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Unhappy rafter

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Unhappy rafter

Postby Doug » 11 Oct 2016, 19:33

I've been boarding a loft & installing a loft hatch & ladder, I pointed out to the customer that the roof didn't look in a great shape, what makes you say that ha asked

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I've never seen such long spans of 3x2" timber used for rafters, there's deflection in them all, :?
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Re: Unhappy rafter

Postby Tusses » 11 Oct 2016, 19:44

ouch ! :shock:
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Re: Unhappy rafter

Postby Malc2098 » 11 Oct 2016, 19:44

Wow! :o
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Re: Unhappy rafter

Postby Mike G » 11 Oct 2016, 19:45

:shock:

Doug, I'd be very cautious about repairing that ad hoc. That needs a structural engineer's indemnity insurance backing whatever repairs are done, because if something gives way and you've had a go at it, the only person they can coming looking for is you. Be careful.
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Re: Unhappy rafter

Postby Wizard9999 » 11 Oct 2016, 20:19

How old is the building / roof? How could that have complied with buildings reg's?

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Re: Unhappy rafter

Postby Doug » 11 Oct 2016, 20:35

It's late 60's early 70's Terry, it's on a housing estate that's new to me so I don't know much about the houses but from the looks they weren't terribly well built.

There has already been some structural work done on the roof with extra ties having been been installed, presumably when the owners before those I'm working for bought it judging by the timber that was used.
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Re: Unhappy rafter

Postby meccarroll » 12 Oct 2016, 06:33

Hi Doug, 3"x2" is a small section size for a house roof most of the older slate covered roofs had 4"x2" rafters.

I have repaired rafters in the past with 3/4" ply glued to the rafter either side of the repair and then peppered it on with small ring shanked nails. It's a similar method used in the construction of early trussed rafters at node points to join the timbers together. You can make the ply twice as deep as the original timber and fix an additional piece under the section being repaired.

If the rafters are deflecting then it's a sure sign that the section size is not sufficient for the load (roof covering etc) being imposed.

A lot of older roof failure occurs when a slate roof is re-covered with tiles (concrete tiles) which are much heavier than the original slate tiles.

You could install some purlings to reduce the span of the rafters and these can be made up in situ as boxed beams.

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Re: Unhappy rafter

Postby Mike G » 12 Oct 2016, 09:17

meccarroll wrote:........A lot of older roof failure occurs when a slate roof is re-covered with tiles (concrete tiles) which are much heavier than the original slate tiles........


True, and as an aside, most current rooves are designed with the assumption that the heaviest possible roofing materials are going to be used, whether or not they are actually used. Another major cause of roof failures from 60's and 70's rooves is the lack of roofspace ventilation: insulation stuffed hard up to the underside of the felt, no eaves or gable vents, and no ceiling-level vapour barrier combine to have some roof spaces dripping with moisture, leading to untreated timber rotting rapidly, and to the gang-nailed plates you describe failing through corrosion.
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