Outhouse pitched roof with rotten joists ends

[alpenbowl]

Hello,

I have a outhouse length 92cm width 119cm. Its has a pitched roof against a wall and slate covered.

The five joist ends have rotten away from the wall that they where fixed into and are currently being held up by a make shift wall plate. Also seems like someone has cut the rotten ends away before and bolted on a new end of around 2 ft. Its got old cement flashing which is the problem I think.

Is it possible to replace the joist without taking the the whole roof off, if so whats the best way of temporary support? Or is it easier to carefully remove slates and build from new?

This is my first roofing project which is why am here for help.

Thanks

 

[tim00]

You are referring to joists and not rafters? Joists are laid flat/horizontal and rafters are fixed sloping.

1. You could certainly replace the joists one at a time.
2. How come the tails rotted out?
3. Perhaps wrap any new wall plate in plastic, as a membrane.
4. Cement fillets will require replacing with flashband or lead.
5. Perhaps you'll post pics - interior and exterior.

 

[alpenbowl]

Sorry I did mean rafters not joists.

Got some pics attached. You can see the roof has sagged where the rafters have rotten and slipped down and now resting on a temporary support.

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• alpenbowl
• 11 May 2012
• 1

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• alpenbowl
• 11 May 2012
• 1

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• alpenbowl
• 11 May 2012
• 1

Untitled

• alpenbowl
• 11 May 2012
• 1

 

[tim00]

1. The slates appear to have been fixed to T&G boarded over the rafters - perhaps there are battens above the T&G? The boards are probably fungal damaged and, possibly, no felt has been used.

2. You could prop the sagging area back into a rough plane, and replace the rafters. But it would all happen again. And propping might cause further damage/difficulties.

3. You will have to bite the bullet, and strip the roof and flashings, and rebuild and detail in a proper manner. It's a good DIY job.

4. To help, you could mark each slate with crayon - course and position - before lifting them, and use a camera to note and measure how they were set out.

Anyhow, whatever you decide on, come back on here for any further help.

 

[ladylola]

It would definately be best to strip at least the bottom few courses of slates. If the ends of the rafters are rotten then as timm says rot could be elseware and I'd suggest you check the wall plate.
As it's an out building (and you presumably aren't too worried about what it looks like) you could just cut out the rot and sister new rafters on although I suspect there is a purlin and it would be better to take new rafters up to that.

 

[noseall]

We are talking about a tiny roof - bite the bullet, strip the lot off and fit a new one.

 

[alpenbowl]

Thanks for all the good advice. I think I will just replace the whole roof it is only small, plus will keep me busy for a while.

What size wall plate and rafters would people recommend for this size roof as in width and thickness, also whats the best/simplest way of fixing the rafters to the wall plate?

 

[ladylola]

Sizes will depend on the actual size of your span but looking at your picture the rafters could be 6x2 or even 4x2 if you drop a purlin in halfway up. As a rough guide just measure the exsisting rafters and remember it's never a problem to specify or overengineer what you can get away with. By this I mean if calculations come up with 4x2 then using 5x2 isn't going to cause any problems. As to the wallplate something like 6x3 should be fine bedded on and with straps .Make sure you buy pretreated timber and screws are possibily your best option for fixings although nails will also do.

 

[alpenbowl]

Back again. Just drawing up some rough plans so ive got something to work off but cant seem to find an answer am looking for on the internet.

How do I go about getting the rafter to attach to the ledger/wall board? Is it best to cut the correct angle and just lean it against the board and have the birdsmouth at the lower wall plate end only.

Or have a birdsmouth at the wall plate and also cut a birdsmouth in the top end so it can rest on the board and the top face of the raftet will be in touch with the wall?

Hope you know what I mean.

 

[tim00]

1. If you feel competent cutting birdsmouth's then do so, attach at the top ledger with hangers.

2. You might be better off, cutting the top angle and using hangers at the top, and merely sitting the tails on the plate. Then attaching them with clips.
Let your tails run long, dont cut them until you'r ready to fix the fascia. 4x2"'s are well adequate sections.

3. If you have a large open floor space, you can do a full size, section view layout for your roof cutting.