Peter has been asking us about doing the final installation of the monitoring system for our house, so that he can get some data out of it (finally!). In order to make that happen, we needed to finish the electrical work, and that's been a bit of an obstacle because of various lighting needs and also because our electrical subcontractor, Andy Harkness, has been in high demand recently. But we managed to lure him and one of his electricians, Karl, up to the house over the past two days to finish up the electrical work.
Imagine my excitement when Andy called me down to say "Ted, can we combine any of these circuits? The panel's full!" It turns out that we are able to keep all the circuits separate, at the cost of having _zero_ free space in the panel. If we need to add even one more circuit, we'll have to add a secondary panel.
Why so many circuits? Peter wants to be able to measure the power consumption patterns of individual devices and rooms. Along with the per-room temperature sensing and an outside weather station, this will give him (and us!) a really good idea of how the house is actually performing.
The snarl of wires coming out of the wall here are the wires to individual temperature sensors in each room, all of which terminate in the utility closet. There's also network wiring, of course—that's the other, smaller snarl of wires.
This is the control/status monitoring panel for the solar hot water. We may collect some data off of this as well.
This is a flow meter that will detect the flow rate of the hot water. We also want a flow meter for the glycol, but had some trouble sourcing one that would be reliable—Peter originally sent us a flow meter that's mostly made of plastic, and Gary, our solar subcontractor, took one look at it and refused to install it. When I called Peter about it, he told me that there had actually been some problems with the device in the field (nothing serious—one leaked a tiny bit, and another failed after a year). So we aren't installing this particular device—Peter's researching other options.
Oh, the reason for the weird bend in the pipe that comes into and out of the hot water flow meter is that we need a certain length of pipe after a bend or a valve before the flow meter, or the turbulence caused by the water flowing around the bend or through the valve will affect the measurements.
This is the flow meter for the well. We're not actually measuring this—it's just used by the sewer department for billing. But it's a meter, so I included it... :)
Andrea and I started sleeping in the house two nights ago, so some things that I've been noticing about the heating profile of the house are starting to become clear.
When we finally got the HRV running a few weeks ago, I was disappointed to notice that we don't have the kind of evenness of temperature between the upper and lower stories of the house that we were hoping for. My first panicked theory about this was that the HRV wasn't working. Panicked, because the tubes are all nice and snug behind walls now, so if we got it wrong, it's going to be a real pain to fix. The good news is that I don't think the problem is the HRV, although I'm contemplating one tweak to the vent layout which we could do without any wall surgery.
When we talked with Peter Schneider about overheating, he reported his experience with some of the houses that Efficiency Vermont has designed up in Charlotte, Vermont. These all have lots of south-facing windows, and Peter hasn't seen problems with overheating in the summer. Based on Peter's reports, we were kind of hoping to get away without doing one of the features we've got on the plan: active shading on the south-facing windows.
If you look at the drawing of the house at the top of the blog page, which is a view of the south face, you'll see that the lower windows have what looks like louvers on them. These are part of the solar shading plan—the idea is to install them in spring and keep them around until fall, and then take them off and stash them for the winter. These louvers will prevent high-angle light from making it through the window in the summer and heating the interior space. By installing them on the outside, we minimize heat gain inside—hopefully most of the heat that is generated when sunlight is absorbed by these shades will re-radiate into the outside air, rather than heating the inside of the house.
Why is Peter seeing different results? I don't know, but I have a theory. I think the windows in the houses in Charlotte may not have the same solar heat gain coefficient as ours, and may reflect more high-incidence light, while letting low-incidence light in, so that they gain more heat in the winter than they do in the summer, even if the same amount of light is hitting them.
The way our house is set up, we have a heat pump indoor unit on the wall downstairs, right in the center of the house. We have nothing upstairs. So the reason I was worried that the HRV wasn't working is that one possible interpretation of the data is that we're cooling the house adequately, but the HRV isn't doing its job in redistributing the heat evenly throughout the house. If that's the case, it's kind of a big problem.
