Friday, February 02, 2007

We have a woodstove! And we finish the list of weak spots in conventional house construction.

We have successfully installed our new efficient EPA rated wood stove in the farm house. To use a medical analogy, the house was hemorrhaging to death from heat loss. The wood stove, while not stopping the bleeding, has infused a lot of new blood (heat) and now we rarely see our breath while walking around the house. Did I mention my wife is a saint to put up with this “lifestyle”?

Just for fun, here’s a brief primer on wood stoves, since wood heat will get very very popular when conventional fuels double and triple in price.

There are basically two categories of wood stoves, EPA rated, and non-EPA rated. They are easy to tell apart once you know the secret. An EPA rated stove has passed exhaustive and expensive testing to certify that the stove meets efficiency and pollution standards. A typical EPA rated stove will be approximately 65-70% efficient and will emit almost no visible smoke once it is nicely heated up.

When the EPA instituted these standards, the number of wood stove manufacturers dropped by about 95% (S.W.A.G.) because it is very tricky business to engineer a stove to be that efficient without spending half a million dollars on R&D. You may be assured that if a stove meets EPA ratings, they will PROUDLY tell you. If you don’t see a prominent EPA rating of some kind, you can rest assured it does not meet those standards.

Non-EPA stoves still exist because of some loophole or another. The other big tip off is that a few states have banned the use of non-EPA rated stoves due to the pollution issue. If the stove says it is not for sale in California and a couple other states, it’s cheap and inefficient. Typical efficiency of non-rated stoves varies between 10-50% at the very best. This is true even if they make claims that their stove is “efficient”. Price is often a giveaway also.

There are also wood boilers that are installed outside the house, with plumbing to transport the heat to the house. These are billed as safe and efficient. Safe, yes. Efficient, very much not so. Some are better than others, but the very best will likely deliver less than 25% overall efficiency, and many are worse than that. Most of them are also big polluters that smoke like crazy, making you very unpopular with the neighbors. Approach with caution, and be certain to talk to somebody that has actually owned and operated one that you are interested in. Ask them about smoke too. Ask them how much wood they burn in a year.

EPA rated stoves produce, on average, 90% less particulate emissions (that’s smoke/pollution) than non-rated stoves.

These people are handy if you want a real education about woodstoves:

Now we will finish off our list of weak spots in conventional new house construction.

Here’s the summary list. We dealt with 1-3 in our last installment.

1. Orientation
2. House shape and geometry
3. Airtightness/penetrations
4. Heat loss below ground
5. Heat loss through the band joist
6. Properly insulating the attic, even over the exterior walls
7. Movable insulation for windows

4. Most basements are not insulated at all, or minimally. This is especially true of basement floors. Don’t you like a cold floor in January? Me neither.

As a minimum, you need 2 inches of blue Styrofoam insulation under the floor, and 4 is better. This is especially true if you intend to use your basement for anything other than storage. The basement walls can be insulated with foam on the outside, or foam on the inside, or both. Fiberglass is not recommended, as there is always the possibility of moisture issues, which can rapidly reduce the r-value by 50-100%. Blown in cellulose would also not be our first choice due to moisture issues.

Blue and pink Styrofoam are more or less immune to water damage. White Styrofoam is less moisture resistant, and has considerably less r-value per inch. There is a reason the white stuff is cheaper. Brown foam (polyisocyanurate, or urethane foam board) would also be entirely appropriate. There are some specialty rigid fiberglass sheet products that are designed for use below grade and are moisture resistant, but they have much less r-factor per inch.

5. At the end of every floor joist, along the outside wall, there is a board called the band joist. You can generally see the band joist if you have an unfinished basement. If you walk along the outside wall and look at where all the floor joists are attached, that’s the band joist. This is sometimes completely uninsulated, or insulated badly with little rectangles of fiberglass wadded up and/or stuffed in each bay between the floor joists. This is mildly effective at best.

Once again, the preferred method is to use the high r-value rigid foam products. Carefully cut a block of foam to tightly fill the space between the joists, and cover up the exposed band joist. 4 inches of foam will do. That generally means 2 layers of 2” foam. Once you’re done, caulk the edges to limit air exchange and moisture migration into the band joist. According to the national building code, exposed foam is a no-no, so to be completely safe, you would cut a nice fitting piece of drywall and put that over the exposed surface of the foam, and then caulk that into place. Just for comparison, the 3.5” wadded up fiberglass batt method gives you a real world r-value of about r-5 due to air infiltration losses. 4” of blue Styrofoam with caulked drywall gives you at least r-20.

