Greetings, I am working on plans for my home and would like to ask the forum members for assistance. The goal is a code plus build within budget if possible. First, the location is Garrett county,Maryland . This is zone 5A I believe, but it has it’s own climate unto itself. Located in the mountains average snowfall is over 120 inches, code requires a Case Study for snow load but I have yet to find one. This past winter we experienced about two weeks straight of subzero temps, lowest temp I saw on parents house was -23, so when code has design temp as zero I think it should be like snow load and based on a CS. Surrounding counties are usually 10 degrees warmer on average. The house will be built on hillside facing southeast with a walkout basement and one level above. Each floor is 1808 square feet with 9’ ceilings both floors. Now some specifics, site is excavated for basement with a bench cut of 8’. That was all the D6 could go so I’m confident that It’s on solid ground therefore I am leaning towards a frost protected shallow foundation. Basement walls would be poured concrete with insulation on exterior. Don’t want to insulate interior walls for two reasons. It will be easier to tie into slab insulation on exterior and I won’t have to cover inside with fire barrier or wire at this time. Basement will be 8” poured concrete walls unfinished and open but planning placing pex in slab for future. Main floor is also open floor plan. Prefer hydronic heat in floor, looking at warm board. Main floor Exterior wall build up proposed from inside out is sheet rock, 2x6 framing with mineral wool batts, osb sheathing, weather barrier, 2” mineral wool boards, furring strips and vinyl siding. Let’s start there, any comments so far would be appreciated. Like is it ok to change to 2x4 framing? Changes in insulation? Feel free pick at everything so far. Thank you

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In order for the slab insulation to tie in to exterior basement wall insulation it has to go under the footing. Putting foam under the footing requires an engineer to specify the footing & foam, or it will be at a high risk of settling/cracking.

It's fine to drop back to 2x4 framing. IRC code min walls are 2x4/R13 + R5 continuous insulation. The 2" of rigid rock wool is good for R8, so if you went with R15s in the stud bays and R8 on the exterior it would still outperform the code.

Detail the wall sheathing as the primary air barrier, by taping all the seams, and caulking the framing to the sheathing inside each stud bay, and along the seams of any doubled-up framing (headers, top plates, jack studs, etc.)


There are cheaper ways to do radiant than WarmBoard. Under the subfloor heating can still work at reasonably low temperatures below the condensing temperatures of fossil-burner boilers, but you have to calculate and keep track of the design loads as changes are made to the house specs to know what the water temp requirements would be.

What are your space heating fuel options?

With an open floor plan you can do pretty well with modulating ductless air source heat pumps designed for cold climates. Even though most manufacturers won't spec the capacity below -13F or -15F, the are still delivering a decent amount of heat a -20F or colder. (I know of a guy in Quebec who heats his house with four 3/4 ton Fujitsu AOU/ARU 9RLS2H ductless mini-splits that still keep up with the load at -30F or so.) Even when sized strictly for the air conditioning load, cold climate mini-splits still usually cover 100% of the heating load as well in zone 5A locations.

Ikee, your project sounds kind of similar to the house I built. I have 2x4 walls with 2” exterior insulation, 10’ Ceilings, 2500 sq ft per floor. The house is very comfortable year round and we also had two weeks of sub-zero in January. We have in-slab radiant on all floors and love it. For your basement slab it is no big deal. For 1st/2nd floors it becomes an added challenge and expense but I think well worth it. We have 1.5” gypcrete thin slabs on our above ground floors. I found this website after we had our design finished so I had to do the best I could with that plan but it turned out great. The house is brick and I insulated the inside basement poured walls with the blue XPS foam because the flame spread was low enough that my inspector allowed it. Since I am finishing those areas I did not want to put up the usual basement wall fiberglass blanket and then throw it away.

Appreciate the comments so far, had to go out of town for a few days.

Dana, my fuel options are: propane, fuel oil, wood. I have access to timber and cut/split some every year to sell. I am willing to consider it as a primary source for near term but long term prefer it be a backup only. I will look into the mini splits you mentioned but that would negate the floor heat correct?

I admit that the mini splits appeal on their simplicity, but I have been spoiled by a few stays in homes with infloor heat. Also there are only a handful of days that AC would be nice. I did a manual J by hand and an online version which yielded 23,434 and 27,652 btu/hr respectively for the 2x6 wall if I did it correctly.

