We've been living in the house for a little more than four months now, but it seems like much longer than that (in a good way). The long ordeal of planning and construction has faded from our memories, and we're simply enjoying living here.
In most respects the house is performing extremely well. The 12,000 BTU heat pump is having no trouble keeping the entire house comfortable. Outdoor temperatures haven't fallen much below 20°F yet (-7°C), so it hasn't really been challenged, but we're not too worried. We left town for a few days last week and turned the heat pump down to 60° (it's normally set to 68), and it never even ran while we were away. The indoor temps ranged from 62-66°, even though outdoor temps stayed below freezing.
Our one complaint this winter is that the house has been extremely dry (relative humidity ranging between 20-25%), with our heat recovery ventilator running on low, at 62 CFM. This isn't too surprising, since Ted and I are only two people living in a fairly voluminous house without pets. We don't have any houseplants yet either, but I plan to remedy this soon by setting up our indoor vegetable garden upstairs (that will be a whole other post, hopefully in the near future).
For now our solution is to run a humidifier. (I know, so pedestrian!) The main problem is that the humidifier is quite loud, drowning out our whisper-quiet heat pump and HRV. Our long-term fix will be to add plants and see how that affects things, and then maybe get an ERV core for the ventilation system. It's pretty easy to swap cores, apparently, and the ERV will transfer moisture from the outgoing stale air to the incoming fresh air. Naturally, our many geeky onlookers (including Peter Schneider of Efficiency Vermont, who installed all the monitoring equipment) will be curious to see what difference the ERV makes for comfort and energy use.
You may have noticed that this post is called "Winter in a Passive House," and not "Winter in an Almost Passive House." This is because we built a full-fledged, certifiable passive house (pending the actual certification, which we haven't gotten around to yet). We made the decision ages ago, but I never changed the name of the site because I didn't want to jinx things. I'm not so worried now, since we did insanely well on our blower door test (91CFM, which translates to 0.29ACH50). I therefore feel pretty confident about our final PHPP numbers, even if we messed up a thermal bridge calculation or two.
I haven't decided what we should rename the site, so for now I'll just strike out the "Almost" and see where the spirit moves me.
Speaking of winter, here are some lovely new snowy pix!
When Ted and I started this endeavor in 2009, I didn't know the slightest thing about construction. I couldn't have told you how a stud wall is built, or even described with confidence what a 2x4 looks like.
My how things change! Just last night I dreamt I was quizzing a contractor about air barriers and external insulation, while harboring deep suspicions that he hadn't properly managed the vapor barrier on the 2x6 walls of the house he was rehabbing. I was gearing up to explain why polyisosyanurate was a better choice than extruded polystyrene (XPS) for above-grade rigid insulation, since the blowing agent used to produce XPS has a much higher GWP (global warming potential) than the one used for polyiso... but then I woke up.
I honestly never intended to jump into the deep end of residential construction theory! We simply wanted to build a comfortable and energy-efficient house, which led us to Passivhaus, which led us to our energy guru Marc Rosenbaum, who opened my eyes to the rough and tumble world of building science.
I have a problem with the Passivhaus people, because they are building ugly freaking boxes. The only way to get a building to last a long time is if the building is maintained, and people have to want to take care of it. People do not take care of ugly things.
Ouch! That one hurt a bit, probably because I sometimes worry that our house is an example. The exterior is nowhere near as bad as some passive houses I've seen pictures of, but it is not quite as handsome as I would have liked:
I should mention that this is the house's least flattering angle, and it looks particularly odd without the solar collector that will attach to those two white strips on the facade (probably making the house look even odder). I'll post more flattering and accurate photos below, but you can see that we have indeed built a big freaking box.
The house didn't start out like this. We got invaluable advice from our friend Camilo, an architect in New York, and he designed something a lot more stylish:
But reality intervened, and we had to stray far from his plan. Our building site is both sloped and ledgy (i.e. lined with bedrock), so a stem-wall foundation was impractical, and we needed to shorten the house from 58' to 46' to keep the lower piers from rising ludicrously high. This meant lopping off some space (which we probably won't miss at all), and it made it easier for us to reach Passivhaus numbers, but it also made the house more boxy and less "architectural."
We were very sad to have to reverse the roofline, since it drastically reduced the amount of space for solar electric panels. We therefore added the overhang to the top of the south wall, which turned Camilo's dramatic design into a stark-looking quasi-saltbox.
