Wednesday, November 22, 2006

Nitty gritty superins

Nitty gritty methodology, new construction.

OK, we have fiddle faddled around with theory long enough. If you’ve read the whole blog, you realize that there are definite, if not overwhelming advantages to having a well insulated house. By well insulated, we do not mean the paltry “rated” r-17 or r-19 as proposed by conventional builders. That’s as high as they will want to go, since that’s all you can normally get with a 2”x6” stud wall with fiberglass insulation. And they will say, “HEY, that’s pretty good. It’s already 50% better than standard construction.”

True, at least on paper. There are at least three big flaws in their thinking:

1. The actual, measured r-values of fiberglass in very cold conditions (when it really matters) are often half of the rated r-values.

2. Approximately 20% of the wall is wood rather than fiberglass in conventional stud construction. Wood had an r-value of approximately r-1 per inch. So our 2x6 (which is actually 5 ½ inches on a good day, really only has r-5.5. Thermally speaking, r-5 is a hole in the wall.

3. It takes a very well trained and conscientious crew to install fiberglass without gaps, or stuffing, etc. Without a perfect installation, performance suffers considerably.

So, let’s do something different than the herd. If you are going to build a new house, you have a variety of methods available to attain the pinnacle of heating and cooling efficiency, along with unparalleled comfort. I will outline the basics and show you where to get oodles of detailed information.

Obviously, we need a lot of insulation, and a lot of space in the wall to put that insulation. But in addition to that, there are a number of places in a conventionally built house that have little or no insulation, which is dumb. Next time I will show you those weak spots and how to remedy them.

Wall systems:

1. Double wall framing. You literally build two walls, and inner and an outer. Since the inner and outer wall framing don’t touch, that provides a thermal break to dramatically cut heat loss through the wood. This is normally done with a pair of studs 24 inches apart, or “on center” as it is know in the trade. Using two studs every 24 inches is about as strong as using one stud every 12 inches. “Normal” framing uses one stud every 16 inches. So if you live in a place that can get hurricanes, or tornadoes or earthquakes (you know, like all of North America) you will get a stronger house this way as a bonus.

Some framers build the outer wall, then build the inner wall and then build plywood boxes for all the door and window rough openings. Others build both the inner and outer together. This guarantees that all the rough openings will be in the same place and match perfectly, but it also makes the wall twice as heavy to tilt up.

Another advantage of the double wall system is you can have as much insulation as you want with no further increase in framing cost. You can make the gap between the inside and outside wall as big as you want. In my house, I had a 3.5” outer stud, then a 3.5” gap, then a 3.5” inner stud, for a grand total of 10.5” of insulation space. With blown in cellulose that gives you approximately:

r 3.8/in x 10.5in = r39.9

Let’s call it r-40. We will lose some of that since we do have some wood in the wall, and some windows and doors, but we will still end up well above the magic r-30.

2. The 2x6 method. As I have ranted about earlier, just jumping from 2x4 to 2x6 is really not a big improvement, especially when using fiberglass. But there are ways to push this up to very high levels of insulating power.

First, don’t use fiberglass. I don’t know who these people are paying to get their lab results, but this is a big scam. Only in the laboratory will r-13 fiberglass actually give you r-13. In real world conditions, like really cold weather, or really damp weather, or cold damp weather, or a construction crew that doesn’t perfectly install 14.5” batts into perfectly spaced stud bays that are exactly 14.5” wide, with studs that aren’t warped or twisted at all, this stuff typically loses 30-50% of its advertised r-factor. DON’T USE FIBERGLASS.

Blown in cellulose can produce twice the real world insulating power and it’s not hard to get it installed right. So that would give us an actual r-21 for the stud bay itself. To get to r-30, we strap on some foam insulation inside and out. Blue high density Styrofoam insulation is r-5 per inch. If we strap 2” on the outside and 2” on the inside, that gives us:

r-21 + r-10 + r-10 = r-41

So you can literally glue the foam to the studs, and then install your drywall over that using 3” drywall screws. Same thing with the siding on the outside, just use longer fasteners.

Some folks don’t like using the longer fasteners, so there are other legitimate methods as well. You can nail 2x2’s over the 2x6’s, going the other direction. 2x6’s vertical, 2x2’s horizontal. This is called furring out, or strapping out. Installing the 2x2’s at 90 degrees to the studs prevents the wood from all lining up and causing thermal bridges again. This also gives you something solid to nail your electrical boxes to. Plus, you don’t have to use the extra long fasteners, just your normal method of attaching the drywall, screws, nail gun, whatever. You can also use the 2x2 strapping on the outside for easier installation of the siding.

