Roofing & Cladding
QA inspection checklist

Substrate & Preparation

1. 1.

   Substrate clean, dry, and free from debris
   What to look forDecking (timber, metal, or concrete) swept clear of dust, screws, and offcuts. No damp patches or standing water. Joints between boards or panels not stepped — flush with adjacent panel. Surface stable underfoot.
   Acceptable whenSubstrate moisture: timber ≤ 18% MC, concrete < 5% by hygrometer (BS 8203). Steel decking dry, no oil residue. Surface flatness ±5 mm under 3 m straight edge per LRWA / NFRC guidance.
   StandardBS 8217:2005 — Reinforced bitumen membranes. BS 6229:2018 — Flat roofs with continuously supported flexible waterproof coverings. NFRC Technical Bulletins.
   Common defectsTimber decking damp — vapour drives moisture into membraneScrews and offcuts left on deck — punctures through membraneStepped board joints — telegraph through membrane, water poolsConcrete deck not cured — efflorescence under membraneLoose insulation board lifted by wind under membrane
2. 2.

   Falls correct as per design

   Record: Fall (1 in ?)
   What to look forFall checked with level along multiple lines on roof. Flat roof minimum design fall achieved at all points, including at outlets and behind upstands. No back-falls. Pre-formed tapered insulation aligned correctly with set-out.
   Acceptable whenPer BS 6229: minimum design fall 1:80 (to achieve 1:80 finished after deflection); 1:40 typical UK practice. NFRC/SPRA recommend 1:60 finished. Pitched roof fall per tile/slate manufacturer (typically 22.5° minimum for plain tiles).
   StandardBS 6229:2018 (flat roofs). BS 5534:2014+A2:2018 — Slating and tiling. NFRC TB 39 — Roof drainage design.
   Common defectsPonding > 24 hours after rainfall — fall too shallowBack-fall behind upstand — water pools at parapetTapered insulation set out wrong way — water away from outletsPitched roof set below minimum tile pitch — wind-driven rain ingress
3. 3.

   Vapour barrier installed correctly
   What to look forVapour control layer (VCL) on warm side of insulation (i.e. underneath in warm-deck flat roof). Continuous, with sealed laps and details around penetrations. Type and class match design (typically AVCL with SD-value > 100 m).
   Acceptable whenVCL per BS 6229 / BS 5250: SD-value matched to dewpoint analysis. Lap minimum 100 mm, sealed with adhesive tape or welded. Continuous with wall VCL at perimeters. Class A1 fire-rated where required.
   StandardBS 5250:2021 — Management of moisture in buildings. BS 6229:2018. NFRC Technical Bulletins.
   Common defectsVCL on cold side of insulation (cold deck) — interstitial condensationLaps unsealed — vapour migrationVCL torn around services and not repairedWrong SD-value — too low, vapour passes through to insulationDiscontinuous at parapets — water and vapour bridge
4. 4.

   Insulation installed tightly with staggered joints
   What to look forBoards butt-tight to neighbours. Joints staggered between courses (no cross joints). Cut boards full-thickness — not slivers. Mechanical fixing or adhesive bond per design. No gaps > 5 mm.
   Acceptable whenPIR/MW per BS EN 13165/13162, lambda value per design. Joints butt-tight, staggered ≥ 150 mm. Mechanical fix density per wind load calculation (BS EN 1991-1-4) — typically 4-6 fixings/m² in zone 1, more in corners. Gaps > 5 mm filled with insulation foam.
   StandardBS EN 13165 (PIR), BS EN 13162 (mineral wool). BS 6229. BS EN 1991-1-4 (Eurocode 1 wind loads).
   Common defectsCross joints — vertical thermal bridge, line of weaknessSlivers used at edges — wind uplift failsGaps not filled — cold bridges and vulnerable cornersMechanical fixing density inadequate for wind zoneInsulation compressed by trafficking before membrane laid

Membrane / Sheeting

1. 5.

