Balancing airflow and insulation in a coldish environment
We are finishing up a build at 7200 feet in northern New Mexico, USA. We can get lows below freezing pretty much any day from October through May. Daytime high temps are usually ~20-40 degrees F (~10-20 degrees C) warmer than nighttime lows. At the worst we can get a week long stretch with highs below freezing and lows around 0 F (-17 C). In the summer we can get a week straight with high temps above 90F (32C) and the sun is intense.
Our IBC tote is partially submerged about 1 meter below grade in back and 1/2 meter in front. The housing is made of earthbags -- as a retaining wall below grade, up to about a foot (30 cm) above the tank with a sloped metal roof. From about 2 feet (60 cm) below grade the earthbags are filled with scoria (lava rock) for insulation. The walls are ~15" (~45 cm) thick. There is an air gap between the walls and the tank.
The tank has reached above 110F (143C) with the UNinsulated roof on.
We are insulating the underside of the housing roof (including access trap doors) with rigid foam sheets and spray foam. We included two 4" (~10cm) air vents through the earthbag walls just above grade -- 1/2 way up the tank in front, just above the tank in back.
* Our question is whether we have enough venting and enough insulation. *
We are thinking of just sticking in clean trash bags filled with recycled packing material in the big openings where the plastic tank is sealed (so where ventilation is not an issue).
Above the tank opening/access port we are thinking of sewing a ~5" (~12cm) thick burlap "box" with a footprint a bit bigger than the access port that we can stuff with straw, so we will have a somewhat breathable insulation over the opening. This would sit on top of the tank cage which might allow a little gap between the tank and the burlap. We will leave an opening so we can change out the straw periodically.
Thoughts? Does this sound like the right balance between insulation and ventilation? Of course we will be monitoring temps before (and after) introducing worms. Does anyone drill ventilation holes around the top of the tank side walls? Of course this would be a nightmare if the tank ever overflows. We won't do that unless it seems like we have a ventilation problem, and if we did we would make sure the holes are higher than the drainage pipe.
We look forward to any input -- and thank you to Wendy and all forum participants! This website is hands-down our best resource for this work.
(I tried to include a pic of the wormbin with earthbags -- before plaster & roof & insulation & vents were added)
Hi. That's a pretty harsh environment you have to deal with but it's not so very unlike here (Portugal). It's very hard to say whether you have anough insulation in the roof because every installation is unique and a lot is down to trial and error in context. If your ground temperatures are already quite warm then you might benefit from more airflow so warm air doesn't build up around and in the tank. Accessibility is important for regular checking too. If there's any chance of creating some shade over the tank (trees, vines), that can help enormously and massively reduce any likely potential of overheating. I would complete it as you suggest and then monoitor internal temperatures for a week or so before you add the worms. Hope that helps ...
Thank you, Wendy! We will do that.