The better half has requested a gas fireplace, no wood stove, outdoor wood boiler is acceptable.

I would appreciate any suggestions on the heating and domestic hot water system given the above information.

For the ventilation system, I have sent floor plan to 475 to get their opinion on viability of their Lunos products. Trying to keep thing simple and ductless.

Getting back to the foam under the footing, I was planning on using a type that would yield at least 4 ksf and less than 5% compression at that loading.

The site has no water or sewer service so it will be well and septic field, so to meet the fire sprinkler portion of the code I am looking at a system called automist smartscan. No need to have a holding tank or water in the ceiling. Anyone with experience with this system chime in please.

Thanks

At what outdoor temperature was the 23K & 27K heat loads calculated? Almost all online load calculators are going to overshoot reality by a good 20% or more.

An 8kw electric boiler can deliver 27KBTU/hr on it's own at just about any water temperature you need, and are pretty cheap. (Some even have outdoor reset controls to vary the temperature with outdoor temperature.) A 6kw unit delivers about 20 KBTU/hr. eg: The Argo AT082410C or AT062310C 2- stage unit would be suitable for the floor.

https://s3.amazonaws.com/s3.supplyhouse.com/product_files/SeriesC-Brochure1.pdf (The 8kw version is only $1200 at internet pricing. There are cheaper electric boilers than the Argo, but these are pretty rugged and easy to set up.)

If you operate the radiant floors primarily with a floor thermostat, not a room air thermostat, heating primarily with a mini-split doesn't affect the cushy under-foot feeling. A comfortable not hot floor temperature of 72F in a 70F room delivers about 4 BTU/hr per square foot. Assuming you have about 1500' of unobstructed non-closet/cabinet covered floor per story that's 3000 square feet x 4 BTU/ft= 12,000 BTU/hr, roughly half your calculated heat load. Bump that to a still comfortable 74F and it's emitting ~24,000 BTU/hr, which is pretty much your entire heat load (or more). You'll probably need/want to set it up as two zones, zoned by level, since the heat loss characteristics downstairs will be fairly different from those upstairs.

If you install the newer generation Fujitsu 3/4 ton AOU/ARU - 9RLS3H is specified to deliver 11,000 BTU/hr @ -15F , and will deliver 15,000 BTU/hr @ +5F. If you installed one per floor, they would cover 100% of your load without the floor heat. See:

http://www.fujitsugeneral.com/us/resources/pdf/support/downloads/submittal-sheets/9RLS3H.pdf (The "Nominal heating" number is the output level at which it was tested for efficiency.)

If using mini-splits + floor heat you have backup if either one fails, and can economize on electricity use, since averaged over the season the mini-splits will use about 1/3 the amount of power per BTU that an electric boiler does. Setting the floor to 72F and setting the mini-split to 72F or higher, the floor will never drop below 72 (no room air stratification), but the duty cycle of the electric boiler falls to near-zero.

Note: They make wall-thermostats (both wired and wireless) for these things, but unless programmed to use the temperature sensor inside the wall thermostat it's really just a remote, and the room temperature is sensed inside the mini-split head, as if it were operated with the usual hand-held remote. They deliver more stable room temperatures if programmed to sense the room temperature at the wall unit, not the mini-split head. This becomes important if using both an electric boiler and mini-splits for heat.

Mitsubishi has a similar series of cold climate mini-splits. The 3/4 ton MUZ/MSZ- FH09NA is actually smaller than Fujitsu's, 9RLS3, putting out only about 2/3 the amount of heat at +5F or cooler, but it also modulates to a lower level, making it more comfortable during the shoulder season, and might be a better fit if using two of them (or if there is better local support for Mitsubishi than Fujitsu):

https://nonul.mylinkdrive.com/files/MSZ-FH09NA_MUZ-FH09NA_Submittal.pdf

Both manufacturers make 1-ton and 1.25 ton versions of each, but oversizing is not recommended, since they will cycle on/off more, leading to lower efficiency. Even if undersized for the load at -15F a pair of 3/4 tonners could still supply 90% of the annual heat or more, with the electric boiler picking up the difference. You may have to run a 2-stage thermostat (a floor temp sensor and a room temperature sensor) to have the electric boiler auto-magically pick up the slack, but you can also just bump up the floor temp a degree or two when you know it's headed for negative double-digits overnight (or whatever temp the mini-splits stop keeping up.)

