I spoke to a window vendor today who has a lot of experience with Passive House projects. He pointed out that some of our windows are not sized very efficiently. The problem isn't the big windows -- it's actually the small ones that have a high frame-to-glass ratio (the glass has a better U-value than the frame).
With that in mind, I played with resizing the front clerestory windows, making them larger. I removed one of the front windows to keep the glazing numbers from getting too high, and I spaced them 14" apart so they won't look like they're squished in the corner. That will also make them much easier to install.
But Ted is not fully convinced, so we need to run it by Camilo (our architect). Instead of sending the pix in an e-mail I figured I'd just post them here.
It's a good thing we didn't set up a webcam on our building site last autumn, because it would have shown nothing more than snow falling (and now melting). This is because we opted not to put in a foundation before winter. Yes, we had naively hoped to be living in the house by now, but things didn't quite work out that way.
There's an old saying about project management: "Fast, inexpensive, or good -- pick two." Hopefully this means our house will be inexpensive and good! We could have rushed last autumn to get the foundation dug and poured, but it hardly seemed worthwhile to pour a foundation which we'd only worry about all winter. So we decided to kick back and aim for spring, which is almost here.
The good news is that our plans look great! I spent much of the last six months working on our plans in Google SketchUp, a free 3-D modeling application which will surely get its own blog post. This process has allowed me to nip all sorts of problems in the bud, and Ted and I feel very confident about the design.
I uploaded new drawings to the floor plans page. Sorry, they're only 2-D floor plans and not 3-D SketchUp designs, but they reveal the changes we made this winter:
We added a doorway between the main entry and the meditation retreat area. Originally the retreat space was only going to be accessible from outside and from a secret door in the master bedroom, but we decided instead to have a sliding/pivoting bookcase in the main entryway and hide the door behind it.
We removed the ground-floor guest bedroom. This had been a requirement, because we anticipate having guests who won't be able to climb stairs. But it was eating up too much space on the ground floor, at the expense of the kitchen and living room, so we decided to use the meditation room as a ground-floor guest bedroom when needed.
If someone with a disability moves in full-time, they will need to access a bedroom upstairs. We are therefore leaving room for a elevator next to the staircase. I hope we'll never have to install it, but it's good to have the option. And check out the awesome pneumatic elevators we found online!
Removing the ground-floor bedroom allowed us to enlarge the kitchen, living room, and dining room. In the old plans they were mashed into a single room, but now they are quite clearly defined.
We added a mud room! It's next to the kitchen, and I suspect it will be our usual entrance since it's closer to the garage.
There are many more changes and improvements, but I'll save those for the SketchUp post, since they'll be easier to explain in 3-D.
BTW, for the sake of honesty I changed the site name to "Almost Passive House" (from "DIY Passive House"). The house will not be an official Passive House, but we hope it will perform nearly as well. I like to think of it as the green-building version of "Kosher style" or "Be a model, or just look like one!"
I should probably rename the website, because we're not actually building a full-fledged Passive House. But first, this update:
After waiting ages for our permits, we got our well drilled last week! It's 485 feet deep, which is roughly what we were expecting, and the flow rate is a respectable 8.5 GPM. The good news is that no hydrofracking was required (i.e. fracturing the rock in order to get more water out of it), which would have cost an extra $2,500. So that'll cover the cost our blowout engineering meeting a few weeks ago -- whee!
Anyway, we decided at the engineering meeting that we're not going to pursue Passive House certification. We haven't ditched any of our goals for energy-efficiency — we're simply not trying to shoehorn ourselves into a standard the house wasn't really designed for. Passive Houses are already extremely hard to build in North America, and we have the added challenges of a semi-wooded southern exposure and an architect who doesn't specialize in this kind of thing.
The good news is we're still building a really efficient house. It's going to be very tightly sealed, and we're taking extreme care to minimize thermal bridging. We're limiting the overall glazing, ordering fancy-pants windows from Germany (ka-ching!), using heaps of insulation, installing heat pumps and solar hot water, etc. Marc estimates that our heating and cooling load will be less than the plug load in a normal house.
So even though this won't be a Passive House™, it'll still adhere to the Passive House principles and be a major leap forward from standard construction.
We met with our energy/passive haus consultant, our structural engineer, and our insulation expert today.
