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How to replace a window

Introduction

You can get replacement PVCu windows in standard sizes with add-on frame extenders (so you can adjust them slightly to fit), or they can be made to measure. Low-maintenance, energy-efficient and 100% recyclable, PVCu never needs painting and comes in a range of different finishes that include white, woodgrain and even oak effect.


In houses built with solid external stone or brick walls, a wooden window frame often fits snugly in a slight recess (reveal) on the inner side of the opening in the wall. The window will either be flush with the inner wall surface or set back from it, depending on the thickness of the wall. The frame is held in place with nails or screws.

Windows in old houses usually have a stone or concrete subsill which sits below the window frame and any wooden sill on the outside of the house.

Top tip - Preventing wet rot

The best way to protect wooden window frames against wet rot is to apply wood preservative, paint or varnish regularly. Always ensure you treat any new timber you use for repairs or replacement with wood preservative. You should also seal any gaps around the outside of your window frames with frame sealant if it's a small gap, and mortar if it's more than about 10mm wide.


Most houses these days are built with cavity walls, and window frames attached to metal brackets (known as frame cramps) are fitted into the walls as they're built. Special bricks are fitted between the window frames and the cavity to close the gap and prevent heat escaping. There also has to be a damp-proof course in line with the frame to stop any moisture transferring from the outer to the inner wall.

On the inside wall, the sides and top of the window opening (the reveals and the soffit) are plastered when the window frame is in place to give a neat finish. The window frame's wooden sill sits on a wooden window board that is screwed or nailed directly to the masonry.

Conserving warmth and energy

Make sure your windows are all draught-proofed to help you retain warmth and conserve energy. New outside doors and windows must meet strict insulation standards to ensure you reduce heat loss and make your home more energy- efficient. Look for products labelled 'Part L compliant.'


Window glass is secured in a bed of putty or glazing mastic in the frame. Small headless nails called glazing sprigs are tapped into the frame to hold the glass while the putty dries, and spring clips hold the glass in metal frames. More putty is smoothed over the top to make a neat finish.

Sometimes glass is secured with thin strips (beads) of hardwood instead of putty. These beads are cut and mitred individually, stuck in place with putty or glazing sealant, then fixed in place with nails or brass screws.


Preparation

This is quite a long job, and you'll probably take more than a day to complete it. Bearing this in mind, you'll need to cover the opening overnight with a polythene sheet or hardboard. The most difficult part is removing the old window frame.

Make sure you wear safety goggles and heavy-duty gloves to do this, and take care to minimise any damage to the surrounding masonry and plaster. If the sill is old or decayed, it's probably best to replace it as well. You can get interior sills in wood, MDF or PVCu - and they don't need any decorating.

How to remove an old window frameHow to remove an old window frameHow to remove an old window frameHow to remove an old window frame

Step 1

Start by removing any opening windows by unscrewing them at the hinges - ask someone to give you a hand lifting them out. Remove the beading and putty to take out any fixed panes. Then make an angled cut through the upright sections of the frame with a handsaw.

How to replace a window frameHow to replace a window frameHow to replace a window frameHow to replace a window frame

Step 2

Use a long bar (or bolster chisel) and club hammer to take out the frame. Hammer the curved end of the long bar into the cut on one side of the window, then pull it upwards to open the joint and remove the lower piece.

How to replace a window frameHow to replace a window frameHow to replace a window frameHow to replace a window frame

Step 3

Use the curved end of the bar to remove the upper part of the frame. Do this again on the other sides. Take out the sill too if you're going to replace it.

How to replace a window frameHow to replace a window frameHow to replace a window frameHow to replace a window frame

Step 4

If the frame is fixed with screws, cut through them with a small close quarter hacksaw.


Start off by checking the dimensions to make sure that the window will fit. Try to leave a gap of about 5mm all the way round - you can add frame extenders, if you need to. Also, you'll need to fit the handle(s) before you put the window in.

How to assemble a new windowHow to assemble a new windowHow to assemble a new windowHow to assemble a new window

Top tip - Adjusting the frame size

If your new window isn't quite big enough, you can add a total of 40mm to the width or depth by attaching frame extenders.

How to assemble a new windowHow to assemble a new windowHow to assemble a new windowHow to assemble a new window

Step 1

To cut the outer sill of the window to size, measure the depth of the outer wall and cut a notch so the sill fits snugly around the external brickwork. The sill comes with a protective wrapper, so mark this with a pen or pencil and cut it with a hacksaw.

How to assemble a new windowHow to assemble a new windowHow to assemble a new windowHow to assemble a new window

Step 2

Next, screw the outer sill to the window frame. Then attach the frame fixers by sliding them evenly down the side track of the window frame.

How to assemble a new windowHow to assemble a new windowHow to assemble a new windowHow to assemble a new window

Step 3

Screw the ventilator grille(s) into the internal face of the frame and fix the cover vent(s) in place.


Pre-glazed casement windows can be heavy. So get someone to help you lift the new window into place, and remove the opening casement if you need to. Also, remember that the window frame is fixed to the interior walls along both vertical edges, and that you should install the interior sill after fitting your window.

 

Top tip - Getting approval

 

If you're fitting windows yourself, you must apply for Building Control approval and confirm the energy efficiency levels of the windows before installing them. Insulation levels are measured as U values (the lower the U value, the better the insulation level). All B&Q PVCu windows are Building Regulations-compliant. If you live in a listed building or a conservation area, additional regulations are likely to apply - so check with your local planning department before you carry out any work.

How to fit a window and sillHow to fit a window and sillHow to fit a window and sillHow to fit a window and sill

Step 1

Start by marking the fixing points, making a small notch in the internal plasterwork for each one. If you're replacing the sill, cut a notch on each side. Put the prepared window in and wedge it with spacers (called 'shims').

How to fit a window and sillHow to fit a window and sillHow to fit a window and sillHow to fit a window and sill

Step 2

Use a spirit level to check the window is level. If it's not, use spacers to align it.

How to fit a window and sillHow to fit a window and sillHow to fit a window and sillHow to fit a window and sill

Step 3

Check the window is vertical using your spirit level, and add spacers to straighten it if it isn't.

How to fit a window and sillHow to fit a window and sillHow to fit a window and sillHow to fit a window and sill

Step 4

Drill a pilot hole, pop in a wall plug and screw the frame into place at each fixing point. Measure and cut the interior sill to fit around the window reveals. Check that it's level - if not, you may need to insert spacers. Then secure it with a suitable grab adhesive, masonry nails or screws.

How to fit a window and sillHow to fit a window and sillHow to fit a window and sillHow to fit a window and sill

Step 5

Fill any wider gaps around the window's exterior with expanding foam filler. Once it's dry, trim it using a sharp craft knife.

How to fit a window and sillHow to fit a window and sillHow to fit a window and sillHow to fit a window and sill

Step 6

Use a frame sealant to fill in any smaller gaps for a neat finish.

One Planet Home

Well-insulated, double or even triple-glazed windows will reduce draughts, condensation and noise.


Trims and profiles come in lots of different shapes and sizes to cover sealant and fixings. They'll give you a neat, professional finish, inside and out.

How to trim and finish a windowHow to trim and finish a windowHow to trim and finish a windowHow to trim and finish a window

Step 1

You can cover wider gaps around the outside of the window with a PVCu scotia trim. Do this by sealing the frame behind the trim with frame sealant. You can then stick the trim in place with more frame sealant.

How to trim and finish a windowHow to trim and finish a windowHow to trim and finish a windowHow to trim and finish a window

Step 2

Inside the window, use a trim that's wide enough to cover the fixings and secure it into place with frame sealant.