I was on the phone with Marc the other day and he pointed out something that hadn't really occurred to me until he mentioned it: when we hired Ben and Eli, we took on a new job. One of the key things that you will hear from anybody who has any experience building a passive house is that your team has to be on the same page about what you're trying to do, or important things will fall through the cracks, and compromises will be made that make a lot of sense from the viewpoint of one participant in the project, but create a huge problem from the perspective of another participant.
We've made a ton of changes to our house since we first started brainstorming about it with Marc a year and a half ago. A lot of them hit quite recently, when Ben talked us out of our Shogun foundation, and when Eli talked us into flipping the roof. We had to give up some things we'd been looking forward to, but we tried to keep a razor focus on the air barrier and insulation, because together those give us what we really want in this house: a consistently comfortable indoor environment.
But one point that Eli really pushed us hard on was the roof. In order to understand what the controversy was, I need to explain the original roof design that Marc came up with. On the way, let me point out that because Andrea and I are so interested in the details of this process, we never have a conversation with our honored teachers in which we just listen to what they tell us and do it. Consequently, nearly every aspect of the house has our fingerprints on it in some way, and we don't always remember which things we decided to do were "nice to have" and which were crucial. The roof design wound up being one of those things.
The problem with an almost-passive-house roof is that it has to perform consistently in two senses: first, the insulation has to be consistent. We can't have it settling down from the top, bunching up on the bottom. Way back when, when we got our first estimate from Keith at Thermal House on insulating the roof, we were absolutely floored: it was going to cost about twenty thousand dollars. Why so expensive? Because we'd chosen to do a cathedral ceiling, not a sensible flat ceiling.
Flat ceilings are easy to insulate--you can just dump the insulation on top of the ceiling joists and spread it out, or if you want to get fancy, use dense-pack cellulose. Because the ceiling is flat, there is nowhere for the insulation to go. You wind up with an irregularly-sized air gap above the ceiling, since your roof certainly isn't flat, but in most situations it should be pretty easy to get a nice thick blanket up there.
With a cathedral ceiling, you don't have the luxury of flat. Keith solved that problem by using a really expensive foam product that he was confident wasn't going to move. But we can't afford to spend $20k insulating our roof. So Keith and Marc and Andrea and I did quite a bit of negotiating. At the time, we'd been planning to use open-web trusses to support the roof. We were confident we could get trusses that would span the distance from the north to the south wall, and would support the dramatic 7' overhang we wanted on the north. But insulating open-web trusses is really hard, as Andrea explained in her recent post.
What we came up with was that instead of using trusses, we'd use I-joists. Andrea did some research on the Internet, and found a supplier for a 24" deep I-joist that would span the distance we wanted, and additionally would support the cantilevered overhang. Marc and Keith both liked these better, because Keith was confident that he could do a dense-pack cellulose installation without any voids using the I-joists. Marc liked the I-joists because they cause very little thermal bridging: the webbing between the flanges on the I-joist is only 7/16" thick, so even though its R-value is substantially less than that of the roof, there isn't enough of it to create a problem.
At this point I need to talk about roof venting. There are two kinds of roofs: warm and cold. A warm roof is a roof with no air vent. They are popular in applications like ours, because building roof vents is fussy when you can't just vent the eaves into the attic. Typically a warm roof consists of a ceiling, rafters of some sort with insulation packed between, a layer of waterproof sheathing, a layer of insulating board (typically polyisocyanurate), a waterproof layer, and then the roofing material. So it's not a particularly simple roof.
So we got this brainstorm to do a vented roof, even though we're doing a cathedral ceiling. Marc had a clever design. He proposed that we cut a piece of insulation board to the spacing between the webbing of each I-joist. We could then cram this up against the top flanges of two I-joists. This would create an air space between the insulation board and the sheathing that's nailed to the top of the I-joist. Now we have a clear vent running the entire rise of the roof. It's pretty easy to construct, and it'll keep the roof cold.
