Holes in Joists

[disturbed]

I am extending a ring main, with 2.5 mm cables.

Is it best to drill two small holes in a joist, or one big one?

By small I mean 11mm, big I guess about 16mm.

I know that holes have to be three diameters apart, and I'm putting them in the middle of the joists, which are about 7 inches across in my 150 yr old house.

What do you professionals do?

 

[SwindonSpark]

We follow the guidance in Approved Document A of the Building Regulations 2000 (as amended)

http://www.planningportal.gov.uk/uploads/br/BR_PDF_AD_A_2004.pdf

 

[sparky40]

Hello,
Regs say the holes should be within 0.25 and 0.4 of the span of the joists, and at least 50mm from top to bottom,(max diameter is 0.25 the depth of the joist).

I would use a 20mm augre bit to make it easier to pull the cabling in if you can get hold of one. Make sure you stay away from existing holes and other services.
Hope this helps.