   Membrane/sheet type matches specification
   What to look forSingle ply membrane (EPDM/TPO/PVC) manufacturer and product code matches spec. Bitumen membrane: cap sheet thickness, mineral finish, reinforcement type. Tile/slate: type, gauge, source quarry. BBA certificate covers application.
   Acceptable whenSingle ply per BS EN 13956:2012 with BBA / IAB certificate covering substrate and exposure. Bitumen per BS 8747:2007 / BS 8217:2005. Tiles/slates to BS EN 490, BS EN 12326 (slate). Match exposure category and roof pitch.
   StandardBS EN 13956:2012 — Plastic and rubber sheets for roof waterproofing. BS 8217:2005. BS 5534:2014+A2 — Slating and tiling. BS EN 12326 — Natural slate.
   Common defects0.8 mm TPO used where 1.2 mm specified — punctures soonerWrong tile pitch class — minimum pitch not respectedMembrane outside BBA application range (e.g. on combustible deck without barrier)Slates from different quarry — colour banding visibleCap sheet without mineral finish where exposed to UV
2. 6.

   Laps correct width and sealed

   Record: Lap width (mm)
   What to look forSingle ply: heat-welded laps probed with seam probe — no slip. Bitumen: torch-on showing bitumen extruded at lap edge. Tiles/slates: head lap and side lap correct, mortar bedding/clipping appropriate. Underlay laps adequate.
   Acceptable whenSingle ply welded lap ≥ 30 mm (TPO/PVC) or ≥ 75 mm (EPDM tape). Bitumen lap ≥ 80 mm side, ≥ 150 mm head. Tile head lap per pitch (typically 65-100 mm at 30°+). Underlay lap ≥ 150 mm horizontal, 100 mm vertical.
   StandardBS 6229. BS 5534:2014+A2. BS 8747. NFRC TB 49 (single ply).
   Common defectsCold weld in single ply — visible "fish eye" or no extrudateLap width undersize — water enters at high windsTile head lap below pitch table — wind-driven leaksBitumen lap with bare felt visible — scorched but not bondedUnderlay lap reversed — water flows under
3. 7.

   No wrinkles, fish mouths, or bridging
   What to look forMembrane lies flat on substrate. No bubbles, lifts, or wrinkles after relaxation. Internal corners coved with detail strip — no folding. External corners full ply with reinforcement. No bridging between insulation joints.
   Acceptable whenPer BS 6229 / NFRC TB 49: no wrinkling, fish mouths, or air pockets in finished membrane. Internal corners coved with reinforcement strip ≥ 100 mm. External corners reinforced with patch.
   StandardBS 6229. NFRC Technical Bulletins. SPRA (Single Ply Roofing Association) guidance.
   Common defectsWrinkles — membrane unrolled and walked on without relaxation timeFish mouths at lap ends — applicator not pressed lap edgeBubbling under membrane — outgassing from substrateBridge at insulation joint — visible later as a permanent creaseFolded internal corner — no detail strip, eventually splits
4. 8.

   Mechanical fixings at correct centres
   What to look forFixings to NFRC / manufacturer wind uplift tables. Fastener pattern denser at edges and corners. Plates seated flat — not over-driven. Penetration covered with patch / cap. Ballast (where used) at correct loading.
   Acceptable whenFixing density per wind uplift calculation (BS EN 1991-1-4). Typical for low-rise: zone 1 (centre) 4-6 fixings/m², zone 2 (edge) 8-10/m², zone 3 (corner) 12-16/m². Corners typically 1.5-2 m wide. Ballast 50 kg/m² minimum on loose-laid systems.
   StandardBS EN 1991-1-4:2005+A1 (Eurocode 1 wind loads). NFRC TB 49. BS EN 13670 fixings — Annex.
   Common defectsUniform fixing density across whole roof — inadequate at cornersFixings over-driven — plate cuts membranePlate proud of membrane — wear pointBallast undersize or loose — blown off in stormsWrong fixing for substrate — telescopic only into thin steel deck
5. 9.

   Sheet profile and colour correct
   What to look forFor metal cladding: profile (box, trapezoidal, sinusoidal) matches spec, gauge correct (0.7 mm typical), colour matches RAL/PPC. Fixings clipped through ridge or valley as designed. EPDM/butyl washers in good order.
   Acceptable whenMetal cladding to BS EN 14782 / BS EN 14783. Coating to BS EN 10169 (PPC) — typical 25/35 μm Plastisol or 20-25 μm PVDF. Gauge to manufacturer's structural design tables. Colour fastness Class 3+.
   StandardBS EN 14782:2006 — Self-supporting metal sheet. BS EN 10169:2010 — Coil-coated steel.
   Common defectsProfile inconsistent — different manufacturers mixedColour banding — deliveries from different runsCoating damage from cutting on site (hot blade) — corrosion within 5 yearsWrong fixing position — ridge fix where valley fix specifiedCracked/missing washers — water entry at fixings

Details & Flashings

1. 10.

