Standing Seam Metal over 3-tab?? - Contractor Talk - Professional Construction and Remodeling Forum

EcoWise inc. · 03-16-2007, 09:05 AM

We have a special situation where a tear-off could be quite detrimental to delicate landscaping. The owner is worried (as are we).

We use 24 gage steel, Standing Seam, in a 17" wide panel, it is strong & tough. I do not believe that irregularities could telegraph thru the panel surface.
The house is less than 20 years old & has a single layer of low-end fiberglass 3-tab.

Does anyone have experience with covering asphalt shingles?
I am pondering something like fan-fold foam, dense enough to support our snow loads or a Fiber board product.

I have seen some products at the International Roofing show in Vegas where the fiber board or foam has a built-in synthetic underlayment. Has anyone used these products? Good?? Bad??

Dan Merrill
EcoWise inc.

roofwiz74 · 03-16-2007, 03:14 PM

whenever I go over a asphalt shingle roof with metal I lathe it out with 1x.

Same Old · 03-16-2007, 03:18 PM

What about a 1/2 extruded polystyrene sheet? That should be strong enough and add a little insulation to boot!

tinner666 · 03-16-2007, 04:54 PM

We lathe them out with 2x4's. Usually cut a slot near the eave for venting, same at ridge. 10" gaps between ends of lathes. Even 24GA 16" wide shows the lathe. Not too badly though if 12" OC.

red_cedar · 03-16-2007, 07:52 PM

edited our reply.

roofwiz74 · 03-16-2007, 11:55 PM

Quote:

Originally Posted by Same Old

What about a 1/2 extruded polystyrene sheet? That should be strong enough and add a little insulation to boot!

why would you do that?so the shingle roof would rot faster.I would want it vented to help moisture get out.

roofwiz74 · 03-16-2007, 11:56 PM

Quote:

Originally Posted by tinner666

We lathe them out with 2x4's. Usually cut a slot near the eave for venting, same at ridge. 10" gaps between ends of lathes. Even 24GA 16" wide shows the lathe. Not too badly though if 12" OC.

you gotta be kidding?who's metal system are you installing?

AaronB. · 03-17-2007, 05:19 AM

Whats wrong with that process? There was successful metal roofing before there were mfg warranties, dude. I think Tinner makes his own copper roofing.

**joasis** · 03-17-2007, 05:56 AM

We lay metal panels (26 gauge) right on the shingles....no problems....providing the shingles are laying flat. I would probably use the 1X's for the SSR.

roofwiz74 · 03-17-2007, 07:58 AM

i meant about the 2x4's

Same Old · 03-17-2007, 09:16 AM

Quote:

Originally Posted by roofwiz74

why would you do that?so the shingle roof would rot faster.I would want it vented to help moisture get out.

it was just a thought. But I don't see how the polystyrene would trap moisture? He said it is a 20 year old house. The attic must be ventilated, where is all this rot causing moisture going to come from?

roofwiz74 · 03-18-2007, 08:25 AM

the metal,there's going to be some condesation from time to time.
the attic will be vented but what about the space inbetween the roof and the metal?
never put metal right on the shingles anyway,those old shingles are going to do a number on the protective paint.

tinner666 · 03-18-2007, 09:13 AM

2x4's give the minimum 1 1/2" breathing space required to keep the panel from sweating too badly, if at all. I used 24 Ga, standing seam metal panels at times. Usually by MBCI.
Putting the panels, which will always be moving at they expand and contract, directly on top of '40 grit' shingles is a bad idea. While doing it, you might go on and give the customer an estimate on the re-roof, at the price you figure you can do it at, in 10 years or so. Save you an estimating trip at a later date.

Same Old · 03-18-2007, 09:27 AM

The moisture comes from the metal?

I just don't see a trapped water issue here. You can only get condensation if there's water vapor behind the panel, where would it come from? The house has a vapor barrier, the attic is ventilated. This sounds like it would be a pretty dry location in the building to me.

tinner666 · 03-18-2007, 09:34 AM

At least you're sure that no moisture gets into the area from the house. I never am. I just continue following old specs originally required by Follansbee. My head is deep in the mud.

red_cedar · 03-18-2007, 09:43 AM

Metal condensates all the time. It comes from the moisture in the air or in some cases if precaution was not taken, from the inside.
If one puts an underlayment / slip sheet. over the substrate ( asphalt ) then abrasion factor will not be a problem with expansion and contraction.
I believe there are several ways to address the post. a wood batten system, a metal batten system, solid type of backing.
Either one of these have advantages and disadvantages.

Determine the end users needs., budget in order to help them
It was never said if the roof was walkable or not, could be a factor in how to best help.

Same Old · 03-18-2007, 09:46 AM

Quote:

Originally Posted by Same Old

The moisture comes from the metal?

I just don't see a trapped water issue here. You can only get condensation if there's water vapor behind the panel, where would it come from? The house has a vapor barrier, the attic is ventilated. This sounds like it would be a pretty dry location in the building to me.

...

AaronB. · 03-18-2007, 10:44 AM

Only a 100% seamless impermeable airstop can act as a vapor barrier. Most homes I see have Visqueen, which is, at best, a vapor retarder.

Evo Roofer · 03-24-2007, 10:07 AM

We never put metal directly on shinles. We use Aire Foil or Retro eaves depending on whether homeowner wants added insulation. 1/2 or 3/4 polystyrene sheets also not a bad idea.

dennis · 03-24-2007, 09:28 PM

I think you're better off carefully removing the existing roof than having to worry about condenstation,battens,insulation,grit,telegraphing ,etc.
And you would get a better roof.