roof truss

[magpie]

Recently applied to council for approval of carport, I designed it using trusses which will be held together by knuckle nail plates. Trusses are 3.2 metres long and 0.5 metres high. Surveyor is telling me that i cannot fabricate my own strusses and have to go to truss manufacturer. Even if a structural engineer has given a certificate of compliance. Brochure for knuckle nail plates says you dont need any special pressing equipment, all thats neeeded is a hammer. Can anyone tell me why we are not allowed to build our own trusses.

[OBBob]

If you can build a roof any of the old stick meathods I don't see why you can't make your own trusses!

However on a side note, you may find that it is a similar cost to ge the trusses prefabbed for you. Those companies get the materials very cheap and do teh job much quicker than you probably could. May be worth looking into?

[sol381]

If its only 3.2 m wide why dont you just pitch teh roof. Roof beam with rafters going into it. If you are set on trusses its pretty much impossible tomake your own. How do you plan on attatching the gangnail plates to the webbing and top/bottom plates. At teh truss plant they are doen with hydraulic presses, you cant just belt it with a hammer.
As obbob said though it woudl be just as easy to buy them ready made. To get 8 or so trusses at 3.2m will only cost a few hundred dollars. Save your time, its a lot more valuable than a few dollars.

[echnidna]

If you use coupled rafters with a collar tie on every pair of rafters you essentially have a truss type configuration without it being a truss. Its just coupled rafters.
Easy to make and fit.
Just drop a ridge beam in after your "claytons trusses" are up.

[ausdesign]

Magpie, if the structural engineer has certified the design of the 'trusses' the surveyor cannot refuse the application.
There must be more to it ??

[pawnhead]

Belt in knuckleplates aren't as strong as a factory pressed plate. I suppose the ones that you nail in with clouts would be if you put enough nails in it, but how much is it going to cost you to get an engineer to certify them? With coupled rafters you still have to worry about the ceiling. You'll save on ceiling joists with a 3.2 span. There's less timber in a trussed roof so I don't know why they don't make a standard so you could build your own just using tables. It would be handy if you just needed a few, and you were in a hurry, or you had nothing else on and were trying to keep busy.

edit: - When I did the Builder's Certificate twenty years ago they taught us how to design trusses but we weren't certified to do it so of course I've forgotten the whole lot now.

[attie]

Magpie, if the structural engineer has certified the design of the 'trusses' the surveyor cannot refuse the application.
There must be more to it ??

I agree Peter, but the surveyor is probably looking for a certified truss maker. Things like that irk me, especially when a competent person is held back by someone crossing T's and dotting I's

[ausdesign]

Building surveyors [rightly so ] cover their backsides for any construction method that is outside the 'timber framing code' by asking for computations.
Their aim is to pass the design not hinder it.
The word 'Truss' would immediately trigger a request for a manuf. specification & certification which would be supplied [as blanket specifications ] by a structural engineer working for the manuf.
In Magpies case an engineer would look at the 'holding specifications' as designed by a structural engineer for the knuckle plates & incorporate this into a 'truss' design that would be have to be accepted by council.
Building surveyors are only able to process designs that meet the BCA requirements - a part of which allows for alternate design methods which are certified by a suitably qualified person.
Over the years we have employed 'Structural Engineers' to meet these requirements & so far have have not had a Surveyor who has rejected a design.
Having said that I agree with echidna - this is not a big deal construction wise on the face of it & there are several construction alternatives that would readily meet the requirements of the BCA with cheaper construction methods.

[magpie]

Thanks for your help guys
I have abandoned the carport, since after having payed $470 council fee and a certified engineer (cert. of compl.) $$ for a new design not my original. Now the surveyor is requesting council to approve the length of wall on boundary, this includes my existing garage and new carport together. Council told me i have to get my neighbours consent gave me a form which i had to take to neighbour get it filled out and then return it and pay $150 (thank you very much were does it end), i told them where to go. Can I ask you guys one more question, if i erect a steel frame say 50x50x3.2 square hollow section members and then cover with mesh (fabric) does this require council approval.

[pawnhead]

It depends on the council. For example the Wattle Range Council wouldn't require approval so long as you follow these guidlines, but I don't know whether yours would or whether you'd be able to find the information on the net.

Just ring them and ask.

[SilentButDeadly]

Can I ask you guys one more question, if i erect a steel frame say 50x50x3.2 square hollow section members and then cover with mesh (fabric) does this require council approval.

Probably not. Especially if it doesn't have a closed in roof. Your council should have a copy of their summarised building code available to tell you what you can and can't build with council approval though.

That said though......50x50x3.2 is an awfully massive (and expensive) steel RHS profile for a carport roof...especially if you make a truss style frame. I just re-did an old carport into an outdoor thingy for wisteria to grow on. Made three trusses from 25x25x1.6 angle to span 3.5m - I can do chin-ups on the damn things so they are more than strong enough....

I used downloadable calculators from http://ca.geocities.com/xpf51/index.html to figure out the angles and design. Very helpful.