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Twisted rafters

Does what it says on the tin
MyNameIsUrl
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Twisted rafters

#329773

Postby MyNameIsUrl » July 30th, 2020, 4:51 pm

I’ve just noticed several of my rafters are twisted over at up to 45 degrees. I have no idea if they have moved recently or been like that for decades (house is 1970s).

I clamped a piece of timber to one to gently test out whether it could be rotated back to vertical and there is a little movement there but I’m conscious there are nails through the battens into the top of the rafter which I don’t want to disturb.

Do rafters have a tendency to twist over time? Or would it be very unusual? Should I try to brace them in their current position, twist them back, or get a professional in?

richlist
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Re: Twisted rafters

#329801

Postby richlist » July 30th, 2020, 5:39 pm

Is your roof leaking of has it been leaking in the past ?
Wet timbers are more likely to twist/move.

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Re: Twisted rafters

#329809

Postby MyNameIsUrl » July 30th, 2020, 6:07 pm

richlist wrote:Is your roof leaking of has it been leaking in the past ?
Wet timbers are more likely to twist/move.

No, nothing like that, and the roof tiles look ok from outside. I really don't know if it's moved recently or been like that for ages.

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Re: Twisted rafters

#329850

Postby 88V8 » July 30th, 2020, 10:46 pm

Sounds like unseasoned wood was used. Nothing to be done about it now.

V8

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Re: Twisted rafters

#329878

Postby richlist » July 31st, 2020, 7:14 am

I guess the next question for you is......did you have a survey of the property when buying it and did it identify the issue ?
Provided the structural integrity is not affected and visually the roof looks ok there is no need to do anything.

If you sell and the buyer has a survey it will likely be picked up.

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Re: Twisted rafters

#329888

Postby Wizard » July 31st, 2020, 8:29 am

MyNameIsUrl wrote:I’ve just noticed several of my rafters are twisted over at up to 45 degrees. I have no idea if they have moved recently or been like that for decades (house is 1970s).

I clamped a piece of timber to one to gently test out whether it could be rotated back to vertical and there is a little movement there but I’m conscious there are nails through the battens into the top of the rafter which I don’t want to disturb.

Do rafters have a tendency to twist over time? Or would it be very unusual? Should I try to brace them in their current position, twist them back, or get a professional in?

I presume it is a cut roof structure (rather than pre-fabricated trusses), if so are the rafters still securely fixed to the ridge board, wall plate and any purlins? What would worry me a little is how they have been able to twist that much when they should be attached to other roof members at various points. Can you see if they are still securely fixed?

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Re: Twisted rafters

#330237

Postby MyNameIsUrl » August 1st, 2020, 5:44 pm

Wizard wrote:I presume it is a cut roof structure (rather than pre-fabricated trusses), if so are the rafters still securely fixed to the ridge board, wall plate and any purlins? What would worry me a little is how they have been able to twist that much when they should be attached to other roof members at various points. Can you see if they are still securely fixed?

It looks like the rafters on one side of the ridge board have been nailed through into the end of the rafter, and on the opposite side have a single nail driven through the side of the rafter at an angle into the ridge board. Consequently any twisting force is tending to pivot the lower edge of the rafter off the ridge board, ie it's not constrained. The rafter rotates on the nail, and such a force would also tend to split the rafter around the nail.

What I'm contemplating is clamping a length of timber onto the rafter at 90 degrees to allow me to twist it carefully (partially) back into position, and put a big screw through below the nail. And repeat for 20 or more rafters.

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Re: Twisted rafters

#330242

Postby Wizard » August 1st, 2020, 6:06 pm

MyNameIsUrl wrote:
Wizard wrote:I presume it is a cut roof structure (rather than pre-fabricated trusses), if so are the rafters still securely fixed to the ridge board, wall plate and any purlins? What would worry me a little is how they have been able to twist that much when they should be attached to other roof members at various points. Can you see if they are still securely fixed?

It looks like the rafters on one side of the ridge board have been nailed through into the end of the rafter, and on the opposite side have a single nail driven through the side of the rafter at an angle into the ridge board. Consequently any twisting force is tending to pivot the lower edge of the rafter off the ridge board, ie it's not constrained. The rafter rotates on the nail, and such a force would also tend to split the rafter around the nail.

What I'm contemplating is clamping a length of timber onto the rafter at 90 degrees to allow me to twist it carefully (partially) back into position, and put a big screw through below the nail. And repeat for 20 or more rafters.

A nail would be better than a screw as nails are much better at resisting a shearing force.

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Re: Twisted rafters

#330250

Postby MyNameIsUrl » August 1st, 2020, 7:30 pm

Wizard wrote:A nail would be better than a screw as nails are much better at resisting a shearing force.

I agree. What I was thinking was screws would avoid me having to bash potentially dozens of nails into a roof structure whose integrity is already worrying me. But I take it you're not opposed to the principle of twisting the rafters back into place manually?

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Re: Twisted rafters

#330275

Postby Wizard » August 1st, 2020, 9:23 pm

MyNameIsUrl wrote:
Wizard wrote:A nail would be better than a screw as nails are much better at resisting a shearing force.

I agree. What I was thinking was screws would avoid me having to bash potentially dozens of nails into a roof structure whose integrity is already worrying me. But I take it you're not opposed to the principle of twisting the rafters back into place manually?

I have twisted joists back that have moved, but to be fair it was not by as much as 45 degrees so I have no idea if it will work or not. The forces involved are pretty significant, if you have a sash clamp it would be better than clamping a second piece of wood to the rafter as the clamp may not hold it. But, if you are as concerned as you sound about the structural integrity of the roof it would make sense to get a structural engineer to take a look at it. If you did have the property fully surveyed before purchase was it highlighted in the report? It does not sound as if this has happened over night. If they did not mention it then maybe a conversation about what they did when surveying the roof structure.

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Re: Twisted rafters

#330332

Postby sg31 » August 2nd, 2020, 12:45 pm

Most properties aren't fully surveyed before purchase. I have sold a lot of properties over the years, I can only remember one that was fully surveyed and the guy that did that one wasn't fit to survey a garden shed.

I remember one survey where I offered the surveyor a ladder to have a look at the roofspace but he refused as he was afraid of spiders.

In this case a structural report might be a good idea.

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Re: Twisted rafters

#331338

Postby 88V8 » August 6th, 2020, 11:03 am

MyNameIsUrl wrote:What I'm contemplating is clamping a length of timber onto the rafter at 90 degrees to allow me to twist it carefully (partially) back into position, and put a big screw through below the nail.

The rafters are - what - 4x2 or more likely in a newer house 6x2?
There is no chance of twisting them back.
And if you could, you would be nailing or screwing near the end of the rafter and it would just split.

Quite apart from the fact that the battens will be nailed into the rafter as it stands and so the battens and tiles would be disturbed.

The rafters do not need to be affixed with any great strength at the ridge. All they are doing is holding up the ridge, which in turn carries minimal load. The rafters in our cottage are bits of hazel trunk, the ridge is another bit of hazel and they are fastened with wooden pegs and have been for 400 years..

If it will make you sleep easier, get some metal strapping and screw it to the rafters and ridge board to bind them together.
Inch x 10 screws will be plenty.
https://www.ebay.co.uk/itm/Simpson-Stro ... SwuWha5FC9
Your local builders' merchants will stock something similar.
Also available in stainless.

Forget straightening the rafters, they are what they are.

Then if you wish to avoid huff n puff from some future surveyor, once you have screwed them together, clad them underneath with some tg matchboard so they disappear.

V8


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