Cutting Loft Joists

[ldoodle]

Hey,

Got my mad scientist hat on... thinking out loud.

Could I cut 340mm out of the length of 1 joist, the second in from the external wall (parallel to the wall) to make a mini loft hatch opening. It's not near the existing loft hatch and won't use the 'same' joist as the loft hatch.

It's mad because I thought about making a small alcove to recess the shower head. Ceiling height is about 2300mm, minus I assume 100mm for the bar in a ceiling mounted shower head, minus the height of the bath doesn't leave a lot of head room for a 6ft3in man!

http://www.betterbathrooms.com/show...signer-round-300mm-shower-rose-&-ceiling-arm/

So rather than like this;

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• ldoodle
• 7 Jan 2014
• 1

It would look something like this (the big circle represents the shower head;

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• ldoodle
• 7 Jan 2014
• 1

The cut out would be about 150mm from a side-to-side mahousive timber that all the joists are fixed to, and would actually be in the eaves part so no traffic weight from above. The length from the other end of the cut joist to the edge of the eaves would be about 1200mm.

!!

 

[Blagard]

So long as your ceiling joists are not the bottom member of a roof truss I think it is fine to do what you sketched. Personally I always use screws when working on existing attached to plasterboard as risk of damage to plasterboard (or lath and plaster) is reduced.

Alternately consider a bit of DIY surgery like take out some bone from the offending lanky persons legs (5' 8" wot low ceiling ?)

 

[ldoodle]

What do you mean by bottom member - I don't know all of the terminology.

Logic is telling me that if the joists are the lowest thing (i.e. at the bottom), then they're the bottom members?

This is how it's laid out;

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• ldoodle
• 8 Jan 2014
• 2

PS: Risk to existing plasterboard and plaster is not an issue as it's a complete refurb of the bathroom, including replastering. So I'd want the strongest method of fixing, not the 'cleanest'.

 

[r896neo]

He means you can not simply cut it if the roof is made of trusses rather than a cut roof with purlins and rafters.

Your sketch kind of looks like it could be both confusingly??

If your house is more than 30 years old its probably a cut roof but if your unsure post some photo's for confirmation.

A cut roof will have large purlins which would be big timbers like 8''x3'' mid way up the rafters. A truss roof will not

 

[ldoodle]

House was built late 50's, early 60's. Can't remember exactly. Either way it's over 30 years old.

Will take some pics tonight.

PS: I definitely have purlins half way up my rafters. I also have hangers, struts and binders. It's pretty much like the cut roof as designed here;

http://www.diydata.com/general_building/roof_construction/roof_construction.php

except I also have binders at the bottom of the struts, one of which is cut due to the loft hatch. My binders a huge, much bigger than as shown in the link.

 

[Blagard]

ldoodle
From your replies you don't have roof trusses so you are good to go.

Most modern housing use a truss for the roof and the bottom chord is used like a ceiling joist. You would not just cut through it. So in case you had them I had to mention it.

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• Blagard
• 8 Jan 2014
• 1

 

[ldoodle]

Thanks guys.

OK, then so how would I go about it. If I cut through it willy nilly will things sag until I brace it up.

Or can I temporarily brace it until it's all in, then remove the braces?

I'm thinking of a sort of diamond bracing system where the joist to be cut has 45 degree timbers to both neighbouring joists, both sides of the cut.

Or is there a 'pro' way of doing it?

 

[Blagard]

So long as you keep your weight off the cut one you will probably be able to cut the section out and fit the trimming pieces across the cut ends without to many problems. I would anticipate that there will be some plasterboard fixings to the bit that needs to come out, so some damage will be inevitable

Great care is needed as the cut gets close to the plasterboard. A circular saw would be great except that it would take a big one to get the depth!

However a temporary plate across the area below the ceiling and a prop of sorts would give a little more security as you work. (May not be practical with a bath there tho!)

Definitely put some boards in the loft to work off.

Actually a tricky job to do as you try to leave the plasterboard intact.

Make sure the area is clear of cables or pipes.

 

[ldoodle]

Check to all that.

- Not bothered about plasterboard damage as i'll be cutting it out anyway to make the alcove
- Once I've cut out plasterboard i'll be doing the work from below - tricky to get in that part from above as shallow eaves and the hangers have diagonal braces between them, so unless I can train my 2 year old boy to do the work no normal sized adult can get in there!

Will prop it up with some 2x4. Then once the opening is done I'll use the same 2x4 to additionaly brace across the joists where the cuts are to the 2 neighbouring joists, if that makes sense - like an additional binder.

Thanks for your help. What length/dia. screws?

 

[Blagard]

I would use 5 x 80 or 5 x 90 (metric) No10 imperial. Also as they are fairly long, drill a pilot hole first it will make it easier and reduce risk of splitting where going into end grain. 2.5mm drill bit Buy a long one if you can find one!