More thoughts on insulation

I got a lot of great comments on my recent post on insulation, so I thought I’d write another post to summarize some of the common issues that have been pointed out, and to also elaborate on my plan.


A few readers pointed out the higher labor cost of gathering more firewood. I said in my post that I was ignoring that, but I think it deserves a few more words…

Economists call it opportunity cost. When I was in college, students would queue up at one of the campus coffee shops, which served milkshakes for a dollar on Wednesdays. Obviously, this tradition, knowns as “Shake Day”, was a popular diversion among students who would wait in these long lines with their friends, socializing (or simply pondering silently in solitude) as they waited for their tiny cup of sugary molten goop. An Economics professor once criticized this tradition, by invoking the concept of opportunity cost. The professor argued that the cost of waiting in line outweighed the potential upside of buying a shake for a dollar. Instead, presumably, students should be doing homework to prepare for high salaried careers, or perhaps be peddling their time to low-wage campus jobs for $10/hour.

Of course, this “criticism” wasn’t entirely serious (I hope), but in my eyes, it represented a common perspective in our society that I find troublesome, as it is the very reason we have lots of fat wealthy people who are unhappy and unhealthy. Yes, I can be sitting at a desk, selling my time for $125/hour (or more). But if that’s what I wanted, I wouldn’t be living in the woods. For me, an excuse to get outside, be in the woods, and do a little physical work, is worth far more than what money can buy. More generally, gathering my own fuel makes me more aware of my resource consumption, and having to go out to the woods to gather fuel will also give me better insight into how quickly (or slowly) I am depleting the resources I have, and in turn, get a better assessment of how sustainable (or unsustainable) my lifestyle is.

And yes, it is also entirely possible that I’ll decide at some point that I’d rather spend less time gathering wood. If that’s the case, I’ll change something, but until I try it, I won’t know.

Insulation is for summer too

I focused mostly on how insulation will impact my life in the woods should I stay for the winter, but, of course, insulation matters in the summer too. However, as far as I understand, insulation in the winter and in the summer are actually two different problems.

In the winter, the goal is to keep the cold air outside, from cooling down the interior. Heat is transfered mostly through conduction and convection. That is, the warm air inside heats up the structure’s sufaces, which in turn conduct (and radiate) heat to the outside cold. Or, cold air gets into the structure, displacing warm air. So the common solutions are to use insulation materials that prevent conduction, like foam and batt insulation, and prevent air exchange.

In the summer, the goal is to keep the interior cool, but the main problem isn’t the warm air outside, but rather direct radiant heat from the sun. Up in my area, the air is very dry in the summer, and at 4200ft elevation, the air stays fairly cool most of the time. But the sun beats down relentlessly, heating anything it touches. So the goal is to reflect that heat away from the structure, and to prevent it from heating up the surfaces. To reflect radiant heat, you don’t need thick batt insulation; a coat of white paint, or shiny material like mylar will do the job quite well.

Granted, from what I understand, most homes don’t make a distinction between the different heat transfer characteristics. And indeed, you don’t have to. In the summer, you could let the sun heat up your roof, and then prevent that heat from getting conducted inside by using a ton of batt insulation in the roof and attic. That way, you’re dealing with conduction in the summer and winter, and can use the same insulation for both scenarios. The kind of insulation that works well in the winter can also be beneficial in the summer if you want to make efficient use of air conditioning (which I don’t have), or want to keep the structure from heating up during the day, once it has been cooled at night.

In my particular case, since I am trying to minimize insulation, I plan on trying to reflect sun as much as possible during the summer, instead of relying on insulation. I’m planning on buying light-colored roofing panels, and also lay down a layer of mylar (which I have l left over from Hut 1.0) under the roofing panels to keep the roof from getting too warm in the first place. I won’t be able to expect the structure to be any cooler than the ambient shade temperature, but that’s good enough for me (for now). If I need additional cooling, I might make a swamp cooler, but if this summer was fairly typical, I probably won’t need it for more than a few weeks each summer.


Another issue that I didn’t really address is moisture/condensation. I considered using housewrap, but decided instead to seal up the cabin through other means (namely, by taping up seams between the exterior insulation boards, and by using spray foam insulation and caulk). However, that still leaves the issue of moisture, since sealing up the cabin will simply keep moisture from getting out, which in turn could cause condensation and all sorts of other problems.

Wood stoves too hot?

A couple of commenters also pointed out that a wood burning stove might get too hot. I guess this sort of depends on how big/hot of a stove I get, but right now, I’m leaning towards getting an old fashioned cast iron stove from the local antique shop. I have no idea how much heat those things give off, but I could see how it could get kind of warm.

