The science of finishing basements

If I should be so blessed as to be able to build a wofati home with and for my family, I'd be in heaven but in the interim period, I seek your help. Can you help me glean reliable knowledge on the best, most healthful way out there to finish a basement. Our basement is made with poured concrete - the foundation and walls. We'd like to create a liveable warm space in our basement for our cold winters. We live in the cold white north where the winter temperatures can drop to as low as minus 35 degree Celsius and our summer temperatures can go upto 38 degrees Celsius (albeit only for one two weeks in the year).

I'd be very grateful for pointers in the right direction to learn more about healthy flooring and insultation options that are beyond sustainable. I don't know where to begin so I've come here - to seek advice from people I trust and admire. I can't get over how special and valuable this site is. Thank you Paul for creating it and thanks too to the good folks who help you keep it up and running

Hi, Shazi. I'm a home energy auditor based in Kansas. Most of my knowledge is based in this climate (warmer than yours), and on synthetic building products rather than natural ones, but I'll answer as best I can to get the ball rolling...

The current wisdom in the building science world is that the best, most energy-efficient place for insulation -- both above and below ground -- is outside the thermal mass of walls and floor, not inside it. Since your basement is already built, you're already settling for second-best by putting the insulation inside. I don't mean to be discouraging, but it's important to know where you're starting from. Obviously any insulation outside the building would have to be non-biodegradable, i.e. not a natural product.

When considering insulating the inside, a lot depends on how reliably dry your basement is. If you can't count on it to be 100% dry all the time, then any kind of biodegradable insulation will create a terrible mold problem. Even if you build in drains and a moisture barrier on the wall side of your insulation, you're asking for trouble. My recommendation for a wet basement would be non-biodegradable foam insulation, either in panels or sprayed, down to the frost line, with no insulation below the frost line. You can then build a frame floor and walls to separate the living space from the cold, wet walls, being sure to isolate all biodegradable materials from any possibility of moisture.

If you know your basement to be 100% reliably dry, then you can consider putting biodegradable materials in (or preferably just near) contact with the walls. Light-clay-straw is an option, or straw bales, or recycled cotton batts. In any case, think seriously about the possibilities of rodent infestation and mold, and build your walls and floors in a modular way so that part can be removed without gutting the whole basement. That is, I would not recommend a seamless coat of plaster over the wall, because if anything goes wrong in there, you'll have to break the plaster.

Good luck! I look forward to seeing what else other people suggest.

Great advice from Ben. If its really wet, you might want to install some interior foundation drainage; to daylight if possible or to a sump pit if not. As Ben mentioned, insulation on exterior is best but usually requires heavy excavation which is cost prohibitive. BSC has done the most research on the subject and has many articles for doing what Ben proposes. Here is one to get you started but they have many more:
http://www.buildingscience.com/documents/information-sheets/basement-insulation/files/bscinfo_511_basement_insulation.pdf

Thanks Ben and Brian for your helpful posts. Currently we have fibreglass insulation upto the frost line on the foundation walls. It seems there are three layers on the walls:a black vapour barrier, fibreglass insulation and then a clear plastic vapour barrier. I wonder if it would be a good idea to spray on a radonseal on the foundation wall (as we will be using the same for the foundation floor) and then use a natural cotton insulation over the sealed walls. Does sealing the concrete create more problems down the road?

I agree that the first thing would be to assure it's dry: drain pipe/tile around the inside perimeter and a sump. You might want to consider a rocket mass heater, run the exhaust through the band joist and build a chimney up outside. You could take out a basement window and turn it into a wood chute so you don't need to carry it in. I put a barrel stove in my basement in the 1980s and loaded it through an old coal chute. Good luck. It's a worthwhile idea.

Up here in Canada there's a popular Reno guy on tv called Mike Holmes who recommends using insulated foam boards glued to your basement walls. You can find some that are notched to join together so there's no cracks. On the floor he also recommended using those boards and where ever there were cracks where they meet he used spray insulative foam from cans. Plywood was then placed over the floor and the walls could then be framed.