So that's the roof design we'd been planning on for nearly a year. But then Eli comes along, and he has a number of problems with it. And they are real, serious problems. First, the top flange of the I-joist is going to be really cold on a cold winter's night. The bottom flange is going to be really warm. So the bottom flange is going to expand, and the top flange is going to contract. The roof is supported on both ends, so it might bow in the middle, or the I-joists might warp a bit, but the bottom line is that there's going to be some unwanted movement. Eli felt that this was potentially a big deal; Marc wasn't sure it was, but he didn't claim it definitely wasn't, either. I have no informed opinion on the matter—I have to trust Eli and Marc.
The bottom line is that this got Eli to thinking about some other advantages of trusses over I-joists. One of the big problems we'd left somewhat unsolved with the I-joists was how to construct the overhangs. Remember that there are four overhangs. We'd been planning to stick the I-joists out over the north and south overhangs, and didn't really have a solution for the east and west overhangs. Eli didn't like the idea of sticking the I-joists out like that, because it was going to potentially expose the webbing in the I-joists to moisture on the ends, and possibly wick moisture into the roof. He wasn't entirely clear on how big a problem this was, but it was definitely a concern.
Also, whereas the I-joists are only strong if the webbing and the flanges are preserved, trusses can be engineered so that what sticks out past the envelope is thinner, and yet still provides enough support. We'd been trying to figure out how to avoid having the overhangs be two feet thick, and were talking about cutting off the bottom flange and attaching something to the webbing higher up. Eli didn't like that idea from an engineering perspective.
A final advantage of trusses is that they are open, which means you can stick things into them. This gave us a way to do the rake overhangs—the overhangs on the east and west sides of the house. With the I-joists, we had no answer for the rake overhang other than nailing a box to the side of the roof. This could probably have been made to work, but making it structurally sound would have been quite involved.
I heard about Eli's counter-proposal on roof structure while we were up at the site seeing what had been done, I think on Monday. We'd been talking about using trusses for a while, but on Monday we came to the conclusion that we really couldn't use the I-joist roof as originally designed, and we were starting to go down the path of figuring out how to insulate the trusses. We also started thinking about going back to a warm roof, because the cold roof was starting to look like it would be pretty difficult to build with trusses.
I should mention that in the background we'd been hearing about another scheme that Ben, the structural engineer, was thinking about, that involved a two-layer roof. I didn't really like the sound of that, because it sounded like a lot more work, so I hadn't made the effort at this point to find out precisely what he was talking about. I had visions of having to insulate two sets of cavities. Not a happy thought.
On Tuesday, Marc called Andrea to weigh in on the rash of changes we were suddenly making. I was sitting in my chair minding my own business, working on something or other, and suddenly Andrea thrust the phone at me and said, "You talk to Marc." So I wound up explaining the whole truss thing to Marc, and Marc of course was asking his usual intelligent questions and making comments, and I was starting to feel pretty sheepish about where we'd gotten with Eli.
I mentioned some harebrained schemes for mitigating the problems with trusses, and Marc was pretty patient with me, but he reminded me of what we'd been trying to accomplish with the trusses, and the complexity of getting a good air barrier with trusses, and so forth, and by the end of the conversation I was back to believing that I-joists were the right thing, and that we just had to figure out how to make them work. Marc also explained why warm roofs have insulation on top. In a warm roof, you have warm, moist air below, a piece of wood, and then a moisture/vapor barrier. This means moisture can condense on the wood, and has nowhere to go. Venting the roof provides a place for the moisture to go. Without it, the wood could rot.
Andrea reported the outcome of this conversation to Eli via email. A while later Eli called me and set up a Skype session so that he could draw stuff in his CAD package while I watched. What he drew was a roof that used I-joists for structure, but then had a venting system on top of it. The venting system is essentially a second roof, with ribbing that mostly runs parallel to the I-joists.