We first met Marc, our energy consultant, this winter up at his place south of Lebanon, New Hampshire. We found him because he's an expert in Passive House, which is a building technique we'd become interested in because of its energy efficiency and the level of comfort it would provide. It's turned out to be a good choice, because although we are not going for full Passive House certification, Marc is a very general expert, and mostly uses Passive House techniques rather than necessarily going for full Passive House certification.
This flexibility is good for us, because it turns out that there are a number of architectural features in the house that aren't really compatible with Passive House--in order to both have those features and have Passive House, we would have to go to some very expensive, high-tech materials. Conversely, we could compromise on the aesthetics. We don't really want to do either, and Marc has been helping us to navigate that.
Going in to the conversation today, we were planning to build a 14" thick double wall, with 6" studs on the outside and 4" studs on the inside, and some combination of fiber and foam inside the cavity. We were planning to use open web trusses for the second floor cantilever (see floor plans), as well as in the roof.
Our structural engineer came to the meeting with a wall section, which was pretty good, but had some thermal bridging issues (that's why we have an energy consultant) and insufficient insulation in the slab. He'd done the roof the way we expected, but switched to 2x10's in the floor because of some ambiguities in the architectural drawings. He was the one who's proposed going to 6" studs on the outside wall--we'd originally been planning to use 2x4's.
At the end of the conversation, we'd kept his 2x10's, and his 2x6's, but at Marc's suggestion switched from open web trusses in the roof to I-joists. Instead of building a second inside wall, we're going to add somewhere between 4" and 6" of foam to the outside. Why?
The roof I-joists work better than open web trusses because of the way they're constructed. An open web truss is essentually a structure built up of dimensional lumber, with plates to connect the lumber and form a lattice that joins the top and bottom members, which are continuous along the length of the truss. So there are a lot of irregular air gaps inside the truss, which is handy for running ventilation pipes--that's why we wanted it in the second floor.
Unfortunately, these same gaps make the labor of insulating the roof substantially greater. In addition, there's no convenient place to nail a blocker that would allow us to vent the roof. Consequently, if we want to vent the roof (and we do), we would have to add additional 2x3's along the length of the each truss on either side to provide nailing for the vent--a fairly substantial amount of work, and additional expense. In comparison, the top member of the I-joist is in the perfect place to act as an offset to which we can nail the blocking for the vent.
Unless we hear something really surprising, we're assuming at this point that we're going with I-joists in the roof, and not web trusses. Really surprising would be that the I-joists cost thousands of dollars more than the trusses. We really don't expect that to be the case.
Another concern we had is that a 2' I-joist, which is the thickness we need to get a clear span (no supporting wall in the middle), is pretty big. It's going to stick out a long way on the north side, so we're essentially going to have a 2' box sticking 7' out on that side. We spent a bunch of time thinking of ways to make the box smaller, and then I asked Camilo, our architect, what he thought of a box that size, and he said he didn't think we needed to be concerned about it. That simplified things quite a bit on that end.
Additional complexities on the roof--the south overhang is probably going to be constructed as a box that we nail to the rim joist on that side, rather than an extension of the I-joist. This is because a 2' box sticking out 1' on that side really would look odd. We'll do the same thing on the sides. As I type this I'm already starting to think that we would be better off keeping the box, but that's something to debate with the engineers later. The reason is that since the roof is at about a 30º angle, the overhang if we kept the 2' box on the south side would probably be in the ballpark. And the side box has to match up against the south box and the north box, ideally, or else it's going to look a bit strange. But it could work either way, I think--just a question of aesthetics.
Why did we switch to single-wall, exterior insulation? Mainly because I've been really sweating it on the question of moisture in the wall. I really don't want a wall that rots after ten years. I don't want moisture accumulation in the wall. One of the ways moisture accumulates in the wall is that the wall is colder than the dew point. The way this happens is that insulation runs through the wall. On the inside, it's, say, 68 degrees--well above the dew point. On the outside, it's below zero--well below the dew point. Somewhere inside the wall, then, vapor is going to condense into water droplets, which are then going to make the wall wet.
