Yeah that sounds like what it would be like.

My thought was uninsulated unconditioned stairs going up, to a landing and exterior door at the top of the stairs, but I guess the stairs could be enclosed.

You could try a boxed in chase for the water pipe, with lots and lots of insulation and good air sealing. Might work (or might not.)

Check with your building code regarding the stairs and egress to the upstairs living quarters. We found that thinking of the loft as a completely separate space from the garage during design was needed. That led us to place the entry door to the loft stairway on the ground floor exterior and thus allowed proper fire rated drywall barriers for the stairway. You run in to a number of such issues when you plan to have living space above the garage. Good luck with your project.

OK thanks, so yes it ends up that the stairs are separate from the garage, conditioned space and contain a plumbing chase.
It's not clear to me how to heat the stair area.  The stairs will be open to upstairs (no door separating them).

 The upstairs will heated by a Fujitsu RLFFH (new low wall / floor mount ductless mini split).

Maybe just a small electric resistance heater?

https://c2.staticflickr.com/4/3710/32839070114_2297a51390_b.jpg

Heating a small utility chase is more efficient than heating an entire stairwell.

That is true, we could just heat the chase and let the stairs get cold-ish. They probably won't really get that cold being part of the envelope and open to the conditioned area upstairs.

I've been designing a home for Iowa incorporating the FPSF and ran into problems with the local building inspector. He will not allow it unless an engineer signs off on it, which is another cost. I did consult with an engineer over the phone who like the drawing I sent him. The big question in my case was reinforcement for the 4 inch slab. He suggested rebar on a 3' by 3' grid. He did not recommend wire mesh because in all of his years of investigations mesh ends up in the bottom. I have had concrete guys tell me I don't need any rerod or mesh. In my situation we are going to use two courses of ICFs set on a footing.

I've been designing a home for Iowa incorporating the FPSF and ran into problems with the local building inspector. He will not allow it unless an engineer signs off on it, which is another cost. I did consult with an engineer over the phone who like the drawing I sent him. The big question in my case was reinforcement for the 4 inch slab. He suggested rebar on a 3' by 3' grid. He did not recommend wire mesh because in all of his years of investigations mesh ends up in the bottom. I have had concrete guys tell me I don't need any rerod or mesh. In my situation we are going to use two courses of ICFs set on a footing.

Rebar will minimize the size of cracks. I'd use some.

My understanding is that there are prescriptive FPSF provisions for heated buildings in the IRC. But the better FPSF designs are a little different and also work in unheated buildings.

28x28 Garage is going up now, ended up doing a 4 ft frost wall.  There will be R15 on the inside of the wall all the way down and R15 under the slab and vapor barrier.

Apartment is above garage.  Stairs to apartment are inside of garage, NOT separated from garage.  Exterior door at top of stairs into apartment.

Have a few questions about how to insulate this building.  I am considering insulating the garage walls and heating the garage to maybe 45F-ish.  This is in "USDA Zone 4" in VT, lowest temps around -20ish F.  If this is the case, would I still want to insulate between the garage and apartment above...?

The walls are 2x6.

Ceiling upstairs is a sloped ceiling.

The roof and sidewalls are already spec'd out and will not have exterior insulation under the roof or siding, so that leaves what choices for interior insulation?  Technically only need R20 on the sidewalls but can achieve more with closed cell and batt.    Need R49 but prefer more on the roof. 

Windows are 0.28.  This building will not be occupied full time, maybe 100 days a year, throughout the year.

USDA climate zones are useless in energy use discussions. You're in DOE climate zone 6A.

