Windows and doors: Watchpoints
Nearly all window suppliers and many door suppliers will insist on coming to site to measure the openings directly. The reason is that more often than not the built opening size is slightly larger or smaller than the construction drawings. It is important that a sufficient gap is left to allow for specialist airtightness foam to be applied to help prevent any gaps.
If the frame fit is too neat it may prove difficult to do this. Bonding the airtight membrane to the windows and external doors is also an important and time consuming task which requires a lot of care. It is probably, therefore, a task best left to someone other than the installation team unless they can be supervised very closely by an experienced person. After all, it won’t matter how well a product scores in the various tests, if the installation is poor.
It is hard to understate the importance of this particular aspect for poor workmanship during installation around the airtightness detailing will undermine the thermal performance of the unit. For a new build, a good supplier will provide a quote for installation and perform water hose and air testing as standard.
Even if the external wall cavity is to be filled with pumped insulation later, the sides (jambs) of the openings, behind and under the sills and between the lintels and dpcs will all need to be fitted with snug-fitting board insulation (not squeezed-in quilt) as the build progresses, so attention to detail is vital to avoid gaps. Make sure that this is all correctly in place before the window installers get on site.
In most cases the window supplier will quote for supply and fix so they are responsible for the installation; your builder or yourself will need to treat them as any other tradesman in terms of scheduling. Note that when you place the window order delivery will be quoted in weeks, but this doesn’t allow for holidays and some European manufacturers close for a month in the summer.
If buying second hand or end of line windows you will need to rely on the expertise of your builder or a joiner. You will usually pay a deposit when the order is placed, often half the amount, then the rest upon satisfactory fitting of all of the units. Check they all open and shut properly and there is no damage to the glass or frames.
Remember that windows and doors are installed during the first fix which means that there is a lot of plastering, cutting and painting still to come. Covering the frames and handles in a protective material will save hours of laborious cleaning in the future. That said once second fix is finished, make sure to remove the protective coverings as the glue on some of the sheeting supplied by manufacturers can become very hard to remove if left for too long.