4" hole on 8" x 2" floor joist

[markspark101]

I am fitting a shower extractor fan in a down stairs shower room. The ducting will be above ceiling in between floor joists. Sounds simple but unfortunately I need to go through a floor joist so that I can position the vent in an outside wall, missing the lead flashing of pitched roof-line. The joist are about 6-8 ft long. Where should I cut the 4" diameter hole in the length of the joist and how should I reinforce the joist where I have drilled through it. Please do not advise that this can't be done. I need to find a solution. Thanks in anticipation. Mark.

 

[big-all]

all holes must be central and no more than 1/4 so 2" 4 inch will be around 5" on the outside with clearence

so without a structural calculation i dont know

 

[RonnyRaygun]

Get 2 bits of 3mm thick steel plate, around 600m long by 200mm high, with a (slightly larger than) 4" hole plasma cut in the middle.
Reinforce the joist by bolting either side with ,say, 4 M10s either side of the hole (150mm centres lengthways, 120mm centres on height.

 

[Framer]

as said above you could plate the joist with steel or another way is maybe you could create a false ceiling if you have enough headroom so the duct is below the joist

 

[markspark101]

Guys, Thanks very much for your suggestions. Unfortunately Don't have enough clearance to make a false ceiling so I guess two pieces of steel is the way to go... I have been thinking though whether I'm making a big deal of this. The floor upstairs carries very little weight and the span is small. If I make the hole in the last third of the length of the joist, not too near the end (I've read the regs!) and keep the 4" hole exactly central vertically and bearing in mind the upstairs floor is a single sheet of 3/4" chipboard so the weight is spread evenly across all joists, there are noggins spaced across the centre, surely there is little chance of structural failure even if I don't reinforce. That said, I'm thinking of adding a piece of steel on each side of the joist above and below the hole. Each piece would be about 3' long. The top pair would look after the compression force and the bottom pair would look after the tensile forces. 4 coach bolts in each pair. What do you think?? Mark.

 

[Framer]

if you feel happy it is not carrying any load you could probably get away with fixing a bat strap above and below on both sides

 

[markspark101]

Upstairs is a smallish study (designed as a bathroom but never fitted out - previous owners used it as a box bedroom). All I have is a few guitars and a computer desk in there.... Would like to do things properly but don't want to make myself a shed load of work. I assume what I described in my last message were the 'bat staps' that you suggest or is this a trade name for a specific product. (showing my ignorance here...). Grateful for further advice if you have any. I am a competent DITer but this area is new territory. Mark

 

[Framer]

sorry yes its a brand name
[url]http://www.google.co.uk/imgr...=135&ty=114&page=1&ndsp=30&ved=1t:429,r:3,s:0[/url]

 

[Framer]

this was a similar situation when a young plumber put a pipe where he shouldnt have and there was no way of changing the joists

the ply was cut round the pipes and wires on both sides with the cut out pieces glued back in place then bat straps screwed over the top

Untitled

• Framer
• 2 Jul 2011
• 1

 

[markspark101]

Thanks for that Framer. I'll go for the widest I can fit which will be about 1.5" above and below the hole I guess. In your opinion do you think this approach is OK? - Just checking..... Mark

 

[Framer]

its not ideal but as long as you dont get any deflection when its done you will be fine, if you find there is deflection then you could beef it up with some thicker steel or angle iron

 

[markspark101]

Thanks for your advice. I'll go for it. Cheers. Mark.

 

[Nige F]

convert the round to oblong ducting - then same as- with the steel plates etc.

 

[markspark101]

Nigel F, how do you mean? Do you mean change hole shape to a wider flatter shape so that the metal plates can be wider and less wood is taken out of the joist vertically? If that's what you mean I get it. Please confirm.

 

[freddiemercurystwin]

Yes that's what he means http://www.wickes.co.uk/content/ebiz/wickes/resources/images/gil/93.pdf