Top tips on surveying for windows and doors

Top tips on surveying for windows and doors

Quickslide‘s Adrian Barraclough takes a look at surveying for windows and doors.

I have seen so many window and door installations that were ruined well before the frames were even made, because of poor surveying. ‘How hard can it be?!’ has been the attitude taken by so many who think that a window or door is just something that fills a hole. Well the simplest oversights can cause the severest problems, which then blight the whole job, sucking the profit out of it along the way.

So these are my top tips for surveying for windows and doors:

  • Allow 10mm for expansion – any material, any window and any door.
  • Measure three different points vertically (top middle and bottom) and two points horizontally. Find the narrowest point and still deduct 10mm.
  • If the window is set back behind the outer skin of the stone (‘in check’) add 20mm to the total width of the window.
  • Be aware that if the internal window sill is less than 800mm apart from the finished floor. The glass must be toughened. If you have a window seat or perhaps even a bath (something that is fixed near to the window) you must measure from the height of that.
  • On renovations, you must check on the heads of the stone- or brickwork that there is a single leaf lintel in place to carry the bricks or stone work. If there isn’t you must install one.
  • On renovation projects you will need to measure both internally and externally. If there is a large difference between the internal and external measurements (+30mm) you will have to use the smallest measurement and allow for an add-on to be included onto either the top, bottom or even the sides, depending on whether the difference is caused by the internal window sill height, internal head height, tiled walls etc.  The add-on will appear as an external window ‘extension’ filling the gap caused by the differing internal and external measurements. You should only ever have about 10mm hidden in plaster or timber work internally.
  • Be aware of Building Regs.
  • New builds = you may need trickle vents.
  • Bedrooms must have escape hinges.
  • Laminated glass – Doc Q .
  • When surveying, it’s important to explain the process to the homeowner – explain why they may need different extras so that nothing comes as surprise.
  • And always double check your measurements!


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