Roof truss matching

[23vc]

Hi
Trying to specify exact dimensions for my new roof trusses, and having fun and games with it so looking for any tips. Basically I took the 5 measurements requested by the truss manufacturer for the existing roof that I have to match (only matching the back as the front is stepped down) but I wasnt too confident that I could get these bang on because I had to crawl around in the loft and I don't think the existing roof is that consistent. So I mocked up a full truss to the dimensions of the calculated "match existing roof" truss and sure enough it was out by about 1.5 degrees which made a significant difference. So I corrected it and offered it up again and it seems good. I've been pretty thorough about checking the measurements of my mock up so planning on using that to spec the new trusses.
Anyway sorry for the ramble, but I've concluded that the only way for me to get a confident idea was to mock up a truss and try it. If anyone thinks thats a silly idea then any advice appreciated.
On a related note, I guess if you're trying to match an existing roofline with new trusses, then there's very little scope for correction if it's not absolutely spot on, I guess at a push you could double up battens/use deeper battens where needed or is that a complete no no?

 

[John D v2.0]

If you're about to spend a lot on trusses, it seems very sensible to mock up!
If it's slightly out you could always counter batten it with firrings, ie those tapered treated battens. You might need some blocking/noggings if they're too deep therefore unstable but it doesn't seem likely I'd imagine someone else will be along to advise better than me.

 

[23vc]

Pic attached for anyone who's interested, this is after I corrected the pitch

 

[Ian H]

I have no idea but noticed on the photo that the top piece of wood is bent. Could that effect yours measurements?

I'd do it with the same size wood that your truss'sss will be made of.

 

[23vc]

It does sag a bit yeah, but I'm pretty confident in the top and bottom position and the angle.
Re. Size of wood, didn't fancy the weight of anything more than 2x2 for this, but made sure the seat depth and top of rafter was the same as it's supposed to be on the real thing.
Anyway still hopelessly confused by it as pitch of barge boards seems about 2 degrees different to pitch of rafters measured within the loft, so the mystery continues.
All I know is I'm not ordering the trusses until I've figured it all out
Also the front and back pitch of existing house is different by enough to make a difference, which doesn't help