1930s Roof Support Beam Question

12 Mar 2014
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United Kingdom

DIyer here.. however this job seems beyond me.. I'd really appreciate some opinions on what you guys think would be a reasonable solution - some context/knowledge/insight, before I'm swamped in quotes. Or in the event I decide to do it myself.

This is my mum's house, and the diagonal support beam (I don't know what it's actually called) for the rafter joist has significant wood rot. I don't know if you can see from the pictures, but you can actually see all the way through the middle!o_O I was picking away at it with my fingers and had to stop because I was starting to worry there would be nothing left and don't want the roof to fall down..

I'm not sure if you can see from the pictures, but to me it looks like the rafter joist is also sagging slightly downwards towards the end, although, there is substantially less wood rot in the joist and it seems it still has most of its integrity.

Would do you guys think is a common or reasonable solution to this?
- Sister the existing support beam somehow? Above and below perhaps? I have sistered joists before but this is obviously more complex
- Construct a new support beam nearby?
- A metal rod somewhere?

If simply replacing the existing support beam is a good idea, how would the contractor (or I) reasonably go about supporting the structure of the roof while it is replaced? Would I need some brickysmates or something?

Thanks, any help much appreciated... particularly if anyone has encountered anything like this before :)


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richiecafc, good evening.

As datarebel above, not looking good at all.

Not a DIY job, unless you are a Joiner / Builder ?

The roof presently supported by the rot affected brace will need to be supported during a replacement of the damaged brace.

Can I suggest you have this area of damage inspected sooner rather than later??

Do you know of any other similar work undertaken in the surrounding area? If so, suggest you ask that contractor [if he is any good?] to cost up your job, having done one replacement the builder should have a good idea of what is what.

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If nothing is done and quickly, that entire corner is going to very soon collapse - then repair cost will be quite considerably more.

I wonder why there are V's notched in the outer face of that timber? Has it perhaps been replaced before with some second hand timber?
looks to me like the whole lot needs stripping out and rebuilding. would get a reputable builder who knows a good joiner
and between them complete the task. my guess it would have to be done on a 48 hr building notice as this looks structural.
Thanks for the replies! Much appreciated! I've been working as a carpenter/roofer/all sorts during lockdown (best part of a year now) but I know that's not long and I still have a lot to learn. Would love to take some time to do some qualifications!

The notches on the diagonal piece are decorative, they are the same all the way up and down the road. If it is load-bearing - then I agree that is a bizarre choice for the people that built these 1930s wonders. Why weaken the part that is load bearing! Part of me wonders if the strut is mainly (but not entirely) decorative, partly for that reason. I've looked at other properties that have a similar strutted purlin roof build and they don't always seem to have a strut. I wonder what the the max allowed overhang is for a cantilevered roof like that.

I also don't understand how the strut necessarily holds its own weight unless it is mortis and tenoned into the rafter above. They are definitely separate pieces of timber anyway! I guess I'll find out tomorrow.

The strut is still sound (just) so fear not, I will definitely get this looked at soon and update the thread :)
I suspect you will find a length of timber behind the fascia which catches the rafter feet (6x3" maybe) which that strut is helping to support.
cubed rot

Yes, looks a lot like Dry Rot? drawback is this is external??, very unusual to see Dry Rot externally.

OK on the inner surfaces of external walls, I have generally assumed that Dry Rot did not like sunshine or indeed any light source.

Thanks again for the responses! Really appreciate you guys taking the time. I don't think this is dry rot, the cuboidal cracking is quite small, there is no fungus visible, also the rotted wood (on the horizontal beam anyway) has lightened and is fibrous in texture..might be a combination though I guess. Whoever "treated" the wood before, put on some sort of bizarre gloss which seemingly trapped the moisture in the strut, which is unfortunate. Emailed like 7 local roofers tonight so hopefully have some bites for tomorrow.
Look for someone who has done this repair before?

If it has happened on your property. there is a fair chance it may be a defect in the design of the property?

I think it would be wise to get it properly checked.
There could be fruiting bodies elsewhere .
Fingers crossed I'm wrong

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