1-way vents for membrane over damp foam?

I have a flat-roof building with 20+ year-old sprayed polyurethane foam + elastomer membrane with some deteriorated areas and bird-pecked holes. I was waiting for summer weather to dry out the areas under the broken membrane before patching (with Metacrylics elastomer and their recommended fabric), but summer weather only lasted a week or two this year and now we are into rain. I don’t think I have any leaks or seriously saturated foam, but there is definitely moisture under the membrane locally around the breaks in the membrane.

I don’t want cause or propagate delamination by patching over the damp membrane without providing for escape of moisture and relief of pressure on warm days. I understand there are 1-way vents that can be patched into the membrane over damp areas with valves (presumably rubber flaps) that will allow moist air to escape under negligible pressure but prevent air or water from getting back in under the membrane. I believe they “pump” moisture out by the diurnal thermal cycling.

Am I correct in my understanding of their function and value and, if so, who makes them and where can I find them? Any recommendations appreciated.

One way vents are available from most distributors. Plastic and spun aluminum. If you have moisture in your roofing system under the foam, don’t hold your breath waiting for one way vents to “pump” out the moisture. You may achieve some dryness directly under the vent, but not likely to help you for the whole roofing system. Also consider the possibility that you may be causing more problems by putting a hole in the system and then trying to patch in the vent.

Thanks for your thoughts, donl. I’m not concerned about the potential problems of poking holes in the membrane to install the vents because the holes (birdpecks and a few tears) are already there, open to the great outdoors. It’s a matter of how to deal with them now in the rainy season without causing greater problems with my fix.

As far as I know, I don’t have serious moisture under the foam - just in the foam in the immediate vicinity of the holes. As far as I can tell the foam is still somewhat - but not perfectly - resistant to water penetration.

Do you recall any specific product names I can search for or ask for? The clerk at the nearby roofing supply did not know what I was asking for. The only item I found by Googling was the spun aluminum Dow VRS Vent which looks like vast overkill for my situation at height and base diameter of 1 foot. I was hoping to find a moderate cost item a few inches in height and diameter.


I deal with problems like these all the time. SPF foam is virtually waterproof and will not allow water to travel interstitially through it. If there is a leak in a foam roof it is typically isolated exactly where the hole, crack, peck, or any void is. With having a BUR asphalt roof as a base, is a good thing. Unless water has permeated the BUR under the foam, then water can travel through the layers and damage is progressive in nature. Best shot is to wait for dry weather (48 to 72 hours minimum sunlight) and prepare all the voids. This may mean cutting out some of the foam to help dry out the affected areas. The voids can be filled in fairly inexpensive with a polyurethane caulking (sikaflex, or Vulkem), or for large holes the void can be sealed with a polyurethane self leveling poured material then coated with an elastomeric coating. SPF manufacturer’s used to make and sell repair kits and A and B two part fillers for large holes. You could always fill the void with polystyrene and then use the polyurethane caulking over that to get you through to a proper foam repair and re-coat project.

Thanks for the suggestions, roofimprovement. Do you have any experience with the very low modulus silicone sealants like Dow 752 or GE “LM” of which I have a lot left over from a concrete porch sealing task? (I think those are the designations. I’m not near the stuff right now.) They have very low durometers of 25 Shore A. I think both the silicone and the urethane sealants demand dry substrates.

Any experience with the membrane vents?


Yes, the sealants you mention will not work correctly with the SPF roof membrane. Many people try to use other sealants because they might work at the time of application. But silicone and others like will not perform and will shrink and delaminate from SPF. Asphalt roof cement will melt the foam. You need to use a polyurethane sealant, and yes, to use these sealants the surface must be dry and prepped (cleaned) first. A good application of polyurethane sealant protected from the UV can last up to seven (7) years. Silicone will last weeks.

In regards to the vents, any moneys spent to install vents into the SPF will not extend the service life of the membrane. Vents may limit the rate of failure to the rest of the membrane, but will likely do nothing for the areas already infiltrated with water or water vapor. It would be most cost effective to cut open the affected areas, dry, and fill them with a sustainable material. Once foam is lifted, it will not go back down if vents are installed.

Thanks for sharing your experience, roofimprovement. I appreciate your comments on the sealants and the vents.

I’ll go with the polyurethane sealants. A foam applicator who did some maintenance for me years ago also recommended them at that time. I presume the Sikaflex 1a low modulus sealant would be satisfactory.