Say Bye Bye to Thermal Bridging

Say Bye Bye to Thermal Bridging

Bye Bye to Thermal Bridging!

Check out this equation… “Thermal Bridging = Thermal Bypass = Energy Loss = Wasted Money”

Energy Efficiency in Owensville MO

This house in Owensville MO got a little tender loving care from it’s owners who decided to add energy efficient and comfortable living space. Custom home insulation and energy efficiency upgrades are a Foam Engineers specialty and we were glad to be invited to help! The owners also went with all LED lighting (I’ll only purchase LED lights from now on) and a bamboo floor for added insulation and sound control. Keep reading to learn more about this project…

Exterior view of house in Owensville to be insulated

Thermal Bridging

To understand why the project was done with spray foam insulation you need to understand thermal bridging. That is a term normally used to describe wood or metal in a framed wall that is not a good insulator. In most walls the framing allows heat to transfer through it (wood and metal are not good insulators) and reduce the overall thermal efficiency of the wall by 30% or more. So a wall insulated with batts between the studs might only be as efficient as an R8 insulation system because the wood allows heat transfer. Of course there are other inefficiencies when using batts such as imperfect installation and convective loops, which I’ll talk about below, but for now I’m going to stay on topic and just talk about thermal bypasses (which is the same as a thermal bridge)! If you look carefully at the walls in the picture below you will see the wood furring spaced off the foundation by about one inch. This will allow closed cell spray foam to expand behind the wood. This adds insulation where it is really needed – directly to the foundation wall and behind the framing. With just one inch of closed cell spray foam we can achieve an R7! Then the wood stays warmer and the overall energy efficiency of the wall is improved. In this wall assembly we sprayed 2 inches of closed cell. One inch behind the studs and one inch in the cavity between the studs. Of course the owner only cares about a more comfortable living space that does not cost an arm and a leg to heat and cool.

This basement wall is furred with 2x4's offset from wall to reduce thermal breaks, also known as thermal bridging, and is ready for spray foam insulation

Moisture Control

Water gets into everything – especially where it is not wanted. I think that’s some kind of law or something (just kidding). Water also gets into basement walls which absorb moisture from the ground. Concrete is a bit like a sponge and wicks moisture from any damp areas. Some amount of water is able to find it’s way through, or around, exterior applied damp proofing and into the basement. Now, I’m not talking about running water. I’m not even talking about dripping water. I’m talking about a wall that has no visible water on it but simply has a high enough water content that water is evaporating from the wall and making the air in the basement more moist/humid than it would otherwise be. The evaporation of water makes the wall cold (it’s evaporative cooling like how your body cools when you sweat). This often makes a basement cool and humid which means a less healthy and comfortable living space. How does closed cell spray foam help control moisture? Well, in addition to being an insulator, closed cell spray foam is also a vapor retarder (it’s not a vapor barrier) so it retards the amount of moisture that comes from the soil, through the wall, and into the living space via evaporation off the wall surface. Yes that’s right, the water just can’t evaporate off that cold basement wall because it’s covered by spray foam that does not wick water and greatly slows the amount of water that can diffuse through it. Of course, the owner only cares that the living space is dry and comfortable – nobody want’s to live in a wet cave!

Closed cell spray foam at basement wall. Foam trimmed away from stud face ready for drywall.

Convective Loops

Okay. I was going to talk about convective loops and air barriers as one topic but they are really two separate issues. Let’s start with convective loops and why you don’t want them in your basement. Then, in the next section, we can talk about the reason why air barriers are good for your home, and your wallet! Here we go… I think about convective loops when I cook on my grill (yes, my engineering mind is always going). I see the air heated by the charcoal rise to the top of the grill where it hits the cool lid and then drops back to the bottom and is reheated again. Of course I open the louvers at the bottom and top of the grill to let some fresh air in and some hot air out (after all, fire needs oxygen). But, if we were inside the grill, we would see some amount of convective looping; after all, the charcoal is hotter than the lid of the grill. This happens in a wall assembly too. But in a wall it happens slowly and steals your money without you even knowing it. Fiber insulation does not stop air flow. Therefore the hot air within the wall cavity rises to the top and the cold air falls to the bottom. Air can move through the fiber insulation or behind it where there is a gap or a stud. Moving air reduces the thermal efficiency of the wall. BUT, and here’s the good part, spray foam insulation does not allow convective loops! Air cannot move through the foam. Also, since foam is spray applied directly to the wall there is not a continuous gap to allow air to move. Air movement is a big energy hog and we wont have any of that!

Foam Engineers spray applied foam insulation on furred out basement foundation wall

 Spray Foam and Air Barriers

Spray foam has the ability to stop convective loops and also the ability to stop air from moving from the exterior to the interior of the building through tiny cracks and gaps in the walls. A product that stops uncontrolled air movement into or out of a wall or ceiling assembly is called an Air Barrier. A foundation wall does not leak air… so stopping moisture and convective loops is the primary role of spray foam against the concrete. But when we get to the rim joists that’s another story. Here spray foam excels – air cannot flow through it. Anyone who has held their hand up to a wall switch or outlet and felt air rushing in knows how uncomfortable air leaks can be. The role of an air barrier is to stop those air leaks and now air barriers are an essential part of any energy efficient home or building. In fact, building codes are putting an end to homes that have high R-Value but leak air like a sieve!

Foam Engineers applied closed cell spray foam to walls and rim joists for air sealing and insulation

Benefits of Spray Foam Insulation

I make no apologies. Spray foam insulation is the best performing insulation material – period. Other materials may cost less to install but, when installed properly by a reputable contractor, spray foam will save you money. As you saw above, closed cell spray foam insulation provides thermal efficiency (R-Value), controls moisture by being a vapor retarder, eliminates convective looping, and is an air barrier. Wow, now that’s a lot of jobs for one product and that’s why spray foam insulation is growing in popularity. I also like spray foam because it’s maintenance free. Unlike air conditioning systems, solar panels, and hot water heaters which all wear out or breakdown… if you contract Foam Engineers to install an awesome insulation system you are done; no repairs or replacements – forever!