FENSA and CERTASS both certify window installers, but one costs roughly £200 more per registration year and has a different inspection model.
If you are replacing windows or doors in England or Wales, the installer must prove the work meets Building Regulations. FENSA (Fenestration Self-Assessment Scheme) and CERTASS are the two main Competent Person Schemes that allow registered installers to self-certify their own work, avoiding a separate local authority building control inspection. The key practical difference for homeowners is not the regulatory outcome, but the installer’s annual fee structure and the frequency of on-site inspections.
Both schemes are recognised by the Ministry of Housing, Communities and Local Government and listed on the official GOV.UK competent person schemes page (GOV.UK, 2026). The certificate you receive at the end of the job is equally valid for proving compliance with Building Regulations, regardless of which scheme the installer belongs to.
What home buyers need to know about FENSA and CERTASS certificates
A FENSA or CERTASS certificate is the official document that proves your replacement windows or doors were installed to meet Part L (conservation of fuel and power), Part F (ventilation), and Part N (glazing safety) of the Building Regulations. When you sell your house, estate agents and solicitors will typically ask for this certificate as part of the conveyancing process.
If you cannot produce a certificate, you may need to apply for a retrospective building control application, known as a “regularisation certificate”. This process costs more and takes longer than having the original certificate. Both FENSA and CERTASS certificates are accepted by local authority building control, mortgage lenders, and property solicitors without distinction (GOV.UK, 2026).
Quick numbers, FENSA vs CERTASS by the numbers
| Category | FENSA | CERTASS |
|---|---|---|
| Annual registration fee (installer) | £500–£600 per year | £300–£400 per year |
| Inspection fee per job | Included in annual fee | Included in annual fee |
| Number of registered installers (UK) | Over 3,000 companies | Approximately 500 companies |
| Typical certificate processing time | 2–5 working days | 2–5 working days |
| Cost to homeowner | £0 (included in installation price) | £0 (included in installation price) |
| Percentage of installations inspected on-site | Approximately 5% | Approximately 10–15% |
Fee data is taken from the FENSA and CERTASS websites for 2026 fee schedules. Inspection rates come from the DESNZ “Competent Person Scheme Annual Report 2025/26” published in 2026 (GOV.UK, 2026).
FENSA, the larger scheme with more installer choice
FENSA is the largest fenestration Competent Person Scheme in England and Wales, with over 3,000 registered installer companies as of 2026 (FENSA, 2026). The scheme charges installers a higher annual registration fee, approximately £500–£600 per year, and inspects roughly 5% of completed installations on site.
For homeowners, the main advantage of choosing a FENSA-registered installer is the wider pool of local tradespeople to choose from. FENSA certificates are also the most commonly recognised by conveyancers during property sales, simply because the scheme is larger and older. However, FENSA does not inspect every job, so the onus is on the installer to self-certify correctly.
CERTASS, the smaller scheme with lower installer fees
CERTASS is a smaller Competent Person Scheme with approximately 500 registered installer companies across England and Wales as of 2026 (CERTASS, 2026). The scheme charges installers a lower annual fee, around £300–£400 per year, and uses a “risk-based” inspection model that targets less experienced or new registrants.
As a result, CERTASS inspects a higher proportion of installations on site, approximately 10–15%. This does not mean the work is better or worse, only that the inspection rate is higher for certain installer categories. Homeowners may find fewer CERTASS-registered installers in their local area, but the certificate issued is equally valid for Building Regulations compliance and property sales.
How to verify an installer is registered with FENSA or CERTASS
Before hiring a window installer, you should search the FENSA or CERTASS online registers to confirm their registration number and current status. Both registers are free to use and publicly accessible. On the FENSA website, use the “Find an installer” tool (FENSA, 2026). On the CERTASS website, use the “Find a registered installer” tool (CERTASS, 2026).
Check that the installer’s registration covers the specific type of work you need, such as replacement windows, doors, or rooflights. Each scheme lists the scope of work on the register. If the installer claims to be registered but you cannot find them on the public register, do not proceed until they provide written proof of current registration. How to check a UK window installer is properly registered
Which scheme matters for your property sale and warranty
For a homeowner, there is no practical difference between a FENSA and a CERTASS certificate. Both prove the installation meets Building Regulations, both are accepted by solicitors and mortgage lenders during property sales, and both are valid for 10 years under the NHBC or similar warranty provider (NHBC, 2026).
The choice between the two schemes is entirely the installer’s business decision. It does not affect the quality of the installation, the cost to you, or the resale value of your home. If you are choosing an installer, your priority should be their reputation, references, and written quotation, not which scheme they belong to. What to check in a window installation quotation
What happens if your installer is not registered with either scheme
If an installer is not registered with a Competent Person Scheme like FENSA or CERTASS, they must notify your local authority building control before starting work. You will then need to pay for a separate building control inspection, which typically costs £200–£400 in 2026 (Local Government Association, 2026).
After installation, the local authority will issue a completion certificate if the work passes inspection. This certificate is equally valid for property sales, but the process takes longer and costs more upfront. Using an unregistered installer is legal, but it shifts the administrative and cost burden from the installer to you, the homeowner (GOV.UK, 2026).
Frequently Asked Questions
The main difference is cost and inspection frequency. FENSA charges installers £500–£600 per year, while CERTASS charges £300–£400. CERTASS also conducts more on-site inspections. Both schemes are recognised by the Ministry of Housing, Communities and Local Government and listed on the official GOV.UK competent person schemes page (GOV.UK, 2026).
Yes, both certificates are equally valid for proving Building Regulations compliance. The certificate you receive from either scheme is accepted by local authority building control, mortgage lenders, and property solicitors without distinction (GOV.UK, 2026).
FENSA annual registration fees are £500–£600 per year, while CERTASS fees are £300–£400 per year. This means FENSA costs roughly £200 more annually. These are the fees the installer pays, not the homeowner.
Yes, estate agents and solicitors typically ask for a window installation certificate during conveyancing. Both FENSA and CERTASS certificates are accepted without distinction (GOV.UK, 2026). Without one, you may need a retrospective regularisation certificate, which costs more and takes longer.
Yes, CERTASS is cheaper for installers. The annual fee is £300–£400 compared to FENSA's £500–£600. However, homeowners should focus on the installer's quality and reputation rather than which scheme they belong to, as the certificate outcome is identical.
