Insulate garage slab WITHOUT floor heat

[premis]

I'm building a new home in central Iowa. The house will have a 1780 sq ft garage attached. I'm not going to put radiant heat in the floor, but I will insulate the garage with fiberglass batts in the 2x6 walls (about R19) and blown in cellulose (R40) in the attic. I plan to use an overhead Reznor or similar gas heater.

My question is, will I get any significant benefit from putting 2" foam board under the slab even though I'm not using floor heat? Will the foam board make a significant performance difference or make the slab warmer even without the floor heat?

If it matters, the back 14 feet of the garage (shaded in red in the attachment) is where I will do most of my work, it also has pre-cast under the slab because there is a 14x30 under-garage under that part. The under-garage has insulated walls but it will not be heated.

 

[Kaizen]

Yes it will have some affect but probably nothing you will notice. Basically absorbing heat from air into concrete. Not a quick process.

The cost of pex heat is the foam. If you can afford that spend another couple hundred and install the pex. Even if you don’t use its cheap insurance. Wish I had the money when I did my shop. Cause it’s damn cold right now.


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[Jakemedic]

I’m in SE Iowa. Right or wrong, my concrete guy put 2” foam around the foundation walls, 2’ high below the slab. Then he put 10 or 12 mil poly vapor barrier sealed. Said that it would help keep the slab warmer. It’s an experiment for me, time will tell. The vapor barrier does a nice job of minimizing moisture coming through the slab, which is a good thing. Enjoy building your new home!

 

[premis]

The cost of pex heat is the foam. If you can afford that spend another couple hundred and install the pex. Even if you don’t use its cheap insurance. Wish I had the money when I did my shop. Cause it’s damn cold right now.

The cost of the foam is already in our bid, I'm estimating it's about $3,000 (about $1.70/sq ft). The additional cost to add the pex in the concrete is $4,000 (about $2.25/ft). We are already over-budget, so I'm not sure I can convince the wife to spring for the extra $4k.

I’m in SE Iowa. Right or wrong, my concrete guy put 2” foam around the foundation walls, 2’ high below the slab. Then he put 10 or 12 mil poly vapor barrier sealed. Said that it would help keep the slab warmer. It’s an experiment for me, time will tell. The vapor barrier does a nice job of minimizing moisture coming through the slab, which is a good thing. Enjoy building your new home!

Have you noticed that the concrete floor is warmer with that 2" foam around the foundation walls?

 

[Ak Jim]

I’d strongly suggest you go find a garage with radiant heat. See how it is and then decide. You can’t put the pex in later.

https://www.supplyhouse.com/Wirsbo-Uponor-A1250750-3-4-hePEX-plus-300-ft-coil-
2025000-p?gclid=EAIaIQobChMIlvXg2f3m7AIVlRh9Ch0msATPEAUYAyABEgJgLPD_BwE

300’ for $340. You’d need 4 or 5 at the most.

 

[premis]

I’d strongly suggest you go find a garage with radiant heat. See how it is and then decide. You can’t put the pex in later.

https://www.supplyhouse.com/Wirsbo-Uponor-A1250750-3-4-hePEX-plus-300-ft-coil-
2025000-p?gclid=EAIaIQobChMIlvXg2f3m7AIVlRh9Ch0msATPEAUYAyABEgJgLPD_BwE

300’ for $340. You’d need 4 or 5 at the most.

My dad has radiant heat in his pole shed, I've used it and like it a lot. My home builder won't let me put the PEX in myself, even though I've done it a dozen times (I worked in HVAC in college and did my dad's shop). The quote from his HVAC guy was $8,800 for the basement (1906 sq ft) and the garage (1780 sq ft). We want to do the basement, I figure that's $4,800 of the quote. I'm just not sure I can justify the other $4,000 for the garage floor. I don't plan to maintain the garage at a specific heat, other than above freezing which should be doable without a heat source 98% of the time. I don't use my garage a lot, maybe 1-2 times per week for an hour or so, unless I get into a big project. I know I'll need a regular ceiling-hung heater to bring the temperature up when I want to work out there since I won't maintain a high heat all the time. So, the benefit to radiant heat to me really comes down to a warm floor. I'm just not sure I can justify it, especially when we are already over $100K over where we wanted to be on the house.

