Mr Skill

Replacing an existing window is a fairly specialist job and best done with the assistance of a local window fitter in London. However, if you are a keen DIY-er, it may be a project that you would like to take on yourself to improve the appeal and value of your home.

As with most major home improvement projects, good preparation is the key to a successful conclusion, and we have divided our project advice on installing a replacement window into three parts to distinguish between the tasks that need to be performed before you remove your old window and the installation of the replacement window.

Part 2 Preparing the Frame

Once you have measured up for your replacement window, the next step is to remove the old window from the window frame. In most cases this will involve prising off or unscrewing the stops and beads from your old window – unless your existing window was fitted with a sash-replacement kit, in which case there will not be any beads.

If the window frame was fitted with vinyl or aluminium jamb liners, use a crowbar to prise them free – removing any remaining stops from the window frame but leaving the interior and exterior casings intact. Scrape off any loose or blistered paint and patch any holes or dents in the frame casing with exterior-grade wood putty. Then sand the jambs smooth and prime and paint the surfaces.

If you are replacing old sash windows, now is the time to remove the old sash weights and insulate behind the window frame. First unscrew the access panels on each side jamb and remove the weights and any excess fibreglass that exists from the original installation. Then drill three equally distanced 10mm (3/8”) holes in the sill and head jamb before filling the area behind the casing with minimally expanding polyurethane foam. It is important that you use the minimally expanding type because you may damage the remaining window frame with anything stronger.

Once you have given the insulating foam time to dry (usually about 6 hours), cut off any protruding foam and sand down to a smooth finish. Now the frame is prepared, you are ready to install your replacement window.

Any element of this three-part guide can be done by yourself, or you can use the services of a local window fitter in London for specific areas in which you could benefit from the experience of a professional London tradesman. You may also wish to review our Guide to Replacement Windows before you start or once you have prepared the frame for your replacement windows jump ahead to our project advice on “How to Install a Replacement Window”.

Replacing an existing window is a fairly specialist job and best done with the assistance of a local window fitter in London. However, if you are a keen DIY-er, it may be a project that you would like to take on yourself to improve the appeal and value of your home.

As with most major home improvement projects, good preparation is the key to a successful conclusion, and we have divided our project advice on installing a replacement window into three parts to distinguish between the tasks that need to be performed before you remove your old window and the installation of the replacement window.

Part 1 Measuring Up

Measuring the dimensions of an old window is not quite as straightforward as it may seem. Some windows will have been in a property for more than thirty years, and in that time the frames may have warped or bowed due to the elements.

Start by measuring the inside width of the old window frame, jamb to jamb, in three places: across the top, middle, and bottom. Write down the smallest of the three measurements. Note: It is important that the smallest measurement is recorded because if you purchase a replacement window which is too wide for the frame at a certain point, it will create more work for you later when you have to adjust the frame. Next, measure the frame’s height from the top of the sill to the underside of the head jamb in three places: at the left jamb, in the middle, and at the right. Again, record the smallest measurement.

Check that the length and breadth of the frame is actually parallel by measuring the diagonals from corner to corner – the two dimensions should be the same, but if the frame is out of square by ¼ inch or so the replacement window can be shimmed to fit. Any larger discrepancies may require adjustments to the frame, or if the frame is so bowed that a square replacement would not look right and you will need a full-frame replacement.

Any element of this three-part guide can be done by yourself, or you can use the services of a local window fitter in London for specific areas in which you could benefit from the experience of a professional London tradesman. You may also wish to review our Guide to Replacement Windows before you start or once you have measured up your replacement windows jump ahead to our project advice on “How to Prepare a Frame for Replacement Windows” or “How to Install a Replacement Window”.