So what if we put R-25 on the outside of the wall in the form of 4" of poly-iso-cyanurate closed-cell insulation? What happens is that the dew point is now inside that poly-iso. Poly-iso is closed-cell, so very vapor-resistant. As a consequence, we don't expect condensation at all. But if there is any condensation, it's going to be inside the poly-iso, outside of the structure and the sheathing, where it can't cause any harm.
My main resistance to this kind of construction is that I've never done it, and hence don't know how. Marc explained how, and managed to convince me that I could do it. Going this route has a lot of advantages. For one thing, I need to build only one set of outer walls. For another, I can build the walls now, and insulate on the outside later. Given the lateness of the season, this is a very good thing.
As for the 2x10's, we decided to stick with them because they're easier to work with, available off the shelf, and we decided that everything we wanted to put inside the trusses, we can just do in soffits, because nearly all the wall space where the soffits would go is either in the kitchen or in utility rooms; in the kitchen, it's space that would otherwise be virtually unusable, above the cabinets. So there's a bit of soffit in the downstairs guest bedroom, maybe, but we may not even need that. So we get a lot less complexity in the floor design, in exchange for not that much complexity in the ventilation design. I'm inclined to leave the ducting exposed in the utility rooms, but I expect we'll cover it in the kitchen.
Oh, as far as the insulation goes, the main takeaway was that we can do it with dense-pack cellulose, both in the roof and the walls. This is good because cellulose is cheap compared to some of the stuff we were looking at. We'll probably get about R-70 in the roof, and either R-40 or R-50 in the walls, depending on what Marc's models tell us to do. R-50 would require two inches more of poly-iso.
Hm. We have bearing walls in the middle of the house, so that requires a thickened slab under the bearing walls. We went over the insulation detail for that--we're looking at about 6" of foam under the slab, and where the bearing wall runs we'll have to dig down an additional 6" to install more foam, with an overlap and a hole to account for the thicker slab at that position.
We're tentatively going with a window design for the big windows in the front where we have a 4x6" stud between each window. Need to follow up with Camilo on whether or not that will look okay. This prevents us from having to levitate the corner of the building, and we probably need structures that strong to hold the windows anyway, because they are large and contain a lot of glass--on the order of 50 pounds, which has to swing out without bowing the thing it's attached to.
My husband Ted and I are building a house in southern Vermont. We actually plan to build it ourselves, with only the occasional subcontractor. Ted comes from a family for whom this sort of thing is normal, but in my family we consider it a big accomplishment to hang a picture successfully, so this will be a wild new experience for me.
Which is why I'm overthinking it and creating a website! I'm a freelance web designer so I throw together new sites all the time, and I'm hoping this will be a good place to organize my thoughts and ideas. I'm also posting all the construction tips and tricks I pick up from books, online, and on selected home-improvement shows, just so I can remember them when the time comes to put hammer to nail or whatever I'm supposed to be doing.
Oh, and we're not building an ordinary house — our goal is to build something resembling a Passive House. Passive Houses, which originated in Europe, use 80-90% less energy for heating than conventional houses do. Here's an overview of the approach (adapted from Homes for a Changing Climate):
Eliminate thermal bridges: 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.
Make it airtight: This is done partly by wrapping an intact, continuous layer of airtight materials around the entire building envelope.
Promote indoor air quality with mechanical ventilation: Because passive houses don't "breathe" the way a normal leaky house does, an energy recovery ventilator (ERV) is used to exchange indoor and outdoor air. Heat loss is often minimized by passing the air through an "earth tube," which is roughly 130 feet (40m) of 8-inch tubing buried 5 feet underground (this minimizes cold-air loss during summer as well).
Use high-performance windows and doors: Triple-paned, low-E, etc.
Use passive-solar principles when designing and orienting the house.
We aren't currently striving for full Passive House certification — mostly because the calculations and approval process would eat up too much of our budget — but we hope to build something that functions just as well. We are getting help from a first-rate green building consultant and other local experts, plus we're reading everything we can find on the topic.
Our secondary goal is to demonstrate that building an energy-efficient house is not impossible for laypeople or insanely expensive. Ted is convinced it can be done; I am skeptical but not entirely without hope. Keep reading and we'll see how it goes.
Ordinary houses breathe through leaky joints and poor seals, losing heat and wasting energy. But our house won't leak, so we'll use a heat recovery ventilator (HRV) to admit fresh air and expel stale air, transferring heat from one stream to the other.