Flat(ish) metal roof layers


#1

Looking at new construction and wanted to get some feedback on a simple square roof with a .5:12 pitch using a standing seam metal roof. There are a few manufacturers that provide products with that low of a pitch. The home will be in SE North Carolina along the coast, but not on the water.

Here are my layers
Sheathing (5/8 OSB + Carlisle WIP 300HT) OR Zip - looking at pricing
4" Foam panels (iso or eps)
Carlisle WIP 300HT
1" x 4" furring strips with gaps for air flow
Standing seam metal roof (the roof is 60’ in length so a few pieces are needed per run)

The 2nd layer of WIP 300HT may be overkill, but that was done on a blog by Matt Risinger and he says that is a best practice in Texas.

Thoughts on the layers - missing/better alternatives/overkill?

Thanks - Don


#2

When talking about metal, .5 /12 isn’t flatish…it’s flat. I would consider either a low slope membrane, or build the roof with more pitch. Someone may claim there metal will work, but will they still be in business after the first 5 or 10 years of your “50 year or lifetime” warranty to stand behind it?

If a customer wanted us to install something like that we would walk away.


#3

You raise a very good point (I used the “ish” because it wasn’t .25, but yes, it is flat).

Most reading I have done suggest 3:12 as the minimum, but what if you went to 1:12 with a standing seam product (where they claim it is good at .25:12 and .5:12) - is that a roof that would make sense?

Thanks again - Don


#4

We have done 1:12 double locked copper real standing standing, back sealing the locks, and soldering everything that wasn’t double locked, but would never try it with steel.


#5

Ok - thank you for the information…it gives me pause as I investigate claims of products vs real world application. You have been most helpful.