call me picky but my double-glazing contractors should:0
firstly, make a rough-ish measurement of window sizes in order to prepare a quote
secondly, if accepted, make a second true measurement, which, in my book, means hacking through plaster to get down to brickwork in order to make true measurements
If you need the windows a close fit to unrendered external brick, as I did, you measure, measure and measure - at different heights and at various points across (brickwork is seldom parallel, vertical or horizontal!).
With care you can get a 5mm +/- gap all round which seals nicely with foam and sealant.
However, if the finish is rendered outside and plastered inside, it is less important.
Once the frames have a few fixings and are foamed in (they will do that) you could have an inch gap and be pretty solid.
As long as the frames are a bit bigger so they will recess into the plaster and render, you won't tell once it is made good.
One question I would put to them though:
Will they make good the plaster/render or just slap trim all round. The latter is the default usually unless you specify (and pay for) the extra work to do the former.
They will measure to the size of the opening in the render. It opens up a whole tin of worms if they start messing about with the rendering or cement fillet over the brickwork of the exterior opening. What if it all falls off when they 'it wi' 'ammer? Would you be happy to pay for having the house re-rendered? They certainly won't want to pay.
Remember to specify that plaster work/render is to be made good with plaster/render not plastric trim bits stuck on over the gaps. They may or may not foam the windows in. They may or may not seal them properly, under cills seems to always get forgotten. They may or may not seal the window onto a cill properly such that driven rain can get into the wall behind the outer frame sealing.
good enough for a quote since the manufacturing costs are calculated to the nearest 100 mm or whatever. Once you've accepted the quote, the "surveyor" tales a closer look, assesses the render/plaster, and generally discusses any potential problems. They usually know from experience where the edge of a window frame is, even if it's partly overlapped with render. FWIW I've never had reason to criticise DG fitters.
The surveyor who came to me in January said that usually once he'd measured one window he knew what the rest would be - didn't stop him checking though.
I agree. I would expect a rough measure from the klod who comes around to do a quote. Then a surveyor comes over to measure more accurately and to cast a more expert eye over each proposed install to confirm sizes and any potential issues. I wouldn't expect the surveyor to turn up until the contract has been agreed.
I tried that once, on an estate house by a large building co (with a helicopter in the advert) All the windows were the same width, 6 feet (imperial) The one I didn't measure (poor access) was metric width. The replacement (timber) needed some work with a plane to make it fit. I no longer assume anything.
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