When do desires/requirements compromise any energy efficiency?
For our new house in MN we have some requirements and desires that go somewhat against energy efficiency.
– We need to be able to comfortably host my wife’s 40+ person family (lots of brothers & sisters who’ve produced lots of nieces, one nephew, and now grand nieces and nephews along with our own children and, hopefully one day, grandchildren) and 3 ensuite guest rooms that all add up to a gob of square feet.
– On a lake so lots of west facing windows for views of the lake. We are also having difficulty getting windows on the south face with the current design which has really stressed me out.
– Externally exhausting 200/400/800 cfm. range hoods and makeup air. Lots of cooking for ourselves and entertaining. We’ve not found a good option that adequately keeps cooking odors in check.
– Having used condensing dryers in the UK and EU my wife says that we’ll have traditional externally exhausting ones.
– Perhaps worst of all, two wood burning fireplaces. Yes, I know… But we like wood burning fireplaces and we like to hear them and smell them so, at least while burning, the doors will be open. One thought here though is how well can they be sealed when not in use? EG, our house operates in two modes; inefficient fireplace mode a few hrs per week and more efficient the other 98% of the time.
My question then, given these significant compromises to energy efficiency regardless of any other decisions, is pursuing energy efficiency even worthwhile? Are we so compromised from the beginning that almost anything we do will cost much more than it’s worth? Or are there viable solutions in the grey areas beyond the black and white do this don’t do that?
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Replies
W.,
1. If your house is large, all the more reason to emphasize energy efficiency.
2. If you have lots of west-facing windows, make sure that they have low-SHGC glazing.
3. Find an HVAC contractor who can design and install a makeup air system for your range hood. Here is a link to an article with more information: Makeup Air for Range Hoods.
4. There is nothing wrong with a clothes dryer that has an exhaust duct.
5. Choose wood-burning fireplaces with tight dampers and well-sealed glass doors. Open a window a crack when you light a fire.
6. Find an architect and a builder who understand energy-efficient construction methods.
Good luck!
If you build it to IRC 2012 code min it'll be tight enough. Going for low-gain windows on the west side and scaling them back as much as you can without impeding the view is something you have to consider carefully. On sunny winter days even low SHGC windows will have decent and desirable amount of solar gain, but it WILL roast you out in summer if you don't limit the size.
In large houses with a favorable shape, the heating loads don't necessarily scale with the square footage of conditioned space, and you don't necessarily have to heat & cool the guest suites to comfortable levels when they're not in use. Designing the interior partitions so that the guest suites can be doored-off, and zoning the mechanicals to allow them to run at dramatically different setpoints than the space that is used all the time can do quite a bit for efficiency.
A most-favorable shape is a simple square footprint right-rectangular prism, with no bump outs or ells. (Think, "shoe-box with gable" :-) ) The exterior surface area (where all the heat loss/gain is happening) to usable floor area is minimized that way. Going to an oblong rectangle or a simple L shape isn't dramatically worse, but avoid going with a bunch of bump-outs, bay windows, & dormers, limit the footprint to no more than 6 corners if you can. Every corner is a thermal bridging point an a potential point of air-sealing failure.
A simple gable roof with an east-to-west ridgeline gives you some photon-farming acreage to work with, offsetting some of the other inefficiencies of an oversized house. MN has pretty inexpensive electricity compared to much of the US, but with taxes and other incentives it's not insane to install solar right now. The installed cost of PV solar is falling fast, and at some point within the next 15 years installing PV is likely to become a no-brainer type investment. But if you've oriented the roof in a less favorable manner or cut it all up with a gazillion dormers (a bad idea in snow country anyway), you will have designed yourself out of being able to take advantage of it.
