Underlayment for Aluminum Standing Seam in Hurricane Zone

Charles Gordon
7/29/2014
I am getting ready to install an Aluminum Standing Seam Roof =/- 80 squares on new home located on South Texas coastal island; Roofer sent bid on .032 Aluminum; 20" panels with Titanium underlayment; clips 16 on center. Neighbor recently installed .040 Aluminum Standing Seam roof but used a peel and stick 60mm product that contains a Tar/Asphalt material that binds not only to the plywood roof sheating but also at 93 degrees it melt and binds to the aluminum roof panels. He says that the adhesive nature of the Tar/asphalt underlayment provides protection over 200 mph with clips every 12 inches OC. 1) Do you recommend an underlayment like my neighbor or does the binding to the aluminum panel cause problems. If you recommend such underlayment, what types or brands? 2) My house is foam insulated to provide a closed inside system. Does the non-breathing underlayment cause problems/mold under metal panels? If so, what underlayment will solve that problem? 3) I read that underlayment that helps with footing sometimes has "grit" that causes the metal panels to corrode because of expansion and movement of the panels. What do you recommend? 4) what general advise can you offer?
Todd Miller
Classic Products, Inc.
7/30/2014
Thanks for your questions. I personally have never heard of an underlayment that intentionally gets "stuck" to the back side of the metal in hopes of increased wind resistance. Normally, this is something we avoid, sometimes even using a slip sheet between the underlayment and the roofing. If your home / building panels / insulation have been properly sealed so as to prevent moisture migration form inside the home to the roof decking, then a non breathable underlayment will not cause problems. The gritty underlayments are not something I recommend with metal standing seam roofs. They are probably less risky with aluminum than steel but I still do not recommend them. I have a metal roofing educational website at www.asktoddmiller.com which may have some things of interest to you.
Charles Gordon
7/30/2014
Thanks. Are you able to give me names of any premium brands/models of peel and stick underlayment products that you can recommend for use along the coast in a hurricane zone that do not have abrasive surface and are synthetic so as to not foster mold growth?
Todd Miller
Classic Products, Inc.
7/30/2014
RoofAuquaGuard MT is the one my company sells but there are many others as well.
Guest User
7/30/2014
In addition to Todd's comment, make sure you use a high temperature underlayment. In high wind zone areas, you will need to increase the number of clips and fasteners needed around the perimeter of the roof. In some cases this can be as close as 6", consult with the panel manufacturer and the testing lab that test the panel. Also, if you are building close to the shore do not use a hemmed edge on the drip edge (even aluminum) as corrosion will occur in the hem due to condensation coupled with the salty environment. thanks for selecting an aluminum roof on an island.
Charles Gordon
7/30/2014
Todd - Thanks for your good input. What are the differences between your MT product and your MT-HT product? Which is better for my application and will hold up better as a hurricane protection if the metal roof fails? Is there much cost difference between the two? You can see my application above. The house is on a barrier island on the bay side of the island in a hurricane zone. I am thinking of using it under .032 Aluminum standing seam roof. The house is a closed system, sealed with foam insulation. Will your product cause any problems due to it further sealing the wood sheathing? The roof is mostly a 12/9 pitch with some 12/4 pitch. Dick - Thanks for your help also. What is a hemmed edge on the drip edge? Is that where they mechanically crimp the aluminum on the bottom of the drip edge to turn it under? The specs for the roof call for the clips and fastners to be 6" OC on the edges and 16" on the rest of it. If I move it to 12" OC on the rest of the roof, will that be good or should I request it to go to 9" OC? How much more protection does every inch closer give you? Also, I have seen some metal roof specs in Miami Dade that require them to use Liquid Nail on the top of the clip/fastener so it glued the top panel to the clip. Is that advisable?
Charles Gordon
7/31/2014
I noted that I made a mistake on the pitches in my last Reply. The roof is mostly 9/12 pitch (not 12/9) and some of the roof is 4/12 pitch (not 12/4).
Todd Miller
Classic Products, Inc.
7/31/2014
The MT-HT product is thicker than the MT product. Something like 60 mil compared to 50, Other than that, the products are very similar. Both are going to offer similar weather tightness. Ultimately the thicker product will offer a little greater protection. I do not feel that a self adhering product will pose any problems on your construction. Yes, Dick is referring to a situation where the lower edge of the standing seam panels has been field-formed to lock over the starter. I am not familiar with the Liquid Nail thing ... I would not do anything unless it is called for by the manufacturer. The closer clips will be helpful but I feel that, with a good panel, closer than 12" is not necessary. I hope this helps.

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