   Flashings dressed and sealed at all upstands
   What to look forUpstand height ≥ 150 mm above finished roof per BS 6229. Membrane terminated under counter flashing or cover trim. Lead/aluminium flashings dressed into chase or behind cladding. Sealant continuous at top.
   Acceptable whenUpstand min 150 mm above finished roof level (BS 6229). Lead flashing min code 4 (BS EN 12588), max chase length 1.5 m, lap 150 mm. Cover flashing min 75 mm below top of upstand. Sealant gun-grade MS polymer or polyurethane.
   StandardBS 6229:2018. BS 5534:2014+A2 (pitched). BS EN 12588:2006 (lead). LSA "Rolled Lead Sheet Manual".
   Common defectsUpstand < 150 mm — wind-driven water over topLead too thin (code 3) — punctures, fatigue cracksCounter flashing not chased into wall — dressed over and clipped, blows offNo sealant at top of cover flashing — water tracks behindLap < 150 mm — capillary leak
2. 11.

   Penetrations sealed (pipes, vents, rooflights)
   What to look forPre-formed pipe collars or hot-air-welded patches. Rooflight upstands ≥ 150 mm above roof. Lead slates dressed around flue pipes per LSA detail. No bare cut edges of membrane.
   Acceptable whenPenetrations per BS 6229. Pre-formed collars to manufacturer's system. Rooflight upstand ≥ 150 mm. Tested and certified upstand details. Mastic sealant only as secondary line of defence — never primary.
   StandardBS 6229:2018. BS EN 1873 (rooflights). NFRC TB 49.
   Common defectsSealant relied upon as primary water defence — fails in 2-3 yearsRooflight upstand too low — splash entryPre-formed collar oversize — gap at pipe, sealed with masticMembrane cut around pipe with no patch — splitsMultiple penetrations bunched — no clear water path between them
3. 12.

   Gutters and outlets clear and draining
   What to look forOutlets sized for the catchment area and rainfall intensity. Strainers in place — clear of debris. Outlet sumps recessed below membrane level. Overflow outlet provided. No back-falls on gutters.
   Acceptable whenOutlets sized per BS EN 12056-3 / BS EN 752 — typical UK rainfall 75 mm/hour design event. Outlet recessed 10-15 mm below membrane to encourage flow. Overflow weir set 50-75 mm above main outlet.
   StandardBS EN 12056-3:2000 — Roof drainage. BS 8490:2007 — Siphonic roof drainage. BS EN 752:2017.
   Common defectsOutlets sized for old 50 mm/hour rainfall — undersized for current intensityNo overflow — internal flooding if main outlet blocksOutlet blocked with debris — common on flat roofs after installGutter sagged between brackets — water pools, ice damageOutlet flush with membrane — no flow encouragement
4. 13.

   Edge trim fixed and aligned
   What to look forEdge trims (drip, gutter trim, parapet trim) aligned along the run, no kinks. Joints in trim with sleeves or covers — not butted. Fixed to substrate at correct centres. Membrane bonded under trim.
   Acceptable whenEdge trim per NFRC TB 49. Aluminium 3 mm typical, 1.5-3 m sections, joint sleeves at every length. Fixings ≤ 200 mm centres. Membrane to be carried up under trim and sandwich-fixed.
   StandardNFRC TB 49. SPRA Design Guide. BS EN 1462 (gutters).
   Common defectsTrim joint butted with mastic — fails first hot day with thermal movementTrim bowed where wall is bowed — installer didn't packFixings into mortar joints — pull outTrim end stops missing — water enters end of runMembrane terminated below trim, not turned up — short-term leak
5. 14.

   Warranty documentation provided
   What to look forManufacturer's warranty (10/15/20/25 years) issued in client name. Single-point system warranty — covers membrane + insulation + adhesive. Installer's workmanship warranty separate. Maintenance schedule attached.
   Acceptable whenWarranty per manufacturer scheme — typically 10-25 years system warranty (e.g. Sika, Bauder, IKO) requiring approved installer. Maintenance regime to be followed. Warranty void if substrate or detailing not per manufacturer guide.
   StandardManufacturer warranty terms. BBA / IAB Certificate. NFRC Code of Practice.
   Common defectsWarranty in installer name not client name — no recourse on insolvencyComponent-only warranty — no system-level cover for adhesive failureMaintenance regime not given — warranty voids if not followedWarranty paperwork missing details (date, address, system code)Installer not on manufacturer's approved list — warranty invalid

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