The short answer: no. If you fit your own windows, you cannot get a FENSA certificate. FENSA is a self-certification scheme available only to registered installers. However, you are still legally required to comply with Building Regulations. The route for homeowners doing their own installation is through Building Control, not FENSA.
This is one of the most misunderstood areas of window replacement in the UK. A lot of homeowners either assume they need to hire a FENSA-registered company, or that DIY installation is not legal. Neither is true. The compliance requirement exists, but there is a straightforward route to meeting it without a registered installer.
What Is FENSA and What Does It Actually Do?
FENSA stands for the Fenestration Self-Assessment Scheme. It is a government-authorised scheme that allows registered window and door installation companies to self-certify that their work complies with Building Regulations.
When a FENSA-registered company installs your windows, they handle the compliance paperwork on your behalf. They notify the local authority, confirm the installation meets Building Regulations, and issue you with a FENSA certificate. That certificate is proof of legal compliance and is registered with your local council.
FENSA does not cover homeowners installing their own windows. Only approved installers can self-certify through the scheme. If you are fitting the windows yourself, or using a fitter who is not FENSA or CERTASS registered, you need to use a different compliance route.
Is It Legal to Fit Your Own Windows in the UK?
Yes. There is no legal requirement to use a registered installer when replacing windows in your own home. Homeowners are permitted to carry out the work themselves, or to hire a general builder or local fitter who is not part of a competent persons scheme such as FENSA or CERTASS.
The legal requirement is not about who does the installation. It is about whether the installation complies with Building Regulations. You meet that requirement either through a registered installer (who self-certifies) or through Building Control (who independently inspects and certifies the work).
Building Control: The Compliance Route for DIY Window Installation
Building Control is the alternative compliance route to FENSA. Rather than the installer self-certifying, a Local Authority Building Control inspector independently checks and approves the work.
The process is as follows:
- Contact your local authority Building Control department before starting work. Most councils allow you to submit a building notice or full plans application online.
- They may carry out an inspection during or after installation to confirm the windows meet the relevant standards: thermal performance (Part L), ventilation (Part F), safety glazing requirements, and egress dimensions where applicable.
- Once satisfied, Building Control issues a completion certificate. This is your proof of compliance with Building Regulations and is registered with the local authority.
The cost of a Building Control inspection for window replacement typically falls between £100 and £200, depending on your local authority and the scale of the project. Some councils charge a flat fee for minor works; others price per window or per visit.
What Building Regulations Apply to Replacement Windows?
When replacing windows in England and Wales, the installation must comply with several parts of the Building Regulations. The main requirements are:
Part L: Thermal Performance
Replacement windows must meet a minimum thermal performance standard. The current requirement is a U-value of 1.4 W/m²K or better for the whole window unit. Most modern double-glazed uPVC windows comfortably meet this threshold, with quality units achieving around 1.2 to 1.3 W/m²K.
Part F: Ventilation
Replacement windows in habitable rooms generally require trickle vents to provide background ventilation. This is a common area of confusion. If the original windows had trickle vents, the replacements must also include them unless an equivalent ventilation solution is already in place.
Safety Glazing
Any glass within 800mm of the floor or within 300mm of a door must be toughened or laminated safety glass. This applies to the full window unit, not just the glass in a specific zone. When ordering windows, specify safety glazing in these locations.
Egress Requirements
In rooms used for sleeping, at least one window must provide a clear opening of at least 0.33m², with a minimum dimension of 450mm on any side. This is a fire escape requirement. If you are replacing bedroom windows, confirm the new units maintain this opening size.
FENSA vs Building Control: What Is the Difference?
| FENSA | Building Control | |
|---|---|---|
| Who can use it | FENSA-registered installers only | Any installer, including homeowners and unregistered fitters |
| How it works | Installer self-certifies compliance | Local authority inspector checks and certifies |
| Cost | Included in installer's price | Typically £100 to £200 per project |
| Certificate issued by | FENSA | Local Authority Building Control |
| Registered with local authority | Yes | Yes |
| Valid for house sale | Yes | Yes |
| Available for DIY installation | No | Yes |
Both routes achieve the same legal outcome. A Building Control completion certificate carries the same weight as a FENSA certificate when it comes to selling your property or demonstrating compliance.
