Replace a window.

Whether you are upgrading draughty single glazing or replacing tired uPVC units, understanding the process and costs ensures you get a high-quality installation that meets UK Building Regulations. This guide covers everything from material choices to the essential paperwork you need for a future house sale.

What Does the Work Involve?

• Site Survey: Taking precise measurements of the structural opening, checking the condition of the lintels, and confirming the required cill depths.
• Removal: Carefully extracting the old frames and glazing to minimise damage to the surrounding brickwork and internal plaster.
• Preparation: Cleaning the aperture, checking the Damp Proof Course (DPC), and ensuring the opening is level and square.
• Installation: Setting the new frame (uPVC, timber, or aluminium) into place, ensuring it is perfectly plumb, and fixing it securely to the masonry.
• Glazing & Sealing: Fitting the glass units, securing them with internal beads, and applying high-grade perimeter sealant and expanding foam for weatherproofing.
• Finishing: Installing internal trims, window boards, and "making good" any minor plaster damage around the reveal.
• Waste Removal: Clearing the site of old glass, frames, and debris for responsible disposal or recycling.

Typical Costs

Prices vary based on frame material, the number of openings (vents), and the type of glass used. The figures below include professional installation and VAT at 20%.

Factors that push costs toward the higher end include choosing "A++" rated triple glazing, selecting woodgrain foils or custom RAL colours, and the need for specialist equipment like glass lifters or scaffolding for hard-to-reach areas.

How Long Does It Take?

• Single Window: 2 to 4 hours depending on the size and ease of access.
• Small House (4-6 windows): 1 to 2 days of work on-site.
• Full House (8-12 windows): 3 to 5 days, including all finishing and trimming.
• Lead Times: Standard uPVC usually takes 2-4 weeks from order; bespoke timber or aluminium can take 8-12 weeks.

DIY or Professional?

While a competent DIYer can physically fit a window, it is generally not recommended for most homeowners. Professional installers provide an Insurance Backed Guarantee (IBG) and, crucially, they can self-certify the work through schemes like FENSA or CERTASS.

If you fit windows yourself, you must notify your local Building Control department before starting and pay for an inspection to receive a completion certificate.

Failure to have the correct certification will cause significant delays and costs when you eventually try to sell your property.

Choosing the Right Tradesperson

• Accreditations: Ensure they are members of a competent person scheme such as FENSA, CERTASS, or Assure.
• Insurance: Ask for proof of Public Liability insurance and an Insurance Backed Guarantee (IBG) to protect your deposit and warranty.
• References: Look for recent local examples of their work, specifically looking at the quality of the external silicone sealing.
• Questions to ask:
  • Is the quote a fixed price or an estimate?
  • Does the price include the disposal of the old windows?
  • Will you be installing trickle vents to meet Part F regulations?
  • How do you handle "making good" the internal plasterwork?

UK Regulations

• Part L (Thermal): Replacement windows must achieve a minimum U-value of 1.4 W/m²K or a Window Energy Rating (WER) of Band B.
• Part F (Ventilation): Most replacement windows must now include trickle vents to ensure adequate background ventilation and prevent mould.
• Part K (Safety Glass): Toughened safety glass is mandatory for windows within 800mm of the floor or near doors.
• Part Q (Security): New build installations or certain replacements may require PAS 24 rated security hardware.

Common Problems

• Internal Condensation: Often caused by blocking trickle vents or lack of ventilation, rather than a fault with the window itself.
• Blown Seals: If you see misting between the panes, the unit seal has failed and the glass unit needs replacing.
• Dropped Sashes: Heavy windows can "drop" over time, making them difficult to lock; this usually requires a simple hinge adjustment.
• Poor Drainage: If water sits in the frame track, the drainage holes may be blocked or the cill was not levelled correctly.

Frequently Asked Questions