Lbear: Harmon Lake is in the extreme northeastern corner of Morton County ND. It's still in Zone 6, but in a high wind you can spit to Zone 7 from there.

I don't know if ND is has even been updated to IRC 2009 yet, but under IRC 2012 R20+ 5 is code min for zones 6-8.  That's an ~R19 whole-wall R, and build any lower than that doesn't make comfort-sense anywhere north of zone 3. 



It's been said before but bears repeating:  High efficiency mechanical systems don't buy you any comfort, but high efficiency building envelopes do.  At the same energy use and total house + HVAC system cost, it's better to live in the high-efficiency house with the lower efficiency equipment.

Also, I wasn't specifying the SGHC, only a max U-factor.  IRC 2012 also calls out U0.32 max in zone 6 with no SGHC requirement, but I'd agree that within limits a higher U-factor might be beneficial if it comes with a sufficiently higher SGHC.  Bumping that up to U0.34 (or even U0.36) on the south-side-only has negligible effect on the total heat load, but can be highly beneficial for energy use if accompanied with a much higher SGHC.  But at ND's climate the wintertime condensation potential on the interior face of the window of anything over U0.28 is substantial, so there are tradeoffs to be made.  With a really high gain U0.40 window you'd be mopping up puddles on the window sill much of the winter.

ICFHybrid:  You can certainly put geo in ND, and it's comparable in operating cost to heating with natural gas.  A sloppy system design might yield about the same annualized COP as the Fujitsu XLT-H series, but a really good design might break 3.0, but probably not by much.  If it's a decent system design, it'll have lower maintenance and a longer lifecycle than mini-splits, and if the all-in post-subsidy cost is only $4-5K more, it's probably the better deal.  If it's a crummy design it's not worth owning at any price, which is why feedback from multiple actual customers with more than a single season behind them would be useful.

[edited to add]  Just looked it up: ND has been under IRC 2009 for a coupla years now, which means R49 min in the attic, R20 or R13+5 min on walls, U0.35 max on windows in Morton County ND.  So technically, R19 batts are illegal, HD R21s would cut it though. R19 batts only perform at R18 when compressed into 5.5" thickness, and are only R19 when tested at their manufactured ~6" thickness. There are similar issues with low density R22s/23s, which only perform at R19 in a 5.5" cavity.  High density R21 fiberglass or any R22/R23 rock wool would cut it though, as would most cellulose.

With R23 rock wool and R5-6 iso on the outside you'll be at about R20-21 whole-wall, which is a real performance step above R19s and no foam, cutting the wall-loss numbers by about 30%.

On the basement insulation it's fine to insulate from the interior-only, but it takes more than an inch of foam for dew-point control in your climate.  At the above-grade portion it will take at least R7.5 for climate zone 6,  R10 minimum for zone 7.  At only R5-R6 you'll get periods of persistent condensation (even frost) inside the stud cavity on the above grade portion, creating a potential mold hazard. Using 1.5" iso gets you there with a bit of margin.

See:

http://publicecodes.cyberregs.com/i...par025.htm

With R13s and 1.5" iso the basement walls will have the same whole-wall R as the upper floor, which is fine.  When insulating & air sealing the band joist go with 1.5-2" of closed cell foam, and seal it to the top of the wall-foam, the fatten it out to the interior with cut up rock wool batts.

Since foil faced foam is a vapor barrier, the foundation dries only to the above-grade exterior, so the concrete will have periods of high moisture content when wicking ground moisture. This can put the foundation-sill at some moisture risk if using only a cheap foamy sill gasket, which are vapor permeable and not a great capillary break.  EPDM sill gaskets are a clearly superior product, vapor tight, pliable forever, with zero capillary draw.  But no sill gaskets are great at air sealing- it's still worth sealing shot of R10-ish closed cell foam on the interior of the band joist.  See:  http://www.conservationtechnology.com/building_gaskets.html  ( BG65 is the right product for 2x6 sills.)

