We got back into town to see the house had made great progress. All the windows and doors are in, the roof and the side roofs are on, as are most of the shingles. The entire interior of the house is now framed, photos of which I will upload soon. Now that the house is officially closed in (ie lockable), we have been handed our very first set of keys to the new house!
the south wall as seen from the street
house front
back of the house
back of the house. check the grand back porch entrance!
another south wall view
The roof was finished just before Thanksgiving, and the next day Mark and his guys got the first of the basement windows in. By the end of next week we should be “dried in,” which means that I can stop obsessing about the weather report.
From the backyard (the northwest corner)
From the street
Through the neighbors trees in the back yard (southwest corner)
The first of the windows
Anne on the phone to Mom in Göttingen
Tonight Mark and his team hurried to finish at least most of the roof sheeting before the weekend, when snow is forecast. At least when the next storm hits I’ll have much less to shovel!
They are using this neat stuff called Zip System, which is a special OSB board that is then just taped at the seams and is immediately waterproof. You’d think the tape would peel up, but apparently it has years of performance testing behind it.
Rage rage against the dying of the light
No, we're not putting up a billboard in the yard
Earlier in the day
Front View
On Thursday November 12 I awoke to a snowy world. And it kept snowing. I went over to shovel snow out of the upstairs of the house. By the time it was done, there was nearly two feet of snow in the house. It took me five hours to defenestrate it all. (So it took me five hours; at least I get to use my favorite verb.)
Gingerbread house under construction
Front of the house
One day this will be a bedroom
The wet snow stuck to the rafters
The trusses were added today. Finally we get to see what the house looks like in all three dimensions!
Mark Gets Trussed
Here Come the Trusses
All Trussed Up
All Trussed Up Too
So here’s the thinking: If the earth is a constant 50-55F at six feet underground, why not take advantage of that to heat your house? The big “eco-bling” thing to do that takes advantage of that heat is to install a geothermal heat pump. Here’s how it works: You put a huge loop of pipe underground and pump liquid through it. The liquid warms up as it travels underground and expands. When it returns to the house, the liquid runs through a compressor, which makes it even hotter. Then you run air over that hot liquid, the hot air heats the house, and the liquid, now cooled, is funneled back into the ground to complete the loop.
It’s like running a big A/C unit in reverse: instead of cooling a room to heat the outdoors, you’re cooling the earth to heat your house. As proponents like to say: With a geothermal heat pump you heat your house for free (the heat is already in the ground); you just have to pay for the shipping (moving it from ground to house).
Here’s the problem: Shipping is expensive. It takes roughly 1 unit of energy to move 4 units of energy into your house. And since the system runs on electric energy, and producing electricity is only about 30% efficient (ie you have to use 100 units of coal energy to get 30 units of electrical energy) your total net gain of energy of a ground-source heat pump is only about 30%. And the system has high up-front costs.
Then I read about a much cheaper option: the earth air tube (also known as earth-coupled tubes) is simply a big tube that you bury 6 feet underground and then use that as your house’s air intake. Since we’re using an active air handling system in the house (an ERV system, which I’ll discuss in a later post) we can suck the air either straight from the outside or run it through a buried pipe. The theory is that as the air travels through the tube it warms up (or cools in the summer). Here are a few photos of our install:
Mark Installs the section that goes under the house footer
A section of the earth air tube: 12 inch PE (polyethylene) pipe
Digging the trench for the air tube
The air tube intake in the back of the yard
Where the tube comes in the house
So how much does the air actually heat up inside the pipe? That’s a great question. Several experts in the field claim that I will gain a surprisingly large amount of heat, although I remain somewhat skeptical.
A German company, Rehau, makes a system that includes an anti-microbial lining in the pipe that sells for about $4,000. The claim is that the anti-microbial coating is important for condensation that settles in the tube. I was offended at the $4,000 price, since I did some research and I could get a 80 feet of 12″ PE tubing for about $700 (and the Rehau system is just an 8″ pipe, and it’s PVC, which I don’t think is ideal for air you plan to breathe). I looked at coating my PE pipe that I bought from the local plumbing store with that antimicrobial lining (www.bioshieldtech.com), but although the owner of BioShield was willing to give me a great deal, it was still going to cost hundreds of dollars. Even more importantly, since I plan on using the pipe for heating, air flowing through the tube will be warming and absorbing moisture. I think the anti-microbial lining (and advanced condensation drainage) is important if you’re planning on using an earth air tube for cooling your house in a humid place like Louisiana.
