not suitable for cavity trays.
Cavity Tray Installation and Standards
How to check
Ensure cavity trays are correctly installed, include weepholes, and are compliant with relevant British Standards and approvals.
Acceptable when
Cavity trays must be installed over all openings, at abutments, and where specified at sole plate level to deflect moisture. These trays require weepholes to allow collected water to discharge from the cavity. Cavity trays should be marked to BS EN 14909 and hold appropriate third-party technical approvals.
Cavity tray installation requirements
How to check
Verify that cavity trays are installed with the correct fall, integrated into the masonry with appropriate laps, have upturned stop ends, and are clear of debris.
Acceptable when
Cavity trays are vital for directing water that penetrates the outer leaf of a cavity wall back outwards, preventing it from reaching the inner leaf. They must be installed to the correct profile, with proper stop ends and laps, and maintained free of obstructions like mortar droppings to ensure effective drainage.
Cavity tray protection over openings
How to check
Check that cavity trays are present over all openings and that they include appropriate stop ends, especially where required by construction type.
Acceptable when
Cavity trays, or integral lintel trays, must be installed above all openings in masonry walls to prevent moisture penetration into the building. For certain constructions like fair-faced masonry or full-fill insulation, all cavity trays require stop ends to direct water safely outwards.
Cavity tray provision at interruptions
How to check
Verify that cavity trays are installed above all openings and at horizontal abutments, ensuring they are correctly positioned, lapped, and have associated weep holes.
Acceptable when
Cavity trays are essential damp-proof courses installed within the cavity of external walls to prevent moisture from bridging the cavity at openings like windows, doors, and air bricks, or at abutments. They collect water penetrating the outer leaf and channel it safely back out through weep holes.

Most common reasons this visit fails

Mortar snots bridging the cavity

The single most common damp defect. Use a cavity batten, lift it every course or two, and clean the tray before the tray is buried.

High — water penetration claims are the most expensive Buildmark category.

Cavity trays without stop ends

A tray with open ends discharges water into the cavity instead of out through the weeps. Stop ends and weeps get inspected together, so fit them together.

High — structural, and only fixable by taking down brickwork.

Ties at the wrong centres around openings

Ties must be doubled up within 225mm of a reveal or movement joint. The field of the wall is usually right; the edges are where it fails.

Medium to high — invisible once the cavity is closed.

DPC below finished ground level

Levels move after the shell goes up. Check DPC height again once external levels are set, not just at the time of laying.

Medium — usually a rebuild of a small area if caught early.

Superstructure inspection FAQs

Rain into an unfinished wall saturates the insulation, causes efflorescence and leaves lime staining down the elevation. Sheeting the top of the lift at the end of each shift is the single cheapest quality measure in masonry work.

For a typical 50–100mm cavity, 900mm horizontally and 450mm vertically, staggered, with additional ties at 225mm vertical centres within 225mm of any unbonded reveal or movement joint. The tie length and type must suit the actual cavity width including insulation.

At least 150mm above the finished external ground level, measured after landscaping is complete. Where a threshold cannot achieve it, the design needs a drainage channel and an approved accessible-threshold detail.

Normally 150mm each end for openings up to 1200mm and more for wider spans — always check the manufacturer's schedule. Also confirm the lintel is the right way up and the right duty for the load above.

Typically every 10–12m in clay brickwork and 6m in concrete blockwork, plus at corners and changes of height. Position them on the drawing at design stage; retro-fitting is very visible.

That the separating wall is built tight to the underside of the roof covering, that any cavity within it is closed with the correct barrier, and that the fire stopping is continuous and not left for later — one of the most-cited superstructure RIs.

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Where this sits in the build

The key stage inspection sequence on a typical UK housing plot.

Other inspection stage checklists

Excavation & foundations

21 checks →

Drainage

20 checks →

Basement / lower ground

28 checks →

Ground Floor & Slab

19 checks →

Timber Frame Erection

21 checks →

Roof

22 checks →

Windows and External Doors

24 checks →

Insulation & Airtightness

23 checks →

First Fix

28 checks →

Fire Stopping

22 checks →

Pre-Plaster

21 checks →

Second Fix

31 checks →

External Works & Pre-Handover

23 checks →

Pre-handover

22 checks →

General Quality

20 checks →

All key stage checklists

Related guides

Snag lists with GPS photo evidence

How to record and close out defects with evidence that stands up at handover.

NHBC stage inspections on site

Running key stage inspections and keeping the paperwork straight.

Build programme scheduling

Generating and maintaining plot-by-plot build programmes.

BREL report photo requirements

What Part L photographic evidence has to show, and when.

Go deeper: Quality Intelligence

Our free, cited reference library — critical dimensions, build stage guidance, common defects and plain-English guides.

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