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I want to install a vent for loft ventilation and also install a sun tunnel through a gable wall, to help light a severely under-illuminated upstairs room (not going with a window, for reasons of privacy, thermal performance, cost, ease of installation and reversability).

Thinking I'm going to need holes of 6" diameter or more. I can't see this being a structural problem, but presumbly there's a diameter beyond which there would be trouble with insurers, mortgage providers, selling the house etc. (and, in the extreme, catastrophic failure of the supporting wall) so would like to know how to find out what this limit might be.

Answers for other countries' regulations also welcome. (Will be upvoted but not accepted.)

EDIT: the exterior walls are made out of reconstructed stone bricks. I assume there is another layer of brick behind, forming a cavity wall, and the wall is structurally signficant, not just a facade (the house was constructed in the mid '90s). Then of course a layer of plasterboard. No electrics nearby that I know of and no plumbing.

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    It usually depends on what you are drilling though. Sliding/wall covering is less of a concern than making big holes in structural members holding up the house. In North America we usually have 16 inches between structural members to make big holes. In structural members, holes should be less than 1/3, so maybe 1/2 or 3/4 inch max. Explain what you want to make the holes in.
    – crip659
    Jul 1, 2022 at 10:48
  • @crip659 Many thanks, I've added some info. I believe UK houses of the period (1990s) still used supporting masonry walls.
    – user234461
    Jul 1, 2022 at 11:00
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    Your description of 90s UK housing seems common enough - I've got one and I've worked on a couple more. They're all brick (or fake stone) - cavity insulation - aerated concrete blocks (or other masonry) - plasterboard. The plasterboard may be glued to the inner wall, or fastened via wooden battens. Masonry outside walls in the UK are always (or as near as makes no difference) structural, and may be the only structural walls. So @crip659 they're structural but not like the members in a framed house
    – Chris H
    Jul 1, 2022 at 14:11
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    The rules for drilling through timber joists are well documented. No idea if anything similar exists for holes in masonry walls. I wouldn't worry about one 6" hole as that's standard for a (large) kitchen extractor duct, but I don't know what happens if you have several of them close to each other.
    – Carl
    Jul 1, 2022 at 14:36
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    To find out if you have a double wall (bricks) just check at door/widows frames.
    – Traveler
    Jul 1, 2022 at 19:17

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