GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Metal roof & underlayment (AquaGuard – DryTech)

jackofalltrades777 | Posted in General Questions on

Curious to see if anyone has used or seen the product called “AquaGuard Dry-Tech”?

It’s designed to allow airflow underneath a metal roof to drain any condensation that can form under the metal roof and it also provides an acoustical reduction in metal roof noise.

The bottom of the underlayment is NOT breathable/non-permeable and this attaches via peel & stick to the roof sheathing (OSB SIPs).

I am planning to possibly use this product on a 8″ closed-cell OSB SIP roof with a standing seam metal roof on-top. The advantage is that any water that might get past the metal roof will drain/evaporate and the peel & stick membrane will provide a waterproof and air barrier to protect the OSB skin of the SIP.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    I'm not sure if this product makes sense.

    In theory, there are three ways that moisture can reach the roof sheathing or the underside of the metal roofing:
    1. A roof leak.
    2. Condensation of moisture in humid outdoor air that encounters cold roofing.
    3. Accumulation of moisture in the sheathing due to migration of moisture from the interior to the cold roof sheathing.

    If phenomenon #3 occurs, this product doesn't allow any outward drying -- so the product can't help. The sheathing will still stay wet and rot.

    Concerning phenomenon #2 -- this product might make the problem worse, by providing a path for humid exterior air to reach the cold roofing.

    I don't understand whether the manufacturer of this product anticipates that there will be enough ventilation drying to help. Will there be air intake areas near the eaves, and air outlets near the ridge?

  2. jackofalltrades777 | | #2


    With scenario #3 I will do a triple belt and suspender and belt approach to prevent this from happening. I will use a tongue and groove SIP connection with a gasket design and then I will tape the bottom side the SIP joint seams.

    I was told that this product is similar to installing purlins but easier and more cost effective. They said that the product was designed in Europe and is commonly used there.

    So you think this product is not a good choice for my build-up?

  3. fitchplate | | #3

    I doubt its "commonly used" anywhere. Or if it is, they have framing decay and insulation wetting problems. I like the idea of the stand-off feature to enable airflow and condensation pathway to get water to the gutters; but making the deck impermeable is a problem.

    Maybe it can work for a commercial application with 24/7 air-conditioning and dehumidification ... a real energy hog situation.

  4. jackofalltrades777 | | #4


    Actually in Europe there are many products that are "common" there but "uncommon" here in the States. They have big box stores that sell triple pane windows and green building products that are not found anywhere here in the USA. We are 15 years behind the curve to places like Germany in terms of products that are widely available.

    Why would they have framing decay with this product? It's identical to peel & stick products like GRACE and others. The major difference is that it provides a drying/air channel between the metal roof and roof sheathing.

    A closed cell SIP is already impermeable as it cannot dry to the inside and it cannot dry to the outside if a metal roof is attached to it. So the SIP deck is always impermeable (both ways) when you install a roof on it.

    Why would you have to dehumidify the roof deck 24/7? If no air infiltration is getting through the interior due to proper SIP joint sealing. No condensation/water vapor can travel through 6" of closed cell polyurethane.

  5. Expert Member

    Peter, Have you seen a finished installation using the material? Do the panels still lie relatively flat? My concern would be that the underpayment will have to be compressed by the panel screws under the standing seams but then would bow up where there are no fasteners. Maybe the bow is so small as to be unnoticeable.

  6. mtr7982 | | #6

    I would still say 1x4's purlins over your roof sheathing would do a better job, with ice/water shield over the sheathing of course. A metal roof has such a long life span that I wouldn't change what we already know works. Just my thoughts

  7. user-1041981 | | #7

    I just used a sister product "RoofAquaGuard BREA" under my metal roof.

    As you can see in the picture, the metal shingles have been installed on the main roof, but the standing seam hasn't been installed over the porch so it isn't damaged by ladders, etc.

    If you want what I think is the ideal underlayment for a metal roof, see:
    which you can buy here:
    It costs more, but boy does it seem perfect.

  8. user-1041981 | | #8

    The metal roofers in my area wouldn't work with purlins, and ice/water shield over all sheathing wasn't good since I've got a conditioned attic and can't dry inward.

  9. mtr7982 | | #9

    where are you located

  10. fitchplate | | #10

    Peter ... are we back to this again? Lets agree to disagree: I am against making a roof deck impermeable for the reason I said above; while you have no issue with it. I think peel and stick, such as Grace or this current product is a bad idea, whereas you like it. So I think we agree that AquaGuard has at least one good feature: allows the metal roof (underside) condensation to drain off. And may be a much better and easier to install substructure than purlins, particularly on 24 ga and lighter metal roofs.

    I would use a low perm deck bulk water barrier; you would approve or recommend an impermeable bulk water barrier. So with that point of view, the AquaGurad has 2 good features.

    My bet is that the use of this and other non-perm coatings on roofs will pan out to be a lawyers class action litigation dream in the next decade as these materials cause deck failure; at lease in the cathedral ceiling and insulated rafter bays envelope system. Whereas non-perm coatings on non-conditioned attic space probably make little difference.

  11. fitchplate | | #11

    C.B ... that DELTA®-TRELA looks like the best features yet. Allows the deck to dry to the outside (i.e permeable), even and solid sub-structure to protect metal (i.e walk on it, snow loads,etc), stops oil-canning, simple to apply, no horizontal drainage barrier (i.e unlike purlins), great drainage plane for underside metal condensation.

    Wish it was around when I did my roofs. And great for SIPs , too, if moist interior air gets past the seams. Which is more likely to do than not.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |