Best building envelope approach for an owner-built home in northern Wisconsin?
Setting the Stage:
My wife and I purchased a vacant farm (no buildings) with a south-slope in far Northern Wisconsin and have been planning our next home for a few months. We would like to build a “pretty good house” that finds that happy place between great energy efficiency and economy. This would be an owner-built home on a basement foundation. Our forest has plenty of millable pine and oak that we intend to use as much as possible for the build (framing, siding, flooring, etc.).
Our current home is too big, was too expensive and too complicated. I would prefer to stay away from anything too “techy” and have a fairly simple approach to the build. It is also my preference that we use materials that are earth and human friendly with a proven track record. We’re looking at a simple salt-box farmhouse with a single gable, big covered porch on east and south and a shed roof on back as a rear entry. I’ve attached our preliminary main floor plan for your reference.
Ideally, we would have a second floor built into the roof of a 12/12 with a shed dormer that runs eave to gable, but I am open to suggestions if a full second floor is vastly better approach due to insulation and ventilation.
I’ve been reading GreenBuildingAdvisor.com and feel that I have read just about every article on selecting an approach to the building envelope. I go back and forth between 2×6 framing with a 4 inch rigid foam wrap and a double stud wall with blown cellulose in both cases. I don’t really want to use rigid foam because it is kind of nasty and a hassle to install siding over, but at the same time I am concerned about the double stud wall cold-sheathing and moisture problems. The double stud wall seems to have questions to me based on the articles I am reading here.
With that, at risk of writing a novel here, I will leave you with:
– What is the best approach to the wall and roof envelop for a design like this?
– Second floor built into the roof and what framing/insulation approach? Or, do I really have to do a full second floor to have a nice approach to the envelop?
– Would this house be too insulated to have a woodstove or a masonry heater? I think I’d like to run in-floor pipes and have that as a back-up, but I’d be more interested in just heating the house with simple wood.
I have so many more questions, but let’s start with that! Thank you so much for your time.
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You or your builder will need to make a decision on the wall assembly. Either approach will work.
I don't like the idea of 1½ story homes, Cape Homes, or homes with dormers. These homes have complicated envelope shapes that are hard to air seal and hard to insulate.
If you want to live on two floors, build two floors. Then put a roof over the second floor.
Thank you for your response. I thought that might be the answer I would receive regarding 1 1/2 story. We just like the look of these homes better, as they look smaller. That said, I totally get the point.
With regards to the wall assembly... Do you have your own recommendations? I am the builder, so I don't have a builder to consult. I've just been collecting as much information as possible online and am looking for recommendations from folks who have built one or the other, or a different type of wall assembly. Looking for opinions and facts to back those opinions up.
If I had to choose between a wall with thick exterior rigid foam, or a double-stud wall filled with dense-packed cellulose, I would start by investigating two questions:
1. Is there a well-regarded contractor near the job site who has experience installing dense-packed cellulose in thick walls? (If there isn't, that would influence my choice.)
2. Do you have a local source for inexpensive recycled (reclaimed) rigid foam?
Michael. My wife and I are in a similar situation, and we want to go smaller. In our case that means downsizing from 3,200 square feet to about 1,500.
Since you are asking for feedback, here is my two cents:
On stories. We found is that levels end up segregating living areas into smaller and more isolated sections. Putting needed spaces on multiple levels just makes the overall structure feel smaller if you don't have much of a footprint to start with. Stairs also eat up a lot of real estate and drive up costs.
On design. A box or rectangle with a flat roof doesn't have to be boring. Check out ArchDaily if you need some inspiration.
Stove or fireplace. Don't worry about this issue until you have calculated your heating loads.
You didn't ask but, do you really need a basement? I know it's often called "free space," but there is nothing free about it. Creating a basement that is finished, dry, and comfortable is a big challenge because you are below grade.
Thank you both of you!
1. There is an insulation contractor that is very experienced with dense packed cellulose, but they haven't confirmed if they've specifically done double stud walls.
2. No. I've called around and haven't been able to find anything reasonably close
• On stories: Are you suggesting just doing a one floor house? I guess I just feel like I've always heard that it is always cheaper to build up than out...
