Bi-fold door aperture size

6 Aug 2019
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United Kingdom
This is doing my head in!

Despite the reams and reams of information available on this I cannot get it clear in my head.

I want some standard sized bi-fold doors that are roughly 4m in width, and standard height.

I am about to build the aperture, and I want to know the exact size between the faces of the blockwork on each side that it needs to be, to fit a standard sized bi-fold door - i.e. I want to avoid having them custom made, if possible.

So for 4m doors, is the blockwork aperture 4m, or is the door opening 4m and then you have to take into account the door frame - so I guess the aperture would end up be 4.1m or something like that, depending on the manufacturer.

And the same query for the height. Does the standard size take into account the frame, cill etc.. so how big does the aperture need to be for 'stock' doors.

Many thanks
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Be careful on height - you may wish to start a course below finished floor which case you need to know cill height.

Be careful on configuration. Typically window and doors are specified using "as viewed from outside" in the trade.

I would be tempted to allow a little more than 10mm on the don't want cill or head being pushed inwards, easily done over 4 metres.
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Many thanks. So basically, it is worth identifying the manufacturer we will use now and working to their specification.

I think I will indeed start a course below floor level - which will also involve stepping down the DPC one layer below the door... need to check with the BCO on that before I do it. It will make it touch and go between leaving the 150mm difference between DPC and the outside ground level.. a bit of extra drainage may help convince them I suppose.

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