Engineered trusses versus trusses cut and built onsite?

[jsstevenson]

Hello...

I am currently swithering on whether to use proprietary attic roof trusses, i.e engineered attic trusses from truss manufacturer, or whether to go down the route of cutting and manufacturing the roof on-site without involvement of a truss manufacturer (though obviously with Structural engineer to spec. timber sizes, nailing/bolting guide, etc).

The Structural Engineer has informally suggested using Truss Manufacturer, sighting timber sizes as a key issue in this choice (i.e. truss manufacturer will be able to specify smaller timbers than the engineer).

Does anyone have any thoughts on this? For example, timber sizes (big difference?), cost, difficulty!!!?. Is a manufactured attic truss a better option? Is there a greater risk of a sagging roof if cut and built on site?

If seeing the design would help some drawings can be found at:
http://innellan.googlepages.com/home

Any answers, views, directions to companies or websites would be welcome.

Jamie.

p.s. house to be built is in Argyll, Scotland (Central Scotland!)

 

[JohnD]

Will you ever want to walk about in the roof space? I see in your plan you have Velux roof lights. It will be impractical to weave your way through trusses, and they are not generally strong enough to take much weight.

Trusses are cheap and will be made of the minimum sized timber that they can get away with. You will have a crane on site to lift them into position?

 

[jsstevenson]

I have been quoted a cost of £3000 for manufacture and delivery of the trusses - is that reasonable?

 

[jsstevenson]

JohnD - yes I will be organising crane to lift them! Also, roof space is to be the master bedroom!!!
Thanks for your reply.

 

[noseall]

i, without question prefer building the roof myself. i.e cut roof or traditional roof.

but for wall spans of over 5 metres roof trusses are the most practical, unless of course you have access to cheap steel and a mate who can drive a crane.

there is no practical room inside a truss roof unless they are purpose built. and because they are engineered to the limit, not very flexible where alterations are concerned.

 

[noseall]

i'm a b...i...t sss...llll...oo...ww t..o..n..i..g..h..t.

 

[JohnD]

h...e...e... h....e...e... !

 

[markie]

Make up as you go are better if you intend to venture up at anytime, but if not the other option would be fine or what ever is the cheapest.

 

[marksson]

Give me a cut roof everytime, nice sized timbers, alter it as you like (within reason), stick another rooflight in 10 years later without worrying about affecting windloading and so on.
Trusses are ok, for what they are (a skinny bit of engineered timber).
Plus they only ever give you the straight forward trusses, you then have to cut any additional timbers to form part of dormers, valleys etc anyway.
Costing complete roofs I have found there to be little difference apart from on larger jobs, heading towards commercial (of course this depends a lot on your chippie!).