Structural calcs for hips

[Frane Selak]

Hi, over the last couple of years I've been building an extension myself in my spare time, and as I'm doing everything myself there is going to be the odd hiccup along the way. One of my slight problems is the architect/structural calcs guy, basically he is a waste of space. I'm in the building trade (although not a builder) and I used the same guy all the builders I know used as he was cheap, all plans and calcs for about £360 which I got off him no problem. The problem with the guy is he is getting on, mid 70's and he is impossible to get hold of, it took him six months to get my plans into the council, he said he would post them on his way home and then went incommunicado for the next six months. I could have dropped them off myself the next day.

Anyway that's a bit of background and my issue at the moment is the roof. when I put the roof on last year I got the council round for the next inspection, I showed him the calcs for the steels and he was happy, he then asked for the calcs for the hips, which I knew nothing about, he also asked for the calcs for the roof where its sat on the original roof which is a fairly modern trussed roof, again nothing was mentioned about this in the calcs booklet I got from the architect. What I have spotted since though in the smallest writing possible on one of the plans is a sentence saying hips to be 50x250 with a little arrow pointing to the corner of the roof and I've used 50x200 doubled up so effectively 100x200 hips or 4x8's.

Is any of this likely to be a problem, surely 100x200 is just a good if not better than a 50x250, I don't think I could have got a 250 wide hip over the wall plate anyway without cutting most of it out again. Here is a couple of pictures to illustrate what I'm on about.

[OutInTheShed]

Stiffness of a beam is controlled by sectional moment of inertia, 200h x 100w comes out very slightly better than 250 x 50, because the formula has h cubed in it.

[Frane Selak]

Cheers, sounds very technical but I gather that I'm fine, any ideas about the new roof sat on the original trussed roof, there are about the same number of tiles on the new roof as there were on the old roof underneath which I've obviously removed, the council guy was on about putting a 100x100 post on the original wall plate going vertical to where the hips and ridge all meet.



Cant see what good that would do, its a triangle with the ceiling joist attached and isn't on any drawing that I can see. To be fair though, I built the roof how other builders had done theirs as opposed to following the drawings which there weren't really any detailing the roof anyway, asked a couple of questions, watched a few youtube videos on speed squares and away I went. Its rock solid when you walk on it though.

[OutInTheShed]

I'm an engineer in other fields, not a builder.

I would be looking at standard builds.

My feeling is that a vertical isn't very useful if I understand correctly, but:
1) a bit of wood is cheap, engineering design is expensive
2) A vertical might have made it easier to put together?
3) I wonder if you should have a diagonal opposing the diagonal of the hips? i.e. from the middle of the building somewhere to where the hips meet?

I think this reply may mostly be useful in bumping the thread, in the hope that a roofing or building person reads it.
Can you edit the title to draw them in?

If @Aluminati can't help who can?

[smokey mow]

Regardless of the answers you receive on here, Building Control are still going to want to see the calculations which they have asked you to provide.

If your original engineer can’t produce these then you’d be best to contact a new engineer.

[Chumley.mouse]

Its just 1 piece of timber to add, in my experience (diy like you ) if its just something simple to keep the building inspector happy then its worth it. They like you to agree with them and nod your head al lot even if you think they are talking rubbish .

Looks like a decent job to me , hips / valleys are not basic roofing.

[spitfire-ian]

What is supporting the end of the ridge member where it meets the hip?

[Promised Land]

spitfire-ian said:

What is supporting the end of the ridge member where it meets the hip?

The last pair of common rafters, you could put a binder underneath but in nearly 40 years of site work and doing mainly joists and roofs I’ve never fitted a binder on site.

(A pair of common rafters will hold a ridge up, your ceiling rafter tied in holds the roof together and should stop it spreading.)

I’ve also in that time only ever fitted double hips once,it was a very big roof and the architect specified double hips all around but we put a backing bevel on the top edge to let the lath sit flat, the roofer will lath that one above and the hip rafters will be lower due to it being a double.

Do what BC say as they’re holding the cards regarding signing it off, you should always have deeper hip rafters than common, jacks, cripple rafters.