In my area (central MA) heating with cold climate mini-split with 20 cent/kwh electricity is comparable in cost to heating with natural gas at $1.50 /therm, or propane at $1.40/gallon. (At Maryland's average 13 cent retail residential electricity it's about the same operating cost as 90 cents/gallon propane.)

Outdoor wood boilers are expensive to set up, and quite inefficient as heating systems go, and unless you set up a buffer tank big enough to run intermittent burns at high fire the local air pollution is an issue too. (They are even banned in some New England towns due to the excessive sooty particulate emissions when they damper down during a burn.) A small woodstove is both cheaper up front and more efficient, just not hydronic. But with a floor thermostat operated electric boiler the wood stove still "plays nice" with the radiant floor (and mini-split too), as long as the floor thermostat (or mini-split head or wall thermostat) isn't located too close to the stove. In any location susceptible to ice storms taking down powerlines for a day or three at a time it's worth installing a wood stove as the "Hail Mary" backup anyway- hydronic heating systems and mini-splits don't run without power, but wood stoves do.

You're still going to have to let an engineer spec both the footing and the foam under it. If you're going to wing it, bear in mind that wider footing distribute the weight of the house over a broader area, but somebody needs to calculate the weight of the house & contents and design in some margin if insulating under the footing. It's not rocket science, but it's not 5th grade arithmetic either. In my area the code folks and mortgage lenders would need to see the certified professional engineer's stamp on the detail plans (and that's whose insurance company would be on the hook if it fails.)

I much appreciate your thoughts. The manual J calcs were based on the code value of 0 degrees and I used 70 for inside, exterior insulation for basement was 3.5 inches of used eps that I have found for $25/sheet (4x8). code reads r15 for walls and r10 under slab but I thought I would be consistent with r value for both slab and walls (3.5” x 4.2/in. = r14.7 exclusive of concrete contribution. Does it make since to do this or should I drop the slab insulation back down to r10 and do my load calcs seem reasonable?

I really like the idea of combining the mini split and floor heat, the redundancy appeals to me should one fail, I will have to see what that does to the budget. About the electric boiler, I looked at the Argo and I like it, would it also be capable of providing domestic hot water or should I plan on a water heater. My floor plan has two bedrooms on one side of house and the master bedroom on opposite side. Initially I thought about point of use for each side of house. Plumbing I had planned on a home run system with pex.

I will try to post a pdf of floor plan, that may help.

The wood stove will go in the basement, that is the compromise, main floor gets a gas fireplace.

I would like to go back to the main level wall build up. I see a lot of the colored sheathing being used, would you recommend that versus plain osb and an exterior wrap. ( recommend any), After viewing 475 products I have been leaning towards their membranes and tapes.

Thanks

Wood stoves in very tight houses can have backdrafting issues when cold-starting them. A wood stove with a dedicated ducted combustion air supply can help, as long as the inlet is below the fire box of the stove. With the outdoors side of the combustion air duct above the firebox it becomes a secondary parasitic flue when cold-starting, and more likely to backdraft even when fulling firing. Wood stoves located in BASEMENTS inherently have this issue with or without ducted combustion air, since the lowest air inlet to the house is above the fire box. This is even prescribed in code to some degree:

https://up.codes/viewer/utah/irc-2015/chapter/10/chimneys-and-fireplaces#R1006.2

"The exterior air intake, for other than listed factory-built fireplaces, shall not be located at an elevation higher than the firebox."

Even with factory-built air intakes, it's an issue.

I've never seen a building code that required insulation UNDER basement slabs, or even under slab on grade foundations. There are code requirements for slab EDGE insulation for slab-on-grade foundations, and if the slab is headed it adds R5 to the slab edge R requirements. It's standard practice to put a minimum of R10 under a heated slab, but it's not enshrined in code.

See note d regarding the slab edge in the boilerplate IRC verbiage:

https://up.codes/viewer/wyoming/irc-2015/chapter/11/re-energy-efficiency#N1102.1.2

"d. R-5 shall be added to the required slab edge R-values for heated slabs. Insulation depth shall be the depth of the footing or 2 feet, whichever is less in Zones 1 through 3 for heated slabs."

That's it.

But it sure doesn't hurt to put more R under a heated slab than R10.

Ok, I have been reading up on the foam under the footing and the Fijitsu mini splits that Dana has pointed out.

