Mold has reared its ugly, ugly head in my home, and I have recently been consumed with attempting to determine a solution to this problem. I ask readers (especially those with experience living in cob houses in cold climates!) to please read ahead and help me to determine the best course of action. Any advice would be dearly appreciated.
Here are all the details fit to print.
I live in northeastern Missouri, where temperatures can get to below 0º. This winter, we’ve had perhaps four below 0º nights thus far. But typically, our winter lows are in the high teens or 20s, with daytime temps. in the 20s or 30s. My house is all cob, with 18″ thick walls. There is no insulation in the floor, foundation, or roof (other than the soil). (I will never build like that again in this climate…!)
I am having a very big mold/mildew problem on the bottom 15% of the interior walls, particularly on the west and north walls. The walls register as low as 38º towards the bottom of the wall, and the foundation about the same in the mornings. Higher up (at head height) the temperature reads in the mid 50s, and even higher it reads in the 60s. (I tested the wall temperatures with an infrared temperature sensor.)
I believe it is condensation that collects on the face of the cold urbanite foundation and the coldest bottom part of the wall (because of the big temperature difference between that part of the wall and the air inside), and then molds from not being able to dry quickly. Condensation is so great in places that the floor is damp in spots, too. We’ve got the small Morso wood stove and can get the house to about 70º, but most of the walls remain quite cool, of course, even after a day of heat.
Furniture close to the walls on the west and north is also a concern, since airflow is not as great with the bed against the wall, for example.
The mold appears as white fuzz, but in some rare places it is a green mold if I have not been over it with vinegar for some time. The regular task of moving furniture to spray the walls with vinegar to kill the mold is tedious and tiresome. The colder it gets, the worse the problem. I have reason to believe that April”s recent health problems (allergic attacks in the form of swollen lips and eyes) have been the direct result of this moldly living environment, as well, which is a huge concern for us, and more than enough reasons to solve this problem as soon as possible.
My current line of thought is that I must insulate the bottom part of the wall and/or foundation. I imagine it would be better to insulate on the exterior, but all I can imagine is having to build a kind of extended foundation and then somehow build basically another wall (or tapered wall) to insulated the coldest parts of the cob. But with light clay straw or straw bales, I am not sure.
I also wonder about the effectiveness of lime plaster in this situation. Would covering the lower 1/4 of my interior wall in a lime plaster or lime wash prevent mold from developing on the surface of the wall? Would moisture simply condense on the surface, and could I then wipe the lime with a rag if it’s bad enough? Obviously lime plaster would not stop the wall from condensing, but it could stop mold from developing since it is antifungal, I think.
Additionally, we are considering an insulated bale-cob addition on the north of the house for insulating that coldest north wall, but the west wall would still be unprotected and need some kind of insulation.
A greenhouse addition could help to maintain higher indoor temperatures (on sunny days, anyway), but it would doubtful have a big impact on condensation development.
Any advice would be dearly appreciated. I fear my girlfriend’s health is at risk it we continue to live in this environment without resolving the moisture issues.
Also, it is important to note that the humidity is always very high, even in the winter. (Right now it’s around 65% and it can even get higher!) Perhaps we need better ventilation…
Jami McBride wrote:
It is his foundation which is causing his problems, and not the cob. He needs a moisture barrier between the ground and his house. I don't know how he could achieve this now though. I don't think insulating will help at this point. Cob will allow some moisture to pass out of the walls as long as it isn't to overwhelming.
Isn't there a thread somewhere on installing french drains around houses?
Brian Knight wrote:
I think its likely however, that the lack of a vapor barrier or retarder at the ground surface is one of the main contributors to the problem. There are many sources and ways to reduce wintertime humidity in homes but with such cold surfaces, I dont think any amount of breathability or lime is going to prevent condensation problems let alone comfort issues, in mixed humid and cold climates.
Brian Knight wrote:
Iam skeptical that your climate is suitable to cob for most projects. Not enough R value for me. Would love to see any informative links you have to cob in cold climates like Canada. If you have to burn tons of manchester coal or hundreds of cords of wood to keep it comfortable, is it the most appropriate choice? Iam sure its a great choice for some projects but I would prefer to use energy more efficiently myself.
Sean Rauch wrote:
2. Thermal mass does not compensate for insulation, they are two different concepts with two different roles. If your in a really temperate climate where the earth never or almost never freezes and it's usually dry then yea thermal mass alone can accomplish efficiency. Otherwise you need to insulate.
4. Take the design phase of home building extremely serious, it's not a one size fits all equation. A design that works great on one place can be a failure just a mile away. You have to ask the question "why?" a lot. Nobody knows everything, if your builder/consultant only has experience in one or two disciplines that is a sign you need second and third opinions.
Sean Rauch wrote:Everything in context including cob. Materials and practices succeed or fail based on the context in which they are used. So this means that in some climates some materials or practices thrive while in others they fail.
I consider cob to be a thermal mass material and it will generally behave like stone, concrete or other high mass systems. This means not good for cold climates without massive energy input.