Image Credit: Martin Holladay
More Musings of an Energy Nerd
To end my three-part report on my trip to Maine, I’ll describe my visits to two new energy-efficient homes — an elegant home in Freeport, and a compact 1,000-square-foot home in Bath.
The Freeport home was designed by architect Chris Briley and built by Dan Kolbert. Since the owners of the home haven’t moved in yet, the rooms are still empty of furniture.
Most aspects of the home’s thermal envelope are very well detailed. The basement walls are insulated on the interior with R-etro System foam — 4 1/4-in.-thick EPS rated at R-18. The 12-in.-thick above-grade walls are framed with double rows of 2x4s and filled with dense-packed cellulose insulation (R-44), and the insulated sloped ceilings contain 16 in. of dense-packed cellulose (R-60) in unventilated rafter bays.
The weak thermal link in the envelope is the windows. Instead of triple-glazed windows, the owners chose double-glazed double-hungs from Bonneville. The 2,600-square-foot home ended up with a design heat load of 50,000 Btuh; according to REM/Rate, it has a HERS Index of 36.
Chris Briley prepared a spreadsheet for the owners to compare several space heating options. The installation costs on the spreadsheet ranged from $20,519 (for a propane boiler and a solar domestic hot water system) to $61,908 (for a propane boiler, a PV array, and a large solar thermal system providing DHW and some space heat). The system chosen by the owners — a Viessmann wall-hung propane boiler and a large solar thermal system providing DHW and some space heat — cost $38,325.
Space heat is distributed through in-floor radiant tubing in thin concrete slabs poured over wood-framed floors. The home’s total projected annual energy cost for electricity (at 15¢/kWh) and propane (at $2.50/gal.) is $2,085.
Almost Passivhaus
The last house I visited in Maine was on a wooded site on a hill in…
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18 Comments
I'm intrigued, especially
I'm intrigued, especially after Chris Briley's recent discussions on Passivhaus, if PH numbers/economics were calc'd for the Brewer home.
The max annual energy costs for an all electric passivhaus maxing out on source energy (38kBTU) would be ~$1,480 (2600 sf x .92TFA x 14.07kBTU/ft2a = 33,655 kBTU or 9,863kWh @$0.15). This would result in annual savings of $600/year (worst case scenario). The utilization of solar DHW would bring that cost down dramatically, and along w/ the elimination of the Viessmann boiler, could have offset the extra insulation needed and probably upgrade to decent triple pane windows - assuring better buffering against rising energy prices.
That probably puts me at odds w/ Martin - as I don't think (LCA) the double pane are cheaper than triple pane - except on first cost. Also, I'm a big fan of the unpainted shingles. The weathering of the building will be a nice touch over time. One of my favorite projects of all time is Zumthor's shingled (larch, probably) Chapel in Sumvitg, which has a slight flare (almost imperceptible) where the building touches the earth. This flaring exposes the shingles to the weather, resulting in a really interesting effect:
http://farm2.static.flickr.com/1272/938522776_8e2447c94d_o.jpg
Reponse to Mike Eliason
Mike,
I'm somewhat confused by your comments, and we're probably not at odds.
In the caption to the photo showing some of the windows, I wrote that double-glazed windows are less expensive than triple-glazed windows. That statement is undeniable. Of course, if upgrading to triple-glazed windows allows one to simplify the heating system, and if one wants to include lifetime energy costs into the equation, triple-glazed windows are probably a very wise investment. That's why I've been advocating in favor of triple-glazed windows -- at least in cold Northern climates -- for many years.
Clearly, the house has a solar thermal system which is larger than average -- so that part of your advice is already covered.
Eliminating the boiler is always possible, but the house still needs a source of heat for the cloudy months of November, December, and January. What type of space heating system do you recommend?
Finally, I agree with you completely about unpainted white cedar shingles. That's what I have on my house.
Shingles
The shingles were actually found by Annemarie Brewer herself - we bought them directly from a Maine mill - Dow Shingles in Corinth. They are 18" with a 5/8" butt - beautiful shingles, and about the cost of Maibecs with bleaching oil. We love them, and are using them again on the King/Tweed project Martin wrote about previously.
I was not part of the system design process - I'll let Chris weigh in on some of those decisions if he wants. It was a fun project.
Windows
Martin,
In the picture of the window and cedar shake siding, what protects the wood window sill from rot?
The other window you feature is surrounded by SM foam. Does that window have nailing flanges? How will the window be finished and weather proofed?
Sqft/Occupant and Walk Score
I love the well-executed details and technologies shown in all of the site visits. However, if the intent is not only to show how well a home is built but perhaps also to "show off" its "green" factor, I believe metrics like sqft/occupant and Walk Score (http://www.walkscore.com) should top the list.
Green builders often take a homeowner's idea for a green home and bring it to reality. This means that for the most part green builders are not involved in the decisions involving the size of the home and site selection - the onus almost always falls on the homeowner. These decisions have the biggest impact on energy use.
My question is whether there is a market and/or interest for green builders to engage homeowners before these decisions get made to offer guidance. Is this idea even realistic? At times it seems to me that it would be out of the scope of a builder... but how about a green builder?
martin,
i wasn't disagreeing
martin,
i wasn't disagreeing with you in that first cost of double pane windows is less expensive, although wolfgang feist recently mentioned the price of PH triple pane was only slightly more than standard double pane now. in the long run, however, the reduced energy bills and HVAC sizing with triple pane - as you say, especially in heating-dominated climates - absolutely makes economic sense. even in a relatively mild climate like portland, oregon - we're finding that to be true.
as for recommended heating systems, not so sure on this one, especially as my familiarity w/ region/climate isn't there. it's what i struggle with the most for PH. i prefer the all electric stuff so that comparability w/ grid-tied PV is relatively easy. the projects we're working on now, mini split or electric resistance are fine and relatively cost effective. i'd imagine it's the same for this house - if the peak heat load is a high (for passivhaus) 6 BTU/ft2hr, the max output would be less than 15,000 BTU/hr.
