FENSA — building-control sign-off for new windows & doors.
When you replace a window or external door in England or Wales, the new unit must comply with Building Regulations Part L (energy efficiency) and Part B (fire). FENSA-registered installers self-certify the work; their certificate is the document conveyancers ask for at sale.
What is a FENSA certificate and do I need one?
FENSA (Fenestration Self-Assessment Scheme) is the competent-person scheme for replacement windows and external doors in England and Wales. A FENSA-registered installer issues a certificate within 30 days of finishing work — confirming the new units meet Part L (U-value ≤ 1.4 W/m²K) and Part B (egress + fire). At sale, your conveyancer will ask for the FENSA certificate for any windows replaced since 2002.
Replacement windows since 1 April 2002 must be FENSA / Certass / LABC-certified.
Part L1B 2022 thermal performance ceiling for replacement windows in dwellings.
Typical price drop where replacement windows have no certificate.
FENSA — the terms that matter
Plain-English definitions for the 5 terms you'll see in any quote, certificate or enforcement notice for FENSA Window Replacement.
- Fenestration Self-Assessment SchemeFENSA
- A government-authorised competent-person scheme operated by GGFi for the replacement window, door and roof-window industry in England and Wales. Established 1 April 2002.
- Approved Document L1BAD L1B
- Building Regulations 2010 statutory guidance on conservation of fuel and power in existing dwellings — sets the U-value ceiling for replacement windows.
- Approved Document BAD B
- Building Regulations guidance on fire safety — sets minimum egress dimensions for upper-floor windows in habitable rooms.
- U-valueU-val
- Thermal-transmittance coefficient measured in W/m²K. Lower is better. Replacement windows must achieve ≤ 1.4; new-build is tighter at ≤ 1.2.
- Window Energy RatingWER
- BFRC industry rating from G (worst) to A++ (best). Sales-side proxy for U-value; FENSA installers list it on quotations.
How to replace windows and stay Part L compliant
Five steps from instruction to certificate. Total time: 3w.
01
Pick FENSA / Certass installer
Day 0
FENSA, Certass, or BSI Kitemark KM 567778 are the three main competent-person schemes. Verify the registration number on the body's public register before signing the quote.
02
Confirm spec
Day 1–3
Quotation must state U-value ≤ 1.4 W/m²K, BFRC WER, glass spec (low-E coating, argon fill), egress hinge for upper-floor habitable rooms, and trickle vents (mandatory since 2022).
03
Install + commissioning
Day 7–14
Install typically takes 1 day per window. Installer fits new sealed unit, weatherproof seals, and tests opening / locking. Defective panes can be swapped within 30 days at no cost.
04
Certificate issued
≤30 days
FENSA posts certificate to homeowner and council within 30 days of completion. Building Regulations Compliance Certificate covers Parts L + B + Q + F.
05
Store with deeds
Forever
File the FENSA certificate with title deeds. Conveyancers will request it at sale; no certificate = price negotiation or retroactive LABC fee.
FENSA Window Replacement. Done compliant.
Every TradeMatch-listed tradesperson covering FENSA Window Replacement carries the relevant scheme registration. Verified at onboarding, re-verified annually, certificates posted to you within 30 days of any notifiable work.
FENSA installer vs unregistered fitter — what changes for you
Side-by-side comparison of the compliant route versus the unregistered shortcut. Most rows trace a straight line from regulation to financial exposure.
| Factor | FENSA / Certass installer | Unregistered fitter |
|---|---|---|
| COMPLIANT — RECOMMENDEDBuilding-control sign-off | Self-certified — certificate within 30 days | You must notify LABC before work + pay £200–£450 fee |
| Insurance-backed warranty | 10-year IBG via FENSA / Certass mandatory | Optional — depends on individual fitter; rarely insurance-backed |
| Sale-time disclosure | FENSA certificate satisfies conveyancer | Buyer's solicitor flags as risk; price negotiation typical |
| Spec verification | Body audits sample of jobs annually | No external audit — quality varies |
| Cost | £400–£1,500 per window installed | Sometimes 10–20% cheaper, but retro LABC clawback closes the gap |
| Mortgage lender stance | Standard — no extra question | Underwriter increasingly asks for proof of compliance |
Source: FENSA Public Register, Certass Public Register, GOV.UK competent-person scheme directory.
The questions homeowners ask before they commit.
Do I need a FENSA certificate for every replacement window?
In England and Wales, replacement windows installed since 1 April 2002 must be certified — FENSA, Certass, BSI Kitemark KM 567778, or LABC. New-build first-fit windows are covered by the new-build Building Regulations Compliance Certificate, not a separate FENSA. Repairs and like-for-like sealed-unit swaps in an existing frame are not notifiable.
How much does a FENSA-certified window installation cost?
A standard uPVC casement window runs £400–£700 installed; a triple-glazed sash £900–£1,500; a larger bay or sliding patio door £2,000–£3,500. London adds 20–30%. The FENSA registration premium is typically nil — most replacement-window businesses are FENSA-registered as standard.
What if windows were replaced without a FENSA certificate?
You can apply retroactively to the local council for a Regularisation Certificate — typically £200–£450 plus an inspection that may force remediation if specs don't meet Part L. At sale, the buyer's side may either demand the regularisation upfront or negotiate £500+ off the asking price. Indemnity insurance is sometimes accepted as a cheaper alternative for solicitors.
How long does a FENSA certificate last?
A FENSA certificate is permanent — it certifies the installation complied on the day. It does not expire. The 10-year insurance-backed guarantee that FENSA installers must provide is separate and runs from completion date.
Is FENSA the same as Certass?
Both are government-authorised competent-person schemes for the same Building Regulations Part L compliance. FENSA (operated by GGFi) is the larger of the two; Certass is the alternative. Either certificate is equally valid at sale.
Do I need FENSA for windows in Scotland or Northern Ireland?
No. Scotland follows the Building (Scotland) Regulations 2004 — replacement windows need a Completion Certificate from the local council or via a SAPS (Scottish Approved Person Scheme) installer. Northern Ireland follows Building Regulations (NI) 2012 with broadly equivalent thermal requirements.
Going deeper.
New windows, fully certified.
TradeMatch window fitters are FENSA / Certass registered with 10-year insurance-backed guarantees. Certificate posted to you within 30 days of install.