6. Insulating the attic, all of it. Traditionally, there is a problem with insulating ALL of the attic. Way out on the periphery, where the rafters or the roof trusses sit on the exterior walls, there is physically not a lot of room for insulation. If you picture in your mind the classic triangle roof shape, the vertices where the roof meets the walls come to a point. Likewise in real life, the rafter or truss sits right on the top of the wall. If we install good proper superinsulation levels in the attic, that means r-40 to r-50. Blown in cellulose has about r-4 per inch, so that mean 10-13 inches of cellulose.

In the typical attic, we don’t have 13 inches of space between the roof/rafter and the exterior wall/floor of the attic. Even worse, we can’t even fill the space that is available since most attic ventilation occurs at this intersection as well.

What to do, what to do. The answer is to raise the roof. There is a thing called a superinsulation truss, or a raised truss. It does exactly what it sounds like. It raises the roof by a foot or so to provide room for everything, insulation, ventilation space, etc. They just cost a bit more, and that’s ok. For remodelers, we’ll deal with that in a later discussion. In 1985, they’d barely heard of such a thing and I had to build my own trusses. Tedium upon tedium. These days, they are a standard item.

You may have to fight the contractor to get 13 inches of cellulose for your attic. They will argue that it is uneconomical to go past 8 or 10 inches at the most. In the long run, they are wrong. Just persevere. Tell them you know with certainty that your house is going to end up with r-50 in the attic. You are not so sure which contractor is going to build that attic. Hey, it’s your money, and your house, and your future energy costs that are at stake here.

7. Windows. They are a blessing and a curse. Old single pane windows (one piece of glass) are only slightly better than having a gaping hole in the wall for the winter to come howling in. Glass has abhorrently bad insulating properties. Anti-insulation you might say. One layer of glass has about r-1 insulating power. Since we are shooting for r-30 to r-40 in the walls, r-1 is completely unacceptable.

Alternatively, we could buy state of the art, double or triple glazed, argon filled, low-E (E stands for emissivity), thermally insulated frame “super” windows. These are unquestionably better, but still only manage r-3.5 to r-6 maybe. Compared to our walls, that’s still pretty bad. There are alternate measures to work around this…

First, don’t have huge amounts of glass in your house. Many houses with lots of glass have them covered with drapes or blinds 99% of the time anyway. Majorly dumb. Lots of glass will cause overheating in the summer and high heating and cooling bills all year ‘round. A nice rule of thumb is to have about 10% of your floor space in windows. If you have a 2,000 sq. ft. home, you should have about 200 sq. ft of windows. Put them, as far as possible, on the south wall where you will get some solar/heat benefit from them. Next, east and west windows, and least desirable are north windows. They are the energy black holes of windowdom.

Second, consider some kind of insulating window coverings to be closed at night and on cold cloudy days. Some drapes are available with extra layers that slow heat loss somewhat. If you want a traditional look, they are better than nothing. The problems is, they don’t seal the window off from the air in the room. Then the space between the drapes and the window starts to function like a chimney. The air in there gets cold from the window. Cold air is more dense than hot air, so it falls. This sucks in more room air at the top of the drapes, and you set up a nice little convection loop that pumps cold air from the window into the room.

There are other ways to beat this, called movable window insulation. Some products are extremely expensive, and no matter how much energy you save, would never pay back over your lifetime. But careful shopping will find some reasonable compromise. There are roller shades, whose edges run in tracks, so that when closed, the window is truly sealed. This can easily double the r-value of the window and dramatically cut down on drafts and convection currents.

If you are handy, you can make your own. The library and the internet will yield a number of do-it-yourself solutions. Search for moveable window insulation. You can carefully cut extruded polystyrene (blue board or pink board from the hardware store) to fit inside the window frame and glue thin plywood (luan) or poster board to cover the foam. Bolt a couple of nice handles or knobs on for easy handling and you’re in business. There are laminated fabrics available that incorporate a radiant barrier and an insulation barrier that is geared to the do-it-yourselfer.

This can be friction fit, or there are magnetic products to make it stay on the window. You could also build “shutters” that look nice and are easy to operate. While some have difficulty with the aesthetics of a window covering like this, others use this creatively. Mount a quilt top, or put a copy of a Monet watercolor, etc etc etc. There is no reason for them to be unattractive.

This covers the major flaws in conventional new house design. We will deal with the problem areas faced by the remodeler as we overhaul our own house.

Finest regards,



Rachel said...

I like your would add alot:)

troy said...

You are absolutely right. Pictures would add a lot. Pictures will be added in the not too distant future.

Finest regards,


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