Tile roof, roof trusses

[cjalex]

We've had problems with the construction of our new home and just had an engineer inspect and go over the house plans. Our home has a Monier tile roof, and the roof trusses are 24" OC. The engineer says that the trusses should be 16" OC, but the architect says 24" is fine. How can I find out which one is correct? I have the spec sheet for the trusses if that helps.

[grumpydasmurf]

The engineer is paid to know these things. The architect is more of a "designer". Architects know rule of thumb and code. Engineers know math and physics. 24" may be acceptable by code but if an engineer told me 16" I would do 16".

Don't engineers usually design truss systems? Who designed this system?

[Rich]

Beyond what just the o.c. spacing is you will need to look at the plywood sheathing also. If the architect is calling for 24" maybe he's showing 3/4" and the engineer says 16" with 1/2" plywood.
Other than that - I agree with Grumpy .. the engineer prevails.

[cjalex]

Our home is 75% built and because of other problems, we had an engineer inspect it. We weren't even thinking that the roof was a problem but the engineer says it is. The architect's plans called for 24" OC with 1/2" plywood roof sheathing, but they were builder's plans and left a lot of the final decisions up to the builder. The builder is the one who ordered the trusses, but we don't yet know exactly who designed them, they probably gave the local truss company the house plans and let them design them. I was just wondering if there was a standard for concrete tile roofing. Thanks for the replies.

[Rich]

Currently the home I am building has trusses at 24" o.c. with some 35' spans. We will also have concrete tile or 3/4" slate on them. We have 3/4" plywood for ours though and a 12/12 pitch. Just to give you an idea. I would think around a 5 or 6/12 pitch with the same situation would require some pretty beefy trusses and sheathing.

[k54kenny]

Hi, first time in, here goes,
My problem (if there is one) sounds very much like cjalex's.
We had a house fire in Dec. and are just starting to re-build.
Existing roof was monier concrete tile on skip sheathing(no plywood) with a 4:12 pitch. The trusses were constructed with 2x6 top and bottom cords and spanned from the front of the house to the back (39.5 ft), 24"O.C., with flat ceilings throughout.
The replacement roof/trusses are going to be 6:12 in order to incorporate a vaulted ceiling to 12' in the center with a 9' flat ceiling in the kitchen. According to my contractor, the new trusses will be 2x4 top & bottom cord as designed by the engineer at the truss company. I've heard that the 2x6 cords may help increase strength but also add more weight to the overall structure. Also the new roof will have plywood sheathing, paper and replacement concrete tiles. The insurance is allowing for 1/2" plywood but after reading this thread I'm thinking that my naivety is glaring. Should I insist on 3/4"? What other kind of problems am I overlooking? (I am aware of the increase in drywall work, building up the interior walls[this question is for another area of the site],
electric & plumbing, and painting).
Thanks for your input,
-Kenny-

[Rich]

My personal opinion (not backed up by any structural analysis) is to use 5/8" minimum on any roof... and when using heavier than asphalt shingles is to use 3/4". The weight difference between asphalt shingles and concrete tile is pretty significant. I've walked on 1/2" sheathing that deflects 1/2" or more between trusses and that's with the clips installed. Doesn't give me a good feeling by any stretch of the imagination.

[k54kenny]

I talked with our truss engineer myself this morning and he said that 2x4 was adequate but that 2x6 on the top cord would be much stronger and deflect less, (and of course be about 20% more expensive.) The plan is for 5/8" sheathing.

[k54kenny]

*Etiquette Question*
I just realized that I jumped into cjalex's thread.
should I start a new one? This is my first time on a forum. Sorry.

[Rich]

Not a big deal - it's on topic at least :)
It might be easier though if you do start a new thread in the future. Easier to scroll down to see the names of the original poster.