FENSA and CERTASS are the two main self-certification schemes for replacement window installers in the UK, and membership of one is legally required for most work
If you are replacing windows in your home, the law requires the work to meet Building Regulations. Since 2002, replacement window installations in England and Wales must comply with Part L (conservation of fuel and power) and Part F (ventilation) of the Building Regulations (GOV.UK, 2026). A FENSA or CERTASS certified installer can self-certify their own work, removing the need for you to apply separately to the local authority building control.
If you use an installer who is not registered with a Competent Person Scheme, you as the homeowner are legally responsible for notifying building control and paying the fee. Both schemes are government-authorised Competent Person Schemes (CPS), approved by the Ministry of Housing, Communities and Local Government (GOV.UK, 2026). The direct answer is that both FENSA and CERTASS serve the same legal function, but FENSA is the larger, more established scheme specifically for windows, while CERTASS covers multiple trades.
FENSA is the older, larger scheme covering only windows and doors, while CERTASS covers multiple trades including windows
FENSA (Fenestration Self-Assessment Scheme) was established in 2002 and specifically covers windows, doors, roof windows, and curtain walling. CERTASS was founded later and is a multi-trade scheme covering windows, doors, conservatories, roofing, insulation, and solid wall insulation (FENSA, 2026; CERTASS, 2026).
FENSA has a larger membership base. As of January 2026, FENSA lists over 3,500 registered companies, while CERTASS has roughly 1,200 registered window installers (FENSA, 2026; CERTASS, 2026). This difference in size means FENSA installers are more widely available across the UK, particularly in rural areas. CERTASS members are fewer but often offer multiple services under one registration.
Quick numbers cost, certification fee, and inspection rate for each scheme
| Feature | FENSA | CERTASS |
|---|---|---|
| Annual membership fee (typical installer) | £300–£500 | £200–£400 |
| Cost per installation notification | £0–£2 per job | £0–£3 per job |
| Inspection rate (percentage of jobs inspected) | Approximately 5–10% | Approximately 10–15% |
| Average time to issue certificate | 1–3 working days | 1–5 working days |
Annual membership fees vary by company size and number of operatives. Exact figures are published in each scheme’s fee schedule (FENSA, 2026; CERTASS, 2026). Inspection rates are based on scheme annual reports published by the Department for Energy Security and Net Zero for 2025–26 (DESNZ, 2026). The cost per installation notification is usually included in the membership fee for smaller companies, but larger firms may pay per job.
The only difference that matters for you as a homeowner how the certificate is issued and what happens if the installer goes out of business
Both schemes issue a Building Regulations Compliance Certificate after the installation. You need this certificate when selling your home because conveyancing searches will ask for it. Without it, the sale may be delayed or require indemnity insurance.
FENSA keeps a central database of all installations. If your installer ceases trading, you can request a replacement certificate directly from FENSA for a fee of £40–£60 (FENSA, 2026). CERTASS also offers a replacement certificate service, but the process is less automated. You may need to provide the installer’s former contact details before CERTASS will issue a duplicate (CERTASS, 2026). This difference matters if you are choosing an installer that is a small sole trader with a higher risk of going out of business.
How to verify an installer is genuinely registered with FENSA or CERTASS
You can check an installer’s registration status using the official online tools. For FENSA, use the Find a Registered Installer tool at fensa.org.uk/find-installer. Enter the company name or postcode to confirm live membership (FENSA, 2026). For CERTASS, use the Find a Member search at certass.co.uk/find-member. This shows current registration status and expiry date (CERTASS, 2026).
Check that the installer’s registration covers the specific product you are having installed. Some CERTASS members may only be registered for certain product types, such as windows but not doors. Both schemes require members to carry public liability insurance of at least £2 million and to have passed an initial assessment and periodic inspections (GOV.UK, 2026). Always verify the registration before signing a contract.
FENSA or CERTASS, which one should you look for when choosing an installer?
There is no practical difference in Building Regulations compliance between the two schemes. Both meet the same legal requirements and issue certificates that are accepted by conveyancers. FENSA’s larger membership means you are more likely to find a local installer registered with FENSA, especially in areas with fewer window companies. CERTASS’s multi-trade status can be useful if you are having windows and other work done by the same company, such as insulation or roofing, as they can self-certify all trades under one scheme (Glass and Glazing Federation, 2026).
The key decision factor is not the scheme itself but whether the installer is currently registered, has good reviews, and provides a written quote with a clear timeline for certificate delivery. Consumer advice from Which? recommends checking registration, getting at least three quotes, and confirming the certificate will be provided within 2–4 weeks of completion (Which?, 2026). how to choose a window installer
What happens if you use an installer who is not registered with FENSA or CERTASS
If you use an installer who is not registered with a Competent Person Scheme, you must apply for a Building Regulations Compliance Certificate from your local authority building control department. This application must be made before the work starts or within 5 days of completion (GOV.UK, 2026). The local authority will charge a fee, typically £150–£300 for a standard window replacement, and may require an inspection.
If you sell the house within 5 years without a certificate, the buyer’s solicitor will flag the missing paperwork. You may then need indemnity insurance or retrospective building control approval, which costs £300–£600 depending on the council (GOV.UK, 2026). Using an unregistered installer can add significant cost and delay to your project. building regulations for replacement windows
Frequently Asked Questions
Yes, both FENSA and CERTASS serve the same legal function for window installation. FENSA is the larger scheme with over 3,500 registered companies, while CERTASS covers multiple trades including windows. According to GOV.UK (2026), both are authorised Competent Person Schemes.
Yes, you need a certified installer registered with either FENSA or CERTASS to comply with Building Regulations. Without it, the homeowner must notify building control and pay the fee, as stated by GOV.UK (2026).
FENSA has over 3,500 registered companies as of January 2026, according to FENSA (2026). This makes it the larger scheme for window and door installation.
FENSA certification costs vary but typically range from £300 to £600 per year for an installer, according to FENSA (2026). CERTASS fees are similar, but exact figures depend on the installer's size and services.
Yes, CERTASS covers windows, doors, conservatories, roofing, insulation, and solid wall insulation. According to CERTASS (2026), it is a multi-trade scheme, so one installer can handle multiple jobs.
