Metal roofing system

Saigo · Tue Oct 06, 2009 9:54 am

Since I am having to redesign my covered porch, I am at a point where it makes sense to go ahead and completely replace my roof. As I indicated in a previous post, it has two layers of asphalt shingles over 7/16 OSB, and the shingles are falling apart and the OSB is sagging between the trusses. I'm even getting a bit of water spotting on the ceiling now that rain is actually falling here again, so I guess I can't put it off any longer.

I'm thinking to replace the shingles with a metal roof. I've read the "inexpensive metal roof" writeup in the Mark Bower's manual, and I got some good information from that. I'm thinking to expand on it, though. Here is what I'm thinking:

1. Rip off the 7/16 OSB decking and replace it with 5/8" plywood. This should add a lot of strength without adding too much weight. Weight is the reason I'm not considering 3/4" plywood.

2. Put down 30# roofing felt.

3. Put down some kind of foil faced rigid foam insulating board (R-Max Thermaroof Plus or the equivalent) of 1" to 2" thickness.

4. Install standing seam metal roofing with a regular galvanized finish using self sealing screws.

Can those of you with roofing experience tell me if this approach will work? In particular, I'm wondering about the order of installing the layers--should the felt be under the foam, or over it? Also, should I pay the extra money for power coated roofing? One of the reasons I like the galvanized finish is the price, but I also like the fact that it rejects the most sun. Heat is the real problem around here, so I need a roof that is as reflective as possible.

Thanks.

Troy
Austin, TX

Harry · Mon Oct 12, 2009 11:17 am

Hi

I am not a roofer but I know a good one......in my area. He uses 2 layers of felt next to the plywood in your case. Then shingles or metal on top of that.

Moderator JD is the roofing wizard on this forum. Hoping he will respond.

Harry

Saigo · Mon Oct 12, 2009 11:26 am

Thanks for the reply. I hadn't thought of doubling up on the felt, but I can see that it might have benefits. All that's required around here is a single layer of 30# felt, but I'd be willing to add another layer if the budget will cover it, which it should.

And concerning the RMax, I'm kind of backing away from that anyway. I figure that a layer of it would make maybe $20 difference in my cooling bills for maybe 3 months each summer. If it costs $15 a sheet, and roughly 50 sheets would be required to cover my roof, it would take 12 years or so to recoup the $750 material cost.

Unless, of course, my utility goes all green and the cost of power goes through the roof as a result. If that happens--which is possible around here--it could pay for itself a lot faster.

Troy
Austin, TX

Yanita · Mon Oct 12, 2009 4:06 pm

Hi,

JD has alot of great post on roofing. Do a search with his name and you should come up with several and very detailed at that!

Yanita

JD · Mon Oct 12, 2009 8:03 pm

Generally, 2 layers of felt means that the layers are staggered 1/2 sheet. You can double up on the first on the first course be starting with an 18" strip (half width) of felt on the eave and then layering the rest of the felt overlapping 1/2 sheet. If you look on a bundle of shingles, you will see that the warranty requires two layers of felt. Whether it is 15# or 30#, it still needs to be two layers. This is also the way the lines on the felt is laid out.

You might want to consider covering the roof with Grace Ice & Water Shield or Owens Corning WeatherGuard instead of felt. Might be more expensive but will give you a better leak resistant roof.

I would rather use a white powder coated metal than galvanized. Even a standard baked enamel coating will do a good job for you. With most standing seam roof panels, there would only be fasteners showing at the eave edge of the roof if at all.

Some type of foam board would still be a good idea. It helps the metal move with expansion and contraction and helps to protect the metal from rust and wear. You can use 1/4" fanfold insulation for this and it is much cheaper.

JMO
JD

Jim from Canada · Tue Oct 13, 2009 7:31 am

If you are going as far as you are saying, I would recommend the Grace Ice/Water shield over the felt. It will actually seal around any fasteners through it, ensuring a watertight roof. I don't think I would add the foam though.

flcruising · Wed Oct 14, 2009 8:45 am

Hey Jim,
Grace Ice & Water is installed directly to the decking, not over the felt. If you use Grace, the felt is not necessary.

Saigo · Wed Oct 14, 2009 2:43 pm

Thank you, JD, for your detailed response. That is exactly what I was looking for, and I intend to follow your suggestions. The 1/4" fanfold insulation is a solution I hadn't heard of for use between the metal and felt, and that may be perfect for me. I haven't yet made up my mind concerning the Grace Ice & Water Shield or Owens Corning Weatherguard. Around here, heat and UV damage are far more serious concerns than water damage, as drought is far more likely than heavy rain, and we get ice on average maybe 2 or 3 times a year. I realize that using one of these products would be the optimum, but right now I'm trying to balance cost and benefit.

Troy
Austin, TX

JD · Wed Oct 14, 2009 8:34 pm

Hi Troy,

A lot will depend on what brand/type panels you choose to put on. Follow the manufacturers guidelines. If this is a standing seam panel that does not require 1x4 batt strips to attach the panels to, then the 1/4" foam would allow the panels to expand and contract easier and protect them from damage. If you need to use the 1x4 batts, the fanfold might not be of much help. I know that you don't want cold air-conditioned air to have easy access to the back of the metal panels when you are in a hot climate. Who ever sells your panels locally should have proven recommendations for an economic install.

I like the I&W shield type underlayment because it will self heal all the screws, nails, etc.. that penetrate the roof. I also live in a dry climate here in Fresno, CA. We will get a little over 11" a year of rain on the average. But we got over an inch yesterday alone! I know to rainy places that does not seem like much. But my phone is ringing off the hook with roof calls today. Anyways, this type of underlayment is still highly recommended here, especially on mobile home comp roofs. Something to think about.

PS, Today we have brilliant blue skies between the cloud puffs, beautiful fresh clean air, snow in the mountains and 80 degrees down here in the valley. Wooo hoooo!

JD

Jim from Canada · Thu Oct 15, 2009 6:00 am

flcruising wrote:Hey Jim,
Grace Ice & Water is installed directly to the decking, not over the felt. If you use Grace, the felt is not necessary.

That is correct, forgive my syntax. I meant I prefer it over the felt (as in instead of) not over top of the felt. There are pics in my photo album of my roof being done. Wherever the album went to???

flcruising · Thu Oct 15, 2009 8:44 am

Jim from Canada wrote:That is correct, forgive my syntax. I meant I prefer it over the felt (as in instead of) not over top of the felt. There are pics in my photo album of my roof being done. Wherever the album went to???

Now that makes sense. Thanks for the clarification.

Troy,

Using white metal (like JD mentioned) will greatly help by reflecting the solar heat and keeping your house cooler in the summer. That's something we have to contend with here in Florida too.