Trusses Question

[gg23]

hi,
Have been looking at our costs for trusses for our extension. I have come across a supplier who sells the trusses for half price as they come from botched jobs. He tells me that to use trusses that are slightly (ie 200-300mm) oversize in the span is not an issue if they are properly braced. Will this pass an inspection? Does the truss supplier need to provide a compliance cert?

Thanks
Greg

[Tommy]

These will be ok.The truss company should supply engineering details for them as the building inspector will definately want to see them.

[gg23]

These will be ok.The truss company should supply engineering details for them as the building inspector will definately want to see them.

hi tommy,
not sure if this mob will supply engineering drawings as they collect trusses from botched jobs and resell them at half price. So from what you are saying slightly oversized is ok?
re the compliance certificate, I gather this is not needed.

greg

[joe greiner]

If the trusses come from their own botched jobs, they should have engineering documents available. Having established whether or not documents are available, ask the building inspector what he/she needs to see before you buy or set your final budget. Unusable trusses will be a waste of your time and money. I see no basis for your interpretation that a compliance certificate is not needed. Oversized alone is not sufficient.

Joe

[Tommy]

More often these days inspectors want to see engineering details or extracts from standards that cover the job you are doing..It is to cover the inspector back as well as your own ,Details include spacings and bracing details which simplifies the inspectors job when inspection time comes around.

The place you are buying them from should be able to provide these for you.Today trusses are often designed by computer programs and take things into consideration as wind rating, load rating, truss spacings, grade of timber and the list goes on.


Trusses designed for one job can be different for another even though the trusses are the same length .This is why details are often asked for .Our council asks to see them at the time of building application.Although they will process applications if you tell them they are on there way.This may or may not be the case where you are so it wouldnt hurt to talk to an inspector and get there opinion. Hope this helps.

[gg23]

If the trusses come from their own botched jobs, they should have engineering documents available.

Ill check with the supplier.But I recall him saying something about comps not provided. IS this the same thing?

Having established whether or not documents are available, ask the building inspector what he/she needs to see before you buy or set your final budget. Unusable trusses will be a waste of your time and money.

I will contact the inspector

I see no basis for your interpretation that a compliance certificate is not needed. Oversized alone is not sufficient.

I am new to all of this so I am just going by the info that was provided in a previous post. So you are saying that comp cert IS required?

Thanks
Greg

[gg23]

More often these days inspectors want to see engineering details or extracts from standards that cover the job you are doing..It is to cover the inspector back as well as your own ,Details include spacings and bracing details which simplifies the inspectors job when inspection time comes around.

The place you are buying them from should be able to provide these for you.Today trusses are often designed by computer programs and take things into consideration as wind rating, load rating, truss spacings, grade of timber and the list goes on.


Trusses designed for one job can be different for another even though the trusses are the same length .This is why details are often asked for .Our council asks to see them at the time of building application.Although they will process applications if you tell them they are on there way.This may or may not be the case where you are so it wouldnt hurt to talk to an inspector and get there opinion. Hope this helps.

Thanks Tommy, will speak with the inspector to see what is required here.
greg

[joe greiner]

With a distance of about 8000 miles (straight through), or about 12000 miles on surface, as well as separate jurisdictions, we may have a slight difference in terminolgy. Upover here, engineering documents would consist of calculations (may be just computer output) and a certificate of compliance signed and sealed by the engineer. Your local building inspector can enlighten you much much better than I can, about his/her requirements.

Joe

[thebuildingsurv]

I would suggest your building inspector will not accept these trusses unless the come with site specific truss comps done by the supplier or an independant engineers certification. Only time these trusses would be of any use if you were doing shifties without a building permit.

[silentC]

Hmmm, I always thought that the bottom chord of the truss had to finish flush with the supporting beam with no overhang. I suppose if there was an overhang, you would need bracing between the bottom chord and the rafter above the beam, but then you would be altering the properties of the truss and that would void the engineering documentation, wouldn't it?

Sounds dodgy to me. Is it worth it to save the money?

[Tommy]

Not always silent..Trusses can overhang to keep the same roof line and the walls underneath return for a verandah for example.There will be extra webs installed and the trusses will counterleaver so to speak..One job we had the trusses were ordered to the out side of brick measurement instead of frame measurement which meant the trusses overhang 150mm each side .We had the truss mob come out (before we installed them) and they gave us the go ahead to use them ,with a 90 x 90 installed tight between the bottom and top cord.I suppose what Im trying to say is they may be able to be alright but I would still want some form of confimation in writing.

cheers

[joe greiner]

Hmmm, I always thought that the bottom chord of the truss had to finish flush with the supporting beam with no overhang. I suppose if there was an overhang, you would need bracing between the bottom chord and the rafter above the beam, but then you would be altering the properties of the truss and that would void the engineering documentation, wouldn't it?

For the amount of overhang Greg is proposing, a wedge between the lower chord and the rafter and some extra gusset material should satisfy bearing requirements and also reduce buckling length of the rafters. Trusses are (or were) usually designed as if all pinned connections, even though the connections have some moment resistance due to the large gusset or nail-plate region. Still need a confirmation from the engineer, though.

Joe

[silentC]

Understand. It's just that if you make changes to the truss as delivered, it is no longer covered by the engineering design under which it was built. It might be stronger but because it has changed, the inspector (if he's on the ball) will knock it back because it's not being used in the situation for which it was designed. A bog standard truss, as far as I know, has to bear on the top of the top plate or beam exactly at the point that the rafter intersects.

Having been through this a couple of times, I know you are relying completely on the roof plan and the certification printed out by the truss mob's software. If you're changing it, or don't have that documentation to begin with, I believe it would require certification from an engineer. I just wonder if it's worth all the effort to save couple of grand. Maybe it is, but it's something to consider. I don't think it is a straight forward thing is all I'm saying. I would personally run a mile...

[ausdesign]

They definitely won't be accepted without comp's & site specific details.