The best way that I can think of to add a large amount (20+ tonnes) of thermal mass to a solar home is by adding concrete floors. By doing this, one can get two uses, thermal storage and a finished floor, out of the same investment. Furthermore, since the mass of a concrete floor is so spread out around the home, thereby giving it a large surface area with which to absorb and release heat, it really is the ideal thermal storage medium for a house with large solar gains.
So we added a 2.5 inch topcoat of concrete over the subfloor. In order to support the extra weight we had to add (recycled!) beams that run the length of the house (north to south). After it was poured, the concrete was simply trowelled as a preliminary finish.
pouring concrete floors over a regular subfloors (the walls had to be made 2.5 inches higher to compensate for the depth of the floors)
a freshly trowelled concrete floor
For the final finish, we were partial to an acid-stain because we've seen some gorgeous stained finishes. Peter Amerongen convinced us to go for a water-based dye for environmental reasons. Man those green types can get in the way sometimes!
A talented man named Skip from Desco Coatings did the final finish. Peter describes the finish as such:
”We sealed the concrete with lithium silicate, then dyed it with water-based dye. The final coat was an epoxy coating, 2-part , 100% solids (so no offgassing because the soldis do not evaporate)."
The finished product is wonderful – a bit different at first, with an organic, charactery type of feel to it (yes, I just made up the word charactery).
The floor has been growing on me by the day.
we love the saw cuts in this floor
the variations in the floor’s texture took a bit of getting used to.
mmmm…floor near recycled-fir stairs
I think it looks great Conrad.
When I build my next house I'll likely go with a concrete topping coat with in-floor heating. I think 1.5" is optimal for the following reasons:
1) It's a simple double bottom plate to make up the 1.5"
2) Part 9 of the NBC allows for increased floor spans with up to 39mm of concrete topping; beyond that you need an engineer
3) Concrete releases 0.4 tons of C02 per ton of portland cement (about 5 bags or 1000lb of cement is used per cubic yard)
http://ecoworldly.com/2009/01/02/cement-that-eats-carbon-dioxide-invente...
To make up for the reduced thermal mass I like the idea of an under-slab inter-seasonal store; I did a small one on my house but this one is better.
http://www.tonyshouse.info/
Looking at the pictures, I see another big benefit to the concrete topping coat that I never thought of before. The topping coat will seal the crack between the bottom plate and the subfloor at exterior walls, which should improve airtightness. I think your 0.39@50Pa blower door test supports this thesis.
Ralph, the joint between the subfloor and the OSB bottom plate is well sealed with Weathershield acoustical sealant at the exterior side of the double wall and there's 16" of insulation (and 16" of bottom plate) between that joint and the concrete so I don't think it would have much effect. It might be a benefit with conventional single wall construction.
B.
Hi Conrad,
I have been following this blog for the past year and have a few questions about your house:
1. Did you ever consider adding ductwork to reduce the temperature differential between the sunny loft, for instance, and the back room? In retrospect, is that something that you wish you had added or would advise someone else doing on a similar project?
2. Because the basement is the least valuable living space (there's a reason it's not used in the square-footage calculation) and virtually impossible to heat from the sun, why have one? I know this question sounds odd to someone living in Edmonton and accustomed to having a basement, but in many places, like the Southwest United States, basements are very rare and generally not missed. So my question is: on a percentage basis, roughly how much less energy would be needed to heat this same home if it did not have a basement?
3. I asked this question before but was wondering if you had looked into it further: have you looked at the negative impact of the fireplace due to its solar bridge effect? Is it negligable? Is there even a way for HOT2000 to evaluate its effect?
4. As far as I understand, the sealing of the house is done by installing a plastic liner behind the drywall. What if you put a nail through the wall? Wouldn't you puncture the seal?
5. Are you planning on having an open-house over the holiday season similar to the one at the Riverdale Net-Zero house last Christmas? I for one would love to check it out in person.
Thanks,
Dave
Hi Dave,
1. This winter the differential has been small. The back rooms have been getting plenty of heat just by leaving their doors open. One observation that Rob Dumont has made is that in such a well insulated house heat distribution isn't a problem - the heat can't escape, so it distributes quite evenly. So no, I wouldn't add the ductwork on a future project.
2. We will be heating the basement with excess heat from our solar hot water tank. Obviously that's less than ideal. We also have a root cellar in the basement, the mechanical systems are down there (hot water, electrical, HRV), and most importantly to us, there is a potential suite in the basement. The suite is vital to our financial plan moving forward.
I don't have my HOT2000 files with me right now, but I would guess that the heating requirement would be about 15-20 percent less without the basement.
3. We could get an approximation using HOT2000, but we haven't yet. I suspect that it would be similar to a small window - 100 kWh per year. We also haven't modeled the light pipe that's in our upstairs bathroom.
4. I believe that we would. At the studs, there is acoustical sealant behind the drywall so that the screws (and any nails) don't create a hole (the sealant just gloms in around the screw). If we put a long nail through the 0.5" drywall, though, it would surely puncture. There's no designing for some types of occupant behaviour I guess :)
5. Sorry but we won't be having an open house for at least a couple of months. The whole family was sick for a while and that put us back. We want to finished getting unpacked first!
Conrad
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