 

[like2wheel]

In that case, I would do what Jakemedic did in post #3.

 

[Kaizen]

The cost of the foam is already in our bid, I'm estimating it's about $3,000 (about $1.70/sq ft). The additional cost to add the pex in the concrete is $4,000 (about $2.25/ft). We are already over-budget, so I'm not sure I can convince the wife to spring for the extra $4k.



Have you noticed that the concrete floor is warmer with that 2" foam around the foundation walls?

Why would your builder not let you and some friends staple down pex one night after they put down the board? I’m not saying do any mechanicals just get tube in there for potential future use. Probably 300 bucks in materials.
Yes the insulation will be a thermal break any way.


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[Jking24]

I have pex and foam in mine but have not connected the Tubing yet. In my opinion it is well worth the investment even if your not gonna heat it. The slab doesent get near as cold as it would without witch inturn reduces the cost to heat when you want it and makes it more comfortable. The perimeter insulation is as important as the under slab maybe more

 

[mike93lx]

Why would your builder not let you and some friends staple down pex one night after they put down the board? I’m not saying do any mechanicals just get tube in there for potential future use. Probably 300 bucks in materials.
Yes the insulation will be a thermal break any way.


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What does the builder have to gain from having a bunch of guys messing around on the jobsite? Who is going to get blamed when there is a leak or it doesn't work right?

 

[theoldwizard1]

I’m in SE Iowa. Right or wrong, my concrete guy put 2” foam around the foundation walls, 2’ high below the slab. Then he put 10 or 12 mil poly vapor barrier sealed. Said that it would help keep the slab warmer. It’s an experiment for me, time will tell. The vapor barrier does a nice job of minimizing moisture coming through the slab, which is a good thing. Enjoy building your new home!

Vapor barrier is key ! Same with foam on the foundation walls.

I have heard, that if you do 2 layers of 1" closed cell foam, staggered so that there are no directly overlapping seams and the top layer is taped, vapor barrier is not required. 2" plus vapor barrier might be cheaper.

 

[Kaizen]

What does the builder have to gain from having a bunch of guys messing around on the jobsite? Who is going to get blamed when there is a leak or it doesn't work right?

I wouldn’t expect anything from the builder short of not puncturing the lines. I’d make sure they are pressurized. Really not difficult or anywhere near the cost quoted. I put this in the same area of going around and air sealing after electrical is done.
Only reason I could think of is if the builder still owns land and building and does not want a liability of injury.


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[mike93lx]

I wouldn’t expect anything from the builder short of not puncturing the lines. I’d make sure they are pressurized. Really not difficult or anywhere near the cost quoted. I put this in the same area of going around and air sealing after electrical is done.
Only reason I could think of is if the builder still owns land and building and does not want a liability of injury.


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That's great that you have certain expectations, but those are probably unique and without them in writing, are extremely hard to enforce. Again, what doss the builder have to gain?

To the OP, I would find a way to make it happen and cut something else that can be done later. This is something you can't ever change

 

[spudley]

That's great that you have certain expectations, but those are probably unique and without them in writing, are extremely hard to enforce. Again, what doss the builder have to gain?

To the OP, I would find a way to make it happen and cut something else that can be done later. This is something you can't ever change

Who cares what the builder gains. He's hired to do the job by the home owner. He gains a reputation of being flexible and willing to work with people who hired him.

But your point is taken which is exactly why I don't hire builders and I sub any thing I can't do myself out. If some builder told me what I could or couldn't do on my own home, we'd part company real quick.

And yes OP, make it happen especially if you're putting in foam.

 

[premis]

The builder owned the lot that we wanted, so we are stuck with him. He builds a nice house, but is difficult to work with. He prefers to use his subs to keep things on track and probably transfer the liability if something goes wrong. To him I'm just some guy that thinks he knows what he is doing, even though I have experience doing this. I am doing the low voltage wiring in the home (I'm a bit of a tech nerd and plan to run 2+ miles of Cat6) getting him to allow that was tough, but it was a deal breaker.

I'm going to see if he will split it with me. His guy can do the basement and he lets me do the garage. We will see.

