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Jonnyboy

Roof trusses

Is it feasible to make my own roof trusses for a garage/car port?

It's going to be covered with corrugated roofing sheet so the weight will be less than concrete or slate tiles. I reckon if I buy ready made roof trusses for a double garage it's going to costs me around 600ish.
MarkS

Yes.

There are tables for the sizes and spans for joists etc in one of the building regs documents.

But what info do you need for Building Control ? Or do you not have that in Oirland?

Who is it that does timber frame buildings on here ?
Graham The Builder

Modern roof trusses are structuraly designed components which carry a gauruntee from the manufacturer. If your double garage was, say 6m * 6m, you would need 10 trusses at 600mm centres each costing around 40 each + vat. If you made your own trusses you may have to employ the services of a structural engineer to check that what you are doing is structuraly sound - which may cost you 200 + for any calculations carried out.
Jonnyboy

Cheers Graham
RichardW

Graham The Builder wrote:
If your double garage was, say 6m * 6m, you would need 10 trusses at 600mm centres each costing around 40 each + vat.


I would have thought that 6m with 600mm centers would give 11 trusses not 10?

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justme
Gervase

Of course it's feasible - although my own preference would be to have fewer, heavier trusses at wider centres, with decent purlins to provide a sound anchorage for the wrinkly tin. The fewer trusses, the less requirement to get them all to match to the millimetre, and the chunkier and easier to work will be the timber.
If you made your trusses as A-frames of 7x3 and sufficient purlins of 3x3 with halved joints on the trusses - all carcass-grade timber - you could get away with six foot centres.
Building Regs as they stand are merely approved documents which provide guidance, and are not law. The only legal requirement is that the building be constructed so that the combined dead, imposed and wind loads can be borne safely and without causing deflection and deformation of the building or the ground.
What you eventually settle upon for your roof is a matter for negotiation between you and the BCO, and if you can show that the loadings areadequately catered for, you can have whatever roof you like. Most BCOs will want you to comply with BS 5268, but you can argue that you won design more than adequately covers that.
To be honest, most BS guidelines are overengineed by a huge factor, with three and sometimes four times the structural strength that you actually, realistically need. It enables BCOs to cover their collective arses.
The relevant guff can be found in Part A of the Regs, which you can download from here.
Graham The Builder

Justme wrote:
Graham The Builder wrote:
If your double garage was, say 6m * 6m, you would need 10 trusses at 600mm centres each costing around 40 each + vat.


I would have thought that 6m with 600mm centers would give 11 trusses not 10?

0mm 1
600mm 2
1200mm 3
1800mm 4
2400mm 5
3000mm 6
3600mm 7
4200mm 8
4800mm 9
5400mm 10
6000mm 11



justme


Yep, your right, justme. Embarassed
Graham The Builder

Gervase wrote:
Of course it's feasible - although my own preference would be to have fewer, heavier trusses at wider centres, with decent purlins to provide a sound anchorage for the wrinkly tin. The fewer trusses, the less requirement to get them all to match to the millimetre, and the chunkier and easier to work will be the timber.
If you made your trusses as A-frames of 7x3 and sufficient purlins of 3x3 with halved joints on the trusses - all carcass-grade timber - you could get away with six foot centres.
Building Regs as they stand are merely approved documents which provide guidance, and are not law. The only legal requirement is that the building be constructed so that the combined dead, imposed and wind loads can be borne safely and without causing deflection and deformation of the building or the ground.
What you eventually settle upon for your roof is a matter for negotiation between you and the BCO, and if you can show that the loadings areadequately catered for, you can have whatever roof you like. Most BCOs will want you to comply with BS 5268, but you can argue that you won design more than adequately covers that.
To be honest, most BS guidelines are overengineed by a huge factor, with three and sometimes four times the structural strength that you actually, realistically need. It enables BCOs to cover their collective arses.
The relevant guff can be found in Part A of the Regs, which you can download from here.


There is a lot of designs which could would create a structurally sound roof for this garage but it all comes down to money and simplicity. Your preference of heavy truss combined with purlins is quite an antiquated design. I'm not saying that it is a flawed design (except on the size of your purlins) but unless you are going to build it yourself and have a good level of ability in woodworking it would work out much more expensive in labour time and possibly even materials than if you used a modern factory made roof truss.
Gervase

Ah, you've rumbled me!
My work is old fashioned - most of it involving traditional buildings, and suggesting 7x3 was a nod towards a lightweight construction! There's something very satisfying about working with 9x4 timbers and larger, and making your own iron hasps!
Jonnyboy

At what point were you going to tell me that I needed to build 3ft thick supporting walls?
sean

When he'd lured you into signing up for his 'wattle and daub/cobb' building course.
Gervase

And what's a car port when it's at home? Surely anyone with aspirations to gentility needs a coach-house and stables...
Jonnyboy

Don't even, I'm already fighting a rearguard action against a bloody pony.
Cathryn

In that case bbetter make it big enough for more than one stable and with enough room for a hay barn....

The sad stony broke voice of experience Rolling Eyes
Graham The Builder

Gervase wrote:
Ah, you've rumbled me!
My work is old fashioned - most of it involving traditional buildings, and suggesting 7x3 was a nod towards a lightweight construction! There's something very satisfying about working with 9x4 timbers and larger, and making your own iron hasps!


Looks like we have something in common then, Gervase. Wink I prefer working on older properties as a rule but have to take the rough with the smooth. Not so long ago we extended a thatched cottage which all had to match in with the existing house. The odd thing was that we had to use 8" * 3" rafters (as required by the structural engineer) and the house roof was constructed from not much more than bean poles. As you previously stated, there is a high degree of safety factor when taking timber sizes into consideration (snow and wind loads etc.)

Here is some of my work:

http://greenwelliesbalertwine.myfreeforum.org/ftopic854-0.php
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