That said, I don't think our house is ugly enough to invite future neglect. In real life, it looks a good deal better than that first photo would suggest. You can't really see the garage in that photo, and the garage's south-facing roofline complements the house nicely:
It looks even better from the road (which of course is how most people will see it):
And the best part, frankly, is the interior. While we mercilessly chucked most of Camilo's exterior design, we consulted him regularly about the floor plan and followed his advice even when it would have been cheaper or easier to ignore it. We refused to replace his vaulted ceiling with a standard attic, which meant we had to find joists that were deep enough for Passivhaus insulation and also strong enough to bridge a 26' clear span. We also sacrificed upstairs floor space to preserve an atrium-like expanse above the dining area. I spent countless hours in SketchUp tweaking and tuning the interior, and now that the house is drywalled I can see that my time was not entirely wasted. It really is a cool space, and it doesn't feel generic or boxlike at all.
One of the special challenges of building a Passive House is heating it during construction. The standard solution for temporary heat is a portable forced-air propane heater, but there are two reasons why we can't use one of them:
They put out a tremendous amount of moisture, which would take ages to dry out in a tight house.
It would release a lot of nasty combustion chemicals into our building envelope.
But it's winter in Vermont, and our various crews and subs are oddly cranky about working in a frigid building. So we had to come up with something.
Once again, it was Eli to the rescue. He somehow found a weird exterior heating device, and we're pumping the heat into the house through a temporary hole in the floor. This puts the combustion outside but fills the house with delicious heat. (Note that we have to open a window first, or else there's nowhere for the warm air to go.)
It's cantankerous little devil — Eli spent the better part of a week getting it to work, seeking advice from a wizened engine guru of his vast acquaintance. Ted and I live in vague fear that it will either (A) stop working or (B) explode, but we are also grateful that it has shown up to lend us a hand.
In other news, the garage is nearly complete. Mark and Luke (from Eli's team) will start the roof edge trim later this week, and the roofing will soon follow. Windows and doors will arrive by the end of the month, and we look forward to being able to store stuff inside. I'll upload more garage photos soon, since it's truly a cool and wonky little building, deserving of its own post.
Here's a photo from this morning. Can you spot what's funny about it?
One of the many things I like about building websites is how easy it is to change things later on. Want to change some wording or add a new photo? Piece of cake! Need to change something complicated like the page layout? That's a bit more work but 100% doable — change a few settings and template files, and you've got a new layout.
Changing a building? Not so easy. You can't just edit the source files and hit "Reload." Nope, changing a building involves crowbars, debris, dumpsters, and a whole lot of work and expense. My sole consolation about building a house from scratch is that it's apparently less painful than trying to remodel, so we're making every effort to do things right the first time around.
This has meant paying constant attention to detail and making sure we're designing for longevity. The idea of doing things right is so deeply ingrained that we don't even ponder the alternative, and so we often forget how unusual it is.
For example, Ted recently shared some photos of our garage on Google+ and received unexpected praise for the generous overhangs:
I designed the garage myself, and when it came to sizing the overhangs I simply asked Eli what he recommended and went with that. It didn't occur to me not to have overhangs, or that sizing them properly was unusual enough to attract praise.
And yet it is. When people with building experience come visit our house, they're astonished by how well-built it is and how little we've compromised. The most recent was Russ, our new rep from the building supply yard. He said he's worked with lots of customers who initially intend to build a super-insulated, passive solar, [insert eco-adjective here] house. But then they see the price for all those green-building features, and they scale it back until they wind up with a house that's only marginally more "green" than a conventional house.
Russ told us what a thrill it is to see a house where this hasn't happened. Quite the opposite — our original target was an almost-passive house, and yet here we are building what is now likely to be a certified passivhaus with solar hot water and a 3.96 kW photovoltaic array. I honestly can't think of a single corner we've cut with regard to the building's performance.
We've certainly trimmed some other corners. Heck, we lopped about 500 square feet from the original floor plan. The bathrooms are small and simple, the bedrooms have ordinary (not walk-in) closets, the kitchen cabinets are stock rather than custom. But we can't bring ourselves to install anything we'll want to rip out and upgrade in a few years. Hence no formica counters, vinyl floors, or any of the other money-saving standbys.
Alas, there is a reason so few people build this way. It's really expensive! I know I've posted about this before, but it's such a big part of our building experience that I can't help repeating myself. Nearly every estimate we receive is like getting the wind knocked out of me — it seems impossible that construction could be this expensive, and yet apparently it is.
One of the hardest parts is how often I feel ashamed or that I've somehow failed. When I started this blog, I really wanted it to describe how we built an almost-passive house for some cute number like $100 or $125 a square foot. But we've sailed past $200 a square foot, and I don't yet know what the final number will be. I'm not looking forward to taking out that mortgage, nor do I relish the possible eventuality of selling the house for less than we put in.
