It's been a busy couple of weeks on our building site, and I've been fearfully remiss about blogging. I will now right that wrong.

After weeks and weeks of downright biblical rain, we had great weather on October 5 and 6 for the crane. It was no ordinary crane -- due to a last-minute switcheroo from the equipment company we wound up with a 165-ton crane, practically the largest in New England. This was a fortunate switcheroo, because our building site is awkwardly shaped and the pre-constructed walls would have been hard to lift and place with an ordinary little crane.

Here's what our site looked like at the beginning of the day:

The north wall is raised:

Behold our lovely 24" framing:

They braced it from behind:

The west wall:

Nothing warms a homeowner's heart like seeing a crew member wield a level.

A woolly bear caterpillar turned up, prompting a conversation with Milt the crane operator about what kind of winter its coloring foretells (answer: no clue).

Speaking of the crane operator, here's the ginormous crane:

The following day they used the crane to place the 24"-deep roof joists, shown here from the second floor.

They also placed the timber-frame awning, which will hold up the solar panels. It was definitely two dramatically productive days!

Eli's crew has been busy on-site ever since then, but the time for Ted's and my DIY phase had arrived. Last weekend Ted used a laser level to start laying out the interior walls (note autumn foliage in the background).

But our DIY plans hit a major obstacle the next day when Ted had a bicycle accident and broke his collarbone :-(

He's scheduled for surgery in a few days, and he'll be unable to swing a hammer for a solid six weeks.

But work continued, culminating yesterday with the arrival of our windows. Eli and I worked all day Tuesday preparing the rough openings with Vycor, flex-wrap, and flashing tape.

Eli overhead Patrik and Tomas from European Architectural Supply say that we had the best-prepared rough openings they'd ever seen. They even took photos, presumably to shame their other clients.

It was a marathon, but the EAS team and Eli's crew managed to fully install the windows and the front door in a single day. The first one (on the north wall) peeks out into some lovely woods:

So at last we have a weathered-in house! No insulation yet, but it's already warmer and more comfortable than our drafty apartment.

This week Eli and his team got a start on cutting wood for the house. I want to talk a bit about Eli's process, because it's very different than what I normally see done by builders. Rather than trucking raw materials to the site and cutting them to order on site, according to a blueprint provided by the architect, Eli (who is actually an architect among his other talents) has a really high-end CAD package he uses to prepare detailed drawings and cut lists.

This gives him a degree of precision in his plans that allows him to hand his cut lists off to his team, who pre-cut all the wood in the house and pre-assemble what they can in Eli's shop. This means that they can use tools that are set up on a nice flat concrete floor, and store the wood under the roof, and not haul stuff to the site that's going to have to be hauled to the dump afterwards.

I personally find this process both frightening and inspiring. Frightening because I would not have the confidence to go from a CAD drawing to cutting in a shop and shipping the results to the site. Inspiring, because this is exactly the right way to do a custom house: you design the whole thing in a piece of software that is intended to produce accurate cut lists. You have a crack team that can follow the cut lists and reliably produce a stack of pieces that really do fit together. You do as much work as you can in the shop. Then you load it all on a truck and bring it to the site.

This is where we are in the process now. Eli calls it "making sawdust." Eli's crew is going to be cutting and assembling all next week. Nothing's leaving the shop. I think they may still be doing a bit of cutting the following week as well.

Another key aspect of this process is that as the pieces are cut and assembled, Eli's crew marks them, so that when the time comes to put them together on site, all the measuring is already done. So at that point all the team has to do is put the pieces together according to the markings.

Why do I think this is so cool? Because it's efficient. A well-built house, which I think everybody should get when they buy a new house, requires a lot of labor. But a lot of that labor is dead time where you're hunting for things, or switching tools, or whatever. Builders put a lot of thought into saving time on the site, but by doing things in the shop, the time savings are substantially more.

Also, because Eli knows precisely how many pieces are going to go into the building, we started out with a clean bill of materials that we don't expect to have any substantial surprises on it, and Eli is also able to predict with some accuracy, based on his past experience with his team, just how much labor is going to be involved in assembling this.

