A new garage

FranklinD

Howdy, Wall-Folk...

I've decided to request advice from the largest (and brightest) heating-related knowledge base on the 'net.

I'm a mechanic by trade (people get stumped around here when I refer to myself as an automotive technician, so I say mechanic). I take care of my small city's aging fleet of police and, now, fire vehicles. Anyway...

My current garage, built in the 50's, is crumbling. The slab is cracked into quadrants, the roof is sagging, and someone put on an addition that leaks like a sieve. So I'm looking at plans to replace it, and due to where I live, heat it comfortably and efficiently.

I spend a goodly amount of time out there...I take jobs on the side by word-of-mouth only, and average about a vehicle per week. I really enjoy the diagnostic issues that stump other shops and have had many referrals come my way via local dealers (I was a Ford Master Tech for 8 years). I also do a ton of custom low-voltage electrical, custom harnesses, and so on. I've been using a design temp of 60, though while working I like it a little bit cooler.

The garage will likely be 24x30, with a hopefully 12 ft ceiling, though I may be limited to 10 ft finished height. It's too early to guess at heat loss numbers, but anyway...

It gets cold here. In Jan-Feb 2014 we had 30-some consecutive days with highs around 0 and lows around -24(f). Our design temp is -19 I think. Thus my fears: if I go with a heated slab, I imagine I will HAVE to use glycol in one form or another. I'm worried that if there's an issue, or if the power goes out, etc, that it'll freeze up on me. The new garage will likely have a 5" slab, 2x4 walls (insulated with FG), and a regular low-rise peaked roof. The ceiling will be open, but the rafters will be insulated (we use the space for winter storage for lawn stuffs).

Budget, as always, is a concern. I have hot water heat (cast iron radiators and a newer Burnham ESC4) in the house 40 ft from the garage, but I'm not sure tying into this system would be the best way to go. I do have natural gas, both in the house and piped out to the current garage (I imagine it will be plumbed into the new garage as well).

I've been making do with a 35k btu propane torpedo heater for the last 4 winters, and it's loud, inefficient, and creates condensation on everything. In other words, it's awful.

Regardless of what I end up doing, I will be insulating under and around the slab with 2-3" xps and plan on laying a couple circuits of 1/2" barrier pex in the slab, probably 6-8" on center. The ground under the slab will have to be built up about 18" above grade prior to the pour, as the back of my lot is low-lying.

So....long way around to the question: what is the best way to heat this place comfortably and economically? I'm really not in favor of adding $80/month to my gas bill to heat it 24/7, but with a slab that's kind of where I am, right? I would MUCH prefer radiant heat, but I'm open to all possibilities here. As I'm in the designing and dreaming phase here, no possibilities are out of line.

One other tidbit: the service drop to the house currently passes over the garage. The plan is to upgrade to 200amp service, drop it to the garage with a 200amp panel, and make the house's 100amp panel a subpanel. So 100amps of electric service will be available. We do have off-peak "heating rate" available here too, about half the price of regular residential electric rates.

Thanks for reading, and thanks for any ideas/experience/wisdom/knowledge you great people can add to my expanding file folder that is titled "The Great Garage Debacle".

- Andy

FranklinD

I feel compelled to add that I do NOT work on the police and fire fleet vehicles in this garage...it is for personal use only. Sorry if that point wasn't clear

SWEI

What are your NG and electric rates actually like, including the off-peak?

With that kind of design temp, I suspect your frost depth is 36 inches or more. Probably impractical to bury lines between the buildings below that, so you'd almost certainly need glycol for that approach. Trenching, a bit of PEX, and a plate HX should cost less than a small boiler will.

Slab insulation is relatively inexpensive, especially for a small, simple floor plan like that. I'd run a few scenarios through the Uponor app and see where the sweet spot lies. I suspect you're going to want at least 4 inches, maybe 6 around the perimeter. Protecting that is important -- there are several strategies you can use depending in large part (with termites) on what's above it. Using ICFs for the first foot or two of the wall can help a lot there. You might be able to avoid glycol in the garage, but snowmelt on the door apron can be awfully nice to have...

For intermittently occupied spaces in cold climates, I'm a fan of using radiant in the floor with a low setpoint (e.g. slab sensor at 50°F) plus overhead radiant gas to bring the space up to working temp quickly.

Firecontrol933

I'd suggest you start your project with spending everything you can on putting as much into the structure as far as insulation as possible. Money spent on this will save you money in the long run and make it easier to heat and more comfortable.

In a garage floor you can easily get by with 12" on center tubing.

I also would suggest using the floor for "maintaining" minimal heat and then I'd add a gas fired unit heater to boost the inside temp when you are in there working.

rick in Alaska

I would also not build any heated structure without having a minimum of 2 x 6 walls. I am in Alaska in a "moderate "area, and I built my house with a 2x 4 wall in front of a 2 x6 wall and filled it with insulation. Insulate as best as you can and it will pay for itself down the road.
Rick
p.s. I envy you even getting a garage! Maybe this year.....

Paul48

I don't know this to be fact, but it is what I was told. About 12 years ago, a young engineer I was working with was building his home. I asked if he was using 2x6 for exterior walls, and he said no. I asked him why not, and he said he had run the numbers, and it would take 75 years to recover the difference in cost, from savings.

FranklinD

You're telling me! Heh, I've been waiting for this for about 15 years now. I'm hoping to demo the old garage and have fill added to the site before next winter arrives...thus giving it the winter and spring (one good freeze/thaw and spring rains) to compact the fill.