Ted suspects that a lot of our costs are because this is a custom home. Yes, all the eco-bling is adding a lot, but not as much as the general costs of building a distinctive home on a challenging site.
Perhaps this blog will help illustrate the need for production-scale passivhaus construction. Such construction is common in Europe, and it's beginning to take off in North America. Builders of modular homes are getting in on the game as well, and perhaps very soon it will be possible to get a house like ours much more easily and cheaply than we are. I certainly hope so, because I wouldn't wish this process on anyone, and yet I definitely want more people to have this kind of house.
Due to some prior commitments, Eli pulled his crew from our job for much of November and December, and the pace of our construction slowed down accordingly. Eli already had a busy year lined up when we first called him last spring, but he couldn't resist the lure of building southern Vermont's first (almost) Passive House. He was able to pull it off thanks to a lot of schedule-shuffling, and once we were weathered in it was our turn to be shuffled.
Fortunately, I am such a sporadic blogger that I still have heaps of photos to share. And things are swinging back into high gear, so there should be more rapid and dramatic progress soon.
Let the photos commence! Our solar panels went up in November — 3.96 kW of DC goodness. We're not hooked up yet, but that will happen by the end of this month.
The plumbing work began — I suspect a lot of rough plumbing looks like something drawn by M.C. Escher, but ours is pretty over-the-top:
With Eli's team off in Guilford, we hired a pair of building pros to put up our exterior polyiso (rigid foam) insulation , housewrap, and strapping. We probably won't put up the siding until spring, which means our house will have that classy Typar look for several months. Eli once mused that they ought to sell housewrap printed to look like painted clapboards, but that most Vermonters would then never bother putting up real siding on top of it. I concur.
Anyway, here's the polyiso going up the north wall:
I am pleased to report that Ted's collarbone surgery was a success and that he is recovering nicely. This means that he is back in the DIY saddle, and for the last week we've been busy constructing the two loft spaces.
Ted at the chopsaw:
Before sharing the photos, I should explain the two loft spaces. We haven't built any of the upstairs interior walls yet, because we want to install the ceiling drywall all at once, creating a nice uninterrupted vapor-barrier. But we can't put up drywall until the roof insulation goes in, and it's hard to do any of that with a ceiling that's 25 feet high in spots (above the staircase and the two-story dining area).
Ted and I therefore decided to build the two loft platforms — one is a utility loft over the upstairs office area (it will house the PV inverter and the heat recovery ventilator), and the other is a cozy space we've dubbed the "manatee cave." Ted and I are inordinately fond of manatees (especially dwarf land manatees), and we thought that a manatee cave was much more original than a mere man-cave.
Anyway, here's the upstairs before we started building the lofts:
And here it is afterward:
The manatee cave is on the left, and in the foreground you can see the utility loft. Today we built a temporary platform connecting the two lofts (to facilitate the insulation and drywall work), and tomorrow we plan to build a platform between the utility loft and the west wall, which is where the curved staircase will go (the current staircase is merely temporary).
This last photo won't be very exciting to anyone but a building science geek, but it is very exciting to us. It's the readout from our first blower-door test, taken in December. A blower-door test quickly measures how much a house leaks. If Ted and I want to achieve Passivhaus certification, we need to build an insanely tight house (0.6 air exchanges per hour when pressurized to 50 pascals, roughly equivalent to 0.04 air exchanges per hour in a non-pressurized house).
We had no intention of running a blower-door test this early, because we haven't begun to seal the obvious leaks. The walls and roof are already very tight, but we can still see daylight at the window corners, and the exterior subfloor is completely absent (we need to finish the rough plumbing and electrical work first). But we wanted to insulate the roof so we could put up the ceiling drywall and build the interior walls, so we arranged a preliminary blower-door test to check for leaks around the roof (much harder to fix once the insulation is in). We taped over some of the gaping leak points to prevent them from wrecking the test altogether, but otherwise we haven't done any post-construction sealing.
We weren't expecting a result anywhere near the Passivhaus requirement. So we were quite happily gobsmacked to discover we're very nearly there:
The readout shows that the pressurized house is leaking at 227 CFM, which in our house converts to 0.65 ACH@50Pa. Which means that before we've even insulated or added the ZIP-sheathing subfloor, we are within spitting distance of the rigorous Passivhaus requirement. The test was run by Bill Hulstrunk of National Fiber, and he said that of the thousands of houses he's tested, this was the tightest house he'd ever seen. I am too superstitious to remove the "Almost" from the name of this website, but things are looking good in that department!