What Happens if You Replace Windows Without Any Compliance Certificate?
Replacing windows without either a FENSA certificate or a Building Control completion certificate is not a criminal offence, but it creates a practical problem when you come to sell the property.
Solicitors acting for buyers routinely ask for evidence that window replacements comply with Building Regulations. If you cannot produce either a FENSA certificate or a Building Control certificate, the sale could be delayed or the buyer's solicitor may request indemnity insurance as a condition of proceeding.
Indemnity insurance covers the buyer against the risk of enforcement action but does not prove the windows comply with Building Regulations. It typically costs between £180 and £500 and is a workaround, not a substitute for proper compliance documentation. It also does not cover defects in the installation itself.
What About CERTASS?
CERTASS is a separate competent persons scheme that operates alongside FENSA. Like FENSA, it allows registered installers to self-certify compliance with Building Regulations. If your local fitter is CERTASS registered rather than FENSA registered, the outcome is the same: they can handle compliance on your behalf and issue a certificate.
If you are hiring a local fitter to install supply-only windows, check whether they are registered with either FENSA or CERTASS before the work starts. Ask to see their registration and confirm they intend to issue a certificate once the work is complete.
Supply-Only Windows and FENSA: What WSD Customers Need to Know
When you order windows from WSD, you are buying the product. Compliance with Building Regulations is handled separately, through whichever route applies to your installation:
- Using a FENSA or CERTASS registered fitter: they handle compliance and issue the certificate.
- Using an unregistered local fitter or self-installing: you notify Building Control before work begins, they inspect, and issue a completion certificate.
WSD windows meet the thermal performance standards required by Part L. All units are manufactured to BS 7950 and the product range is FENSA approved, which means registered installers can use WSD windows as part of a self-certified FENSA installation without any additional compliance step.
If you are unsure which route applies to your project, contact your local authority Building Control team before ordering. The process is considerably simpler than most homeowners expect.
Order Supply-Only Windows Direct From the ManufacturerWSD manufactures and supplies made-to-measure uPVC windows direct to homeowners, local fitters, and builders across the UK. Prices are online and transparent. No personal details are required to configure and price your order.
Frequently Asked Questions
You need proof that any window replacements carried out after 1 April 2002 comply with Building Regulations. That proof can take the form of a FENSA certificate, a CERTASS certificate, or a Building Control completion certificate. All three are acceptable to solicitors and mortgage lenders. If none exists, indemnity insurance may be required as an alternative.
No. FENSA certificates are issued by FENSA-registered installers, not by homeowners. If you fitted the windows yourself, the correct compliance route is Building Control. Contact your local authority to arrange an inspection and obtain a completion certificate.
Costs vary by local authority. For a standard window replacement project, expect to pay between £100 and £200. Some councils charge a flat fee for minor works notifications; others apply a per-visit rate. Contact your local Building Control team for a specific figure before you start.
If Building Control inspects and finds the installation does not comply, they can require remedial work to bring it up to standard. This is why it is worth ensuring windows meet the relevant specifications before installation, particularly on thermal performance, safety glazing, and ventilation. WSD windows are manufactured to meet current Part L requirements.
They achieve the same outcome but operate differently. FENSA is a self-certification scheme run by a private body: registered installers certify their own work. Building Control is an independent inspection by your local authority. Both routes result in a registered certificate that satisfies Building Regulations compliance.
Before. You should notify Building Control and, where required, submit a building notice or application before the installation takes place. Notifying after the fact is possible but complicates the inspection and may result in higher fees.
Fitting Your Own Windows: The Compliance Checklist
Before ordering and before starting work, work through these points:
- Contact your local authority Building Control team and notify them of the planned work.
- Confirm the windows you are ordering meet Part L (U-value 1.4 W/m²K or better).
- Specify trickle vents on all replacement windows in habitable rooms.
- Check safety glazing requirements for your specific window locations.
- For bedroom windows, confirm the replacement unit maintains the minimum 0.33m² egress opening.
- Once installation is complete, contact Building Control to arrange an inspection and obtain your completion certificate.
- Keep the certificate with your property documents.
None of these steps are complicated. The most common mistake homeowners make is completing the installation and then discovering they have no compliance documentation. Starting the Building Control process before the windows arrive costs very little time and avoids a much larger problem later.