Hydronic Floor Heat Insulation Question

[coreyschaff13]

I am currently in the process of building a house with floor heat in the garage. I have been browsing this site for the last couple months trying to gather as much info as possible.

I am located in North Dakota, 1120 sq. ft. attached garage (3, 9' overhead doors, 2 walk in doors, and 2 3'x4' windows). 10' walls, 2x4 contrustion w/3.5" FF insulation. 16" insulation in ceiling.

Using 4 loops of 1/2" pex, 12" centers. Loops will be 250'-260' in length. Plan is to keep the garage at around 45-50 degree for most of the winter, with the occasional rise to 60-65.

The heat loss calc I had done suggested that I would have a heat loss of 43,000 BTU's at 65 degrees.

My plan was to use 2” XPS insulation underneath the slab and around the top 2 feet of stem wall/footing. My builder is trying to convince me to not insulate the wall between the house and garage for the fact that it is going to be warm on the other side. He also does not want me to go to the top of the slab with the 2” XPS. Instead he wants me to use 2 “ along the wall up to the bottom of the slab, and then between the slab and wall he wants to use a ¾” expansion joint as a thermal break.

All of the research I’ve done is to use 2” XPS all the way around the slab and walls.

The builder put a knock out 2x6 into the wall forms for the garage so that the top 6" of the garage wall will only be 4" wide (3.5 2x4 with 1/2 Sheetrock)so that the framed wall and concrete wall are flush. If I put 2" XPS all the way to the top of the concrete wall, then I will have a 2 inch lip where the concrete ends and the framed wall starts. My concern with doing it this way, although I think this would be the most efficient, is how does a guy go about finishing the wall so that its flush?

I want to tin the bottom 4-6 ft of the walls for washdown purposes.

My orignal thoughts were to have him frame out the garage with 2x6's instead, and he said he could do that, but he thinks its a waste of money. According to him, almost all garages around here are 2x4 construction. Money is an issue (of course) but I dont think that the 2x6 construction would be a waste.



I was wondering what your guys' thoughts on this would be.

P.S. sorry for the lengthy post, but I hope I explained this well enough.

 

[tdkkart]

According to him, almost all garages around here are 2x4 construction. Money is an issue (of course) but I dont think that the 2x6 construction would be a waste.

HEATED garages??

You're in frickin' NORTH DAKOTA, 2x4" walls on ANY heated space should be against the law. Walls should be AT LEAST 2x6 with R19 or more insulation, no question.

I have to question some of your contractor's thinking.............

 

[coreyschaff13]

Although I feel the same, I would have to back him up on that statement.

All the houses that I've seen have had 2x4 garages. I think where most people justify it is that you are going to loose a majority of your heat through the overhead doors anyways, so going overkill on the walls doesnt make much sense to them.

And I can see that line of thinking.

He is willing to do whatever I want, but he is just trying to not lead me astray, and I can appreciate that. He is a very honest guy, with plenty of years of experience.

You have to remember, in ND we are usually 5 years behind the rest of the country with everything. haha.

I guess it all boils down to the law of dimishing returns.

 

[coreyschaff13]

I guess my main question is what have most of you guys done?

2" insulation on the wall all the way to the top of the wall?
2" insulation on the wall to the top of the slab?
or
2" insulation on the wall until it meets the insulation under the slab?

I've seen that some people are cutting the insulation at a 45 to allow the concrete to flow overt the top - has anyone had any horror stories with the edge of the slab cracking?

would putting it all the way to the top of the wall be foolish?

 

[theoldwizard1]

You pay for insulation once, you pay for energy to heat/cool your space every day ! Put as much money into insulation as you possibly can, even if it means you don't complete the project for a couple of years.

• 2x6 walls
• 4" of XPS under the floor
• 4" of XPS on the outside of the footing to the full depth of the footings but you have to protect it with something when you back fill

Check into the cost difference between fiberglass insulation and "wet" cellulose. This is also a DIY project. Check YouTube.

