Method Statement for Window Installation — UK
A free, FENSA/CERTASS-aligned method statement for UK window installation — covering the safe removal of existing units, manual handling of glazed sashes, working at height, and the COSHH controls for sealants and primers.
UK (RAMS) example document — Two-Storey Rear Extension — 14 Birchwood Lane, Reading. Client: Mr & Mrs A. Whitfield (Private Client). Site: 14 Birchwood Lane, Reading, RG1 5JT. Scope: Construction of a two-storey rear extension (6.4m × 4.2m) to an existing semi-detached dwelling. Works comprise breaking out of existing rear elevation, trench-fill foundations to 1.0m, traditional cavity blockwork to first floor, pre-stressed concrete lintels, timber roof structure with natural slate finish, plus alterations to existing rear wall to form structural opening with rolled steel joist (RSJ 203×102 UB23). Works programmed over 9 weeks with a peak site team of 6 operatives. Hazards assessed: Manual handling — blocks, lintels, plasterboard, Working at height — independent scaffold & roof structure, Buried services strike during excavation, Collapse of excavation / trench wall, Hand-arm vibration (HAVS) — breaking out, drilling, Silica dust — cutting blocks, brick, concrete, Vehicle/pedestrian segregation — narrow domestic street.
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Built around recognised UK method statement structure — hazards, controls, sequence, PPE and sign-off. Ready for competent-person review.
Window installation is deceptively dangerous. A standard 1.2 × 1.5m triple-glazed unit weighs 65–80 kg, almost every installation involves working at height (often from a ladder against a flat that has no scaffold), and the COSHH profile of low-modulus silicones, expanding PU foams and bonding primers is significant. The Grenfell Tower Inquiry Phase 2 report (Sept 2024) drew explicit attention to the role of window-fitter assumptions about insulation and cavity barriers — and competent-person scheme audits (FENSA, CERTASS) have tightened since. This page sets out what a defensible UK window installation method statement looks like in 2026, covering domestic single replacements through to commercial curtain-wall packages, with a free editable template.
When is it required?
Window installation in any commercial or multi-occupancy building under CDM 2015 needs a written MS before mobilisation. The principal contractor or building owner will demand it alongside the FENSA or CERTASS competent-person scheme certificate, the F-gas and refrigerant declaration (if removing sealed units containing argon/krypton), the lift plan for any unit above first floor that needs a Hiab or MEWP, and the COSHH assessments for every sealant and primer. For domestic single dwellings the legal MS requirement is lighter, but Approved Document L (Conservation of fuel and power) and Approved Document Q (Security) compliance must be evidenced — the MS is the cleanest way to do it.
What a good one looks like
A defensible window installation MS runs to 8–12 pages and names every specific. It identifies the unit (e.g. 'Internorm KF410 timber-alu, 1.2 × 1.5m, U=0.78 W/m²K, 78 kg'), the access method (1.5m × 2.0m scaffold tower vs MEWP vs ladder for ground floor only), the lifting equipment (vacuum cup, manual lifter), the sealant system (e.g. 'Soudal Soudaseal 215LM low-modulus silicone, Soudaprime primer'), the cavity barrier and reveal detail (post-Grenfell critical), and the disposal route for the removed unit (separate WEEE for any sealed unit with argon). It is signed by a FENSA or CERTASS competent surveyor who has done the survey, not the office.
Window Installation hazards & controls
The site-specific hazards a window installation MS must address, with the controls that take residual risk to an acceptable level.
| Hazard | Persons at risk | Controls | Residual |
|---|---|---|---|
| Falls from height during removal and refit (above ground floor) | Fitters, occupants below | Scaffold tower (TG20:21) or MEWP above first floor; ladder use only for ground floor and only to BS EN 131-1 with three points of contact; no working from internal sills wider than 200mm; safety harness with engineered anchor for commercial curtain-wall | Medium |
| Manual handling — glazed units 40–120 kg, frames 25–50 kg | Fitters | Two-person lift mandatory above 25 kg; vacuum cup lifter for any unit >40 kg or >1.5m² (e.g. Bohle Veribor); no carrying glazed units up ladders; pre-staging at sill level using a glazing trolley or Hiab to the sill | Medium |
| Cuts from broken glass during removal | Fitters, occupants, cleaners | Cut-resistant gloves (EN 388 cut level 5); safety glasses or face shield; carpet protection inside and dust sheet outside; broken glass swept and bagged immediately into rigid container; first-aid kit with glass-cut trauma dressing within 25m | Low |
| COSHH — silicone sealants, PU foam, bonding primer (isocyanates) | Fitters, occupants | COSHH sheet on site for every product; nitrile gloves; FFP3 RPE during PU foam application in confined or unventilated spaces; isocyanate primer used outside or with mechanical ventilation; no smoking within 5m; eye-wash bottle on van | Low |
| Falling tools/materials onto people below (especially terraced and city-centre) | Public, occupants | Tool tethers above 2m; bucket-and-line for sealants and small parts; 3m exclusion zone on the pavement below with cones and signage; banksman where pedestrian flow is high; permit from highways for any oversail of public footway | Low |
| Asbestos in window putty, asbestos cement reveals, AIB panels behind reveal (pre-2000 buildings) | Fitters, occupants | R&D asbestos survey for any pre-2000 building before disturbance; any suspect material — stop, sample, do not disturb; licensed contractor for any AIB or sprayed coating; non-licensed work only with HSE-approved training | Medium |
| Damage to wall structure during removal (lintel disturbance, brick spalling) | Occupants, fitters | Pre-installation survey of lintel and reveal condition; props in place before any timber lintel disturbance; brick-cutting with wet diamond saw and FFP3 RPE; reveal made good with matching mortar; building control notified for any structural change | Low |
| Fire safety — cavity barriers and intumescent seals (post-Grenfell) | Building occupants | Cavity barrier installation per the FRA strategy — Approved Document B compliant; intumescent perimeter seal where the FRA requires; install record signed and photographed for the FRA file; never compress or omit cavity barriers to make a unit fit | Low |
Step-by-step sequence
- 1
1. Pre-installation survey & briefing
Surveyor confirms dimensions, structural condition, lintel state, and any pre-2000 asbestos concerns (R&D survey reviewed). Fitter briefed on this MS, the COSHH sheets and the unit specification. FENSA/CERTASS card photographed to site file.