In the basement you also want to put an inch of EPS or XPS under both the studwall plate and the cut edge of the polyiso to prevent wicking of ground moisture into the iso or wood. Since it's not a structural studwall, the compressive strength of the EPS doesn't matter, but it's both a thermal & capillary break against ground moisture coming through the slab & or foundation.  With no insulation on the exterior of the foundation wall, it's worth putting R8 (2" of EPS) under the slab at least for perimeter within 4' of the foundation wall, particularly wherever the slab is less than 4' below grade.  The material cost is about 80 cents a square foot, buck a foot installed. To keep stuff stored down there from getting moldy it's worth at least an inch of foam under the rest of the slab, which keeps the slab sufficiently above the dew point of summertime air that a box on the floor won't be taking on moisture from the air all summer.  Sub-slab and wall foundation are THE solution to the "musty basement" issue, and that option is only cost-effective BEFORE you pour the slab. (The Building Science guys call out R10 everywhere under the slab in climate zone 6, R15 zone 7, and 3" of EPS under the whole thing wouldn't be insane, but it's a cost adder.)

On the windows you might go with non- Energy Star windows with a higher SGHC on the south side, keep the EnergyStar windows for the rest.  Read the specs carefully, and it's worth playing "what if" using the crude but effective freebie ResFen tools on them.  (No rocket scientist training required for getting up to speed on this tool kit, but you DO need more than the glossy brochure specs on the windows.)

Forgot to mention: When you do the sub-slab foam, (even if it's just the perimeter, not the whole slab) install 1.5" EPS or XPS at the slab edge rising up at least 4" above the top of the slab to "float" the slab, breaking the thermal bridge where the slab would otherwise meet the foundation wall. The 1.5" polyiso can then meet the 1.5" EPS at the slab edge without a step-back or interruption.

Unfortunately, my footings are already in so I don't think I'll be getting anything beneath the slab. My basement walls are 8' and 6' below grade. I don't know if it would be a waste to put an inch of foam on the outside (to match the upstairs). Right now, it looks like I'm leaning towards a 1" XPS foam on the outside with taped seams, 1/2" osb, and r21 fiberglass batts. I'm not exactly sure what to do for the vapor barrier. Is it the same as an exterior vapor barrier (tyvek)? It seems like that is going to be the best bang for my buck at this point. It can still break the thermal bridge and the fiberglass batts are about 1/2 the price of the wool.

For the slab, is Type II EPS adequate enough or should one step it up to Type IX, Type XIV or Type XV?

I know for an ICF/concrete home, it is recommended to go the route of Type XIV which has a compressive strength of 40psi. Type XV would give you 60psi but most residential concrete homes would be safe with 40psi. Last I checked, Type 14 EPS at 2" thick is around $20 for a 8x4 sheet.

Natural soil is generally rated as "good" if it has a rating of 3,000 lbs per foot² or 20 psi. Type II EPS is rated at 15 psi (compressive strength).

Does one have to lay an additional vapor barrier on top of the EPS prior to the concrete pour for the slab?

Even 2,000 psf (14 psi) soil is considered strong enough to not require wider footings with most houses - but check the exact details in your code. Some sources claim that foam should be de-rated to 1/3 of the rated value and then compared to actual footing load to reduce creep. But for non footing use, any EPS foam should be OK.

Posted By jonr on 21 Sep 2013 01:31 PM
Even 2,000 psf (14 psi) soil is considered strong enough to not require wider footings with most houses - but check the exact details in your code. Some sources claim that foam should be de-rated to 1/3 of the rated value and then compared to actual footing load to reduce creep. But for non footing use, any EPS foam should be OK.

For a wood-framed structure 2,000 psf would be OK but on an ICF home, especially a 2-story ICF/concrete home, wouldn't 2,000 pounds per foot² be inadequate?

I don't think I'll be getting anything beneath the slab.

There's no insulation under the basement slab?

Posted By ICFHybrid on 21 Sep 2013 10:44 PM

There's no insulation under the basement slab?

The footings are already done and he stated that there will be NO insulation under the slab.

For a few hundred dollars he should have done some EPS foam and he would have had at least R-10 underneath there.

I didn't even know code allowed no insulation down there. In North Dakota. I guess it is an unheated basement now.

I suppose I could still do foam under the actual slab and along the walls, but there wouldn't be anything stopping the thermal bridge from the footings to the walls. The basement will be insulated with foam and then batts of some sort on the interior. That is the "standard" around here.

wouldn't be anything stopping the thermal bridge from the footings to the walls

The foam and batts you are talking about on the walls insulate the concrete in the basement walls from the interior. Without any insulation under the basement slab, you will lose significant heat through the floor in Winter. If you ever want to have a finished basement, insulate the basement slab now. Even if you don't want to ever have it habitable down there, it still represents heat loss and you run the risk of getting condensation in Summer as warm humid air comes down and contacts the cool floor.

