Garage - timber for roof trusses

All - thanks for all the help in the recent and not so recent past! Here comes a new phase of d-i-y for me (apart from the brickwork and a jcb/man/lorry for demolition and digging and a bit of joinery labour).

I'm demolishing my old garage and building a new one 10m * 6.5m. I'm in Scotland.

Planning permission, building warrant, etc all sorted.

That said I'm still pondering a few things like roof trusses & the type of bricks (conservation area and I want it to match the rear of the house which has 100 y/o vistorian "buff" bricks - or i might consider sandstone blocks 'cos the front of the house is facing sandstone). This pondering is valid since the planning's conditional on the council approving the bricks / slates and the building warrant needs a certificate from the truss company or a structural engineer.

My initial questions (there'll be a lot more, I'm afraid) are about the roof timber.

I intend to put a room in the attic of the garage Velux windows, so I need "attic trusses".

I've been quoted £65 and £100 for each of the attic trusses from 2 different suppliers (obviously they'll come with certificates). They say i need 20 trusses (extra because of the velux).

I tried to price up the timber to get a joiner to make up the roof (300m will cover it i think) but i'm struggling to get it in the 7m lengths which will be necessary to get a continuous run from front wall to back wall, although the drawings for the trusses show a join on that length of timber. it's not clear what technique would be used to make the join though or what the overlap will be.

My question is, what would be the technique to make a joint in the standard lengths to get a 7m span and what would be the overlap (if any) required? Would i put a length of timber on each side of the joint and bolt them through?

Please be assured that i will pay a structural engineer to design the roof and certify it for the building warrant - i'm more than happy to do that. I just want some ideas so i can price the timber, factor in the labour and make cost comparisons - and factor in £200 - £300 for the engineer.

If anyone's interested or needs more information, i'll post the drawings up on the web.

TIA Paul

If you are talking about proprietary trusses, the joint in a continuous length of timber is either formed from a finger joint (a glued zig-zag across the width of the timber) or a gang nail plate. Both can only be manufactured by machine and the joint can be designed to be stronger than the timber either side.

Usually a steel plate + bolts is used.

If you ask, the proprietary trusses will come with a set of calculations which are suitable for submission to BC (well, I have never had any problems in England).

Dont forget that with proprietary trusses you save the cost of a seperate engineer but you need to add in the extra cost of timber for additional longitudinal, chevron and diagonal bracing.

Andy W