The eaves are cantilevered on the ribbing, but the ribbing is also used to form ventilation channels. The corner overhangs are done by installing a rib at each corner at a 45-degree angle to the I-joists. The rake overhangs are done by installing ribs at 90 degrees to the I-joists. Throughout the rake and corner overhangs, ribbing is also installed parallel to the I-joists to form vent channels, and vent holes are drilled in all the ribbing that is not parallel to the I-joists, so that even the corner and rake overhangs are still vented.
Of course, this roof has a problem as well. Because it's so nicely vented, if you get a wind across the roof, it can form a relative vacuum at one of the vents. This vacuum can then suck rain or snow into the vented part of the roof, which falls into that roof. If the roof isn't waterproof, the wood gets wet. So Eli is proposing to put down some kind of waterproofing.
One thing that just occurred to me while I was typing this, though, is that now we essentially have a warm roof with wind channels above it, because the bottom layer of sheathing has a moisture barrier on it. So I need to try to understand whether that aspect of this roof really makes sense. But at least from the perspective of supporting the eaves, this roof is the best design we've seen so far, and I'm feeling pretty good about being able to iron out the details.
But now perhaps you can see what an interesting job the prospective owner-builder faces when trying to get a passive house built with the help of a lot of really talented and experienced people. I feel very lucky, but Marc is right in saying that this is a significant job.
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.
After months (years?) of theoretical house planning, suddenly everything is progressing at top speed. Eli (the local builder/architect) is trying to hurry our job along so it will fit into his crew's schedule, which means we're suddenly moving very very fast.
In the last few weeks we:
Completely revised the floor plan, obliterating roughly 500 square feet
Reversed the roofline
Revamped the windows
Committed to a pier foundation
Cut down several more trees (*sigh*)
Just today Ted had very long conversations with both Eli and to Marc, working out the roof assembly (24" I-joists) and many other issues. More talking needs to occur, but much progress was made.
I'm completely wired/exhausted from all of this, and I still have heaps to do. The good news is that we seem to be heading in a good direction. After only a day of excavation the site looks downright buildable, albeit in a Vermonty ledge-riddled way. And I prefer the smaller floorplan, even though we bid adieu to our walk-in closet. (Resale value? Bah!)
Photos, floorplans, renderings -- all coming soon!
In the process of trying to make the transition from planning to building, Andrea and I have been having some serious conversations with a local green builder, Eli, about how to turn our dream house into an actual house. I'm not going to go into too much detail about the actual conversation. I think Andrea has plans for that. But I do want to talk a bit about the thought process that followed, because I suspect this is a thought process that anyone trying to built a house might wind up going through.
During the course of planning this project, a number of people have made the same observation: that wall to the north is awfully tall. The first structural engineer that we talked to was concerned that the foundation was going to be imposing. The excavation guy had some suggestions for how to conceal it artfully. The landscape architect we consulted had some plans as well. The second structural engineer compared it to the wall of a Shogun's castle.
On Thursday, Eli got a bit stern with us about it. He pointed out that with the roof rising almost 40' above the terrain, lots of things that would otherwise be cheap get more expensive. Even putting siding on becomes a serious challenge, to say nothing of insulating the roof and putting on roofing. Furthermore, with the land sloping away to the north, having the roof rise above it means that rain will be falling off the roof on the uphill side, where it will want to run back under the house, instead of on the downhill side, where it will naturally run away from the house. Of course we want to control rain with gutters anyway, but gutters in New England live difficult lives.
The bottom line was that we were going to wind up with a house that was quite a bit over budget, without getting much for the extra money.
So with this reality check in mind, it was time to revisit our goals. Why did we want the roof to slope down to the south, rather than to the north? Why did we want to have a recessed entryway? Why did we want to have an attached meditation space? What exactly are we trying to accomplish with this house: are we really building the house we want to live in, or some other house?
When we originally set out to build this house, I had been planning to do a three-year meditation retreat in an attached retreat area inside the house. We also wanted the house to be something Andrea could be comfortable in during the retreat, and we wanted it to be a place we'd want to live after the retreat was over. We wanted it to be energy-efficient. We wanted it to be attractive outside, and pleasant, welcoming and interesting inside.
