Sistering Slightly Rotted Rafters - Help/advice

[scruffybiker]

Hi,

I posted on here a couple of weeks back, I found 3 rafters that have fairly minor rot in them. The rot is near the ridge on all 3 rafters. The rot is only on the top side of the rafter and doesn't go all the way through the wood and extends for about a foot.. I scraped out the rot & treated with wet rot wood hardener. Looks like old wet rot from a previous leak many years ago. But paranoia has got the better of me and I want to sister them for a bit more piece of mind. I bought some 2x4 rafter lengths yesterday,to do the job, but obviously there not the full length of the rafter. But there long enough to reach over the purlin. So would it be ok to sister the rafters aslong as I carried over the purlin? and should I sandwich the exsisting rafter or just one side? I have coach bolts etc to secure it. Cheers

 

[KenGMac]

Any chance of a few pictures?

 

[^woody^]

M10 bolts and spur connectors. A single timber will do.

If the rafter is more than 3m long, I'd suggest 3 bolts at 400 centres, otherwise 2 bolts. For length, the timber just needs to be 100mm past the last bolt

 

[scruffybiker]

Thanks for your reply woody, would you advise me to carry the new piece of timber over the purlin? Cheers

 

[^woody^]

No need to go over the purlin, so only do this if it makes it easier to do.

If you do that, you are effectively replacing the rafter, so you can then just screw the two rafters together instead of bolting and spur connectors.

 

[KenGMac]

Would suggest that you introduce a barrier between the original rafter and the soon to be introduced new rafters, or rafter, i think a bit of roofing felt or similar, say a bit of blue Damp proof course, placed between the existing and new rafters just to ensure that any still live rot on the original rafter does not get to the new replacement rafter.
on a different tack, some years down the line you want to sell up and move on? a Surveyor pitches up and undertakes a survey and sticks his head into the loft??? what does he see??? a slightly odd arrangement at the rafters, suggest you colour up the new rafters to as closely match the existing as possible ?
Final point ensure that the joint between the new rafters and the Ridge is a good tight fit.

Ken.