What should I consider before I take steps to replace my windows?
Planning and permissions
Most like-for-like replacements fall under permitted development, but there are exceptions. If you live in a conservation area, a listed building, or a flat, you may need planning permission or listed building consent. Either way, replacement windows in England and Wales must comply with Building Regulations for energy efficiency, and the work needs to be either signed off by your local authority Building Control or done by an installer registered with a competent person scheme like FENSA or CERTASS, who self-certify and give you a certificate. Keep that certificate — you’ll need it when you sell.
Energy efficiency and glazing
Look at the energy rating (WER, A++ down the scale) and the U-value, which measures heat loss — lower is better. Decide between double and triple glazing; triple costs more and is heavier, and the gain over good double glazing is modest in a typical UK home therefore in reality the extra cost for triple glazed units will result in such a marginal difference the payback would be many years therefore not a good investment in most cases. Consider the gas fill (argon is standard), low-E coatings, and warm-edge spacer bars. If you’re on a busy road, acoustic glass is worth pricing up.
Frame material
- uPVC is the cheapest and lowest-maintenance. It also offers the widest variety of colour options with a foiled overlay finish.
- Aluminium gives slimmer sightlines and a more contemporary look, and suits large openings, but costs a lot more.
- Timber looks best on period properties and may be required on listed buildings, but needs upkeep with a repaint on a regular cycle.
Each has trade-offs in cost, lifespan, appearance, and thermal performance.
Style and function
Think about how each window opens (casement, tilt-and-turn, sliding sash) and whether that suits the room and how you use it. If not in a conservation area you can change the designs and openings to suit your needs and desire, but ensure you match the style to the age and character of the house, especially front elevations. Consider sightlines, glazing bars, and colour/finish.
Safety and regulations
- Habitable rooms need a certain amount of openable area for ventilation.
- Upstairs rooms often need at least one window that meets fire-escape (egress) requirements. However, if replacing existing windows the regulations state you must not make worse the fire escape so the regulations for new build do not apply – just don’t make it worse (although if possible to enhance it makes safety sense!).
- Glass in or near doors and low-level glazing must be toughened safety glass, your SevenDay depot can advise on the rules regarding toughening.
- Upstairs windows will need restrictors on newbuild to avoid a minor falling, although not mandatory it should also be considered if replacing existing windows.
- Security hardware matters too — look for multipoint locks and also hinge guards to protect from attach on both sides of the opening window. PAS 24 standard is required on new build or a product with Secured by Design components.
Condensation and ventilation
New sealed units/frames are often far more airtight than what they replace, which can shift condensation and damp problems elsewhere in the house. Trickle vents are now generally required on replacement windows for habitable rooms and help manage this with background ventilation.
The installer and the contract
- Get recommendations, check out review platforms of your installer on the likes of Trustpilot and if unsure get an alternative quote for comparison.
- Check the firm’s registration, accreditations and confirm exactly what’s included — making good the plaster and reveals, removing the old frames, disposal, and so on.
- Ask about the product guarantee versus the workmanship guarantee.
Practicalities and budget
Factor in lead times, how long the install will take, and the disruption (rooms exposed, mess, access). Build in a contingency for surprises once the old frames come out — rotten timber or damaged lintels aren’t unusual. And weigh up doing the whole house at once versus phasing it, since doing it together usually works out cheaper per window.