The first question is why we were attracted to the Passivhaus style of building. I grew up in Western Massachusetts. Andrea grew up in the Chicago area. So we've both lived in cold climates, and we've lived in houses that were, frankly, poorly suited to cold climates. You can build a house, enclose the walls with sheathing and siding on the outside and plaster on the inside, put in a massive furnace, and be warm all winter. You will be getting a visit from the oil company every month, and it'll be an expensive visit, but you'll be warm.
What you won't be is comfortable. Andrea and I moved from Chicago to Tucson in 2004. We had been living in a brick apartment building in Chicago's Lakeview neighborhood. It was an old tenement building, with lots of thermal mass but not much insulation, so the walls were cold in the winter. The heat would come on, the air would warm up, the heat would go off. We'd be too warm. Then over the course of ten or twenty minutes the air would cool down to the point where we were too cold. Then the heat would come on again, and the cycle would repeat.
So there was a period of about a minute out of every twenty when we were actually comfortable. Except of course that with all that heating, the air was very dry. So we were really never comfortable. We weren't freezing, and we were certainly better off than most people have been in the course of history, but we were spending a lot of money to get a pretty marginal result. I suspect that our apartment would have showed up in an infrared picture as a glowing menace, with the outside walls well above the outside air temperature.
Whether you're an environmentalist or not, it's hard to get around the fact that wasting this much heat is dumb. Energy costs money. So when we moved to Tucson, we were adamant that we'd live in an efficient house; one that didn't use more energy than necessary to stay cool in the summer, or warm in the winter. We went with a design that had a ton of thermal mass, which is a good thing in Arizona, and was insulated on the outside to keep that mass isolated from the environment.
This worked out pretty well. The house was usually pretty comfortable inside. Granted, it was dry, but that's more because Arizona is dry than because we were heating too much air. Our heating and cooling bills were quite modest, and if we turned off the air conditioning and left for a month, which we did from time to time, we'd come back to a house that was still more comfortable inside than out. So when we moved to Vermont, we didn't want to lose that.
It was the process of searching for a housing envelope that would give us the kind of thermal stability we had in Tucson that we stumbled across the Passivhaus concept. Passivhaus is efficient, but that isn't what sold me on it. What sold me on it was hearing that in a Passivhaus the temperature at the top of the room differs very little from the temperature at the floor. That the walls are not cold. That even the windows are not cold. That the thermal cycle is a few degrees, not ten degrees. That so little heating is needed that the air doesn't dry out.
But here's the thing: once we started going down the Passivhaus path, we started to think of ourselves as building a green house, rather than building a comfortable, efficient house. So despite the fact that our lot is fairly shaded, we wanted solar, because that's green. If you look at solar as a value proposition on our lot, it's not a very good value proposition. Our lot is not the best place to generate solar power.
But we were strongly attached to the roof facing south, which is necessary to generate solar power on our lot, because we had gotten into the mindset that we were trying to build a zero-energy house. And so we were about to spend a significant amount of money to create a roofline that was going to get us the solar we "wanted," and there was no way this was ever going to pay off.
The other thing that kept us focused on the south-sloping roof is the picture that used to be on the front page of the site. It's quite a handsome facade. If you turn the roof around, it's not as handsome. This matters to us. You can call me shallow if you want, but I think aesthetics matter. I want the house to look good. And we've put a lot of effort into keeping the facade the way it is in that picture, as the project has become more concrete and less abstract.
So when Eli strongly suggested we slope the roof the other way, our tendency was to resist. When he said to shorten the footprint, our tendency was to resist. And our reasons for wanting to resist are not bad reasons. But they are not central reasons. The house is going to be a comfortable, energy-efficient house whether the roof slopes north or south. We'll figure out a way to style the facade so that it looks good.
