Vented Attic’s Are Stupid!
Well friends I am once again back from a continuing education seminar that I found quite informative. It was taught by Joe Lstiburek, Ph.D., P.Eng., & ASHRAE Fellow. ASHRAE is The American Society of Heating, Refrigerating and Air-Conditioning Engineers founded in 1894. They are the go-to authority when it comes to all things building.
The title of this article is a direct quote from the good Dr. Joe. I must tell you though, I thought I knew a lot about building science until I had the pleasure of hearing this man speak. If you having any interest in building science and you have a chance to hear Dr. Joe speak I recommend you go for it — he is well worth the price of admission.
So why if we have been building houses with vented attics for years, is it suddenly stupid you ask? The fact is it has always been stupid. In this case the science to do it better had not been thought of yet. I know I’ve said this in the past; however please bear in mind air conditioning houses has only been a main stream commodity for the last sixty years or so and we learn new things every day.
The reason vented attics are stupid is very simple when you stop and think about it, we are in most cases taking something we are trying to keep cold and putting it in one of the hottest places on the planet. Florida attics on a hot summer day top out at 140-150 degrees with ease and yet we run tubes with 50 degree air in them through the attic. Talk about total opposites can you see any problems here? Oh, I don’t know… waste of energy, condensation, mold, and total inefficiency all come to mind. Running duct work in a hot attic just doesn’t make sense. So as usual the question becomes how can we fix it?
Well, we could tear all the houses down and start over, however that seems a bit impractical to me, so what if we could bring the attic in the house? There is an idea that just might work. Actually it is not a might work idea it is a proven theory for more than 20 years now. The process is actually relatively simple. We begin by sealing the soffit vents in the home. For those who do not know what a soffit vent is wander outside and look up at the eve of your house, I’ll wait. You see those screens in the eve about 8” wide and around 18” long? Those are your soffit vents. In old building science the theory was the house needed to breathe and those vents allowed that to happen. No, your house does not need to breathe by the way. So, step one is to seal the soffit vents, and step two can be accomplished in a couple different ways. We need to determine how we are going to insulate the attic.
You can insulate our attic space with the traditional blown in style up to 20” deep and the beauty of this is we don’t care at this point if the ducts get buried. In older attics ducts will sweat if in contact with any other material, in this style of building, because we are now controlling the atmosphere, no duct sweating will occur. The other method we can use for insulating the attic is a spray foam product. There are a couple different types of foam that can be used and there are advantages and disadvantages to both styles of insulation which I will get into in upcoming blog post article.
We are now moving on to step three, move the attic inside. Very simple to do, in a closet or two in the house we put a screen into the attic. This will allow some air to interchange between the house and attic. Next, we are going to add just a small amount of air from the AC unit into the attic. Tada, we have now moved the attic indoors!
This will suffice in most cases however bear in mind on occasion we may need to take things one step further and add a dehumidifier to the attic. If we need to do that depends on the style of roof your home has. Some homes have what are called ridge vents along the top of the roof. If your home has a ridge vent and a moisture barrier installed the dehumidifier will likely not be needed.
A ridge vent by the way is exactly what you are thinking of it is a vent running along the peak of your roof to allow air transfer. I know this contradicts what I said about breathing houses however in this case the vent is needed and functional because it is located at the highest point in our structure and water vapor rises. Just call me Bill Nye the science guy baby! Wait… on second thought I’d probably get in trouble for copyright infringement so just stick with House.
Alright next time we talk about the differences between insulation and weigh the pros and cons, until then I have a pet pig I’m teaching karate and I think I’m changing his name to Pork Chop. House Whisperer out!!