MN has defined a "Value of Solar Tarriff" (VOST) calculation methodology that covers all utilities in the state, but allows the individual utilities the option of either simple net-metering (running the meter backward), or paying the VOST. At the current time the VOST calculation comes in significantly higher than the residential retail rate, and SFAIK no utility has opted to pay on that basis. But as more solar gets built the VOST begins to fall, and since whether they're net-metering or paying a VOST , it's locked in for something like 20 years (I'd have to look that up), and fairly soon it might be cheaper for them to compensate with the alternative method. Either way, the installed cost of rooftop PV in the US is currently $3.50-4/watt, down by more than half from just five years ago, but still 2x what they're paying for solar in the mature markets of Germany and Australia. When PV costs $1.50/watt, even financed at 5% interest it would be cheaper than retail electricity in MN on a lifecycle basis, even without subsidy. That price point is already being hit on large scale projects in the US, and it's only matter of time (maybe a decade), before small-scale rooftop arrays are crossing that threshold.
Thank you both. The current house shape is quite poor from an energy standpoint with 16 corners. That includes two corners that are actually 45 degree corners so I counted those as 2 ea rather than 1. It also has 8 half dormers (think Pennsylvania farmhouse w/ a bit of Cotswolds cottage). So trade-offs and compromises... Character vs Energy Efficiency... It would be much easier if our clear over-riding priority was energy efficiency and then we could easily design for that. It's not. We're trying for historical accuracy and energy efficiency.
We are planning for considerable zoning with each of the 3 guest suites having their own zone as well as the basement rec room, locker rooms, and other rooms throughout the house. Builder mentioned possibly sealing the doors to the guest rooms with a gasket of some sort but I'm not sure that would do much. Should interior walls, floors, ceilings be insulated?
The aesthetic cost of solar isn't yet outweighed by the benefits.
Agree on the windows. My understanding is that interior shutters or curtains provide little real benefit from summer heat? I'm wondering if we can find an exterior shutter that can work, close/open automatically, and fit aesthetically.
Minnesota Co-op power providers are exempted from some of the net-metering regs, and the Republican Party sought to put more solar restrictions in this years jobs and energy bill, which may be passed today, but we won't find out the exact language for a few days. So it depends on your location what your solar options may be.
W, in an odd way I admire the lightness you feel toward these dilemmas. But you asked, "is pursuing energy efficiency even worthwhile?" Kind of an odd question to post on this site, but I'm glad you're here. As long as you apprehend energy efficiency as just another check box on a long list of options and add-ons rather than a basic tenet, then no, there is very little worthwhile about energy efficiency. When evaluating the worthiness of energy-related design, many folks like to think ahead to the lifespan of the structure, rather than making decisions based on the current economy. Your present needs may or may not extend to the next generation; your heirs might have trouble keeping the place up, especially if you don't build in a BUNCH of real efficiencies. And consider dropping a few of those corners, egads, they are expensive to build.
Nate has a very good suggestion. Make it a compound where the guest cottages help form and define the outdoor space. Or situate them in a separate house that can function as a residence in its own right in the future. Houses designed for occasional large gatherings usually don't function all that well the rest of the time.
Compromises, compromises. As you're discovering, an extremely large and complicated house with luxurious amenities is difficult to square with the desire for energy efficiency. And the result of all of this will be very high cost. But it's still possible.
If you're open to radical changes, how about scaling down the main house by removing all the guest bedrooms and their attendant bathrooms, and relocating them to a guest cottage? You can shut down the cottage when there are no guests (likely the overwhelming majority of the time) or even rent it out to local college students or something to recoup some of the cost of ownership of this very large property. Your guests may even prefer this for multi-day stays; it's nice to have a little private hotel of sorts on the property rather than bumping up against you and your wife and children. Guests and hosts mix well during parties, but less so when it's time to get dressed, shower, eat breakfast, go to bed, etc.
Keep the chimneys of your wood-burning fireplaces within the thermal envelope. No exterior solid brick chimneys. If you insist on the look, build a fake brick chimney with thick insulation under the brick veneer.
