I recall reading somewhere that one of the benefits of cob housing was that it was better able to control indoor humidity control when you have dry summers and wet winters. I've found less information about Straw bale in the Pacific North Wet, and I'm wondering whether people have ideas of how it would cope with our *very* damp winters - would it keep houses more comfortable and would our dry summers be dry enough to "recharge" its capacity?
We started running a dehumidifier in the bedroom in the daytime in the winter, just so the bed wouldn't feel damp when we went to bed. I don't like the electricity that entails, but our wood stove wasn't drying the house sufficiently to solve the problem.
Adding something on a topic I saw on another thread, but mentioned in Jay's post, is the concern about whether a straw bale building is suited to the wet, damp Pacific North West. It is! However, as in any building where moisture could cause a problem, care must be taken to keep the bales dry. There are many straw bale buildings performing well in parts of the North West that receive in excess of 60" of rain each year. If the building has been designed for the site and built well, it'll last for a very long time. The general rule is to make sure the structure has a good hat (large protective roof overhangs), good boots (water proof sills and elevated above grade to prevent rain splash from soaking the walls) and a coat that breaths (vapor permeable plaster skins).
The exterior of a plastered straw bale wall is a reservoir system. Wind-driven rain that strikes and soaks into the wall won't cause any harm so long as that moisture can come back out on the next dry, sunny day. That works well in my part of Southern Oregon where wind-driven rain is common as a storm front moves in, but tapers off after an hour or two. Most of our rain tends to fall straight down for the rest of the storm--a few hours to a day--followed by a week of sunny, dry weather. But where wind-driven rain can be constant for days and weeks, and dry days are far and few between, there's little opportunity for the moisture to evaporate out. The wall system could be overwhelmed and the liquid water can begin soaking into the bales, raising the moisture level to a point where microbes thrive and start to compost the bales!
Knowing the year-round weather conditions of a building site informs the design. Where long periods of wind driven rain can be expected, all is not lost. Wrapping the vulnerable sides of a bale building with a full depth porch (minimum 8') affords great protection and relatively low-cost outdoor living space. Landscape solutions like a trellis, hedge, or screen of trees can offer protection. Many straw bale buildings have siding on them, with a proper rain screen. The bale walls receive a scratch and brown plaster coat, then siding is attached to furring strips that have been planned for during the house framing and bale stack. The flatter the bale walls are, the flatter the furring strips, the flatter the siding. An air gap between the siding and plaster is screened at the top and bottom to protect against insect intrusion; any liquid water that makes it through the siding drips harmlessly to the base of the wall, while water vapor migrating through the wall from inside can still escape. I understand that yet another option is mineral paint, though I haven't worked with it yet. These long-lasting, highly vapor permeable paints are reportedly much more water repellent than lime plasters, and they're also more durable than a clay plastered exterior wall that hasn't been treated to make it more water repellent. You don't want to confuse mineral paint with the kinds of paint usually used on conventional siding, e.g. latex paint, which is considered much less permeable, if not a vapor barrier after a few coats.
What about persistant, high humidity outside? Like Jay, I live in the damp northwest. I also live next to a pond and a wetland, and am on a north-facing slope. So, between the fall and spring equinox, there's maybe a total of 4 days in which it's dry enough, long enough, to dry clothes outside. Every night, the dew falls (even if the rain doesn't) and covers everything with water. The grass stays damp, and never dries during that whole time (unless we actually get and stay below freezing all day, which happens like 2 times a year, usually).
Would there be any way to make strawbale work in such a climate? I only get, during the darkest 3 months, maybe 2 hours of sunlight in any given spot during the day, if that. I can't even dry clothes inside my manufactured home, because mold starts growing on the walls. I'd love to have a more natural building, and strawbale seems so cool...I just don't if there's anyway to make it work...
@Nicole - I'm wondering if having a Rocket Mass Heater in strawbale homes in our wet climate would make a difference? Would the even dry heat help, or would it just push moist air through the walls to condense there?
I have read that homes in Newfoundland coped with their high moisture levels because they were so leaky that the moisture kept moving. When they started "sealing" the leaks, the houses started going moldy and having problems. Unfortunately, a leaky house using traditional heating systems wastes a lot of resources. I'm also wondering whether a simple fan that keeps the air circulating well in a house is enough to stop mold from forming? Or more complex, like an air to air heat exchanger?
I have always been interested in alternative building techniques and have thought about straw bale construction but couldn't find much information on the subject.
This sounds like it is exactly what I have been looking for!
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This question, " Is it just too damp where I live for straw bale? " is a hard one, because it depends on so many other factors. Bad news first: even though straw is made of the same basic ingredients as wood - lignin, metalignin and cellulose - the far great surface area of bales means that if the 20% relative humidity conditions that allow cellulose eating molds to grow is reached, bales will grow mold quicker than wood.
The good news is that I have yet to hear, in 27 years involvement in bale circles, of a bale house whose straw was compromised by ambient moisture, including in the North Wet. But in a climate as radically damp as Nicole describes, it would be wise to have means of reducing the humidity of the air inside the house. Otherwise, any time the surface of your floors and walls reaches the dew point, they will accumulate moisture. Rather than rely on freestanding dehumidifiers, I would look into a whole house ventilation system with a heat exchanger and dehumidifier built in.
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