How Do You Install a Timber Window?

Q We’re self-building our first home and to save on costs we are taking on a lot of the work ourselves. One concern we have is measuring up and installing our timber windows — do you have any advice on getting this right? Matt Stevenson

A MARK WINTER SAYS:

If you’re purchasing timber windows from a reputable supplier, they will be designed and manufactured to a standard which gives them ultimate quality and performance. But if they’re installed poorly, even the best quality windows can be compromised. If done the right way, it will save both time and money in the long run and prevent damage.

The first thing is to measure up accurately. The opening must be between 10mm and 20mm bigger than the total window size, so if you’re measuring an existing space make sure to take 10mm (5mm each side) from the smallest point of the opening. This means you can input your window specification accurately.

Before you continue with fixing the window, you should ensure the window is packed on all four sides and is level. Side packings should be located where the fixings will be. Both the sill and the head packings should be no more than 150mm away from the vertical part of the frame, known as the jamb, and should be under each mullion (the vertical part of the frame that splits the window). It’s essential when fitting your window to ensure the frame doesn’t become distorted. At this stage, you should also double-check that the casements (the hinged sash which is fitted inside the jambs) work and open fine, too.

Now it’s time to place the fixings. Side fixings should be fixed 150mm from the top and bottom of the window frame and there should be no more than 450mm between every side fixing. Large windows which are more than 1,800mm wide should also have fixings in the centre of the head and the sill. Pre-drill your frame and wall to help when fixing your window in place.

You can fix your windows into brick- work using either a screw and anchor plug or a self-tapping concrete anchor. The fixings need to be at least 25mm deep but we would always recommend going in 50mm using 8mm x 120mm fixings.

To prevent air infiltration between the window and the wall, you will need to seal the gap. You can use an expanding foam seal and then use another seal on the top, preferably a silicone or polysulphide-based sealant.

If your windows aren’t pre-finished, they should be finished in dry weather before they are fixed into place. It’s worth choosing a good-quality finishing material; opting for the cheaper product will mean you’ll end up having to reapply it sooner.

If done properly and with care and consideration, you should be able to install your windows with ease and to a good standard.