Work is now kicking back into high gear — in the near future we hope to get roof insulation, ceiling drywall, rough electrical wiring, and a garage. Our winter has been largely snow-free, a fortunate circumstance I attribute to Ted's and my purchase of a heavy-duty snowblower and season lift tickets at Stratton and Okemo. So I hope to have lots of thrilling new photos soon.
Andrea promised a while back that I'd explain how the foundation works, but I haven't done that yet. We went through a fairly long and painful process to get to the foundation we have now. I think it was worth it—the current foundation looks very cool, and I think it will function well. So let's take a tour.
What you see to the right is the pier foundation as viewed from the west side, looking east down toward the road. You can just see the roof of the car behind the foundation of the garage. That's the sort of U-shaped bit of concrete to the far right, which I will not be talking about, since it's pretty much just a normal foundation.
The horizontal bar of concrete that's closest to the camera is a grade beam. It's mostly resting on footings that have been pinned to ledge, although there's a point in the center where the ledge comes so high that there's just grade beam on ledge, with no special footing underneath. What you can't see from this angle is that the ledge drops off pretty steeply on the other side of the grade beam.
In the center, you can see a wall heading east from the grade beam. This is a shear wall—it's there to prevent racking in the east-west direction. It's solidly on ledge all the way down. The big dark grey wall that's further down the hill is another shear wall that's to prevent racking in the north-south direction.
Racking is a situation where there is a differential force on a wall that tends to try to bring it out of square. The force is called a shear force. Shear walls are shaped so as to resist the shear force. Shear force in earthquake country comes from the ground moving, while the inertia of the house tends to want it to stay in the same place. So the foundation accelerates in the direction of the shear force, and the top of the wall has to move to catch up to it. If you don't have a good shear wall, the wall can fail.
A house that's on piers has limited shear strength, because the piers are just big sticks poking up out of the ground. The footing might look like it will have some shear strength, and indeed the rebar that connects the footing to the pier, combined with the rebar in the pier, does give it some shear strength. But many homeowners in the San Francisco Marina learned the hard way that a house standing on piers with no shear wall is likely to collapse.
But we don't get earthquakes in Vermont, right? Well, not as often as California, but it's best to be prepared. What we do get, though, is high winds. With winds, the ground wants to stay in place, and house wants to move, which will tend to make the piers fall over. We have a pretty tall wall to the south. So we need enough shear strength to accommodate that wind force without failing. So our structural engineer, Ben, specified these shear walls.
The other advantage of the shear walls is, I hope, entirely psychological: there are two piers that are not directly pinned to ledge. I worry a little bit that these piers might somehow fail—they might start to wander, or we might have gotten the drainage and cover wrong, and they might move due to ice expansion. I don't think this is a real risk—we examined this issue carefully and concluded that the footings were secure. But if for some reason we blew it, the shear walls give us a huge additional safety factor that will allow us to correct any problem that should arise. Even though this is extremely unlikely, the fact that they are there gives me a lot of peace of mind.
Referring back to the picture at the top again, you can see a slot in the north end of the north-south shear wall, and a notch in the south end. These are to accommodate the laminated veneer lumber (LVL) beams that will be running east-west along the tops of the piers. So let's talk about wood for a minute.
Anywhere where there is horizontal contact between the foundation and the concrete, we will have pressure-treated lumber. So the grade beam at the top will have a 2x (two-by, not two layers) of PT on top of it. The shear walls will have 2x or 4x, depending. There are notches on the east side of the grade beam on the north and south ends to accommodate the LVL beams; each of these notches will have first a layer of PT, and then the LVL beam will rest on top of that. The LVL beams will be attached to the piers with metal brackets.
Ultimately, when all the foundation wood is in, we will effectively have a sill plate to rest the floor box on. In places, it will look just like a traditional sill plate. In places, the top of the plate will be an LVL beam.
What ties this foundation together is the floor box. The bottom of the floor box is a structural membrane made of zip sheathing nailed to the bottom of the floor joists according to a nailing schedule provided by Ben. This will create a box that is very resistant to deforming as a result of differential forces. This is what allows the shear walls, which are not otherwise connected to the piers, to keep the piers stable.
By the way, I should point out that while it might sound like I know what I'm talking about here, I'm relaying to you a layperson's understanding of how this all works, not a structural engineer's. Hopefully what I'm saying here will be of some benefit in terms of telling an interested reader what sorts of things to look out for, but it's no substitute for actually hiring a structural engineer to analyze your specific project. If you're flying your house the way we are, you definitely want expert help.
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.