IRC 2015 spells out R30 under the floor unless you're fully heating the garage, in which case the walls would need to be R20 + R5 continuous insulation even in the garage.

https://up.codes/viewer/wyoming/int_residential_code_2015/chapter/11/re-energy-efficiency#N1102.1.2

Closed cell foam thermally bridged by studs is a total waste of foam from a thermal performance point of view. In zone 6A R20 + R5 c.i. meets code from a thermal perspective, but is risky from a moisture accumulation perspective. Dropping back to 2x4/R13 + R10 c.i. meets code thermally without the moisture risk. But even 2x4/R13+ R7.5 c.i. is fine from a moisture perspective, even though it doesn't quite hit code-min thermally:

https://up.codes/viewer/wyoming/int_residential_code_2015/chapter/7/wall-covering#R702.7.1

A 2x4/R13 + R7.5 c.i. wall outperforms 2x6/R20 thermally, and even outperforms a 2x6 flash'n' batt that has 2" of closed cell foam between the studs for dew point control, despite the much higher center-cavity R value. (That's just how badly the thermal bridging robs high R/inch foam!)

What do you have for rafters? Hitting R49 in a vented cathedralized roof assembly requires 16" I-joists for rafters, or 7" of HFO-blown 2lb foam (that get's robbed blind by the thermal bridging) or 8" of climate damaging HFC blown 2lb foam. R49 fiberglass batts are 14" thick, but are the wrong width for I-joists, but 15" of mid-density cellulose installed against 1" deep chutes to preserve the vent space gets you there.

deleted double post

I don't actually know what the roof system is which is silly. I will ask. It's not in the spec's which is odd .

What about cellulose in the walls plus a thermal break on the inside of the studs?

If I heat the garage to somewhere well above freezing, with insulation on the 4 walls of the garage would I still want to insulate between the finished apartment upstairs and garage. I think no?

Posted By patonbike on 11 Oct 2017 12:23 PM
I don't actually know what the roof system is which is silly. I will ask. It's not in the spec's which is odd .

What about cellulose in the walls plus a thermal break on the inside of the studs?

If I heat the garage to somewhere well above freezing, with insulation on the 4 walls of the garage would I still want to insulate between the finished apartment upstairs and garage. I think no?

Building out some interior side thermal break strips of 3/4" polyiso + 3/4" thick 1x furring at the framing (for a total 1.5" of total wall thickness), with a full cavity fill of cellulose (all the way to between the furring) works OK. See:

http://www.finehomebuilding.com/membership/pdf/9750/021250059.pdf

Filling it with 7.0" of cellulose yields ~R25-R26 at center cavity, and the ~R5 polyiso nearly doubles the R of the framing fraction.

In a zone 6 climate you'll still need a Class-II vapor retarder on the interior side, either air-tight drywall painted with "vapor barrier latex" primer, or a sheet of Certainteed MemBrain under the wallboard, detailed as an air barrier.

Only if you're fully conditioning the garage would you skip the floor insulation. Code want's R30 or a full cavity fill if the joists aren't deep enough. If you're heating the garage to 45F and the space above to 70F that's a 25F difference, and even with R2 of subfloor + finish floor a heat loss ~12.5 BTU/hr per square foot of floor. It adds up, and it's also a comfort issue.

Assuming 750 square feet of room above the garage you're talking roughly 9000 BTU/hr of additional heat load for the fully conditioned room, that would drop to under 2000 BTU/hr if minimally insulated, under 1000 BTU/hr at the full R30. You'll probably want at least some crummy kraft-faced R19s (the absolute IRC code minimum) or "contractor roll" R13s snugged up to the subfloor between the joists.

OK definitely not going to fully heat the garage. So we will insulate the walls, floor of apartment/ceiling of garage. Ceiling of garage is very deep trusses.
The roof rafters are 2x12's.
The walls are interesting, the are 2x6's but they are blocked horizontally between every stud . I've never seen that before.

https://c1.staticflickr.com/5/4576/37991162544_935bba5b63_b.jpg

Are those horizontals 2x6s, let-into notched 2x6 studs or something? It's a bit hard to tell in the pics.

they are horizontal 2x6s, cut to fit between the studs and nailed in at the outer edge of the 2x6 studs. No notches. Maybe just somewhere solid to nail in the the Zip sheathing.

Sounds like fireblocking, designed to keep fire from going up chase to room above.

Oops I didn't catch the part that said it was at the outer edge. Maybe blocks at the edge of the shearing? Pretty common on 9 to 20 foot walls and 8 foot sheathing.

My guess is for "additional rigidity".

https://en.wikipedia.org/wiki/Blocking_(construction)