3. 2x6 plus superfoam. There are some spray-in foam products and some ridid foam products that have insulation values of almost r-7 per inch. I hear you ooohing and aaaahing out there. Yes, this is freaking amazing stuff. By comparison, real world r-values for fiberglass (what they want to install in your house) is probably r-2 per inch. So, in theory, we could get:

r-7/in x 5.5” = r-38.5

We still lose a fair amount because every single stud constitutes a thermal bridge that will (relatively speaking) hemorrhage heat out of your house in the winter. We could solve that by putting just a one inch layer of polyisocyanurate foam board over the studs and then drywalling as per normal. This works like gangbusters, but the high tech foam is expensive, both the spray-in kind, and the rigid board kind. But your framing crew will hum along like always which saves time and money, because they have done this framing system a million times. This might be a way to convince a hesitant contractor to give a reasonable bid, since it minimizes the use of “weird” framing.

4. ICF, which stands for Insulated Concrete Form. Pouring concrete vertically (walls, not floors) means building a very strong form, pouring the concrete, and then removing the forms after it gets hard. The forms tend to be expensive and tend to wear out fast. So, some bright fellow thought, “Hey, let’s leave the forms on, and insulate at the same time.” The ICF was born. While these houses are generally not inexpensive, they don’t have to be ridiculously expensive either.

The technology has penetrated the building trades enough that your general contractor won’t think you’re a fruit loop for specifying this method. And because you don’t have to remove the forms, you save labor which offsets some of the cost of the proprietary form system. You will also end up with a tremendously strong house that is fairly resistant to the wind loads that come along with tornados and hurricanes.

There are some downfalls. Concrete is expensive which pushes the cost up. Portland cement (the “active” ingredient in concrete) also requires a lot of energy to manufacture. This is known as embodied energy. Since the whole goal of the exercise is to conserve energy, this is a big minus. This might be offset by the superior durability but the jury is still out on that one.

The promoters of this system sometimes claim performance equal to a conventional r-40 house. Notice how they do not claim r-40 in their product. I think they do this little sleight of hand by using a fiberglass r-40 house for comparison. This is wild speculation on my part. I looked at many web sites promoting ICF’s in one way or another. The vast majority merely stated that they were energy efficient and/or environmentally friendly. Until you show me the data, this is meaningless drivel.

Here’s one that actually names a figure (a whopping r-24), but then boldly state that they perform like houses with much higher levels of insulation. This is actually true if you are comparing it to a conventional house with a just lot of fiberglass stuffed in there, but no additional superinsulation features. But compared with a properly superinsulated house, this is nothing special. We will address the issues of thermal mass in a later column.

So, certainly, ICF’s represent a huge improvement over conventional practice. But I would like to see them get real world r-values over r-30 before I plunk down my money.

So those are the basic methods of building a new house with gobs of insulation in the walls. If that’s all we did, we would make a big difference in energy use, but we would miss some opportunities to finish the job. Next time, we will look at (and eliminate) the thermal weak spots in a conventionally framed house.

If you’re thinking of building any time soon, you need to start a library. Here’s an older book on the subject that has stood the test of time:

Doing a google search for superinsulation will also get you a jillion hits if you’re looking for something useful to do rather than watch bad tv.

Actual progress on the farm house: shot three squirrels with three shots. Squirrel hunters are possibly the primary reason we beat the British in the revolutionary war. Squirrel is not bad eating and has more fat than rabbit. So, back in the day, lots of rural folk shot squirrel to embellish the soup pot and reduce crop losses. But squirrels are tiny, and jumpy. If you can shoot squirrels, preferably in the head so you don't mess up the meat, then shooting a British chap in a bright red suit is a piece of cake. The marksmanship and the weaponry of the Brittish definitely did not compare well with the hunters of the colonies.

I have not heard the little beasties crawling around doing destructive things in my walls. No deer yet, bambi has been very shy since hunting season opened.

Finest regards,

troy and christina


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Rachel Hoekman said...

David said...

Troy, your faithful readers are still waiting on your promise that "Next time I will show you those weak spots and how to remedy them" -- we are also hoping for an update on the squirrel hunting season.

your blog is great

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