• On design: Agreed. We've found many we like, we've just always loved the look of cottages with dormers. I also acknowledge that it adds challenges and a lot more of my time for framing dormers, flashing, etc.
• Stove: I guess I just want to make sure that I don't create a house that is so insulated that I can't heat with radiant heat inside the house... This is our most accessible and renewable source of heat...
• We are looking to have the south end of the basement be a walk-out and build a large root cellar into the basement for winter storage of crops. Additionally, I don't like having a TV in the main spaces upstairs but can't miss football games. A basements gives us a places for these things and utilities/mechanicals. In my area, the basement is about double the slab, but for the square feet it seems very worth it to us.
Thank you both!
We recently bought a lot of used (but very clean and uncut) 3 1/2" EPS foam from someone near Wausau and he delivered two large loads to us in Menomonie, WI. Not sure what you might consider "reasonably close"--where in northern Wisconsin are you?
Hi Jim, I am up in Bayfield, WI. I think we're about 3:15 northwest of Wausau. I would be interested to hear who you got the foam through though... Perhaps I could go down and load up a big flatbed or get a shipment.
Hi, It seems in your design statement that you want "materials that are earth and human friendly". I think the double stud walls would be a bit more earth friendly if both were done equally. I would not worry about too much insulation, you can always open a window and let fresh air in. I built a strawbale house with R60 attic insulation. One winter storm knocked out the power of 3 days, we were still comfortable with the inside temp between 65 and 70 F without power. Our neighbors houses were in the low 50's and they were looking at motels in town.
It would probably be helpful for you to state your building experience level and what you mean by owner built. Do you have zero carpentry/building experience and want to try acting as the GC....or do you have significant building experience and will be doing everything from framing to painting yourself?
My wife and I have been living in our house (NH, zone 6) for almost two years. We had zero building experience and acted as GCs...it was hard/stressful, but turned out well:
A few thoughts based on your questions:
I wouldn't stress about the double stud wall approach. It seems like if you follow best practices for either double stud or exterior foam/Roxul, the wall system will work out. It then comes down to cost and which system will be easiest for you to build.
You should plan to integrate solar PV (maybe ground mount if you have a few acres) into your build. Either right when you build if you can afford it or short term after the build if that expense needs to wait.
I think a great HVAC setup for a small efficient house in your climate would be: solar PV, one or two ductless mini splits, HRV, heat pump HWH, SMALL wood stove for ambiance and backup. Skip the radiant.
I would stay away from the dormers and other design elements that complicate the building envelope, think of other ways to make the house visually appealing to yourselves.
Our house is two stories, but I can see some big benefits to one story: one story living as you get older and easier access to roof (the roof itself, trim, etc) work.
Great to hear about your experience! Nice blog.
By trade, I am not a carpenter or GC. I have however, built many barns, garages, decks, our cabin, etc. on my own without assistance. I've never built an entire house and would rely on other contractors for electric, plumbing, insulation, concrete, etc. but would handle the GC, framing, siding, finishing, cabinets, installations on my own.
• I appreciate the thoughts on double wall vs foam. I think I am mostly just looking for others opinions on which they think is better suited. I was fairly sold on double wall until I read some of the articles on GBA about potential cold sheathing issues and using the drywall inside as the only interior vapor barrier (we want to use pine ship-lap for some of the interior walls). I am hoping someone can tell me which one is the better way to go.
• Totally agree. The property is a 40 acre south facing slope so there is great exposure for PV
• Good suggestions
• Yes, after all the feedback I am getting on that it does seem that would be the way to go. I like the dormer look, but I do recall that putting a shed dormer in our cabin ended up really doubling the work of framing, sheathing, metal roof, siding, insulation, etc.
• I can too. Just trying to find a design that we really like in one story seems to be harder.
The reason that drywall is preferred to pine shiplap boards as an interior finish material has nothing to do with whether or not the drywall is a vapor barrier. It has to do with the fact that properly detailed drywall is an air barrier -- and shiplap boards are definitely not an air barrier.