@edgar,
i don't actually agree that a sq ft/occupant can be an effective metric for gauging the 'greenness' of a home - especially as families change/situations change/etc. nor that walkscores are accurate measures, either. it's possible to build a passivhaus w/ electric vehicle in the burbs that utilizes less energy (without renewables) than a small 'green' apartment with no car in the city.
@ Mike
Hi Mike, thanks for the comment.
I do agree with you that it is possible to build a low energy home with low energy transportation such as a passivhaus with an electric vehicle. Unfortunately, for reasons other than energy, this solution only perpetuates car-centric development.
It's great that there are smart folks out there coming up with ways of improving personal transportation but few have dedicated their time to reducing the need for personal transportation (i.e. new urbanists and transit oriented developers). There are other energy and societal implications that often get forgotten in "burbs" development such as road maintenance, traffic and the lack of independence for those too old/young to drive to name a few.
Walkability does not need to imply high density (e.g. apartment buildings). Walkability can just mean mix use development.
As for the sqft/occupant, it is obviously a metric that changes but can nevertheless be re-stated at a given point in time as required.
To Mike
The the cost difference between the double pane and the most reasonably priced triple pane at the time (InLine, I think) was almost $14,000! That speaks to both the bargain we were getting in the Bonneville windows and the difficulty we had finding "cheap" triple pane. The cost effective UPVC units were nowhere to be found just two years ago, or at least, not on the radar. When you're already pushing the budget ceiling and most of this glazing is all on the south, well, it would take quite a while for those triple panes to start providing a return. Same goes for the additional r-20 all around it would likely take to get this to a true passivhaus standard. That and we'd have to get rid of the passive solar shading over the windows (this is practically a summer solstice photo) and come up with some seasonal shading devices for our climate. As it is, I believe this house is Net-Zero Ready. But I think My clients will be happy to be done incurring costs, and enjoy moving in and living in some of these great spaces. When I get back to the office perhaps I'll figure out a way to upload and share that spreadsheet Martin mentioned. and we can geek out some more.
Chris Briley, Architect
Response to Jim Merrithew
Jim,
Q. "In the picture of the window and cedar shake siding, what protects the wood window sill from rot?"
A. It's far from clear whether coats of paint would make a white cedar window sill last longer or not. Think of a deck: I've seen white cedar deck boards last a very long time, and I've seen painted deck boards rot.
Rex Roberts delved deep into the question in his classic book, "Your Engineered House," and concluded that unpainted wood can last a very long time, as long as it is able to dry out between wetting episodes. Roof overhangs help.
Q. "The other window you feature is surrounded by SM foam. Does that window have nailing flanges? How will the window be finished and weather proofed?"
A. I'm not sure what "SM" stands for -- the foam is extruded polystyrene (XPS). I'm sorry that I can't answer your other questions; perhaps one of the builders on the Bath project will be able to answer.
Window treatments and SM Foam
Martin,
Thanks for your response. In Canada, Dow's XPS foam is identified as SM.
In your response, you mention that wood will dry. This is true of wide exposed areas. However, won't moisture wick up the end grain of the vertical window trim. Any place where there is a connection between surfaces the moisture takes longer to dissipate. I was curious about steps the builders took to reduce the onset of rot at these points.
Raw trim
Jim - we've done plenty of exterior trim with raw eastern white cedar. I think you're actually less likely to have the problems you mention with raw, rot resistant wood species. It dries pretty darn fast, and painted trim will trap moisture a lot longer. If the joints get caulked by the painters, so much the worse where the leg casing hits the sill.
Thank you Dan
Dan,
Thanks for the response and explanation. Do you leave the wood completely raw? Is there any treatment with linseed oil or other similar products?
Could you address the second set of questions I posed? Does the window with the external rigid foam have nailing flanges? How do you cap the foam and finish the window. Thanks Jim
Raw, raw, raw
That's the spirit! Yes, we just leave it alone. You could certainly treat it, but you'd have to re-apply. We haven't had problems with leaving it alone.
And I can't address the second, because it's not my house. I don't know if Alan or Matthew are monitoring this thread, but they're friends of mine so I'll let them know there's a question.
window foam
In response to Jim's questions, the windows are German made and they install with screws through the jambs--no nailing fins. They're positioned half-way into the wall thickness to improve performance, and all of the window buck framing is covered with rigid foam to reduce thermal bridging. The sill will have a custom-bent metal flashing pan installed, and the sides and top will receive extension jambs and painted pine trim.
Martin, sorry I missed you
Martin,
I am sorry that I missed you on your Maine adventure. I could have shown you the "magic box" in my basement in Buxton, ME. The rest of my home is somewhat pedestrian by today's standards, which really speaks to the pace at which things are moving. To reinforce Christopher Briley's comment on the windows, I looked for triple glazed about six years ago when I started building, and the difference with the Loewens I ended up with and the Swiss windows (the only triple glazed windows I could find in New England) was about $60k. Well beyond my budget!
Stop my next time you're in the neighborhood.
Response to Barry Stephens
Barry,
So many interesting houses, so little time!
I agree -- it would have been interesting to see your magic box from Switzerland. Maybe the next time I'm in Maine...
Response to Dan Kolbert
"Raw, raw, raw -- that's the spirit"?
Someone's been spending too many hours with Porgy and Mudhead at Morse Science High...
Or
Too much time waiting for the electrician.
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