roof truss detail for extension

5 Jan 2009
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United Kingdom

I am planning for building timber frame one storey extension c. 7mx3m with brick outer to back of house.

Have got plans approved for hip roof style extension so if you imagine it looks like a "lean to" except at the end walls instead of gable style roof they will be pitched also with hip rafters.

I was wondering if there are any examples on this site of trusswork under the top sloping rafters for this type of design as apart from wallplate to terminate sloping rafters to as am believing I need some horizontal rafters under the roof to a second wall plate to brace plus attach internal plasterboard ceiling as i dont want a vaulted roof effect inside.

Ill get round to doing a sketch but grateful for any thoughts as its a fairly common extension design.

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This is from a canopy roof, but the principle is the same. Ignore the purlin/beam. And there are two alternative assembly methods shown

BTW, you mean a traditional cut rafter roof, not trusses don't you?

And why wasn't the roof detail drawn in the plans? :rolleyes:


many thanks woody and noseall,

yes to confirm i meaning cut rafters and i'm thinking my plan i missing some detail. To try to illustrate my queries I have attached a scan of the plan and a sketch I have made trying to work out exactly how to do the rafters. Referring to my sketch 3 the plan calls up wallplate G only and the 2 off 50x150cross members and the 2 off wall upright struts to which they join at the wall. Anyway you can see from the plan that what complicates things is that the new ceiling is half flat up to approx mid point of veluxes and then starts sloping.

The question that is bugging me is what sort of truss framework to create to both add strength and allow me to hang plasterboard to create this flat ceiling area which is the area ABCD in my sketch. My plan is somewhat lacking in this detail i feel

I’m thinking adding members like F and extending bottom wall plate G but also I’m needing a number more rafters for bracing and to be able to attach the flat ceiling portion to.

THanks in advance any thoughts

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The timbers seem over designed.

50x150 rafters will go to over 3m span at 600centres or 50x125 at 400 centres.

Hip .... something like a 38x175 for 150 rafters or 38x150 for 125 rafters.

You only need 50x100 for the ceiling joists and wall plates etc

No noggins between rafters

Double up rafters to sides of rooflights (bolt together), and you only need a single trimmer to the rooflights - the drawing appears to have these doubled

Otherwise, the section detail seems fine
Sorry for going slightly off topic, but Woody I clicked on your pic to enlarge it and found myself wandering through your album.

Sorry for being a nosey sod. :LOL:

All pretty standard stuff I thought, nothing out of the ordinary - then all of a sudden....:eek:

WTF? :confused: ;)
The last engineer who said he was cr*p at structural design: mummified and living in a loft somewhere in Dudley :)
That's a possibility Shy. :LOL:

It would certainly be preferable to the alternative explanation. I am reliably informed that there are certain "specialist" websites catering for similar "restraint" techniques......:LOL:
Don't panic, the nether regions are fully wrapped: if it was the "Dudley Swaddling Technique" - of which I understand he is also keen advocate (and webmaster for), there would be very carefully crafted circular holes front and rear :LOL:
Hehe, how did that get there? :oops:

I am sure there is a good reason, or was it a simple mistake, I'm not sure!

But duct tape is a wonderful product with a myriad of uses, and IMO everyone should carry some for those unexpected situations or impromptu moments.
Oh don't act all innocent on us, Woodster: clearly there is another protagonist of this particular pecadillo of yours somewhere on DIYnot, hence slipping that in among the more traditional stuff! Does admin know that you are using this site for your obtuse gratificational purposes?
Does admin know that you are using this site for your obtuse gratificational purposes?

I get excited when I see a spliced beam or an attic truss - whats wrong with that? Add a little duct tape though and wheeyhey :LOL:

Anyway less of obtuse gratification, what about the OPS roof!
You secret Pet Shop Boy... ;)

Anyhow, back to the roof, well you did ok there, only forgetting to specify that the top of the common rafters and the hips should be bird-beaked over a plate bolted to the wall, to stop lateral eaves spread.

That obviously is not possible for the jack rafters and there's no ceiling to tie the feet back to, so it's as well to oversize them to give it a bit more strength and resistance against spread for 3m in either direction from the hip corners.
Birdsmouths were in my original image. You've been looking at the wrong one :rolleyes: lol

What about strapping the jack rafters over the hip to stop spread, then?
Ok, give you that one :LOL:

How would that strap detail work? It's got a vertical face fixed to the hip, so the strap won't stop the jack wanting to rotate away from the side. Better way would be to run a batten up the sides of the hip, birdbeak the jacks over them.

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