Roof sanity check

[23vc]

Hi
Getting near the wall plate height with my brickwork, at least will be in a few weeks all being well.
My roof will be gable ended up and over roof, no hips or valleys.
Rafter clear span is 4m, ceiling joists front to back clear span 6.6m.
I've got a vague plan of 7x2 c24 rafters, and a couple of big (8x3?) Ceiling binders and 6x3 ceiling joists.
Aside from that I'm getting the impression that most people reckon trusses are a better bet, but the size of them and getting them up there seems a bit of a scary prospect. Plus I'd just rather do a cut roof for no good logical reason
Any thoughts on the above really appreciated, obviously I will go through it all with the bco when the brickworks a bit higher but I always like a good discussion on here as it helps a lot!
Also I'm planning on building the gable end after doing the roof structure, and also building the inner blockwork skin of the gable off the scaffold from outside, not trying to do it from inside
Sorry that's a bit of a ramble but any thoughts really appreciated as always!

 

[noseall]

Sorry that's a bit of a ramble but any thoughts really appreciated as always!

Purlins and some chunky ceiling binders may help. Also, a large accurate compound saw, a shedload of roofing knowledge, a good grasp of math's (especially trig') and a good understanding of timber will be a must when doing a cut roof.

 

[^woody^]

Trusses are actually light, but just a bit unweildy. You'll need to or three people to set them up and fix.

A cut roof will still need two of you, but you've got the added buggery factor in all the cutting and notching.

Time and material wise there is nothing between them.

If you don't need a wide open roof void, then it's got to be trusses.

 

[garyo]

I've done a cut roof your size single handed and it's certainly possible if not efficient. Interesting job dragging the timbers up a two storey scaffold! You want to minimise and up/down/up/down with the same piece of timber so you need to get your wallplates bang on square&level so that you can make a single common rafter template then mass produce them on the ground.

If you're not building the gable walls first, what's your plan for getting a ridge board floating in position to assemble it all?

 

[23vc]

Thanks guys.
Noseall, yeah my maths and trig is ok. Cant think where I'd need a compound miter here tho - no jack rafters ? Also the 7x2s were to avoid needing purlins
Woody , thanks I may still go with trusses
Gary, I was planning on putting a bit of timber up there on prop one end up, then once a few rafters were up it would be self supporting. Never done this before though!

 

[noseall]

If you're not building the gable walls first, what's your plan for getting a ridge board floating in position to assemble it all?

We never build the gable walls prior to building the roof even when building a ridge beam roof. We use props and tie the wall plates together with temporary joist straps. We fix purlins into their respective b/m's and let them hang until the wall is built up beneath them. They may need a nudge upwards and a packer once the blockwork has set.
In the image below you may just make out the Acro prop supporting the ridge beam just behind the first tie.

20170322_085233

• noseall
• 30 Mar 2017

 

[23vc]

I think I'm better off going with trusses and save my dream of one day doing a cut roof for another time. I just thought you had to have a crane or some kind of elaborate pulley system to get them up there? Or can you literally just manoeuvre them up with enough people? Do you have to take some of the scaffold handrails off? Really appreciate any advice from those who have done it

 

[John D v2.0]

If you use 7x2 by 4m it'll be very heavy too not for one person. Our builders had to lug a few 225 by 60 by 3m and they didn't find it easy at all!

 

[garyo]

I think I'm better off going with trusses and save my dream of one day doing a cut roof for another time. I just thought you had to have a crane or some kind of elaborate pulley system to get them up there? Or can you literally just manoeuvre them up with enough people? Do you have to take some of the scaffold handrails off? Really appreciate any advice from those who have done it

If you get a quote from a truss company they quote the weight of each piece on their CAD quotation PDF will have the weight of each section, so that'll give you a fair idea, but as Woody says, it's the sheer size of it as much as the weight.

 

[garyo]

Gary, I was planning on putting a bit of timber up there on prop one end up, then once a few rafters were up it would be self supporting. Never done this before though!

The last one I did, I used a temporary timber 'king post' to support the end of the ridge beam, and then built the rest of the roof around the beam (two hips and two valleys... almost every rafter was unique and had a compound cut

We never build the gable walls prior to building the roof even when building a ridge beam roof.

I can see the logic in that. However, the one I'm doing at the moment has a gable wall that's 3.5 metres tall and I don't fancy trying to hover a 200KG steel that high in the air, so I'm doing it the backward way. There are many other disadvantages... like not really knowing where your blockwork is going to end, not being able to fit the roof restraint straps as you go, worrying about the stability of the unsupported gable wall.