Hey Michael -
I am also an owner-builder, and not a builder by trade, so take my input as such. I am in the middle of a build similar to what you are planning, and I ended up going with exterior foam. I know what you are looking for: someone to tell you in plain terms which approach is better, and why. I also looked for this information, and there is some bad news - the answer isn't out there. There are strong arguments to be made for each approach, and there are some-watt pesky details to deal with in making either approach work. The good news is that there are well established best practices for both exterior-foam and double stud envelopes. Like Brian said, it just comes down to what you are more comfortable building. I had an easier time understanding how exterior foam would function with regards to potential moisture issues and air-tightness. I also had access to cheap recycled foam, which alleviated environmental concerns. I milled my framing lumber...and I didn't want to drag out more trees or mill more framing lumber. Bottom line is keep researching until you feel like you've reached the right choice, and it will be the right choice.
I'll add that of all the things that ARE a hassle about a wall assembly with exterior foam, I don't think installing siding over it is one of them. The furring you will use to hold the foam in place will create air circulation behind your siding - a feature you should strongly consider regardless of your envelope construction if you are installing wood siding.
I'll also add - and again, take it with a grain of salt - that your dining room looks like it has the potential to be a little dark with the covered porch wrapping around it. With the great southern exposure you have, I would give very careful consideration to the design of a covered porch on the south side of the house. You will get to enjoy the southern exposure while sitting on your porch for a portion of the year, but your dining room and kitchen may lose some sunlight and connection with the outdoors because of the structure.
Hope we get to hear more about your project. Good luck!
I don't have any advice regarding whether you should go for exterior insulation or double stud, but regarding this concern:
"I appreciate the thoughts on double wall vs foam. I think I am mostly just looking for others opinions on which they think is better suited. I was fairly sold on double wall until I read some of the articles on GBA about potential cold sheathing issues and using the drywall inside as the only interior vapor barrier (we want to use pine ship-lap for some of the interior walls). I am hoping someone can tell me which one is the better way to go."
It is my understanding that most of the best approaches to the double stud wall put a air barrier and vapor retarder in the middle of the wall. In many ways, it ends up being a lot like the wall with exterior foam, where there is a barrier in the middle of the wall that is always warm, so condensation issues are avoided.
This air barrier/vapor retarder can either be a sheet material (plywood/OSB) like Joe Lstiburek prefers: https://buildingscience.com/documents/enclosures-that-work/high-r-value-wall-assemblies/high-r-value-double-stud-wall-construction
Or it can be a membrane such as this stuff: https://foursevenfive.com/product/intello-plus/ and 475 has free details here: https://foursevenfive.com/product/double-stud/ but of course are going to be biased towards recommending things they sell (or maybe it's just that they sell the things they recommend!).
Either way, as you're not relying on the interior drywall as the air barrier, it seems like it would be fine to use shiplap pine boards for the interior finish.
Thank you for this distinction. That said, how does one have ship-lap interior finishing in this building style if you have to rely on sheetrock as your air barrier?
Thank you very much for this feedback. Yes, I AM looking for someone to tell me which one is better and why and I understand your perspective. You're exactly right. I also feel like I know how to build a traditional building and then wrap it in foam–I am not as clear about the double stud wall. If I can locate recycled foam I think that is a great option. Your project sounds very similar in that I would also be using all rough sawn lumber from our property.
I have also been concerned about the front porch, thinking that if the windows are big enough it would still be very bright but without direct sunlight. I am a little worried that this much southern exposure will burn us right out of the house during the summer. My current house has a single french door facing south and that room gets insanely warm in the summertime. This is, of course, super nice in the winter. How would one handle this? I see that your design has the shed roof extensions over the windows to capitalize on the angle of the sun... The farmhouse porch is something that my wife has ALWAYS wanted and I am trying to figure that out. The south exposure is also what looks down over the barn, pasture, distant fields and ridgeline, etc. She wants to be able to sit on the covered porch and enjoy.
Thank you for the suggestion on this method. I will read this post and dig in more. I appreciate the references!
Q. "How does one have shiplap interior finishing in this building style if you have to rely on sheetrock as your air barrier?"
A. The easiest and cheapest way to establish an air barrier behind interior boards is to first install drywall; then tape the drywall; and then install the boards on the interior side of the taped drywall.
I've never built a double-stud wall but I've spent a lot of time lately thinking about insulation over the exterior sheathing.