The other problem is that the house was quite long, and our lot slopes in the long direction. Because we wanted the retreat space to be available at the same time as the rest of the house, so that I could start my three-year retreat, the house length was non-negotiable. But I'm not doing a three-year retreat anymore. We don't need that space right away. I'm actually kind of interested in building a Tiny House. A tiny house would be fantastic for a month-long retreat, and there is plenty of space on our lot to site one. Heating constraints aren't as severe, because it doesn't need to be inhabited year-round.
So the tiny house plan is something that would solve our long-term retreat cottage needs in a way that I would actually prefer over the monolithic house we'd originally planned. By urging us to shorten the house, Eli forced me to revisit my motivation for building the long house, and it was immediately obvious that we didn't need to make it so long. Shortening it gives us a lot more flexibility in terms of where we place it, so that it can nestle into the terrain a bit rather than jutting out over a long drop.
It's difficult to let go of the mental freight train barreling toward the finish line that was the plan we had before we met with Eli. If we ignore his advice and build the long, south-sloping house, I think we'll be happy with the results. But we'll have a much bigger mortgage, and having a big mortgage tends to be incompatible with doing retreats. It also seems like a bad idea in these challenging economic times. If we make the changes Eli proposed, we have to let go of our emotional attachment to a few cars on that freight train. But the pieces of the house that we really intend to use—that really matter to us—we get to keep. So at this point we're pretty seriously considering taking Eli's advice.
Today I added a tag cloud to the website. That's the list of tags in different font sizes in the right sidebar -- the font size reflects the relative frequency of posts with that label. I added the tag cloud in honor of today's post with the unhappy label "Expensive mistakes."
I would love not to share this story, but it's been a big part of our pre-construction process, and it would be disingenuous not to talk about our mistakes as well as our accomplishments.
I'm going to describe our unsuccessful and expensive collaboration with a structural engineer who wasn't a good match for us. It's not Ted's or my goal to criticize anyone here other than ourselves -- I certainly don't want to malign an honest and qualified professional simply because we weren't on the same wavelength. My hope is merely to share our experience so that other owner-builders might learn from our mistakes.
Things might have gone better if I'd had a clearer understanding of what a structural engineer does. I thought structural engineering was simply about doing load calculations and making sure that we're not building something that's going to fall down. Our design has a few tricky bits, including an interior cantilever around the main staircase, and I thought that was the main sort of task a structural engineer performs.
I failed to realize that we needed a structural engineer who is every bit as obsessed with energy-efficient construction as we are. The engineer we hired is very experienced and highly competent, but he is firmly planted in the world of conventional building. This was an unfortunate oversight because structural engineering is heavily concerned with the building envelope and the foundation, which are probably the two most critical aspects of Passivhaus design.
It didn't help that our foundation is turning out to be very tricky indeed. Our building site slopes downhill from west to east and our house design is oblong, but for optimal passive solar performance we want the long side to face south. The engineer warned us multiple times that it would be more difficult/expensive to orient the house that way, and we assured him repeatedly that rotating the house was not an option. He therefore suggested we pay a landscape engineer to do a grading plan, which would detail all the earthwork required to build a frost-wall foundation.
In hindsight, someone should have proposed we build the foundation on piers, since this would minimize the amount of earth-moving and keep the overall cost down. (Also, a foundation on piers would look really cool!) But this never happened, and we instead paid for a grading plan and then a foundation plan that will require heaps of concrete, overzealous bulldozing, and masses of expensive compacted fill.
Was our engineer wrong to propose this? He had suggested numerous times that we reorient the house along the milder grade, and we repeatedly told him that solar orientation was more important to us. It was not ridiculous for him to think that we were prepared to foot the bill for our obstinate tree-hugging ways.
We knew when we hired him that he wasn't experienced with super-insulated construction, but Ted and I thought we might be able to educate him along the way. We were willing to pay for a few extra hours of his time if it would leave him with energy-saving strategies he could use on other projects. Unfortunately, "a few extra hours" ballooned into a lot of revisions when he didn't see the logic of our requests. And to be fair, a lot of our questions and proposals were pretty loopy, so I don't entirely blame him for ignoring our occasional valid points.