On the foam I have read that the EPS does not hold as much moisture as XPS but when looking for a product having a high compression value I found foamular by Corning. It’s literature touts less moisture adsorption. The EPS brand comparison was by InsulFoam. Can someone shed some light on which absorbs less moisture and retains R value?

Definitely looking to go with mini split plus hydronic if I do it. The supplemental heat and a shot of cooling when necessary makes since. Are there any cons to going the ceiling cartridge route versus the wall mount unit?

I have attempted to attach a pdf of my floor plan, the deck faces SE .

Dana your input on the wood stove has me considering dropping it, I’m getting too old to mess with it and don’t want to worry about bringing in air. Better off putting the money towards a backup generator since it looks at this time electric will be my heating.

With a properly drained slab & footing (=4" of washed gravel, no fines below, with perimeter drains) neither EPS nor XPS will absorb moisture. Neither are hygroscopic, meaning neither will wick moisture. But if submerged both will take on moisture. The interstitial spaces of the macroscopic beads of EPS fill pretty quickly to 2-3% of the total volume that water also but also drains very quickly when the tide goes out. (They use it for dock floats, after all.) XPS takes on water more slowly, but also retains it for longer.

Under ASTM C272 testing the immersion time is limited to 24 hours and in that short time frame the water absorption of XPS is very low compare to EPS (less than 0.1% compared to a couple percent) but that doesn't mean you can lay it on wet clay soil at/near the water table under a slab and expect it to perform at spec. I've seen reclaimed XPS stacked up directly on damp soil with a tarp over it for a year or two, and weight of the sheet on the bottom was substantially & obviously heavier than any other sheets in the stack. I didn't weight it- just set it aside and marked it "wet- don't use". I'm sure it eventually dried out.

The amount of moisture EPS takes on is a function of it's density, as is the compressive strength. Type-XV EPS (3lbs per cubic foot nominal density) typically runs 60psi @ 10% deformation, and 2% water absorption, max. . eg Insulfoam XV:

https://www.insulfoam.com/wp-content/uploads/2014/04/11009-Roof-XV-TDS_-REV-5-16-web.pdf

Under slabs (and in insulated concrete forms) Type-II EPS (1.5lbs nominal density) is more commonly used, typically rated 20 psi / 3% max absorption. eg Insulfoam II

https://www.insulfoam.com/wp-content/uploads/2014/04/11006-Roof-II-TDS_REV-5-16-web.pdf

Radiant floor folks tend to prefer Type-IX EPS (2lbs nominal) for it's better staple retention compared to Type-II. It's typically rated 25psi / 2% max water volume. eg Insulfoam IX:

https://www.insulfoam.com/wp-content/uploads/2014/04/11007-Roof-IX-TDS_REV-5-16-web.pdf

Most reclaimed roofing EPS is 1.25lb density Type- VIII, which is typically rated 15psi / 3% max water absorption, and it's fine to use under residential slabs, but not under footings. It's the lowest density foam that can be considered a "walkable" roof under a membrane roof, and is widely used since it's the best R/$ foam for large commercial roofs that you can still walk (but not stomp) on without permanent deformation of the foam. Under a 4" steel reinforced slab the weight of the contents of a house are well distributed, and it won't collapse or cause the slab to crack.

https://www.insulfoam.com/wp-content/uploads/2014/04/11005-Roof-VIII-TDS_REV-5-16-web.pdf

XPS eventually loses it's HFC blowing agents over time, and that affects performance. EPS lose it's hydrocarbon blowing agents in day (weeks for large blocks) and has a stable performance over time. XPS vendors typically warranty the performance to 90% of the labeled R over time, but in 20 years it's likely to have crossed that threshold on it's way to the same performance of EPS of similar density. They can comfortably assert a "lifetime warranty at 90%" with the full knowledge that nobody is going to remove a sample decades after it was installed, have it tested by a qualified third party and submit a warranty claim for under-performing foam. But they are acknowledging that the labeled LTTR performance is only temporary, and won't perform at that level over the lifetime of a building. EPS performs at about 85% of the R-value that XPS of the same density gets labeled, but it doesn't go down over time.

Here's the "lifetime warranty" for Foamular:

http://www.foamular.com/assets/0/144/172/174/80986778-f844-4af4-91b4-c86498b2c779.pdf

Near the bottom of the first column it reads:

------------------------------------------------------------------

• retain at least 90% of its advertised R-value**

Owens Corning’s obligations under this warranty will only take
effect if the XPS Foam Insulation is installed (including both the
original installation and reuse installation) in typical building and
construction assemblies in strict accordance with all applicable
Owens Corning specifications, recommendations and
guidelines that were in effect at the time of such installation.
Owens Corning XPS Foam Insulation shall only be placed into
an assembly where the moisture transport mechanism is well
understood and determined to be acceptable in accordance
with accepted engineering analytical practice.