I don't like how foam (XPS) burns, the environmental impact of producing/disposing it, or the total vapor impermeance. It apparently also shrinks a bit. However, it has a high r-value per inch, and in my opinion the outer face makes for a pretty straight-forward and effective WRB / air barrier when you use two layers with offset, taped seams. Roxul ComfortBoard addresses a lot of these concerns but at a lower r-value per inch, comes in smaller pieces, is much heavier than foam, and has a cloth-like surface that doesn't play nice with tapes. Some options would be to either use taped Zip system sheathing beneath the ComfortBoard as the WRB / air barrier, or install an additional building wrap product over the ComfortBoard (I think the latter would be a really finicky detail to get 100% right).
There's no magic answer, but you already knew that.
Polyiso chars in place and has, a higher kindling temperature than polystyrene (EPS / XPS), and uses a lower impact blowing agent (pentane, as does EPS) , than XPS (HFC soup, predominantly HFC134a, which has a global warming impact more than 1000x CO2.)
Surplus reclaimed polyiso roofing insulation shows up pretty regularly, usually from building demolition. There are businesses who trade in it, but there are often decent quality lots that show up for cheap on places such as...
The bigger reclaimed goods dealers will ship, the local one-off or small time dealers maybe not.
Dealers near me typically have 3" polyiso in decent shape for $15-20 for a 4x8' sheet.
With reclaimed foam the environmental hit has already been taken, but by re-using it you are adding to the benefit side of the costbenefit balance. It's as-green or greener than cellulose in that regard, and WAY greener than virgin-stock rock wool or fiberglass.
My wife and I designed and built a pretty good 1 1/2 story reverse salt box in NE Missouri this last year. It is ~1650 square foot with a 285 square foot attic space above the garage, all over a crawlspace. I served as the GC as well as completing/cooperating much of the internal work.
We built with steel SIPs which allowed us to have a long-span cathedral ceiling with a continuous insulation envelope. The second floor was balloon framed and the walls extended down the top of the crawlspace walls so that continuous envelop extends around the entire house. For example, we have no rim joist insulation issues.
Our design worked well with these materials, but, as Martin mentioned, might have been troublesome with other methods.
We heat and cool with two Mitsubishi minisplits: lower level is 18K, upper level is 9K. As you know last winter was mild for the Midwest, but the upper minisplit was never needed even at the lowest temps. We have southern windows and overhangs sized for passive heating, and our window placement helps maximize the chimney effect in summer for passive cooling. No fireplace yet since we're worried one might overwhelm our home with heat. With 4 acres of woods, we'd like one.
Since natural gas is not an option in our area, we may also go with solar PV.
I attached our plans and a pic. We're glad to talk more if you want to get in touch: [email protected].
Jeff: Judging by the shadows on the roof it looks like you would have some serious tree-trimming (or logging) to do before investing in rooftop solar, but you might enjoy the additional light too. You don't have so much south facing glass that you'd have to worry about serious overheating from mid-day solar gain, even if you cleared out quite a bit.
If you want a basement, consider a PWF (Permanent Wood Foundation). They require good drainage and attention to many details like the proper grade of pressure treated lumber and stainless fasteners free draining back fill placed after both the basement floor and floor above are complete etc. No concrete! (pea gravel or crushed stone) is an option for the footings under the PWF But the result is easily insulated with mineral wool and will give a whole wall 25>r >20. The cost is comparable to un- insulated concrete. Hundreds of thousands have been built over the last 50 years and they have fewer problems than poured concrete. They have code approval and there are several excellent.
construction and design guides.
Regarding walls: I favor a double stud system with mineral wool insulation where the outer face of the inner wall is sheathed with OSB and sealed and detailed as the air barrier. This forces the outer wall to be built first and erected without sheathing. after installing the inter wall space insulation and the outer wall insulation (both mineral wool bats) a moisture permeable WRB (house-wrap) is applied followed by a fanfold XPS drainage material then siding which in my case is thin brick on steel substrate panels. FWIW the top of my basement walls are directly under the sub-floor, my rim board is nailed to the inside of the basement wall's studs and the floor joist are supported by face mount hangers nailed to the rim board.