An Idea

So, it seems like I have two open problems: controlling moisture, and keeping the cabin from getting too hot.

Fortunately, there’s a common answer to both problems: ventilation. Pumping fresh dry air in and moist air out solves the condensation problem, and will probably help with the heat problem too. The plan is to have an air intake (possibly with a small 12V fan) near the stove, so that the air that gets sucked in gets heated immediately. The idea is to pump more air into the cabin than the stove needs, and thereby create an over-pressure (this will also prevent cold air from getting in from undesirable gaps). I’ll have a vent at the top of the hut, where hot moist air gets pushed out. Most of this air movement will happen by convection, since the cold fresh air will rise once it gets warmed by the stove.

I should only need to actively vent air when I’m actually producing lots of moisture, for instance, when I’m cooking or drying wet clothes. At night, I’ll probably stop the air exchange to conserve heat, and while I’ll generate some moisture, I could probably dry out the interior again the next morning by getting the stove going and turning on the fans (or by opening the windows if it’s warm enough). If I decide that I need more insulation, I can always fill in the wall cavities, which I plan on leaving open for now. Adding a moisture barrier later won’t be an option, but hey, there’s always Hut 3.0.

Thoughts on insulation

When it comes to insulation, more is better. Or so they say. Of course, I’m always skeptical when people say “more is better.” More may be better in some ways, but there’s always a cost to having more, and it turns out you usually can get away with less. But how much is enough? That is what I want to know.

I’ve been doing some research on insulation, and as it turns out, it’s a rather complicated subject. On the one hand, there’s this deceptively simple formula:

H = ( 1 / R) x A x T
H : heat loss in BTU/hour
R : R-value
A : surface area in square ft
T : temperature difference in Fahrenheit

Using this formula, I can calculate the theoretical heat loss of my cabin. For instance, Hut 2.0 will have a surface area of around 750 square ft, and if I manage to wrap it all up with R-10, and there’s a 50F temperature difference between the interior and exterior, I can expect to lose (1/10) x 750 x 50 = 3750BTU/hour. That doesn’t sound like much. For instance, even a tiny stove designed for boats is rated at 3000 – 8000BTU. In fact, I can even go down to R-5, and will be under 8000BTU/hour.

The reality, of course, isn’t so simple. I just assumed a single R-value for the entire structure, but the reality is that windows will have a much lower R-value, the door another value, and perhaps the walls, floor, roof will all have different values too. On top of that, R-values give you an idea of how slowly heat will transfer through surfaces, but that only accounts for a fraction of actual heat exchange. In a structure, one huge source of heat loss is through air exchange. For ventilation, outside air needs to be brought in, and that necessarily displaces internal air. At the very least, in order to use a stove, I’d need to suck in enough cold air to supply oxygen for the fire (and myself). So the kind of calculation I did above is useful for setting a baseline, that is, I know my heat loss won’t be any less than the calculated figure, but doesn’t produce anywhere near an accurate or realistic number.

On the other hand, I can’t afford to go and buy tons of insulation. Also, the structure is tiny as it is, so to maximize space, I’d like to keep the wall cavities open instead of filling them in with insulation. There’s also the environmental cost too, since most common forms of insulation are made of toxic materials, or at least materials that are non-biodegradable and difficult to recycle. There are “green” insulation options, but as batt or blown insulation materials, and not rigid boards that I can use. I might get away with less insulation if I decrease air exchange by using housewrap, but housewrap is made of plastic, so that’s less than ideal in my opinion. But then, if I really care about green materials, I should probably be building a straw-bale structure, so perhaps there are limits to how green (or warm) of a structure I can build out of timber framing.

My situation is also different to those of typical homes, because I live in the woods and have a practically infinite and renewable source of firewood. For me, firewood is free, so the cost of heating is also free (if I ignore labor, which I do). From an ecological perspective, I have no qualms burning dry dead wood on my property, since if I weren’t burning the fuel, a natural forest fire very well may instead. So while typical houses may be able to justify the financial and ecological cost of additional insulation by factoring in the cost of heating, for me, the cost of insulation is just that: a cost. The only consideration I have, is to make sure that my heat loss doesn’t outstrip my heating option. Though, if that’s all I’m worried about, I think an old fashioned cast iron stove that the local antique store sells for a little over $100 will probably keep my hut warm either way.

So that was a rather long way to say, I’m going to go light on insulation, and instead depend on good heating to stay warm. Stay tuned to find out how that works out come winter (assuming I stick around for winter, which isn’t yet certain).