Why would you want to keep cooking odors in check? If you're good cooks, your guests will love the smell! The few bad-smelling things should probably be cooked outdoors anyway, or not cooked at all. :)
Your many west-facing windows will practically incinerate the house in summer. The lake surface will reflect the sun, doubling the amount of light and heat the west side receives, and making any kind of shading device ineffective. Think of the intense glare in addition to the heat! Nobody will want to be in those rooms during the afternoon. Normally you could plant some big trees, but if the sun is coming up from the water in addition to down from the sky, there's no real option. Your only comfortable option will be exterior shades, in which case, why have windows at all? Strongly recommend minimizing the west-facing glass and building a west-facing outdoor space like a porch or patio where you can enjoy the lake view but escape from the glare in the mid to late afternoon. Huge view windows are overrated anyway; if you're looking at your view all the time, it will lose its charm. On the other hand, if you only see it when you go outside, or go to a specific "beautiful view" room, it will remain magical forever.
Finally, if you're going for historical accuracy, well, most of the Pennsylvania farmhouses I've seen had only four corners. The result may well look better and be more authentic without all the modern ells and bump-outs and bay windows and turrets and such. Simplifying the design will not only pay dividends in the efficiency department, but it will also be easier to build, resulting in lower cost to you and fewer construction errors.
Normally people like us say that closing off and shutting down heat to unused rooms doesn't help significantly. But that's in a house that wasn't designed for it. If you design for it, with a clear boundary between the full time and special use spaces, including insulating the partition walls,using weatherstripped and maybe insulated doors for the relevant interior doors, and using an appropriately designed heating system, you can make it even better energy-wise than the solution using multiple buildings, including the energy use with and without guests.
As far as the question of whether it even matters anymore, the difference in heat loss between an R25 wall and an R40 wall is the same regardless of how much heat is lost elsewhere. As a percentage of you total use, it's smaller than in a passive house, but as far as how much heat loss you save per dollar spent on insulation, you get the very same bang for your buck regardless. It certainly makes sense to think hard about the big sources of heat loss you mention, but even if you don't find a good solution for them, it still makes sense to do everything else to a high standard.
For the west facing windows... retractable exterior shades can control solar heat gain without compromising your view too much. You can get fancy with motor operation and automation to keep the shades down when you aren't around. And you'll probably appreciate having something to cut the glare in the late afternoon!
That's true, Tim, but at what cost? The cost of the shades, the cost of the control system, the cost of a user interface for them, the cost of maintaining and repairing them (electromechanical systems exposed to the elements are hardly maintenance-free) … all on top of the cost of the windows. It seems so inelegant and expensive to add complication to a compromise instead of designing a simpler, more appropriate solution in the first place. In general, it's usually not worth fighting the tide. It's expensive and error-prone. If money's not an object, then go wild, but that's hardly efficient.
Exterior gain-killing shades can be manual- it doesn't have to be an automated system. The cost question is really about "What does it cost to be comfortable?". It may not pay in energy savings, but if the loads for the AC are calculated with the presumption that the shades will be used, it takes off a good chunk of the up front cost of the AC, since we're probably talking on the order of 3 tons of peak load here (a WAG based on nothing but a vague sense of the size of the house & west facing glazing size.)
There's no air-conditioning system invented that provides true comfort in a high-gain greenhouse. Even if the AC keeps the air temperatures bounded the directional radiation temp during peak gain hours is still uncomfortably high. When your head in is in the furnace putting your butt in the freezer brings your average temp to what would otherwise be comfortable, but so what? Large west facing windows without exterior shades are a dubious proposition in any climate (though common in sea-side locations on the west coast.)
Exterior heat rejecting shades on the west window would fix most of that. Interior shades would fix some the radiation temp/comfort problem, but wouldn't do very much for the AC load sizing, since it effectively creates a convection driven passive solar collector out of the window. Less square footage, and heat rejecting windows, with some amount of operable exterior shades works.