- 2
2. Site protection & access set-up
Carpets and floors protected with dust sheets and corrugated board. Scaffold tower or MEWP erected (above first floor) with handover certificate. Internal dust sheets to seal off the room from the rest of the property.
- 3
3. Removal of existing unit
Sash removed first, frame second. Glass scored and broken into the room with dust sheet captures. Frame cut with multi-tool to release fixings. Spoil bagged, sealed and removed to van. Any suspect asbestos material — stop, do not disturb, call the survey.
- 4
4. Reveal preparation
Reveal cleaned of mortar dags, brushed, primed where the sealant manufacturer requires. Cavity barrier (where applicable) installed and photographed. Damp-proof course (DPC) checked and restored if damaged.
- 5
5. New unit lift and set
Unit lifted with vacuum cup or two-person manual to the sill. Packed level and plumb with proprietary packers (no timber off-cuts). Fixed with frame anchors at 150mm from corners and 600mm centres per BS 8213-4. No overdriven fixings (frame distortion).
- 6
6. Sealing & insulation
Low-expansion PU foam to fill the cavity (no overfill — distorts frame). External low-modulus silicone perimeter seal with primer. Internal trims and architraves refitted. All sealant work to manufacturer's datasheet conditions (temperature, humidity).
- 7
7. Commissioning & sign-off
Sash hinge and lock function tested. U-value declaration and Approved Document L certificate generated through FENSA/CERTASS. Customer briefed on operation, ventilation and trickle vent purpose. MS and sign-off bundled to the project file.
12-unit triple-glazed replacement, 1960s council block, third-floor flat
A South London window-installer working on a 12-unit triple-glazed replacement in a 1960s council block flat documented a 10-page method statement that the housing association accepted first time. Key entries: a FENSA-certified surveyor signed the MS after confirming an R&D asbestos survey had cleared the reveals (no AIB present); access was a Boss tower erected to TG20:21 inside the flat balcony with daily handover; each Internorm KF410 unit (78 kg) was lifted with a Bohle Veribor 4-cup vacuum lifter by a two-person crew, never a single-handed lift. Cavity barriers were installed per the building's fire strategy update and photographed for the FRA file. Soudal Soudaseal 215LM low-modulus silicone with Soudaprime primer was used externally; PU foam was 30% expansion only, controlled with a Soudal Click & Fix gun calibrated against a test bead each morning. Trickle vents were left open and the resident was briefed on their purpose. 12 units replaced in 4 days, zero damage to existing decoration, zero call-backs, zero RIDDOR incidents. The MS, the FENSA certificate and the cavity-barrier installation record were the three documents that closed the package out.
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Common mistakes that get a window installation MS rejected
- ·Using a ladder for first-floor and above — the Working at Height Regulations 2005 hierarchy requires a scaffold or MEWP wherever reasonably practicable
- ·Lifting glazed units >40 kg single-handed because the staircase is too tight for a vacuum lifter — re-route or hire a smaller crane
- ·Omitting the cavity barrier line item — post-Grenfell, this is the single most-checked detail on commercial window installations
- ·Generic 'silicone sealant' without naming the product, modulus class and primer (low-modulus silicone for thermal movement is non-negotiable on aluminium and timber-alu)
- ·Forgetting the R&D asbestos survey on any pre-2000 building — window putty up to 1985 and AIB behind reveals are well-documented exposures
- ·Allowing PU foam to over-expand and distort the frame — and then trying to plane the sash to fit (warranty void)
Frequently asked questions
Do I need an MS for a single domestic window?
Legally the bar is lower for a single dwelling under sole occupation, but the FENSA/CERTASS competent person scheme conditions require a documented installation procedure regardless. For any flat above ground floor, an MS is strongly advisable — the access risk alone justifies it.
What's the lift threshold for vacuum cups?
Industry rule of thumb is >40 kg or >1.5m² requires a vacuum lifter; >80 kg requires a powered lifter or Hiab. The L23 Manual Handling guidance and ergonomic risk assessments support this — a two-person manual lift of a 65 kg unit through a 0.9m opening is not reasonably practicable.
How are cavity barriers handled post-Grenfell?
Approved Document B Vol 2 requires cavity barriers at any compartment line crossed by a window opening on buildings over 11m. The FRA must say what's required; the MS must say how it's installed; the install record must be photographed and kept for the building file.
Can I use ladders for ground-floor windows?
Yes, where the work is short-duration (under 30 minutes per ladder set) and the ladder is to BS EN 131-1, set at the correct angle, tied or footed, with three points of contact. For commercial sites the principal contractor may insist on a tower even at ground floor.
What's the COSHH risk on PU foam?
PU foam contains methylene diphenyl diisocyanate (MDI), a category 1 respiratory sensitiser. The COSHH assessment should require nitrile gloves, eye protection, mechanical ventilation in any enclosed space, and FFP3 RPE for sensitised individuals. No smoking within 5m.
Related method statements & RAMS
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