Amid the push to make commercial buildings more earth-friendly, one necessary fix is sometimes overlooked – cutting down on hidden heat leaks by adding a durable air barrier to a low slope roof. Up to 40% of a building's energy costs for heating and cooling are wasted by uncontrolled air leakage, which also contributes to condensation, ice damming, poor indoor air quality, and mold, according to the DOE. Air barrier technology is fast, effective and very affordable. This spray test was done to see the viability using the portable spray sealants machine called the Spray Pod 1.0 to apply the patented AireBarrier Black, to see if an effective roof air barrier could be achieved. This was a great way for fixing tar roofs.
Unlike a vapor retarder, which restricts the flow of water vapor through material by controlling the rate at which moisture diffuses into the building assembly, an air barrier restricts the flow of air, which may be carrying moisture with it. Retrofitting an existing roof system with high R-value insulation but ignoring the air leakage results in little payback – any air leaks must be treated at the source.
When air leaks through insulation joints, it can reduce the thermal resistance of the insulation by up to 10%, depending on the width of the joints and other factors. Adding more insulation won't provide a good return on investment unless you can find and eliminate air leaks at the source. This is why Sealant Technologies created AireBarrier. To make roof air barrier maintenance projects work, for both the contractor and the building owner.
The term "roof system" applies to the design of any roof and its interconnected elements. For instance, a sloped roof designed to deflect snow with air vents for systems and an incorporated chimney constitutes a roof system for a cold climate with heavy snowfall. The elements of a roof system vary depending upon the shape of the roof -- flat, gently sloped, sharply sloped, etc. -- the size of the building and the elements affecting roof construction, including vents, gutters, drains, roof materials, air barriers, climate and more.
A roof air barrier refers to a system used in building design and construction to control airflow and the affects of outside air on a building’s internal environment. The term "air barrier" sometimes refers to an actual buffer used in construction to prevent outside air from entering a building’s environment. However, air barrier systems also incorporate elements like windows, doors, vents, insulation and all the things used on building materials to prevent the penetration of moisture and air, such as caulking, sealants, membranes and coatings.
A roof air barrier refers to one of two things. The term may indicate all the elements of a building’s air barrier located on a roof, including vents, windows, sealants, insulation and more. Or, it may refer to a specific element of the air barriers found in roofs. Known as a roof membrane, the roof air barrier assumes the form of a sealed layer placed on the underside of a roof. This layer traps air coming into a building and helps it leave the building without infiltrating the environment within the building.
Basically, air barriers exist to prevent air leakage, or the process by which outside air seeps into a building. Air leakage helps moisture infiltrate buildings, which can lead to the development and spread of mold spores, as well as cracks and other faults in concrete surfaces such as walls and foundations.. Air from outside a building also brings in undesirable elements such as allergens. Such air places a strain on heating and cooling systems by upsetting temperature balance. The strain on HVAC systems can lead to wasted energy, increased carbon emissions and more
You have to understand the difference between air and vapor. Vapor barriers can be ripped and torn and full of holes because the amount of water vapor that passes through due to diffusion is very small compared to the amount of water that can go through a hole or a crack due to an air pressure difference. I can move air, and if that air moves and there’s vapor in it the air will carry the vapor with it. For that to happen I need a hole and an air pressure difference. The likelihood of having a hole is very high. And the likelihood of having an air pressure difference is even higher.
So it behooves us to get rid of as many of the big holes as possible, and try to get as many of the small holes as well, but at the end of the day we’re still going to have some holes. It also means we ought to reduce the air pressures as much as we can, but at the end of the day we’re still going to have some air pressure differences. No matter how good we are, some vapor’s going to be carried by air as a result of a pathway and a pressure difference. Now let's put that aside.
If I have no holes, and I have no air pressure difference, but I have vapor on one side and I don’t have much vapor on the other side, I’m going to have a vapor pressure difference. And that material, depending on how easy it is for the water molecules to burrow through, will pass the water molecules. We call that vapor diffusion. Gypsum board is very vapor-open, so a lot of water will diffuse through it in the vapor form. But gypsum board is a fantastic air barrier. So if I installed gypsum board on the inside, and if I taped all of the joints together, and I had no windows — in other words a gypsum board box with five sides on a concrete slab, and I just caulked the bottom edge of the gypsum board to the slab — I would have a wonderful air barrier system. And I would have absolutely no moisture carried by air transport.
Now here’s the rub: the vapor transport is negligible compared to cutting a one-square-inch hole in that box and having just a modest air pressure difference between the inside and the outside. So what’s more important in controlling moisture transport? Air tightness. Now for the vapor tightness I could enclose maybe 90% of that enclosure with paint, which would be a vapor retarder. And the 10% I didn’t get — who cares? I’m reducing 90% of a small number. So I don’t really care if my vapor control layer is continuous because it doesn’t move that much moisture. But it’s real important that my air control layer is continuous. So air barrier continuity is much more significant that vapor barrier continuity.
Now where it get’s real exciting, and interesting to me, is a concrete slab. So let’s say I’m putting 4 inches of concrete on top of the ground, and before I pour it I put down a plastic sheet — that sheet will be my vapor barrier. So let’s say before I pour my concrete I walk on the plastic sheet with golf shoes for about two hours. So what’s the total surface area of the punctures compared to the total surface area of the plastic? If I’m there for about two hours, maybe it’s 10%. So I basically have reduced the vapor control layer effectiveness of that plastic sheet by 10%.
Vapor flow by diffusion is a direct function — it’s linear. Airflow is not; it’s an exponential function of pressure. But let’s go back to the slab for a moment. What am I going to put on top of that ripped and torn and punctured plastic? Well, 4 inches of concrete. Concrete is a pretty good what? Air barrier — and it’s also a darn good vapor retarder.
So I haven’t increased, even from a measurable perspective, the amount of water vapor transmission from the ground into the floor with the ripped and torn plastic sheet. That’s why I always laugh at the people that say, “Well, you gotta tape the joints and you gotta be careful not to puncture it.” Give me a break! Now I don’t go out of my way to tell people to rip and tear it, and puncture it and leave gaps in it. And if they’re going to the trouble to tape the joints I’m not going to tell them, “Don’t go there.” It’s just not something I’m going to get bent out of shape about if they do a lousy job.
Now, what would happen if I took that concrete off of the plastic, and now I have a conditioned crawl space, and the only thing I have separating the ground from the inside of my house, which is the air in the crawl space, is a ripped and torn plastic sheet? Well, now I have a problem — because that sheet was supposed to also act as an air barrier. Now the amount of water vapor that goes through that plastic by diffusion is still very small, but the amount that will be carried as a result of air flowing across those rips and tears is huge. It’s typically 2 orders of magnitude — that would be a factor of 100. So that’s why we really care about air barriers, but we don’t care about vapor barriers.