Window Installers: What They Do and What to Check
Replacement windows and doors — with FENSA compliance and realistic prices.
3 min read · Updated 2026
Key takeaways
- ›Replacement windows must meet Building Regulations and be self-certified (FENSA or similar).
- ›Fitted uPVC windows £300–£600 each; bay windows more.
- ›Always check the guarantee covers frames, glass and fitting.
What a window installer does
Window installers measure, remove old windows and doors, fit new frames, insulate and trim around the opening, refit sills and boards, and provide Building Regulations self-certification (via a scheme like FENSA). They fit uPVC, aluminium and timber frames, double or triple glazed, plus composite doors and bifold doors.
Typical prices (UK 2026)
- •uPVC casement window (fitted): £300–£600.
- •Bay window (fitted): £700–£1,200.
- •Composite front door (fitted): £900–£1,500.
- •Bifold doors (fitted): £1,500–£3,500.
- •Per window day rate equivalent: £180–£260.
Questions to ask and common mistakes
Ask whether the quote includes FENSA certification, internal trims and removal of the old frames, and what the guarantee covers. Common mistakes: not insulating the cavity around the frame (cold bridging and condensation), cheap hardware that fails, and no Building Regs certificate when you come to sell.
- ☐Are you FENSA registered (or equivalent)?
- ☐Does the price include removal, trims and sills?
- ☐What does the guarantee cover and for how long?
- ☐Is the glazing A-rated or better for energy efficiency?
Frequently asked
Do I need Building Regulations for new windows?
Yes. Use a FENSA-registered installer and they self-certify, or apply to Building Control yourself. Keep the certificate — you will need it when you sell.
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