The Issue of Rain Water Catchment

Hardly a week goes by without someone suggesting that I set up some rain barrels and capture some rain water. I had a similar notion when I first got the land last year, but I’ve since discarded it as being mostly unfeasible. But, since it keeps coming up, I figured I’d write a post describing why it’s probably not worth the trouble, at least for now.

At first glance, capturing rain water seems like a simple and obvious idea, given my lack of any other local water source. The area I’m in gets over 30 inches of precipitation a year, mostly between the months of October and April. During the warmer months, though, it’s generally very dry. This year has been a bit of an exception, with two very heavy days of rain so far already, but the average precipitation for the whole month of August is less than a third of an inch (although, I suspect the median rainfall for the month is more like zero, with exceptions every few years bringing up the mean).

So, what’s wrong with rain water catchment? The main problem is that most of the precipitation comes down during the colder months, and when I say colder months, I mean freezing months. Last year, lows in November were already falling to the low 20s F, and during the winter months, single digit lows are a regular occurrence. Last winter, it apparently got cold enough that a bottle of soda I’d left in the utility trailer had exploded, and some of my 2.5 gallon water containers had also been damaged. So, freezing weather creates, as far as I can foresee, two problems.

The first problem is that whatever container I collect water in has to be able to withstand freezing. The rain catcher I ended up using for my water tower specifically says that it needs to be emptied before frost. Other rain barrels and water tanks might be sturdier, but even if the container can contain freezing water without bursting, there’s still the fact that big chunks of ice could be difficult to work with if I wanted to use that water during the winter. One possible solution would be bury the water containers below the frostline, but that really complicates what should be a simple solution.

The second problem is that much of the precipitation comes down as snow. While rain can be captured off of my hut roof fairly easily, snow might be trickier since it obviously doesn’t flow the way water does. It’ll first accumulate on my roof, compact, maybe even freeze into ice, then eventually slide off in big heavy clumps. These clumps could come off the roof with sufficient force to either tear off the gutters, or fly right over them. I could create a surface with a nice gentle grade where snow can accumulate and stay without falling off as it gradually melts, but that still leaves the aforementioned issue of the water having to be stored somewhere where it won’t freeze.

These problems (and possible solutions) are further complicated by the amount of water I’d need to make the whole solution worthwhile. This summer, my garden used at least 25 gallons of water a week, and I used another 10 or so for drinking and bathing, for a total of about 35 gallons a week. If we say the dry season lasts 6 months (which is being generous), that’s 26 weeks X 35 gallons = 910 gallons. And trying to bury a 1000 gallon tank, even partially, is no easy task. Besides, a tank of that capacity isn’t exactly cheap; rule of thumb is roughly $1 per gallon for a good tank. On top of that, if I need to build a separate water catchment surface other than my roof, I’d need a surface over 80 square ft in area assuming I manage to capture 20 inches of precipitation, which is probably optimistic (the math: 20 inches ~= 50.8cm, which means 5.08 liters per 100 square cm, or 508 liters per square meter, so to get 1000 gallons or 3785 liters, I’d need 3785/508 ~= 7.45 square meters ~= 80 square feet). And that’s just to barely cover my current needs, which are pretty minimal. I guess I don’t have to try and cover all my needs this way, but seeing how little work it currently is for me to haul water from town, I’d want a replacement to be significantly less work to justify the up-front cost.

Of course, compared to digging a well, which could cost me over $10k, a 1000+ gallon water catchment solution could still be cheaper. So I wouldn’t dismiss the idea entirely, but nonetheless, I don’t think it’s quite as simple as most people seem to think it is. Or maybe I’m over-thinking this. Has anyone successfully setup water catchers in similar climates?

Journal: September 13, 2010

hut 2.0 with rafters

This past week since returning from Burning Man hasn’t been too productive. It rained all day Wednesday and well into Thursday morning, which, though highly unusual for this time of year, and did rob me of my ability to heat up my solar shower, did relieve me of any concerns about irrigating my garden for the week. On Thursday, the temperature barely rose above 60F, and dropped to around 36F at night. I was hoping the growing season would last longer, but it seems likely that I’ll see frost in the not too distant future.

