How to fit new windows

Want to update your property's façade? Fitting new windows can give you home a completely new look and, we promise, it doesn't have to be too complicated...

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Removing old windows and fitting new ones isn’t a difficult DIY task, especially if they’ve been made to measure. However, period timber windows should only be replaced if they’re beyond repair. Modern softwood windows that have rotted are worth replacing, as are failed or broken uPVC ones, which usually can’t be repaired.If you are looking for tips on how to choose replacement windows check out our expert guide. 

Fitting windows is a two-person job, or more for larger windows, and it will take 3-4 hours to fit one. If the windows are above ground floor level, you’ll need a scaffold tower, which can be hired for around £25 per day – visit hss.com for more information. Always consider safety for a job like this and wear a hard hat, goggles, work boots and gloves.

How to prepare for installing new windows

1. Remove the old window first by removing any frame fixings and preparing the opening, usually brick or block, but possibly timber.

2. If the window is fitted from the inside, you’ll need to remove any internal sills and window boards and replace these later.

3. If you’ve bought off-the-shelf timber windows that are the nearest available size to your window openings, you’ll need to make some small alterations. You could add or remove a course of bricks at sill level, or pack out the opening at the head and sides with a treated softwood subframe, which can be painted in later.

4. If your property has cavity walls, insulated cavity closers should be fitted around the opening to seal it. Cavalok makes a retrofit cavity closer

Sash windows

(Image: © Getty)

How to fit new windows

1. Fit the frame at the same depth in the wall as the previous windows – use packers (timber wedges) to hold the frame in place and get it level, and tight up to the window head. You can then side fix the frame into the walls using 100mm frame fixings or metal strapping screwed to both the frame and the walls.

2. Handi-Foam (expandable urethane foam) is often used around frames to fit them in place and seal them at the same time – any excess can be cut away easily.

3. If the frame isn’t a perfect fit, apply external mouldings to cover any gaps./Seal around the frame using an appropriately coloured mastic sealant./Refit internal window sills or boards and make good any damaged plasterwork.

4. If the frames are not pre-glazed, fit the double glazed units and apply the glazing bars according to the manufacturer’s instructions (internally glazed windows are more secure).

5. If the windows are timber and not pre-finished, decorate the frames using micro-porous paint or varnish.

Metal framed windows and doors in a terraced house

(Image: © Mustard Architects )

How much do new windows cost?

Budget £200-£500 for each pre-glazed off-the-shelf softwood window, with a similar price for uPVC. A bespoke sash window will cost £1,000-£1,400.

Do you need planning permission to fit new windows?

Planning permission isn’t normally required to replace a window on a like-for-like basis, even on a listed property. If you’re changing to double glazing, or changing the material – for example, timber to uPVC – permission will be needed on a listed building and any property where permitted development rights (PD) have been restricted or removed, such as some conservation areas and other designated areas). Flats don’t have PD rights.

New windows must comply with Part L of Building Regulations – Energy Efficiency, which means in most cases the window must be double glazed. Exceptions can be made for listed buildings and period houses. If you do it yourself, there’s a fee payable to the local authority – £100-£200 inc. VAT – to check the work. The fee isn’t payable if you use a FENSA registered installer who can certify their own work, which is why it can be cheaper to use a professional if you are installing only one or two windows.

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