The window installation process

Having new windows fitted is more straightforward than most people expect, but knowing the stages in advance helps you plan and spot a professional job. Here is what happens from the moment you accept a quote to the day the certificate lands on your doormat.

Step 1: The home survey

Once you accept a quote, the installer sends a surveyor to take precise measurements — windows are made to fit each opening exactly, so this is more thorough than the sales measure. The surveyor checks access, discusses your choice of frame, glass and colour, notes anything unusual such as lintels or trickle-vent requirements, and confirms the final price. It is a good moment to raise any questions about disruption, timings or aftercare.

Step 2: Manufacturing lead time

Your windows are then made to order, which typically takes two to six weeks depending on the material, style and the installer’s workload. Bespoke shapes, coloured finishes and timber frames usually sit at the longer end. A good firm keeps you informed and books a fitting date once the units are ready, rather than promising a date it cannot meet.

Step 3: Fitting day

On installation day the fitters protect your floors and furnishings, then remove the old windows one opening at a time to keep your home secure and weatherproof throughout. Each new frame is positioned, levelled, mechanically fixed and sealed, and the glass units are fitted and adjusted. A typical house of eight to ten windows is often completed in one or two days. Tidy fitters clear up as they go and take the old frames away.

Step 4: Finishing and making good

After the frames are in, the fitters seal around them inside and out, fit any trims or cills, and “make good” the plaster or render where needed — though on larger jobs some redecoration may be left to you. They will run through how the locks, handles and trickle vents work, and check every window opens, closes and seals correctly before they leave.

Step 5: Sign-off and certification

Replacement windows must meet building regulations, and a registered installer self-certifies the work through a competent-person scheme such as FENSA or CERTASS. You should receive a certificate within a few weeks, which you will need when you sell the property, along with your guarantee paperwork. Keep both somewhere safe. If anything is not quite right, this is the point to flag it — a reputable installer will return to put it straight under the terms of your guarantee.