My orignal thoughts were to have him frame out the garage with 2x6's instead, and he said he could do that, but he thinks its a waste of money. According to him, almost all garages around here are 2x4 construction. Money is an issue (of course) but I dont think that the 2x6 construction would be a waste.

And how many garages has he built with radiant in floor heat ?

 

[SiGmA_X]

HEATED garages??

You're in frickin' NORTH DAKOTA, 2x4" walls on ANY heated space should be against the law. Walls should be AT LEAST 2x6 with R19 or more insulation, no question.

I have to question some of your contractor's thinking.............

This was EXACTLY my first thought! A 2x6 wall in ND should be MINIMUM for a heated garage, and then you need to debate cost/benefits for yourself. My folks are doing R48 walls on their retirement cabin in NW Washington, where its pretty mild compared to ND! That is for a house, but regardless. R13 is jacksh!t.

I would frame it out to 2x6 and go with R19 insulation, and run the tin to the floor (cool idea for sure). Follow what the Wizard says, he speaks the truth. Except, EPS 15psi is a-okay for under slab, and if protected, outside too. It'll save you 20% or so, ballpark. (See if there is a *local* mfg as well, another 20-30% off at least!)

 

[Steve in Mi]

I'll try to be brief in my description of how I did my detached shop/garage built in 1981 or 82. I didn't want any step in the wall/insulation on the outside, plus 2" rigid foam on the outside of framing makes for a long reach (nails) for hanging the exterior sheeting (T1-11 in my case) but I did want 2" down to the frost line. I applied 1" on the outside of my foundation walls from the footings (42" deep) and continued it all the way to the peak of the second story. I put another 1" on the inside of the foundation wall from footing to near the top of my slab. Inside this foam and under the entire floor (28' X 48") I used 1" Dow rigid foam over sand and poly. I used tarred Celotex expansion joint around the top 4" of concrete floor (between block and slab). I have a coarse of 6" block on top of 8" block and my 2" X 6" bottom plate is separated from the 6" block by closed cell sill foam. R-19 fiberglass and poly covered with painted OSB from plate on up.

I heat 24/7 all Winter, nat. gas FA to 63-65 for ~ $150. last year total. My shop stays below 72 for all but a few days in the Summer without A/C. I don't park cars in my shop, one 9' overhead door, 3 - 3' service doors and a 6' double door all insulated. 6 windows all triple pain.

My floor temp lags set point by 3 degrees in Winter except for ~ 6" to 8" near outside walls. I don't have thermo breaks under doors so the margin is greater in those areas.

You say only 5 years, huh? lol

Stick to your guns and you will be comfy in your garage. If you can't find a contractor that will build to your specs., you may have to do it yourself - I did.

 

[tdkkart]

All the houses that I've seen have had 2x4 garages. I think where most people justify it is that you are going to loose a majority of your heat through the overhead doors anyways, so going overkill on the walls doesnt make much sense to them.

I wandered off for a couple days........

I've got garage doors on my house and shop that are steel wrapped inside and out and Polyurethane injected, claimed to be R-17.5.
http://overheaddoor.com/garage-doors/Pages/thermacore-495.aspx
No, they're not that expensive, installed price was only slightly more than the carry out price of the best door available from Menards.

Obviously I'll lose some around the seals etc if they're not perfect, but my point is, if I'm gonna use an R-17.5 door, why would I stop at a 2x4 wall which in most cases is only an R-13??
Residential garages are built cheap because people are cheap, they'd rather have fake granite counter tops than 2x6 walls in their garage, which makes perfect sense for most people because a large number of people only use their garages to store boxes of old clothes and unused treadmills.
Because you actually work in your garage, your requirements are different, and your contractor should recognize this, no different than he would if he was building a house for a handicapped person.

Yes, there is a point of diminished returns, but why purposely build to less than expected standards??