But having just spent the morning sitting down next to the windows with the heat pump off, I have a different theory. For most of the morning, it was nice and cool downstairs, but as more sun came in and the day went on, it started to get hot, just as it is upstairs in the afternoon. In other words, the heat coming in from the windows is heating the upstairs and downstairs evenly; the reason that it feels hotter upstairs is because the cooling effect of the heat pump completely counteracts the heating effect of the windows. I've confirmed this by turning the heat pump back on.
So this gives me some real confidence that when we get around to building and installing the louvers, we will stop experiencing overheating in the south part of the house. I'm still a little tempted to add one more supply vent on the south side of the house upstairs, but that's something I'm hoping to have a chance to debate with the guys at Zehnder. If it needs to be done, it's a really easy fix, because I can do it up in the utility loft, which doesn't have a finished floor.
One of the problems with building a tightly sealed house is that a lot of things we take for granted in a regular house suddenly become difficult when your main ventilation system runs at under 100cfm. A dryer typically blows 150-200 cfm when it's running. This means that it's going to be sucking cold air in through the HRV. On a really cold day, this could cause serious trouble for the HRV—the exchange plate could frost over. But more than that, it's (ironically) blowing warm air out of the house, while at the same time sucking cold air into the house. Again, on a cold day, really not what you want.
Range hoods cause similar trouble—they want to push air out of the house at >100cfm, and the air they are pushing out is generally warm air from the conditioned airspace, which must be replaced with cold air from outside. This seems like a minor issue until you consider that, aside from insulation, one of the main reasons that a Passivhaus has such a low energy budget is that you aren't heating large quantities of outside air as it leaks in through your drafty building envelope. So when you turn on these vents, your undersized Passivhaus heating system may be unable to keep up.
An additional complication is that if you have any appliances in the house that burn any sort of fuel, you are going to be creating a relative vacuum outside of the those appliances, and that might draw combustion products into the interior airspace that ought to be going up a chimney. We already had to tearfully let go of my 30,000 BTU wok ring dreams (actually, Andrea was remarkably dry-eyed) because of combustion products that couldn't be readily ventilated. No gas stove either. But externally ventilated gas heaters are very popular in tight homes, because they can be very efficient. Marc had a wood stove in his house in New Hampshire (although that wasn't a Passivhaus). Anything like this is going to be a potential hazard if you have exhaust fans running separately from your HRV.
Fortunately, we already gave up on a gas heater and decided to go with a heat pump instead. So we don't have to worry about that. But lots of exhaust vents are still something we have to avoid.
What a lot of Passivhaus people do is to set up drying rooms in their houses. This isn't a bad idea—it can be as low-tech as an indoor clothesline, or as high-tech as an enclosed space with a dehumidifier and/or a heater, plus some kind of exhaust fan that exhausts into the living space. We don't really want to dedicate a special room to this task, but we could certainly set up drying racks in the utility room and the mudroom on laundry days, and I suspect we will.
However, on a practical level, there will be times when we will want a dryer, either because we are drying more clothes than we have space for, or we are in a hurry, or whatever. Plus, for resale purposes, not having a dryer is kind of a non-starter. So I did a little research, which I thought I would share here.
The cheapest product I could find is an LG condensing dryer. This works the same way a regular electric dryer does: there's a heating element that heats the clothes to drive the moisture out, and a vent. Where it differs is that instead of leading outside, the vent leads into a condenser system which condenses the moisture out of the air, filters out the lint (sort of, according to some reviewers), and dumps it down the drain.
This would certainly work, and work well, but there are two problems with it. First, it turns out that it consumes more energy than a plain old electric dryer. When you count the cost of heating the replacement air, it's probably a wash, but this is definitely not a win. The second problem is that it cools the condenser with cold water from your tap, which it dumps down the drain. I get the impression that it's not a lot of water, but there are still some problems. Some people love this device, and some hate it. The ones who hate it often talk about problems they've had with leakage and pump failures. I suspect that the Rube Goldberg nature of the condenser has something to do with this.