In snow country if you must have dormers, shed dormers are less problematic than gabled dormers, since it creates less of a snow-trap. Larger roof valleys on the leeward side can sometimes have 5' of snow in them when the average snow depth on the roof is a foot. Don't skimp on the side overhangs of a dormer roof OR kick-out flashing. And don't space the dormers so close to one another that it creates another snow-trap- make it one bigger dormer if you have to- it'll be less surface area, less air sealing issues, and far less snow trapping issues. (I may be a bit hyper sensitive to this issue. I live in a cute 1920s bungalow with a couple of large roof valleys and a couple of smaller ones, and had more than 10' of snow fall between the end of January and mid-March this year, shoveling literally TONS of snow off my roof this season when I could have been skiing.)
It's possible to have reasonably low thermal bridging at 45 degree corners, but you have to design it. It's not really 2x that of a single 90 (or at least is doesn't have to be.)
From a long term energy cost point of view it's still cost-effective to go substantially more than code-min for most of it, and the payoff in comfort happens immediately, even if the NPV on energy use savings might not break even for 20 years at a 5% discount rate. IIRC MN energy code (https://www.dli.mn.gov/ccld/PDF/sbc_1322.pdf )i s still under IRC 2006 which means. 2x6 /R19 is code-min. But that's a pretty crummy wall from a comfort point of view when it's -10F outside, and has a "whole wall R" of about R13. At the SAME wall thickness, going with 2x4/R15 with 2" of exterior foam delivers R18-R20 whole-wall performance, and would be sufficient exterior foam to be able to skip the interior vapor retarders making it far more moisture resilient. In southern MN *US climate zone 6) you'd be able to do that with 2" EPS (R8-R8.4), but has to be at least R10 for northern MN (US climate zone 7) for dew-point control. See: http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_7_sec002_par025.htm
Under IRC 2012 (https://www.dli.mn.gov/ccld/PDF/sbc_1322.pdf ) a code-min wall in MN would be 2x4 R13 + R10 insulating sheathing, so it's not exactly pushing very hard to take it that far, and it's financially rational to take it quite a bit further if you're heating with oil, propane. or electricity rather than natural gas. If you're looking at it from a long term financial rationality point of view, a good starting place is Table 2, p10 of this document:
http://www.buildingscience.com/documents/bareports/ba-1005-building-america-high-r-value-high-performance-residential-buildings-all-climate-zones
Note- those are all "whole assembly" values with all layers and thermal bridging factored in, not center-cavity-insulation values.
You can't always get what you want.
You might just build a sensible, reasonably sized house and send your guests to the Four Seasons.
Mmmmm. Room service.
All these suggestions are good but ultimately Martin nailed it in the final point of his first comment:
"Find an architect and a builder who understand energy-efficient construction methods."
Balancing aesthetic and program preferences with good environmental performance is a juggling act and the right kind of detailed professional help is imperative. Don't try and do it with a hatchet job on a stock plan, and don't try and do it with the aid of professionals who see no value in one or other side of the equation, by which I mean those who single-minded lay pursue energy performance as the only objective or those who act as yes-men to to the client's every whim. The tertium quid, the truly balanced solution is out there. With the right help you can find it.
W. - Will the guests come all times of the year? Building guest space, whether it be a separate house or a separate wing, that is uninsulated and suitable for three season use, is a lot cheaper to build.It could be built to have the plumbing able to drain back easily to avoid freezing, or the bathrooms could be well insulated in a separated area.It is really nice to be able to put up a whole lot of family or friends, but it is a luxury to be able to do that in the winter, when it's maybe a few days a year. Our host, Martin, is kind and non-judgemetal about people's private choices for their homes, BUT our earth is at the brink of a very serious balance point concerning climate change.Since all new buildings don't have to be part of this problem, or at least don't have to be a big part of the problem, many feel it is a responsibility to not be contributing to our demise. Not trying to push Guilt, just raising the question of our responsibility.I wish you the best of luck with your project.