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17 October 2017
How to build a Resilient Home - Closed cell spray foam insulation
In my blog about metal framing, I mentioned that metal frame has two main problems. The first one is thermal bridging which leads to heat loss, condensation, and the subsequent corrosion.
Another issue is the performance of lightweight cold-formed steel buildings during a fire. During extensive heat from the fire, metal frame will lose its ability to support loads which may lead to sudden failure of the structure.
When the issues discussed above are resolved, a metal frame is an ideal choice of a resilient material for your house. In the previous blog, I explained how we address the concern of metal frame performance during a fire with the use of MgO boards throughout the house.
Today, I will explain how the problem with thermal bridging can be solved and how the right solution could turn disadvantages into the more significant strength advantage of a Resilient Home.
None of the methods or the materials that I chose for a Resilient House are new. I am just using these proven technics in a different combination because I have a distinct goal in mind.
My goal is to create a resilient building that is a sturdy, long-lasting, green as much as it is possible, passive, off-grid, energy efficient and cost-effective. My priority is the safety of people comfortably living in a house that is armored against extreme weather conditions or natural disasters.
The most feared natural disaster occurring quite often in Chile is an earthquake. And I want to make sure that homes that we build for our customers are protected against that as much as possible.
To better cope with seismic activity, a house has to be very rigid and ideally to have as less weight as possible. That will increase the chances of a building to withstand massive shocks.
By itself, metal frame has already great properties to survive in a massive earthquake, but we will make it even more resilient. And the best way to increase the strength of a home significantly is to use closed cell spray foam insulation.
There are two kinds of foam insulation: open cell spray foam, with a lower density of about 1⁄2 lb./cubic feet; and closed-cell spray foam, with a density of about 2 lb./cubic feet.
Of course the higher the density, the greater the R-value of the foam. Reasonably, the higher the R-value properties of insulation, the more it costs. But the lower cost is not always the most economical way to do it. As they say, you get what you pay for. Cost savings in the wrong place usually comes with an extra expense down the road.
Open cell foam has an R-value of 3.5 vs. closed cell spray foam has almost the double R-value of 6.5 to 7 depending on the manufacturer of the primary components. The difference in those types of spray foam is not only in the R-value.
The more significant benefit of a high-density closed cell foam is that it adds structural strength and reinforces exterior walls when sprayed in metal stud cavities.
In fact, according to research conducted by the National Association of Home Builders, walls insulated with closed cell spray foam have a structural strength of up to 300% greater than walls without it. Also closed cell foam insulation increases the building’s resistance to wind uplift during severe storms by over two and a half times comparing to conventionally built and insulated houses.
Imagine if you tell that to the victims of the latest hurricane season that had their houses shredded into pieces. Do you think if they were given a chance they would have used a more resilient type of construction for their home? We should think about it and use the chance while we still have a choice.
I understand that closed-cell spray foam is the most expensive insulation on the market today. However, when appropriately installed, it performs better than any other insulation.
Besides increased structural strength closed cell foam is also an excellent air barrier and impervious to moisture. Application of foamed-in-place insulation that fills walls and ceiling cavities entirely creates a waterproof house.
Even in case of a similar event that happened to people in Texas recently, during hurricane Harvey, when the houses submerged into water, Resilient Homes would not get destroyed. Furniture, cabinets, and woodwork along with some other minor things would get ruined of course. But with the help of dehumidifiers, in a short period of time, repairs could be done to the shell of the house.
That is why FEMA has classified closed cell foam insulation as a material that can resist flood damage. And the good thing is that if you use MgO boards, there is no risk of getting mold issues after the flood.
Now I want to address the thermal bridging of a metal frame using closed cell insulation. In my opinion, the best and the most effective way to do it is to use a double wall construction for exterior walls with a double thermal break. The first thermal break should be between the metal frame and the outside sheeting and the second - between the walls.
Closed cell foam insulation will fill all cavities, covering first outside metal stud entirely and creating a stable structure with an R-40+ insulation value.
I understand that at this moment many of my readers will be shocked. To get to R-40+ would require applying six to seven inches of costly material. But would you do it if that will not cost you more then the regular cost of insulation?
Building an off-grid house will require the installation of some energy producing systems. People often build a house that leaks heat like crazy and then they install a substantial solar or wind-powered system to support all of that waste.
For me, this sounds like an upside-down thinking. Isn't it better to build a passive home that will cost more to develop but save money on solar panels and batteries? The bottom line will be about the same anyways. Personally, I would always go for a passive house.
I like the saying that goes something like this: "I am not that rich to buy cheap stuff." What about you?