So I did a little more research, with the help of Green Building Advisor. Actually, a lot of what I learned came from reading GBA, and I recommend this article highly if you want to drill a little deeper than the presentation I'm offering here. GBA talked about a Bosch system called Ecologixx that's called a "heat pump dryer."
When I was reading the Amazon product page for the LG dryer, I just assumed that it had a fan and a dehumidifier, which seemed like it ought to be more efficient than a heating element, but GBA cured me of that presumption. However, the Bosch Ecologixx series of dryer products do in fact work pretty much the way I had hoped the LG would. Most of these products don't seem to be available in the U.S., but the Bosch Axxis dryer is available, and it's actually pretty reasonably priced—about $200 more than the LG. Not everybody loves it, but it looks like a win in theory.
The bottom line is that I feel pretty good about not putting in an outside vent for the dryer. I don't love that this means we have to get rid of our Kenmore dryer, which has been a friend to us for many years, but I suspect that Freecycle will help us to find a good home for it.
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.
I recommend the book highly even if you don't actually wind up building what's in it, because the drawings are really helpful for understanding how to avoid thermal bridges, how to detail the airtight seals between floors, walls and ceiling, and also for ideas about what sort of material to use. I searched it carefully for details that would work for our foundation, but it didn't cover the case we originally designed: a house on a frostwall foundation with no basement. It had some drawings that were very helpful for thinking about how to detail the foundation, and when Marc and Andrea and I were brainstorming about how to build the actual foundation, that detail was very helpful in figuring out what to do (although Marc might argue that it led to me being obsessed with details that weren't all that important).
What the book does not cover at all, however, is how to do a floor when your house is on a pier foundation. Both Marc and Peter were a bit concerned about how that was going to work, but it went pretty well in the PHPP model. Normally in a slab foundation, you'd lay down a really thick layer of expanded polystyrene foam insulation (EPS). This would isolate the interior of the house from the ground. Typically the ground under the house will be warmer than ambient, though, so the EPS doesn't have to do as much work as our floor has to do to keep the house warm.
So we are going with a fairly thick floor—11 7/8" thick, with 4" of polyisocyanurate rigid foam insulation. The floor joists will be I-joists, to minimize thermal bridging. The insulation between the floor joists will be dense-packed cellulose. One really nice thing about this is that the floor will have a lot less foam in it than a typical floor—only 4", rather than the typical 8" or more of styrofoam insulation below the slab that you'd see in a Passivhaus.
An additional complication is that normally to get a good air barrier on the slab of a Passivhaus, you'd have a polyethylene membrane under the slab. This would then connect to the wall air barrier with some kind of sticky tape or expanding foam tape. We don't have that option with the floor box, because there's no place to put the polyethylene membrane.
Instead, the bottom of the box will be sheathed with zip sheathing. Zip sheathing provides an excellent air barrier. The edges of each piece of zip sheathing will be taped together. Remember, this tape is on the bottom of the sheathing. The bottom of the sheathing will be resting on the LVL beam or on the pressure-treated sill plate. This means that the sheathing has to be taped before it's nailed to the plate or to the beam.
In order to accomplish this, Eli's team is going to build the floor box in sections, upside down. They are going to tape the seams on the bottom of each section before flipping that section. When the time comes to install the sections, they will (handwaving, Eli, help!) to seal the joins between the sections.
The joint between the floor-bottom sheathing and the outer wall sheathing will be sealed with a gasket or caulk, as shown below. I'm not sure what sort of gasket to use if we go that route. We'd talked about using iso-bloco tape to seal the edge, but that stuff is very expensive. Another option would be to use EPDM gaskets. I don't know how much the EPDM gaskets cost—maybe they're just as expensive—but I suspect they are cheaper. It may also be that caulk is a good option, although I've heard arguments to the contrary.
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.
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.