The Damaging Effects of UV on Air and Moisture Membranes Left Exposed During Construction
Air and moisture membranes are as much a part of modern building construction as doors and windows. These membranes are wrapped around the building within the wall structure, and they’re meant to help prevent mold, mildew, and other unwanted conditions that can damage the structure and lead to health problems for those who use it. However if these membranes are left exposed to UV light (which they often are for more than 90 days) then you might be putting armor with rusty spots onto a structure.
Damaging Effects of UV on Air and Moisture Membranes Left Exposed During Construction
Anyone who’s ever used a windshield screen to keep a car’s interior out of direct sunlight has seen the damaging effects of UV light. A moisture membrane is no different. If left exposed to UV light, the ultraviolet waves will bleach the material, and begin to break it down. No membrane, whether liquid applied or sheet material, is immune to UV damage. Hence, when exposed to UV rays for extended periods of time they all lose water penetration resistance, tensile strength, and elongation.
A damaged membrane is like body armor with weak spots; some places are protected and others aren’t. The problem is that when it comes to air and moisture, nature isn’t firing a single bullet that you can stop. It’s more like a machine gun shooting at a structure from every angle. If there’s a weak spot, or a hole, then air and moisture will find it and wriggle inside. Once that happens it doesn’t matter that the rest of the structure was adequately defended.
That’s why UV exposure has to be taken into account when it comes to moisture and air membranes. Some companies will claim that their membrane can be left exposed for up to 180 days. Just like a sunburn, every extra day of exposure is damaging the membrane.
You specify a membrane based on its performance specifications. Those specifications are based how the membrane performs prior to any UV exposure. You must realize however, that there are no standard ASTM tests to appropriately evaluate and describe the long-term durability of such membranes. Therefore, the exposure time and amount of exposure differs with each manufacturer. These inconsistencies are a reminder that regardless of what the manufacturer claims, every day that a membrane is not covered and left exposed damages the membrane and shortens its life.
If you expect the membrane to last as long as the cladding, cover it as soon as possible.
While the damage done might not be as visible as rips and tears caused by high winds or storms, UV damage can be just as disastrous over the life of a building.
There are very few products on the market that have been specifically designed for permanent UV exposure. DELTA-FASSADE S, a water-resistive barrier is treated with a UV resistant coating to protect the membrane itself. It is it particularly suitable for use in open joint cladding systems.