Some calculations: my pipe is 80 feet long and has a 12″ diameter, which means it holds about 62 cubic feet of air. My house has a volume of roughly 25,000 cubic feet (three floors of 1,000 sqf with an average ceiling height of just over 8 feet). The standard for air exchanges is one every three hours, although I think this is high. With an air change every 5 hours I would need to move 5,000 cubic feet/hour, or 83 cubic feet/minute. That means that air will spend about 45 seconds traveling through the pipe. How much will that warm the air? I’ll be happy with 5-10F, although one guy I called claimed I could heat 0F air to about 32F with my pipe. We shall see!
An interesting point is that the low thermal conductivity of the plastic pipe apparently matters little. The earth is a terrible conductor as well, so if you used a metal pipe you would transfer the heat that last little distance very efficiently, but it would still take the earth behind it a while to catch up. But apparently that slow heat migration through earth and plastic is enough to heat the air significantly.
There are two benefits to this setup: one is simply the warmed air, which means that my heating system has that much less work to do. The other is that my ERV system will have fewer frost problems. Frost happens when the incoming air is really cold and the outgoing air is warm and relatively moist. When the ERV frosts it has to shut down and go through a defrost cycle. Or you have to hook up an electrical heater to sufficiently heat the incoming air. And the whole point is to avoid heating your air with electrical heat!
One of the benefit of SIP (structural insulated panel) walls is that they go up fast. Mark and his team put up the upstairs walls in two days. This afternoon he slid the last one in place:
Mark puts the last SIP into place
So this is what the house looks like now:
The upstairs looking back to front
From the southwest corner
from the backyard
The view from the front bedroom
Well, we’re getting in on the ground floor. If this were an investment opportunity, this would be where you want to get in:
View from the future back yard (and the current mud pit)
The northwest corner of the house
The Ministry of Funny Walks takes up residence in the future living room
Wait a minute! We didn't order this many skylights!
The walls are going up. Check ‘em out:
Styrofoam Sandwiches - I mean Walls
One of the ways that we’re making our house tight and warm is by using Structural Insulated Panels (SIPs). Instead of using normal stud construction, these are big blocks of styrofoam with Oriented Strand Board (OSB, similar to plywood) on the outside.
Typical walls are 4 or 6 inches thick, have studs every 18 inches, and are filled with pink fiberglass. Not only is fiberglass a mediocre insulator (even when installed correctly, which it is often not), but the wood 2x4s every 18 inches also conduct heat to the outside. Instead, the SIPs interlock to make a continuous wall of insulation all around the house.
At first I asked for a price for 6″ thick SIP walls. Then I found out that they also make the walls in 8, 10, and 12″ thicknesses. Out of curiosity, I asked what the price difference was. It turns out that making my walls twice as thick–a full foot thick–cost only about $2,000 more than the 6″ walls. Anne and I thought about it very briefly and then decided to go for it. You would think everyone would, but the SIP company told me that we are the first in the Gallatin Valley with such thick walls. The only place they really sell it is in northern Alaska. But why not use it everywhere? Seems like a no-brainer. Insulation is measured in R-values. An inch of wood is about R-1. Code requires a wall to be about R-22. These walls are R-48. And completely airtight. They should save $2,000 worth of heating within just a few years–and then save us money from there on out.
Plus, SIP walls go up really fast. Here’s how they go up:
Iwo Jima for Insulation
Sliding the Wall into Place
About One Minute Later -- Done
Here’s the South wall:
south wall SIP
Uh oh. Here was our nice shiny basement with framed basement walls just two days ago:
completed foundation with basement framing
And then we woke up this morning to see this!
let it snow let it snow...but not on our house!
there must be quite a hole in the roof...
