Insulation
QA inspection checklist

Materials & Specification

1. 1.

   Insulation type, thickness, and lambda value match specification
   What to look forProduct label visible — manufacturer, product code, thickness and lambda value. Type matches U-value calculation submitted for Building Control. PIR (Kingspan, Celotex), mineral wool (Rockwool, Knauf), EPS, or phenolic — exact product and grade as design.
   Acceptable whenPIR boards to BS EN 13165 with declared lambda (typically 0.022-0.026 W/m·K). Mineral wool to BS EN 13162 (lambda 0.032-0.044). Thickness as design. Lambda value used must match the SAP / U-value calculation. Approved Document L applies to thermal performance.
   StandardBS EN 13165:2012+A2:2016 (PIR). BS EN 13162:2012+A1:2015 (mineral wool). Approved Document L (England/Wales). PAS 2030 for retrofit.
   Common defectsGeneric-brand insulation supplied with no declared lambdaThinner board than design — U-value not achieved, fails Part LWrong lambda (e.g. 0.025 used in calc but 0.030 supplied) — performance gapMixed product types in same wall — calc invalidated
2. 2.

   Product certification and BBA/BDA certificate available
   What to look forBBA, BDA Agrément, KIWA, or equivalent third-party certificate covering the application (e.g. "PIR insulation in flat roofs, warm-deck"). Certificate current (not expired). System spec matches the certificate scope. CE/UKCA marking on packaging.
   Acceptable whenBBA / BDA / Kiwa certificate covering specific use. CE/UKCA mark per Construction Products Regulation. Manufacturer DoP available. Reaction-to-fire class declared. NHBC and warranty provider acceptance.
   StandardConstruction Products Regulation. BBA Agrément Schemes. NHBC Standards Chapter 6.1.
   Common defectsBBA certificate covers wall use but installed in roof (or vice versa)Certificate expired — product specification supersededNo CE/UKCA mark — non-compliant productWarranty provider rejects unlisted product after install
3. 3.

   Fire classification correct for location
   What to look forReaction-to-fire class on packaging label and DoP — Euroclass A1, A2, B, C, D, E, or F. Compliant with Building Regulations Approved Document B for the height and use of building. PIR/phenolic combustible — only allowed in non-relevant buildings post-2018 ban.
   Acceptable whenPer Approved Document B / Regulation 7(2): buildings ≥ 11 m / ≥ 18 m (depending on use) must use materials of Euroclass A2-s1, d0 or A1 in external walls. Mineral wool typically A1 / A2. PIR typically B-s1, d0 — restricted use post-Grenfell.
   StandardBS EN 13501-1:2018 — Reaction-to-fire classification. Approved Document B (Volume 1 & 2). Regulation 7(2) Building Regulations 2010 (as amended).
   Common defectsCombustible PIR used in ≥ 18 m residential external wall — Reg 7(2) breachCertificate shows class B but design assumed A2Insulation not separated from cavity by cavity barrier where neededReaction-to-fire data not provided — cannot verify

Installation

1. 4.

   Insulation fitted tightly with no gaps at edges
   What to look forBoards or quilt friction-fit between studs/rafters/joists. Cuts neat and follow contours. No daylight visible at edges. PIR butt-jointed; gaps > 5 mm filled with expanding foam. Mineral wool slightly compressed (5%) into width to avoid sag.
   Acceptable whenPer BBA / NHBC: gaps < 5 mm acceptable for PIR (foam-filled). Mineral wool friction-fit, no sag. PASSIVE installation per PHPP / NIEER guidance — air gaps reduce performance by 50%+.
   StandardNHBC Standards Chapter 6.1. BRE Information Paper IP 1/06 — Assessing the effect of thermal bridging. Passivhaus Trust guidance.
   Common defectsDaylight gaps at stud edges — convective bypassInsulation cut short — gaps stuffed with offcutsSliver pieces at last bay rather than full boardIll-fitting cuts at services — large gaps not foamedMineral wool sagging in walls — top of bay open
2. 5.

