GBGC Expert: David Suszko, Dow Chemicals
Outsulation Is The New Insulation: Addressing Air Infiltration, Thermal Bridging and Lowering Your Energy Bill. “What’s That Blue Stuff on The Outside of My House?”
I must start by saying that I am biased. Yes, I admit it. So please, if you feel the need to complain about the fact that I work for Dow and that this article is about Dow products, know that I welcome your opinions but hopefully by admitting my bias we can accept it and move on.
Also, being biased doesn’t mean that you’re wrong, and representing products probably makes me the best person in the world to explain how they work. You’re probably asking yourself, “what product is he talking about?” And if you’re not, I’m going to tell you anyway: insulated sheathing. And it’s really cool stuff.
If you’ve been in the market for a newly built house, you’ve probably seen insulated sheathing and not even known it. It’s used by many highly respected builders in Houston. It comes in several different forms but it probably looks like blue, green or foil wrapped foam and it goes on the outside of the house over the studs. If you have seen it you may have asked yourself “what does this stuff do?” or “why would someone wrap a house in foam?” The answer is simpler than you might think.
As you may have noticed pretty much any time you step foot outside your house here in Houston, it’s hot, and humid, and really stinking hot. We need something to keep that hot, humid air where it belongs, outside. Nerd alert: things are about to get technical for two seconds. Bear with me. The second law of thermodynamics states that heat moves from more to less. For example, when you put ice into a glass it doesn’t add cold but rather sucks out heat. Actually the second law says that things in nature in general move from more to less. Water, like heat, moves from more to less or wet to dry. You can test this theory at home by touching a paper towel to a glass of water and watching the water move or “wick” up the paper towel.
Again, hot to cold, wet to dry. Where do you think that hot, humid air is trying to go the lion-share of the time in Houston when it’s hotter and wetter outside than it is inside your house? Answer: that hot, humid air is trying to get in. And we want to keep it out.
Now this is about the time that someone who has been building for a long time might say in a thick Texas draw, “That house is gonna be too tight. Gonna have moisture problems. We need that house to breathe.”
And that’s where we disagree…to an extent. See, we do need a house to breathe, but not in an uncontrolled manner and certainly not by inhaling hot humid air (how much moisture is that ADDING to the house) and attempting to exhale cold, beautiful, expensive air conditioned air. That’s just silly and robs your pocket book, 24-7-365.
Current building scientists (yes, there is such a thing, they are physicists and really darn smart) would say we should build the house tight and ventilate it. So” build tight, ventilate right.” And that’s exactly what you do by using insulated sheathing. We’re going to button up the house really tight, then because extremely efficient and cost effective products exist today, we’re going to mechanically ventilate the house where needed. And because it’s tight it’s going to be extremely energy efficient.
Did you know that the average code built home has a half mile of gaps and cracks? Think what that does to your energy bill. Also, did you know that air infiltration (or air coming into your home from the outside) can account for nearly 40% of the energy loss in a home? So why again would we want to encourage a house that breathes? That is to say, a house that leaks. Insulated sheathing nearly eliminates the problem of air infiltration through the walls of a home. But it does oh, so much more for your energy bill.
On top of controlling air infiltration that insulated sheathing is, bump, buh, dah, dah! INSULATION!! The average insulated sheathing in Houston is ½” thick and has an R-value of 3. Did you know that a 2” x 4” stud is more like 1.5” x 3.5” and has an R-value around 3? Now think about how many studs you have in your house. Every 16” there’s probably one. Then you add in all the jacks and cripplers to hold up your doors and windows, the extra ones they put in the corners, any additional ones used for bracing…the list goes on. So how many are there?
Short answer: a lot. Did you know if you add all those studs up they make up about 25% of your wall space around your house? That’s like one whole wall being un-insulated. So think about that. That’s like building a refrigerator without a door on it. You know why coolers are built out of foam? Because it’s really good at keeping things inside cool. And that’s what you do by wrapping a house in foam. You make it a cooler.
But it gets worse. See all R-value is not created equal. That is to say the difference between R-0 and R-5 is way different than the difference between R-25 and R-30. The equation’s not linear, it’s an exponential decrease. By increasing the insulation at the studs you double your R-Value at every single stud: R-3 to R-6, in the R-Value numbers that matter…the low ones. It controls a phenomenon known in the building industry as “thermal bridging” or heat flow through the studs. And that “little difference” is a big one. Don’t believe me? Check this out:
These are thermal images, taken by a thermal camera. The house on the left is built with no insulated sheathing and you can literally see it taking on heat. When a house takes on heat that heat has to be cooled by the air conditioning system and the system has to work that much harder. When it works harder you use more energy and your bill goes up. The one on the right is built with insulated sheathing. No heat coming in. Lower bill. Makes sense, right?
“But David, that stuff is more expensive than the cheapest option and it can’t be that big of a difference in my bill.” EH! Wrong! In a study done in Dallas the average monetary increase of adding insulated sheathing and some simple air sealing details (which are probably done in your house anyway and will be the fodder for another blog post) retailed for around $1300 on a 2800 SF house.
But you don’t shell out $1300 at closing, you amortize it over 30 years at some of the lowest interest rates in the history of the United States. That $1300 increase at today’s rates was an average increase in a homeowner’s monthly bill of $7. However, the energy efficiency achieved with the insulated sheathing and air sealing details was a $13 savings in the homeowner’s energy bill. So you give me $7 I give you $13. Every month. Forever. That’s an 85% return on investment from a cash flow basis. Are you getting that money in the stock market right now? If so can you please reply to this blog with contact information for your broker?
So that’s it. Use insulated sheathing and you WILL lower your energy bill by reducing air infiltration and thermal bridging, increasing your insulation value at the studs and in your wall cavities, and making your cavity insulation more efficient. Finally if you still don’t believe that heat can flow through your studs in Houston see the picture below. You can literally see where the studs are. Notice the cross braces?
I took it near the area of 290 and Fry. The house that had this problem was probably $300K when it hit the market. Now you can’t see the problem anymore if you go to that house today because it’s been re-painted or re-sided. How much did that cost and how often are they going to have to re-do it? Insulated sheathing: it’s energy efficient, it’s green, and it’s just good business if you’re buying a house.