Well folks, we just finished another
Insulated Concrete Form (ICF) exterior for a client in The Lakes of Muirfield. This build was three stories of foam block, from the footings right to the trusses.
Nice design but lots of corners and windows! Think it will look great when it is completed. After a winter like this one, I'm sure the owner will appreciate the savings in heating cost over the long life of this building.
A lot of people don't understand just how great ICF buildings are at
conserving heat and protecting the home's
indoor air quality. They look at the raw R-value and say that the two layers of foam only come to between R20 to R-28 but this only tells a part of the story.
There are a number of facets in this construction methodology that make it one of the most cost effective building models for our Alberta climate.
The first is that the outside foam panel stops the cold before it can even enter the wall assembly.
With a normal stud wall, the cold will penetrate at least part way into the exterior wall. As it moves toward that point in the wall assembly where the R-value of the wall becomes sufficient to limit the heat loss from the building interior, it is stopped. This is the point where the warm moist air from the home meets the colder environment, sometimes referred to as the dew point. What happens is the temperature at this location is cool enough for the moisture in the the wall to condense, that is, change to liquid. When this happens, the environment inside the wall becomes a perfect mould growing location. This is one of the reasons we often find mould in stud walls.
In the past, we have tried to prevent this by adding a vapour barrier to the inside face of the wall to prevent the moist air from entering the wall cavity.
In theory, this works very well. No moisture, no mould. Unfortunately, human error almost always circumvents this design. Electrical outlets and window openings are not perfectly seal. The home owner knocks some holes through the vapour barrier to hang some artwork or shelving units. More importantly, wood always moves, contracts and expands, as the temperature and relative humidity changes. This tends to rupture the vapour barrier over time.
Anything that degradates the vapour barrier will allow the moist air from inside the house to enter the cavity. Once inside, the vapour barrier prevents the wall assembly from drying to the inside so all moisture must move to the outside or remain trapped.
And of course, moisture can move into the wall cavity from the outside as well. Poorly flashed windows or the transition point between exterior claddings are the primary causes of this.
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| Back view of the ICF house, ready for the framers |
With ICF construction, not only do we stop the cold on the outside but the whole assembly is air resistant. The moist air will not enter from the inside or the outside. Even bulk water that might enter from the outside can do little harm in an ICF building.
If it gets past the cladding, it will usually drain out the bottom when it contacts the foam. Should some of the bulk water make it through the foam layer, it will drain between the foam and the concrete core. In some cases, the concrete will absorb the excessive moisture and than let it dry to the outside after the rain event is over. So an ICF envelope will offer at lest three levels of moisture protection!
Because concrete has the ability to hold and store moisture and then releasing it back to the outside atmosphere, it protects the inside of the house from this sudden increase of moisture.
As far as mould is concerned, unlike wood or some fibre type insulations, there is no mould food in these walls, so even if some moisture enters the assembly, you will never have mould growing in your walls.
The second item that makes such a difference with ICF walls is the high mass concrete core.
The concrete core limits air movement into or out of the house. This is known as infiltration or exfiltration. If we can limit the air movement into the house, we don't have to waste energy heating the incoming cold air.
It really does not matter how much insulation you put in a wall, if the air can move through or around that insulation, the insulation becomes useless.
It is surprising, the amount of air that will move through fiber insulation, both horizontally and vertically. Most 2x6 stud bays lose heat due to the convectional current that sets up when the slightly warmer air moves up along the interior face of the wall and the cooler air drops along the outside face. As it drops, it scrubs off heat to the outside wall. Still air is an excellent insulator. Moving air, not so much.
Most conventional building methodologies are not very good at stopping air infiltration. Even if they were good when initially built, over time these assemblies break down and air starts to flow into the building.
While there is quite a few net zero units being built in Alberta these days that have very good initial numbers, we need to look closely at what will happen over time. Will these net zero homes still be net zero five, ten or twenty years from now?
We know that the reinforced concrete core of an insulated concrete form will be the same 50 years from now as it is today.
High mass walls also have the ability to dampen temperature loss from the home when we have high temperature swings outside, as in a chinook or just the diurnal daytime swings. This means that the size of the heating apparatus can be substantially reduced and still meet the needs of the house.
The house I live in has about
5200 square feet of conditioned space. Plus the 1000 square foot garage is maintained at about 15 degrees C. Two of the floors have nine foot ceiling. For a conventional house of this size, you would normally have two furnaces of about 120,000 btu capacity. Our house is heated with
only a
54,000 Btu boiler, which also supplies domestic hot water. When we did our heat loss calculations, we used R-50 for the ICF walls. As we have never had a lack of heat in this home, we assume the actual R-value used to calculate the required heating apparatus could of been higher.
Many people who have tried to build passive homes have used high mass walls and floors to store daytime heat from large properly oriented windows. If your calculation are properly done, this can be quite effective. One issue that comes up however, is that if you need to change the temperature in the house quickly, it is almost impossible. All that mass soaks up a lot of Btu's prior to the air in the room getting much warmer. With an ICF wall, the inner layer of the foam, dampens the flow of the heat into the walls. You still get the storage but somewhat slower, so you can get the air in the room warmed without the mass stealing a large percentage of it.
Another nice thing about the ICF high mass walls are their ability to dampen sound. This makes them ideal for high noise areas, like next to a railroad line or airport. When the wind howls, you barely hear it. This of course means you have to be a bit more diligent about you might be in the yard as you often do not hear vehicles pull in.
The third item that puts ICF above much above conventional foundations is
the improve air quality.
How many times have you gone down into your basement and noticed that typically "base
ment" smell? That damp odor? What you are smelling is mould growth! Some people assume that their basement must be leaking somewhere and therefore it smells. Or they just assume that it is a "normal" basement smell. Not usually.
What you are smelling is the moist environment cause by condensate. Think about it. What is the coolest location in your home? What causes condensation? Of course the basement is usually the coolest part of the house and the coolest surface in the house is the concrete walls and floor because they are in contact with the earth. So naturally, as the warm air contacts these cooler surfaces, it releases it's moisture as condensate. With ICF, your basement walls will be just as warm as your upstairs walls. And if you put foam insulation under your basement slab, the slab will be the same temperature as the air in the room. Now you don't have condensate even if you increase the humidity in your house for a small period of time. This is why ICF houses don't have that basement smell. This is why there is. substantially less chance of mould in and ICF home.
If you are thinking of building and energy efficient home, give ICF a careful consideration. Even if you just need the foundation, ICF walls are very cost competitive with cast in place concrete walls and provide a much better basement. One of the comments we often get from our clients is "it doesn't seem like a basement down here at all!"
Don't you desire a little luxury?