Many builders brag about building to code minimum, as if that were an achievement, but really building codes are intended to enforce the absolute minimum level of quality, so that if your house was built to code, you at least don't have to worry that it's going to catch fire for no good reason or fall down in a minor windstorm. Many houses built to code minimum have flimsy walls, poor air quality, poor noise isolation, noisy floors, and crooked, flimsy fixtures. This saves money, and allows the builder to sell the house for a lower price, or take a higher profit. There's nothing wrong with either of these things, but if it were possible to make something better, wouldn't that be nice?

Andrea mentioned money in her previous post, and money is a real worry in a well-built house. The problem is that a home buyer has no real idea what actually went into the house that they are buying. They can't easily tell that they are getting a well-built house or one built to code minimum. Some things are obvious, but some things aren't until you've moved in. By using his CAD/CAM system, Eli is building our house for a very competitive per-square-foot price.

The result is that when this is done, we hope to have a well-built custom house without it being so expensive that if we should need to sell it, it would be impossible to recoup our costs. Anyway, that's the plan.

Today I sent this e-mail to our energy guru Marc:

The joists in question are 24-inch roof joists from Nordic Engineered Wood in Quebec. These bad boys will allow us to have a clear span roof (no internal bearing walls) that's stuffed with 24 inches of insulation (mostly if not entirely cellulose).

The reason Marc wins this round is that Eli (the builder/architect) and Ben (the structural engineer) were agitating for flat trusses. Trusses have some structural and workflow advantages, but joists have the virtue of being extremely easy to insulate.

For those of you not in the know, trusses are made of dimensional lumber (usually 2x4s or 2x6s) joined together with metal plates. They are exceedingly strong and relatively inexpensive. The problem is that it's hard to properly insulate all the gaps, and the wood and metal turns into a thermal bridge when it traverses the building envelope.

As an alternative, Marc has long wanted us to build the roof with I-joists. I-joists are an engineered product, which means they aren't made from old-fashioned wood like the Pilgrims used. Instead, they're an unholy adhesive-bound combination of solid wood flanges (the top and bottom bits) and OSB (particle board's stronger cousin). They're called I-joists because the cross-section resembles a capital I.

Unlike trusses, I-joists are very easy to insulate, and the relative lack of material means less thermal bridging. Our I-joists will be a flabbergastingly-deep 24 inches, which is practically unheard of for residential construction. We want this depth for insulation and also for strength.

It was initially hard to find joists this deep. In residential construction they usually max out at 16 inches, and although Weyerhaueser's commercial line includes 24" joists, they aren't available in New England. Fortunately I discovered that our French-speaking neighbors to the north make deeper joists that are relatively easy to obtain.

Ted promises to write a post explaining the technical challenges with using I-joists and why Eli and Ben weren't initially on board.

My current enormous task is to design a complete framing plan. I am literally mapping out exactly where every single stud and beam will go, which I hope will save us a lot of effort when we're working with actual lumber. I'm keeping a running list of questions to ask Marc and our structural engineer, just to make sure we're not doing anything too stupid.

Obviously our primary goal here is structural soundness, but my driving obsession is to Avoid Thermal Bridges. This is one of the central tenets of Passivhaus construction, so I thought I'd tear myself away from SketchUp for a few minutes and explain what this actually means.

To paraphrase Homes for a Changing Climate, thermal bridges are the path of least resistance for heat to flow out from a house. They occur when an element in the house has higher heat conductivity than the surrounding materials. For example, a balcony slab that isn't thermally isolated from an interior concrete floor can suck the heat right out of the house.

The most common thermal bridge in a wood-frame house might be the wall studs themselves. In a 2x6 wall, studs extend through the thickness of the wall. The inside of a stud wall is normally covered by drywall sheets on the inside of the house and cladding outside the house. In the diagram at the right, you can see that the wall is full of fiberglass insulation, except for where the studs are. So the insulated parts of the wall will have an R-value of, say, R-19, but the studs themselves are only about R-6, meaning that much more heat will escape through the studs than through the insulation batts.

We plan to address this in several ways. One is to raise the wall's overall R-value by putting additional rigid foam insulation outside the stud assembly, beneath the exterior cladding. Another is to use as few studs as we can get away with. To accomplish this we are using Optimum Value Engineering, which does all sorts of clever tricks to minimize the amount of lumber used in construction.

So in a nutshell that's what I've been doing, trying to design our house frame with as few thermal bridges as possible. It's a little trickier than it sounds, at least for a construction neophyte like me.

Incidentally, here's a peek at the framing plan so far. It's missing most of the windows and, notably, a roof, but you get the idea.