The sun finally revealed itself unabated on Friday, warming temperatures up to a balmy 70F. I took advantage of the nice weather to start working on the rafters. I’m using 2x4s, most of which were donated to me by Camp Warp Zone at Burning Man, and were once part of their shade structure (I love recycling lumber, and in addition to those 2x4s, Hut 2.0 contains pieces of my old bed as well). One thing that had me thinking a bit, was the spacing between the rafters. Hut 1.0 has trusses that are a gaping 36″ apart, with a 30 degree pitch, and it seemed to have done okay for this past winter (not sure how much snowfall there was). My original design for Hut 2.0 had the rafters spaced 24″ apart, but I wondered if I should do 16″ instead. I did a little research online, and found some data that seem to indicate that 24″ would be sufficient for my relatively short span and 45 degree pitch, so I decided to stick to my plans. I also paid closer attention to the 2x4s as I was cutting them and putting them up, to try and keep knots that can compromise strength away from the bottom edge, which isn’t something I’ve always done (but probably should). All in all, the whole task ended up being much easier than I’d anticipated, even working alone. After cutting each rafter, I just had to stick rafter hangers on the top-end, hammer in the hurricane ties onto the top edge of the walls where the rafters would sit, then it was just a matter of hammering in the hangers into the roof beam. (Here’s a close-up of the rafters + knee walls.)

The next step is to add a couple of diagonals to the roof beam to firm it up, then start laying on the roofing. I’m just going to use OSB, then lay insulation on top of that, then Ondura roofing panels will go on top of that. I’m planning on completely finishing the roof before working on the lower parts of the hut, since it’ll be easier to hang scaffolding off the sides of the structure if the walls aren’t there yet. Also, now that it’s rained hard twice, it seems like getting the roof done sooner would generally be a good idea.

In other news, my garden is in full bloom. Yellow squash that were finger length when I left for Burning Man had ballooned into giant fruit almost the size of my forearm. I’ve also got more green beans, and a decently sized cucumber. I also have a few egg plants on the way, and giant green tomatoes that have stubbornly refused to ripen so far, but hopefully will soon. The corn has also matured, but the ears are quite small. Planting corn this year was definitely a mistake, though they did a great job of providing shade to the beans, which was a minor unexpected benefit (I alternated rows of corn and beans, and the rows of beans that got good shade from the corn did much better than the rows that were more exposed).

As winds start blowing (or raining) hints of autumn through my camp, I’m increasingly thinking more about my next steps. I’m starting to run low on cash, so I’m rapidly approaching a point where I need to make a decision. Do I go back to work in the city, or do I have other options? We’ll find out soon…


Portable two-axis manual solar tracker

Solar tracker in front of my camp at Burning Man

Last year, I took my beloved Engel fridge/freezer with me to Burning Man, but had trouble keeping it powered when my generator died. So this year, I decided to run my camp off of the new 100 Watt solar panel I’ve been using up on my property for a couple of weeks now. While my fridge only uses less than 10 Watts of power, I wanted to try and build a solar tracker to maximize output on my property, and Burning Man seemed like a great place to test such a device.

In order for the tracker to be useful on my property, I needed it to rotate around two axes: one to track the sun during the course of a day, and the other, the elevation, needs to be adjustable since the sun tracks higher or lower in the sky depending on the season. Additionally, in order for me to bring it to Burning Man, it had to be easily transportable, yet also be able to withstand up to 70 mph gusts in the desert.

The general design had been bouncing around in my head for a while now, and is based loosely on a giant tilt maze game I made a while back. To lock things in place, there are two half-disks attached to each of the rotating pieces, which are locked in place using a pin. The whole thing is held together with 1/4″ bolts, and can be assembled or disassembled within minutes by one person. And, as you can see below, it all comes apart into relatively flat pieces for easy transportation. To save weight and bulk, I also used more 2x2s and 1x4s instead of 2x4s, and I mostly used scrap wood I found lying about. At Burning Man, I put my AGM battery, which weighs about 60lb, on one of the legs, and when particularly strong winds were forecasted, I put one of my water cubes (also 50lb+) on one of the other legs. I had the tracker oriented south, and moved it roughly 3 times a day to catch the morning rays from the east, mid day sun from above, and afternoon light from the west.

All in all, it worked very nicely, and I’m happy to report that it fulfilled my requirements perfectly.

Back in civilization… er, the backwoods.

So, I’m on my way back to my property after spending 8 days in the desert for Burning Man. As luck would have it, last Monday, the day I left civilization, was a record breaking day for this blog, after getting referenced on the Survival Blog. Well, in case those of you who left comments were wondering why your comments went unanswered, it’s because I’ve been in the desert for the last week. But I’m back now, and this blog will return to its regularly unscheduled program.

Also, hello to those of you who are coming to this blog after talking to me at Burning Man. By now, you’ve probably had a hot shower… you lucky bastards. It’s too late to heat up my solar shower, so it looks like I’m going to have to heat up water on my stove or with a fire, and fill a tub the old fashioned way.