Our energy guru Marc met with him last August to discuss the project, and Marc immediately told us that he didn't think we'd hired the right structural engineer for the job. But by then we felt it would be expensive to change course and hire someone new. I suppose this was the "good money after bad" threshold. Sigh... lessons learned.
Other than the grading plan, not much engineering work happened over the winter, and by spring we decided to bite the bullet and find someone else. Marc hooked us up with someone who seems to be a much better match, and we may have a viable and affordable foundation plan before too much longer (blog post forthcoming).
We are wrapping up work with our old engineer, and hopefully there won't be hard feelings on either side. It's been a blow to my pride to discover I'm not immune from making mistakes, and of course it's been a blow to our budget and schedule as well. But we will recover, and if this is our biggest expensive mistake we will be lucky indeed.
Here's hoping that font size in our tag cloud stays very very small!
Geeky details I won't bother explaining, such as 4/16/4/16/4mm triple-glazing and a plastic warm edge spacer of Psi=0,038
In Europe, dozens of manufacturers make windows like that, but in North America hardly anyone does. The best North American window vendors are making a reasonable attempt, but they all fail on at least one of Ted's and my requirements:
Serious Windows' highest-performing windows are casement, not in-swing, which means they open outwards with a little crank at the base. This is mechanically inefficient, and it also limits the size of windows they can sell. We have some gloriously big south-facing windows in our dining area, and we don't want to make them smaller. Also, their best SHGC is 0.42, which is not as good as the standard Passivhaus windows from Europe.
Canadian companies Accurate-Dorwin and Thermotech Fiberglass didn't sell in-swing windows last time I checked. My main complaint about out-swing windows is that the screen is inside the window, which I simply don't like. And yes, I know about retractable window screens, but I'm still not jazzed about opening a heavy triple-paned window with a crank.
Inline Fiberglass makes a tilt-turn frame, but they still aren't big enough for our front windows. They offered to sell us a modified doorframe full of glass, but c'mon! Also, their best windows use Serious glass, which has slightly lower SHGC and VT than the European glass.
I could list a few more North American vendors, but they are mostly using Inline frames and Serious glass, whose shortcomings I listed above. And you'll notice I didn't mention the big-name American manufacturers -- as far as I know, Marvin, Pella, and Andersen aren't even trying to build Passivhaus-worthy windows.
Ted and I are therefore likely to order windows from Europe. If money were no object we'd want something like Optiwin's Passivhaus-certified three-wood window, but sadly we are on a budget, and ever-plummeting dollar doesn't help. But the high-end American windows I listed above aren't cheap either, and there's enough variety and competition in Europe, particularly from the former Eastern bloc, that we can get something good for an acceptable price.
We haven't made our final decision yet, but we're likely either to get German windows manufactured in Slovenia (or possibly Slovakia?) or Polish-made windows. We rejected some Lithuanian windows, not because we have anything against Baltic states but simply because the importer is based in DC and we want to work with someone more local. If we're handing someone a five-figure check just to place the order, we want to be able to drive over and hassle them from time to time.
We're still waiting on a couple more estimates, but once we make our decision I'll post all sorts of titillating window specs and diagrams for your perusal.
[Added on 2011-10-03: It's possible I've been a little too hard on North American glass manufacturers, since there's apparently some difference in how they test glass performance in Europe, but I stand by what I said about tilt-turn vs. casement operation.]
Basement rim joist areas; holes cut for plumbing traps under tubs and showers; cracks between finish flooring and baseboards; utility chases that hide pipes or ducts; plumbing vent pipe penetrations; kitchen soffits above wall cabinets; fireplace surrounds; recessed can light penetrations; poorly weatherstripped attic access hatches; and cracks between partition top plates and drywall.