Cutting roof or buying trusses - 4.4m wide

[Joe Shmoe]

I'm currently beginning a new shed build for me to play drums in.

My last big build (3m wide) was my workshop and it had a gable roof and cement fibre slates. From memory I used 6" rafters along an 8" ridge board and installed a raised tie to give me an extra 1ft or so, of headroom inside.

My new drums shed will be much wider at 4.4m, and I'm intending on installing 2 layers of 15mm plasterboard (for extra sound isolation) and given this extra weight, plus the 4.4m width, I want to ensure the roof is definitely up to the job. Again, I intend on using a raised tie for a little extra room inside, and fibre slate on top.

Are there any charts or guidance that I can refer to, to ensure I'm doing it correctly and up to carrying the extra weight? Would buying trusses from an online supplier be a quicker/safer and/or more cost effective?

Any pointers would be really good.

Cheers everyone.

 

[MikeG.]

What pitch (angle) is your roof?

 

[Inspector]

I searched "Load tables scissor trusses" and got these.
https://www.eden.gov.uk/planning-and-bu ... ber-sizes/
http://wilsonrooftruss.co.uk/wp-content ... Manual.pdf

"Roof truss span calculator" got these.
https://myrooff.com/roof-truss-calculator/
http://www.locketruss.com/roofspan.pdf

Here is an Aussie site with a bunch of construction calculators.
https://www.blocklayer.com

There are apps to explore too that I didn't look for.

Pete

I'll add that a scissor truss will give headroom with an easier to drywall surface inside. 2 planes rather than 3.

 

[MikeG.]

A scissor truss is completely unnecessary for such a small roof. A simple raised tie truss is perfectly do-able, but to calculate it, one will need to know the pitch of the roof.

 

[Joe Shmoe]

Hi all.

Pete - I saw those and they're pretty good but didn't know if they would allow for the extra weight of two layers of 15mm PB.

Mike - still planning at this stage but I suppose 5/12 would be good? I think that's 24 degrees perhaps?

 

[MikeG.]

.....Mike - still planning at this stage but I suppose 5/12 would be good? I think that's 24 degrees perhaps?

That's 22.6 degrees. Nice to see someone doing it that way, the way it's been done for centuries.

You'd be OK with 5x2s at 400 centres, but you are going to need more than that for your insulation, and the point load at the end of the raised ties would make me feel more comfortable with 6x2s anyway. That only gives you room for 100mm of insulation with your ventilated void over. So that's 145x45 C16 CLS rafters @ 400 centres. You could use the same for the joists (ties) so long as you aren't planning on loading up stuff into the loft.

Usual caveats apply: I'm an architect, not a structural engineer. If this building is controllable (ie the Building Inspector needs to look at it), then you'll need calcs from an engineer.

 

[HOJ]

To give you an idea of comparative costings, I am working on an Hempcrete and timber frame building design, to be built in the new year, with a 22 degree pitch at 4mtrs wide by 5mtrs long, price for Fink trusses from my supplier came in at £480.00 inc VAT, with a gable ladder on one end, pricing to cut the roof, the cost of timber alone is up to £485.00.

 

[Joe Shmoe]

Cheers for the info everyone.

Does anyone know if a 2x6 ridgeboard will be okay?

The length of the build is 6.2m, so with overhangs I'm looking a 6.8m or 7m length of timber, and i can only find that length in 6".

How do other people do it?

 

[Stevie B]

Hi Joe
That would be fine although if it was me I'd probably use a 7" ridge so the the whole of the end of the rafter will be touching it.
You can join the ridge to make it longer using a scarf joint if required.
Cheers

 

[MikeG.]

Cheers for the info everyone.

Does anyone know if a 2x6 ridgeboard will be okay?

The length of the build is 6.2m, so with overhangs I'm looking a 6.8m or 7m length of timber, and i can only find that length in 6".

How do other people do it?

As Steve says, that's fine, but 175 or 200 by 50 would be better. The ridge in this case is non-structural. Its functions are to keep the rafters properly located, and to provide something that the rafter can be fastened into top and bottom of the plumb cut to help prevent twisting. Don't even think of putting it up in one piece. Get two bits of 3.6 timber and scarf them, lifting them into position separately.

In the good old days half inch increments were readily available, and an 8"x 1-1/2" would have done nicely. One inch timber is a bit risky in these days of fast grown and over-dried timber, otherwise 175 or 200 by 25 sawn would do perfectly well.

 

[Stevie B]

Agree with Mike

Also don't use a nail gun to fix it all together, but some 100mm hand nails of a decent gauge and it'll be a much stronger roof!

A good tip to hold the ridge in place is to cut 4 rafters and nail them to the wall plate in their final positions, two opposite each other at one end of the ridge and two at the other so you end up with two pairs touching each other at the top and holding each other up so to speak. Then get your ridge board and push it up from underneath and it will all hold itself in place. Then you can make some final alterations and nail it all at the top and then infill the rest of the rafters.

 

[Keith 66]

Though not a workshop, when we had our extension built on our house i foolishly allowed the architect to specify a truss frame roof on it. The builder liked it as it was easier for him.
In reality we ended up with a roofspace mostly filled with timber braces. There is room in the middle for the water tank & little else, boarding it out was a royal pain.
Doing it the old way would have meant a sizeable usable room in the roof.
Now im stuffed!

 

[F Flinstone]

To keep it simple I would use "Fink" trusses, the calculations are done for you and they are easy to fit. If you are doing a larger building and want to use the "upstairs" space then you need "Attic Fink" trusses, my new garage workshop roof is this type of construction, span of 11mts width of 7.5, it then leaves me an upstairs floor area of 7.5x 4.8mt . Ff

 

[topchippyles]

5x2 rafters with a 6x2 ridge is more than ample,Its only a shed after all and run at 400 centres,You joiner guys always go over board on roofing.

 

[MikeG.]

5x2 rafters with a 6x2 ridge is more than ample,Its only a shed after all and run at 400 centres,You joiner guys always go over board on roofing.

Help me out with how you would suggest maintaining a 50mm airgap above the insulation in a 5x2 roof. Curious minds......

And show us your working for the point load from the bolts on a raised tie roof, with 30mm of plasterboard fixed to the underside.