   Joints staggered and butt-tight
   What to look forMultiple-layer insulation — joints between layers offset minimum 150 mm to break the thermal path. Boards butt-tight without overlap. Tongue and groove engaged on board edges (where supplied). No cross joints aligning over a stud or rafter.
   Acceptable whenPer manufacturer technical guidance: joint offset ≥ 150 mm; T&G engaged; joints butt-tight without forcing. Cross joints staggered by ≥ 200 mm. Critical for PIR full-fill cavity systems and warm roofs.
   StandardBS 5250:2021. Manufacturer system specs (Kingspan TEK, Celotex TB4000, Knauf Earthwool). NHBC 6.2 / 7.1.
   Common defectsCoincident joints between layers — line of cold bridging visible on thermographT&G not engaged — gap at sideBoards forced together causing one to bowCross joint at stud — thermal short-circuit
3. 6.

   No compression or damage
   What to look forInsulation at design thickness throughout — not crushed by service runs, fixings, plasterboard, or trafficking. Boards not chewed by rodents or punctured by fixings. Mineral wool quilt fluffy, not flattened.
   Acceptable whenCompression < 5% to maintain declared lambda. Per BRE/NHBC: any local compression > 25% considered defect. Damaged sections to be replaced, not patched.
   StandardNHBC Standards 6.2. BRE IP 1/06. BS EN 13162 / 13165 (declared performance is at uncompressed thickness).
   Common defectsInsulation crushed under floor cassette — full thickness lostCompressed at services — visible as flat zone on thermographPunctured by fixings — air paths throughMineral wool stamped down by trafficking — performance lost
4. 7.

   Continuity maintained at junctions — no cold bridges
   What to look forInsulation continuous at floor/wall and wall/roof junctions, eaves, openings, and at separating walls. Window and door reveals fully insulated. No exposed structural elements bridging from cold to warm side. Junction details match the Accredited Construction Detail / SAP psi-value used.
   Acceptable whenPsi-value (linear thermal transmittance) at junctions per ACD / SAP / PHPP. Reveals insulated to ≥ 25 mm. No metal lintels exposed. Cavity tray and barrier do not displace insulation. Robust details checklist completed.
   StandardBR 497 — Conventions for U-value calculations. SAP Appendix K — Thermal bridging. Accredited Construction Details (Robust Details). Approved Document L.
   Common defectsWindow reveal not insulated — major linear thermal bridgeEaves bypass — cold loft air enters wall cavityLintel uninsulated — visible cold strip on thermograph, condensationSteel beam in floor zone exposed to cavity — cold bridge to slabDefault psi-values used in SAP but ACD not built — Part L fail
5. 8.

   Mechanical fixings at correct centres (if applicable)
   What to look forExternal wall insulation (EWI) and warm-roof PIR fixed mechanically — fixings at design centres and pattern. Fixings into solid substrate (not perp/movement joint). Plate / disc washer behind fixing head. Penetration depth into substrate adequate.
   Acceptable whenEWI fixings per BBA / system designer — typically 4-6 fixings/m² in field, 8-10 fixings/m² at corners and edges (BS EN 1991-1-4 wind loading). Roof insulation per warm-roof spec — typically 4 fixings/m² with 70 mm minimum penetration into deck.
   StandardBS EN 1991-1-4:2005+A1:2010 — Wind actions. EWI Insulation Manufacturers Association. NFRC Single Ply Roofing Association.
   Common defectsFixings missed substrate — pull-out load is zeroCentres > design — wind uplift failsEdge zone reverted to field density — corner fail in stormPlate not behind fixing — fixing pulls through boardFixings into perp joint of brick — no holding
6. 9.

   Vapour barrier installed correct side with sealed laps
   What to look forVapour control layer (VCL) on warm side of insulation (internal face in heated buildings). Continuous across all surfaces. Laps minimum 100 mm taped or welded with proprietary tape. Penetrations at services sealed. Wall/roof/floor VCLs joined.
   Acceptable whenVCL per BS 5250 / BS 6229: SD-value matched to dewpoint analysis (typically Sd > 100 m). Lap ≥ 100 mm sealed. Penetrations sealed with grommets and tape. Continuity at junctions (e.g. with wall VCL, with airtightness layer).
   StandardBS 5250:2021 — Management of moisture in buildings. BS 6229:2018 — Flat roofs. BR 262 — Thermal insulation: avoiding risks.
   Common defectsVCL on cold side — interstitial condensation, mouldLaps unsealed — vapour migration into structureVCL torn around services and not repairedDiscontinuous at floor/wall junction — bypassWrong SD-value — vapour passes too easily

Run this inspection on a phone

The same 9 checks, with the guidance a tap away, photos against each fail, measurements recorded, an NCR raised automatically and a branded PDF at the end. Signed on site. 14 days free.