I know it would be better to have the insulation underneath, but I don't think it will keep me from having a finished basement. There are 4 other houses, all different builders going up near mine right now and none of them have foam under the slab while only 2 had foam on the exterior walls of the foundation. I'm not saying they are all right, I'm just wondering why that many different builders would be wrong.

"I'm just wondering why that many different builders would be wrong."
In a word, ignorance. Most builders are wrong. this isn't to denigrate them, but these methods are just being integrated into builder's mentailty - these builders are doing it the way they learned; the way builders have done it for generations. Its time for that way of building to disappear, but it will take a generation or more. This from a builder who built that way for decades, but has learned. Insulate the floor and put in a vertical piece between the underslab foam and the wall, so the floor slab does not come in contact with the cold foundation. You'll notice the difference.
Yes of course you can have a room in your basement; many people do. Many of them also live with a somewhat damp and at least slighty moldy smell. If thats what you're looking for, do it their way. If you'd prefer a non damp, dry space, do it ths way. It works.

Bob,

Well said.  I could not have said it better.  I hope no one is offended but we have to recognize the problem before it can be solved.

I have spent many years trying to educate future builders and architects to build better.  Slowly, I have seen some results over the last several years.   With access to the information on the internet, more and more homeowners are insisting on homes that save energy and have low maintenance.

Posted By ultimatehomestead on 22 Sep 2013 02:48 PM
I'm just wondering why that many different builders would be wrong.

Like others have chimed in, most builders are building like they did 20 years ago. Technology and energy efficiency have changed dramatically and most builders refuse to change their approach.

So to answer your question, yes, many different builders are wrong. That is the sad but true reality of building today. It's a battle dealing with builders who refuse to change and adapt. I've had plenty of arguments with builders who refuse to put in anything more than R13 batts into walls and refuse to even install a vapor barrier below the slabs.

The 2012 IRC attempts to "force" the energy change but it will be years before communities accept them. Some are still operating on 2006 IRC with amendments.

Parts of Europe like Germany are night and day ahead of the USA in terms of energy efficient buildings. When you have to pay .45 cents per kWh, you begin to build smart and efficient or you will pay dearly for the lifetime of the home ownership.

Posted By ultimatehomestead on 22 Sep 2013 02:48 PM
I know it would be better to have the insulation underneath, but I don't think it will keep me from having a finished basement. There are 4 other houses, all different builders going up near mine right now and none of them have foam under the slab while only 2 had foam on the exterior walls of the foundation.

"None of them have foam under the slab," that is truly a sad statement, especially in Zone 6+ of North Dakota.

You can still have a finished basement even if you don't put foam under the slab but you will pay $$$ an energy penalty for the entire life of the home. Not to mention your comfort levels will drop as will the potential of mold, musty odors and moisture problems.

Just a week ago a forum poster stated that he despised basements and didn't want to build a new home with one because they are musty, cold, and damp. The problems are not basements but the way they are built and insulated. If you insulate it correctly, it won't be a smelly and damp area. You also won't have to pay the higher energy bills to heat it throughout winter.

Thanks guys. When I reread my last post I realized that it came across a little "snotty" which was not my intention. It is frustrating trying to get a quality built project and keep it on budget. With my footings in, I'll have to see if they excavated deep enough for foam underneath. I think I will need 2" of XPS foam under the slab for an R10. That should be on top of a vapor barrier (poly film) which is on top of gravel? I've been searching the internet for a good diagram but haven't found one yet. Do I need a thermal break on the edge of the slab where it meets the basement walls and if so could it just be 1" XPS foam? Now, on to foam on the exterior. Is there a scenario where I can get away with 1" at R5 on the foundation and main floor? I am hoping for some way to do that so my windows will work out. I will probably end up installing the foam myself on the exterior as well. On the basement walls I would just wait until the damp proofing was done and then come back with some sort of adhesive. Above grade I would then use one of the finishing products such as a brush on foundation coating. On the wooden walls I would use a foam nail of some sort. Should there still be an external house wrap such as tyvek on top of the sheeting? Will this seal my house up so tight that I will need an air exchanger?

. . . I think I will need 2" of XPS foam under the slab for an R10. That should be on top of a vapor barrier (poly film) which is on top of gravel?   . . .

You might want to check with Dana1 about the best location for the vapor barrier.  Also, if there is space, using EPS might be better and less expensive.