[Strawbale] earth floors, passive ventilation

[dfugler at cmhc-schl.gc.ca]

Kim,

Two things. The poly under the floor should ensure that there is no 
continuous source of moisture from the soil. Once the earth floor over the 
poly comes to equilibrium with the house, it will no longer be a strong 
source of humidity. That is good. I would insulate under the poly as well, 
so that the floor has a chance to stay warm and avoid summer condensation. 
If you look at the graphs in this highlight: 
http://www.cmhc-schl.gc.ca/odpub/pdf/63728.pdf, you will see that the 
uninsulated floor is cool and the earth below it is cool. When you 
insulate, the soil below the basement is cooler yet and the floor 
temperature is warmer. Basically you have a more comfortable floor and 
less heat loss if you insulate properly under your slab floor.

I have not yet seen successful passive ventilation options but that does 
not mean they don't exist. When you do the calculations or measure what is 
happening in houses, window openings or ventilating chimneys use more 
energy than their mechanical alternatives, while providing less effective 
ventilation. I would prefer to see a decent, ducted HRV in the house (like 
most new houses in eastern Canada) that gets turned off during the periods 
when passive ventilation is practical (e.g. a Nova Scotia summer). That 
seems like the best combination.

Don Fugler
CMHC Policy and Research