Yes, we have pretty wicked frost depths, and spring is rough...everything moves. This is swampy land to begin with, intermixed with gooey clay. No real topsoil to speak of unless it was added later (so about 6-12" of "soil" on top of the clay - it retains water like crazy). Doing the garage also makes me want to repour the walk from house to garage - about 30 feet - with tubing for snowmelt. Some winters (like the last two) we don't get much snow, just the wind/cold...some winters we get 60-70" thru the season. I've lived here my whole life and winters aren't what they used to be, snow-wise.

Electric rates are 10.5 cents per kWh for standard residential, 5.5 for off-peak heating (which requires a separate meter). Natural gas, on average, is about a buck a therm. It deviates up and down all winter long...from $0.90 to $1.05 or so.

I'm in the process of scheduling estimators, so we'll see what they say. I know that 2x6 walls would be ideal, as would 4" xps under the slab... My intention is to also have about 24-36" stem walls of concrete or block around the perimeter of the slab. A big issue around here is water creeping up siding materials. My house has the foundation extending 36" above grade...they built them that way around here 100 years ago so it must be good for something.

I'm trying to lump together everything in one shot with a mortgage refinance...we got lucky with this house in 2010 when the market here was in the toilet. We rented for 5 years previous to that and were starting to wonder if we'd ever be able to own a home. We had "surprise" twin girls in 2006 so money was always tight...but now that they're 10 years old (how did THAT happen?!) and my wife is working full time again, we are actually doing okay. Yay! We owe about half of what the property is currently worth, and a new garage, siding, and Windows would increase the value quite a bit. Not a dollar for dollar increase, but darn close. So there may actually be enough to step up to a mod/con for the house (still kicking myself for going with the burnham 2 years ago...even at 0* ambient my average water temp in the house is 120* - chalk it up to my inexperience and a moronic installer).

The 'minimum heat' idea using the slab is excellent...I would then use either a large electric, ceiling mounted heater (Raynor or the like), or whatever's clever....many possibilities there.

Thanks so much, and keep any advice coming!

Andy

Paul48

@FranklinD

If you're building on fill...are you going to have pilings driven?

SWEI

FranklinD said:

Electric rates are 10.5 cents per kWh for standard residential, 5.5 for off-peak heating (which requires a separate meter). Natural gas, on average, is about a buck a therm. It deviates up and down all winter long...from $0.90 to $1.05 or so.

Net costs per million BTU there come to roughly $10.42 for a 96% mod/con, $12.50 for an 80% appliance, and $16.45 for off-peak electric.

My intention is to also have about 24-36" stem walls of concrete or block around the perimeter of the slab. A big issue around here is water creeping up siding materials. My house has the foundation extending 36" above grade...they built them that way around here 100 years ago so it must be good for something.

Good plan. Do consider ICFs for that. Another option would be to face the CMUs with XPS foam all the way down (below grade) and then cover that with cement board. Use plenty of adhesive/sealant between the layers to prevent capillary action.

JUGHNE

The engineer with the 75 year payback on 2x4 verse 2 X6 wall thickness probably figured the simple R valve difference. Now did he count the electrical boxes that are 3.5" deep, 3.75 high X 2.25 wide (8.34 sq inches each gang) and leave only a 1/2 space behind each box for insulation. They would be placed a minimum of every 12', also more for TV/phone/data etc, and then switches. Not only no insulation for those points but often a loose fitting hole in his sheetrock allowing for air infiltration. Then throw in some DWV piping in the outside wall for sink, lavs etc.
True, the gain of 2" will do little to help with air infiltration. One often throws high R value at cold walls but that has diminishing returns after a certain point. Often overlooked is air infiltration, High R values do little to lower air leakage. If your codes allow, 2 X 6 on 24" centers has been done.......higher R valve having less wood area bleeding heat out thru wall.

What I have always recommended in any garage, even residential is to install surface mounted wiring in steel EMT conduit using steel boxes.....walls and ceiling. No holes punched in the wall at all. (easier to finish inside walls) Looks good and is very expandable. If you are handy you can extend it yourself after the service is installed and key circuits are started from the panel. Often the homeowner can wire his own buildings, as long as the service is not changed.

Your house subfeed panel will then have to become a 4 wire system. (2 hots, white neutral and green/bare ground). Your electrician will know that.

Paul48

I was working on a framing crew when 2x6 exterior walls became the "proper" way to do it. What we had at the time was fiberglass insulation, and you could get a higher r-value in the wall. The same is true today, but there have been many improvements in insulation materials since then. A couple inches of 2lb urethane foam and you can turn a wood framed structure into frozen food warehouse.

FranklinD

Yes! Surface mount boxes with EMT is a great idea. Plus it gives it that industrial look. Heh. It would greatly simplify construction, though, as I doubt I'll be able to do ALL the electrical I want to do right away. This way I'll be able to close the walls right away.

There won't be any plumbing in the garage. That is also a decision I've wrestled with, but the city helped decide for me. If I add plumbing of any kind, it becomes a fully 'inhabitable' structure and subject to a host of other requirements. So water-less it will remain. There will be a floor drain that exits into the alley area...that's okay here.

I'll have to ask the inspectors/contractor about 2x6 stud spacing...not sure on that one.

Excellent ideas, folks, and I thank you all.

Paul48

If you're considering surface mounting the electrical, maybe S.I.P. walls would work for you. I have no idea of price, but it might be worth a look. You could also use them on part of the roof, lose the rafter ties, and gain ceiling height for a future lift.

SWEI

Air infiltration is a big deal, and sheet foam is far better at blocking that than any kind of batt insulation.

If you have water ingress or wicking issues, use XPS. Even EPS is better than urethane (and that includes polyiso.)