FENSA, PAS 24 and Part Q: Replacement Windows

If you’ve been researching replacement sash windows or timber casement windows, you may have come across terms like FENSA, PAS 24 and Part Q. They all relate to windows, doors and building regulations, but they apply to very different situations. Confusing them is easy, but it matters because understanding which framework actually applies to your project can save you unnecessary worry and help you ask the right questions of any installer you speak to.

The short version: if you own a period property and are replacing existing windows, FENSA is the compliance framework that applies to you. PAS 24 and Part Q are not relevant to replacement windows in existing homes. Here’s why.

What Is FENSA?

FENSA (the Fenestration Self-Assessment Scheme) is the government-authorised Competent Person Scheme for the replacement of windows, doors, roof windows and rooflights in residential properties in England and Wales. It has been in place since April 2002.

FENSA was created to give homeowners a straightforward, legally recognised route to Building Regulations compliance when replacing windows, without needing to make a separate application to your local authority’s Building Control department. When a FENSA-registered company installs your replacement windows, they are authorised to self-certify that the work meets the relevant Building Regulations on your behalf. On completion, your installation is registered with your local council, and you receive a FENSA certificate as formal proof of compliance.

The Benefits of Using a FENSA-Registered Installer

Choosing a FENSA-registered installer gives you a number of important protections and assurances.

Firstly, FENSA certification covers the complete installation, not just the product. A high-quality window that is poorly fitted, with inadequate sealing, incorrect fixings, or missing ventilation, can still underperform in energy efficiency, allow draughts, and cause dampness. FENSA registration means the product and the workmanship have been assessed against the relevant regulations.

Secondly, FENSA-registered installers are required to provide insurance-backed guarantees, giving homeowners protection in the event that the company ceases trading. This is a meaningful consumer safeguard.

Thirdly, and practically, a FENSA certificate matters every time you sell your home. Your solicitor will request evidence that any replacement windows comply with Building Regulations. A FENSA certificate provides that evidence immediately and cleanly. Without it, you may face delays during conveyancing, requests for retrospective approval or a requirement to take out indemnity insurance; none of which you want to be dealing with in the middle of a property sale.

What FENSA Compliance Means in Practice: Part L and Part F

When a FENSA-registered installer fits your replacement windows, the installation must comply with the relevant Building Regulations. For replacement windows in existing homes, the two that apply are Part L and Part F. This is with the exception of Conservation areas or Listed Buildings, where the building regulations may not apply.

Part L, the conservation of fuel and power, sets the thermal performance requirements for replacement windows. Your new windows must meet a minimum energy-efficiency standard, measured by U-values, to limit heat loss and support your home’s overall energy performance. This ensures that modern replacement sash windows are a genuine improvement on the originals they replace, which is particularly relevant in period properties where single-glazed windows can be a significant source of heat loss.

Part F, ventilation, requires that replacement windows provide adequate background ventilation. In most cases, this means the installation must include trickle vents: small, unobtrusive devices built into the window frame that allow controlled airflow even when the window is closed. This is particularly important in homes that are being progressively improved for energy efficiency, where increasingly airtight windows can otherwise reduce natural ventilation to below healthy levels.

It is these two regulations, Part L and Part F, that our windows comply with, as certified through the FENSA scheme. Neither PAS 24 nor Part Q form any part of this compliance framework for replacement windows in existing properties.

What Is PAS 24?

PAS 24 (Publicly Available Specification 24) is a product-level security testing standard published by the British Standards Institution. It defines how a complete window or door set must perform under a simulated forced-entry attempt. The window is tested as a finished assembly by a UKAS-accredited independent laboratory, and it either passes or it doesn’t. There is no grading scale.

PAS 24 is relevant only where Part Q of the Building Regulations applies. Part Q (formally “Approved Document Q: Security, Dwellings”) came into force in October 2015 and requires that easily accessible windows and doors in new dwellings be sufficiently robust to resist unauthorised entry, with PAS 24 testing identified as the recognised route to compliance.

The critical phrase there is new dwellings. Part Q applies to newly built homes and to buildings undergoing a material change of use, such as a barn conversion or a warehouse converted into flats. It does not apply to replacement windows and doors in existing properties. If you are replacing the sash windows in a Victorian terrace, an Edwardian semi-detached or a Georgian townhouse, neither Part Q nor PAS 24 certification is a legal obligation. That is simply not what those regulations are designed for.

We do not manufacture PAS 24 or Part Q windows and doors, and there is no requirement for us to do so. Our products are designed and built specifically for the replacement market in existing residential properties, where FENSA registration, Part L and Part F are the applicable compliance standards.

Our Commitment to Full Compliance

The Specialist in Sash Windows is FENSA registered. Every replacement sash window, casement window, front door, bi-fold door, and French door we manufacture and install complies with the relevant Building Regulations (Part L for thermal performance and Part F for ventilation) and is fully certified through the FENSA scheme (apart from within Conservation areas or Listed Buildings). You receive a FENSA certificate upon completion of every installation, with all the legal and practical protections it provides.

We have been manufacturing and installing traditional timber windows since 1999, and our commitment to regulatory compliance is as fundamental to what we do as the quality of the timber we use and the skill of the craftsmen in our Surrey workshop. When you invest in replacement sash windows with us, you’re not just getting windows that look right for your period property, you’re getting windows that are fully compliant, properly certified and backed by the documentation you’ll need for as long as you own your home.

Building Regulations are subject to revision, and specific requirements can vary depending on the nature of your project. If your property is a listed building, sits within a conservation area, or your project involves structural changes, additional consents or exemptions may apply. We recommend discussing your specific circumstances with us before work begins and confirming any planning-related requirements with your local planning authority.

Get in touch today to discuss your project, or call us on 0800 389 7384. You’re welcome to visit our showroom in Cobham to see our timber sash and casement windows and speak with our team directly.