Roof questions

Mudball · April 01, 2006, 08:00:51 AM

We hope to get a roof up on our house this summer some time. I was wondering what general questions one might ask the roof contractor. We know we are going with a 6/12 pitch and its just a straight gabled roof. Also going with metal roof. I thought some of you might know some questions I need to ask the roof builder when getting quotes. Like how far do you space the trusses for the metal roof...any suggestions on good general questions ?

John Raabe · April 01, 2006, 09:46:22 AM

Your roof structure will be determined by the construction drawings not the roofer. The roofer will put the materials down on the basic roof structure - rafters, trusses, sheathing and/or skip sheathing. In most cases the rafters or trusses will be 24" o/c.

Your choice of roofing material and the roof slope will affect such things as sheathing, venting and underlayment (tar paper, etc.) so you will want to have the roofer help you with these choices.

April 02, 2006, 11:44:59 AM

Thanks John Raabe.
There are no blueprint drawings. I just thought of another question to ask and that would be the thickness of the decking. Is 1/2" too thin or would you go with 3/4" for a metal roof ?
Any other questions that I need to ask some different builders on roof questions would be great.
Thanks

JRR · April 02, 2006, 02:12:50 PM

http://www.unioncorrugating.com/pages/installation.html

Amanda_931 · April 02, 2006, 07:03:36 PM

Aha! The guys who sold me the roofing for the barn insisted that the screws needed to be right against the purlins. (as opposed to the nails into bottlecaps through the high stuff that I saw in Mexico) The guy who put it on did it, but thought I had heard wrong.

Here the corrugated roofing is nailed into the high point, screwed into the low.

April 04, 2006, 07:03:16 PM

Great link JRR.
Great tip Amanda_931.
Thank you both for the help.
Glad to see you still here Amanda

I hope to get this roof on sometime this year

jonsey/downunder · April 04, 2006, 10:05:01 PM

That's interesting, I've not seen that before. Down this end corrugated iron is fixed through the ridge with nails or screws. When used as siding it can be fixed through the valley. Although I note they seem to be referring to the larger corrugation type

glenn kangiser · April 04, 2006, 10:19:28 PM

Seems it is because the screws are a positive connection and don't work out easily. When I was a steel building dealer the factory rep mentioned that nails would work out from freezing etc. On the high rib they have a bit of spring under them and will stay tight better - moisture under them on a low rib will push them out if it freezes due to jacking action against the solid member under the nail head as the water expands when it freezes.

jonsey/downunder · April 04, 2006, 10:39:46 PM

I was thinking more of the potential for leaks. The valley is the natural water channel so any damage to the washer could be a problem in that area. The roof fixing screws we use down here have a two-part thread with a small portion of bare shank between. The idea is that the top thread pulls the iron snug to the washer. The screws used in cyclone areas also have a large metal washer that is designed to spread the load over a bigger area

April 04, 2006, 10:51:20 PM

Just about all of the Iron I fasten in the low rib is to steel frame and is the wider flats - not the corrugated - We use TEK screws like you do, Jonesy with neoprene seals.

jonsey/downunder · April 04, 2006, 11:10:06 PM

There is quite a difference in the roofing systems between there and here. We don't use sheathing like you and the corrugated iron down here seems to be a lot thinner than yours. The zinlalume on my roof is 0.42mm thick with 3 fasteners mid span and 5 on the ends. This stuff comes in a range of colours (powder coated). When working on the roof you need to take care where you walk or it will crease.

glenn kangiser · April 04, 2006, 11:16:59 PM

That is just a very little bit thinner than our 29 gauge sheeting which is usually the thinnest we see. Many times it is a stronger gauge of steel when it is that thin.

JRR · April 05, 2006, 05:25:48 AM

I'm beginning a roof using 26ga corrugated. 24ga was available ... wish I had ordered that. In the low-slope areas (porches, etc), the gap between purlins is barely over 13".

No sheathing. But there are diagonal braces running underneath, and attached to, the purlins. Hopefully these braces will provide some "anti-rack".

The corrugated valleys will be attached bottomside to the purlins using poly roofing sealant. There will be generous daubs applied to the steel before it is flipped over into place. Screws, with neoprene washers, will be used top-side only on the ridges.

glenn kangiser · April 05, 2006, 11:41:35 AM

I don't think you will have any racking problem once you get all the screws in place. 26 gauge is what we use on most steel buildings. They are braced with about 3/8 cable braces but their major (or most useful) function is to square the red iron.

While not factored into the calcs, I'm sure if you figured all of the brace strength created by the diaphragm from screw to screw it should be a pretty good amount. It seems this may be less on corrugated due to more ribs capable of flexing but I don't know for sure.