--------------------------------------------------------------------------

Note the final sentence, regarding moisture...

It is possible to buy an indoor wood stove that can heat a radiant slab effectively. Stoves with hydronic output of 70 percent or more are common as dirt in Europe and available here if you know where to look. http://www.hydro-to-heat-convertor.com. I bought mine on ebay in Britain ebay.co.uk and had it airfreighted to the US for a total cost of $2400. (That was back in 2009 when the mortgage market was flat on its back.) If you aren't interested in stove as living room attraction, this Polish site has impressive prices: https://kotly.com/gb/22-hand-fired-boilers.

Sad to say, Europe is also awash in inexpensive air-to-water heat pumps which operate at 50-cycle AC rather than 60. I can't find a good answer as to whether this would affect more than timing functions although the advice of expat sites is to leave US refrigeration at home while preparing for a tour in Europe.

Dana1, a $5 backdraft damper fixes outdoor air supply elevation issues, and kindling in my stove lit lingeringly with a propane torch creates an effective draw in 30 seconds. I suspect the OP knows how to build a fire.

Again, thanks for the input by all, it’s been a help. I think I have the basement/foundation sorted out for the most part and now seek comments on main level and roof.

The walls will be prefab in framers shop and set onsite. I have asked him to let me know what cost difference is between 2x6 and 2x4 walls. As I mentioned intent is to install 2” mineral wool on exterior outside of wb and sheathing. So, what would be the suggested insulation in the stud bays? Framer will be caulking the sheathing. Recommendation for caulk also. I am hoping this addresses air infiltration but is a flash of foam for air sealing and then cellulose? I know it depend on the framing so I’m trying to get suggestions for each wall framing with an eye on cost efficiencies.

What is the way to analyze if extra insulation from 2x6 framing. Do manual J on both wall assemblies and compare the heat load differences?

Then looking at roof build up. I have been told that lunos through the wall hrv’s will work for my layout and where I envision installing the mini split will be in the wall so no ducts above ceilings. To address fire suppression part of code I have sent plans to Plumis for there smartscan automist system. I also do not plan any recessed ceiling lights, so nothing mechanical in ceiling.. I really like cove lighting so as I have read these forums was glad to see that type of lightning receive favorable comments. Most rooms will have a drop down fan and light as well as a couple wall sconces. Therefore what would be the suggested ceiling/ roof insulation as well as vented or unvented roof?

That is it for now, thanks.

If you don't need the 2x6s for structural reasons, then I would use 2x4s and then insulate outside the studs with 2" of EPS and with open cell spray foam between the studs. Dana1 may have a better solution such as flashing between the studs with closed cell foam plus Rockwool, etc.

Alton, The price difference of 2x4 framing and 2x6 is enough that I will stick with 2x4 studs and 2” exterior insulation. I will look at cost of the closed cell spray foam for the stud bays. I won’t know until I get that price but in yours and Dana’s judgement would that provide enough air sealing to not use zip sheathing? I was pricing it and osb and regular osb is $18.50 a sheet at the moment.

The great room has a cathedral ceiling remaining are flat. Since I will not have any ducts or sprinklers in the ceilings is recommended roof ventilated and blown insulation?

Thanks

Since I have been designing and building with alternative technology such as ICFs, metal SIPs, SCIPs, etc.for the last several years where air sealing is not much of a problem, I will defer to Dana1 to answer your question. He may tell you that staggering two layers of EPS will eliminate the need for an air barrier.

I was exposed to a build in Idaho fall before last and exterior insulation was mineral wool and was very impressed with the product so I was leaning in that direction rather than eps. I was planning on a wrb on exterior of sheathing. It just came down to a greater comfort level with the wool, my thought is it would allow better drying should any moisture get in and also more insect impervious.

The best price I have received on closed cell spray foam is $1.25/board foot. I doubt with 2x4 studs a flash and batt is possible therefore I suppose best course is batts and caulk well. Let me know if I am on correct track. That goes for anything I have proposed so far. This site and the comments so far have been a great assistance.

Thanks