Just wanted to get some opinions on the attached wall schematic for a Passive solar house I would like to build
My wife an I have done extensive research on building a passive solar house in combination with as many “Passive House” aspects as we can afford. We have decided to build the house on a slab in order to maximize our thermal mass, triple pain, High solar heat gain on the south etc.. We live in Northeast CT
Heating system: we contemplated radiant heat imbedded in the floor but are leaning toward the use of Mitsubishi mini splits in combination with electric baseboard (gel-filled). We were going to go with all baseboard but like the dehumidifying and A/C ability the Mini-splits offer. (note we are also going to have a would stove) our only concern with this design is we don’t want the floor to feel cold. Although we think this will not be the case as we want to insulate the slab with 8-12 inches of EPS.
HRV/ERV: We have contemplated going with a simple timed – fan venting system but like the idea of an HRV/ERV (much like the house in bath Maine that M. Holiday visited) Our only concern with the HRV/ERV is that we have read they are high maintenance needing frequent cleaning.
ATTACHED WALL SCHEMATIC: I designed this in an effort to obtain opinions on it”s success in our climate. I realized afterwards that I probably could make the exterior wall 2×4 rather than 2×6 to save lumber without compromising structure
Roof / Siding: we want to use Galvalume (standing seam) on the roof if we can afford it and steel siding but I have not found a steel siding that was designed to have venting (screen on top and bottom )
Any opinions will be of great assistance was we need to have a plan drawn up soon
thanks
John and Rebecca
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Replies
Loose cellulose in the lid? (The foam is just to hold back the cellulose?) I suspect your floors will feel cool, as I don't see how they are going to be any warmer than the air if there is no heat in the slab. Even w/ radiant floor heat, your water temp may be so low (so as to not overheat the house) that the slab will be cool. My water temps calc'd out at about 83 F, leaving the floor in the mid-ish to high 70's. (I have not built yet, so I can't say for sure, but that is likely going to be cool.) You may want to consider foam outside the stem wall and under the footer, too.
Rebecca,
Are you currently working with a builder? I am a Passive House consultant out of northeast CT (pending test results). We are currently building superinsulated homes in northeast CT that are heavily based on the PH design concept. They include double stud walls, triple pane windows, mini splits for heating/ cooling and HRV/ERV for ventilation. We include this on every spec house we build so it would be great working with a customer who knows and appreciates how a low energy homes works. Shoot me an email if you'd like to talk.
Nick Lehto
Nicholas . Lehto @ Gmail . com
A couple general points and a specific one:
1. Passive solar and passivhaus design principles have different goals and different methodologies despite their similar names. If you want to combine them you need solid professional advice and an integrated design strategy. Get an experienced, knowledgeable architect/designer or contractor on your team as early as possible. Preferably both. Do not expect to finalize your wall section without their participation. Critiques from GBA, though valuable, are no substitute for the real deal on something this important. Would you perform your own appendectomy after just a little online research? I thought not.
2. John K's point is a good one. To rephrase: your slab WILL feel cold underfoot unless it's actively being heated to a temperature close to that of your body. It's in the nature of the material, no amount of sub-slab insulation will change this. You want a naturally warm floor? Go for a low-conductivity floor finish like cork.
3. Steel siding: we've used master-rib roof sheet run vertically. No particular problem with venting/rainscreen, just be real careful with the flashings, as always. I wouldn't necessarily recommend it in a highly exposed/coastal situation though.
I hadn't seen Nick's post when I composed my earlier response. Didn't mean to exclude PH consultants from the list of key professional resources: you still need the designer and contractor though, and maybe Nick can help you find the right ones for your project.
James-
I forgot to mention most importantly that I am a builder, and also happen to be a passive house consultant.
Speaking as someone who tried the DIY passivhaus approach, I highly recommend you bring in some pros ASAP. A good consultant will save you as much as they cost. It would be a shame for you to pay for all that EPS and concrete without having a pro analyze whether you're getting the best bang for your buck.
BTW, you might find my blog informative -- it's at http://vermontpassive.com
Best of luck,
Andrea
John and Rebecca, I have noticed a difference between your foundation idea and other superinsulated foundations on the web. I am just curious if you have considered the slab encased in foam--like the Sunrise house and another that Darcy Bean has presented at the 2010 PH conference? Maybe these are more costly than the traditonal footing/stemwall as you have drawn?
Mark, the slab in the drawing is surrounded on 3 sides by foam. Is this what you meant? I will try to look at the Darcy Bean and Sunrise house to make sure I understand. Thanks
Nick, we are working with a local builder at this time but need someone who knows what they are doing to draw up our plans, be a consultant, and energy modeling if this is something you are interested in?
James, when you say master rib steel siding, is this like standing seam siding? I see what you mean about the concrete floor being cold. I understand it will not be warm to the touch. Just didn't want it to feel like Ice on bare feet like my current ceramic floor feels in the winter ( we have electric heat and an old damp basement) thanks
Master rib is a through-fastened steel sheet profile, it is not the same as standing seam which has concealed fastening. http://www.unioncorrugating.com/MasterRib.html
The concrete may not feel quite as cold as your ceramic tile but will be pretty close. Don't expect to be comfortable without slippers or a nice thick rug. Preferably both.
Or, as others have pointed out, put flooring over the slab - engineered wood works nicely.
I appreciate everyone's response but does anyone have an opinion on the function of the wall in the attached schematic? I.E. breathability, air barrier, etc....?
Rebecca,
The wall design you have chosen is very common. It's a double-stud wall insulated with cellulose, using ADA as the air barrier. Many builders use this system, and it performs well if properly built.
Hi Rebecca. I'm wondering what you ended up with in terms of slab/floor heating? Which option did you go for and were you satisfied with the results?