 

[meathooker]

My home builder won't let me put the PEX in myself.

Wont “let” you? I can’t get my head around that.

It’s your money, your house.

Put the gash dang tubing in yourself.

 

[mike93lx]

Wont “let” you? I can’t get my head around that.

It’s your money, your house.

Put the gash dang tubing in yourself.

Nvm .

 

[TractorJeff]

There are various Threads about Frost Barrier insulation preventing the Frost from creeping under which in turn allows the Concrete to absorb heat, not letting heat migrate out to surrounding soil.

 

[Bretny]

The builder owned the lot that we wanted, so we are stuck with him. He builds a nice house, but is difficult to work with. He prefers to use his subs to keep things on track and probably transfer the liability if something goes wrong. To him I'm just some guy that thinks he knows what he is doing, even though I have experience doing this. I am doing the low voltage wiring in the home (I'm a bit of a tech nerd and plan to run 2+ miles of Cat6) getting him to allow that was tough, but it was a deal breaker.

I'm going to see if he will split it with me. His guy can do the basement and he lets me do the garage. We will see.

I think the key word here is "owned"...meaning use to own?

 

[rjacobs]

LOL...

My guess is 90% of people commenting on this thread have never had a house built by a builder...

Unless YOU have the construction loan and YOU are writing the checks, most builders will only let you walk through THEIR house until closing... and even at that, at some point, when THEY lock THEIR HOUSE, YOU have to get somebody to come let you in to check progress...

 

[duneslider]

LOL...

My guess is 90% of people commenting on this thread have never had a house built by a builder...

Unless YOU have the construction loan and YOU are writing the checks, most builders will only let you walk through THEIR house until closing... and even at that, at some point, when THEY lock THEIR HOUSE, YOU have to get somebody to come let you in to check progress...

Yep, this is how it is. Some of these builders will let you do some stuff that isn't inspected and won't cause issues. My first house was with one of those small tract home type builders and he let me throw some batts up in the walls of the garage (after insulation inspection before drywall started) and run some wires for surround sound.

I would still think that pex in the floor would be an item that needs to be inspected if there are ANY issues with it the inspector makes the builder deal with it. I don't know a lot about infloor pex heat but I am just guessing in most areas this falls under the licensed plumber's scope of work and that is probably why the builder doesn't want you to do it.

 

[premis]

LOL...

My guess is 90% of people commenting on this thread have never had a house built by a builder...

Unless YOU have the construction loan and YOU are writing the checks, most builders will only let you walk through THEIR house until closing... and even at that, at some point, when THEY lock THEIR HOUSE, YOU have to get somebody to come let you in to check progress...

The land has been deeded to us (or will be shortly) and we are carrying the construction loan and builders risk. But, he owned the land and we had to sign a purchase agreement before he would deed the land to us and build the house. In that purchase agreement it basically states that we are not allowed on the property during construction without his permission. It's in there for liability purposes (as an insurance agent, I understand that part). We made it clear that we would be touring the home during construction, but being careful and not interrupting the work. But, if I just show up and lay down PEX I would be in breach on contract.

 

[shamus29]

Here in Nova Scotia Canada it is code that if you plan on doing any kind of heat to insulate the floor.


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[Innovate1]

I put 2" foam under the basement floor and in our garage. I also put in tubing both places. I use the garage heat as it's the only source of heat in the winter. I don't use the basement heat as the insulation helps keep the floor a bit warmer and the ducted HVAC keeps it comfortable - at least that's how I see it.

I put foam under the slab of my detached garage but didn't do PEX. I would have liked to insulate the edges of the slab better.

Not sure how to advise on the space with garage under it. Really depends on how cold the space below gets. But having some insulation to the ground will help if you want to keep the space warmer than about 50 I think.

 

[ripperd]

LOL...

My guess is 90% of people commenting on this thread have never had a house built by a builder...

Unless YOU have the construction loan and YOU are writing the checks, most builders will only let you walk through THEIR house until closing... and even at that, at some point, when THEY lock THEIR HOUSE, YOU have to get somebody to come let you in to check progress...

This. We had a home built in a development by a production builder. We were pretty lucky in that the builder rep let us come by basically whenever we wanted with a quick phone call beforehand to check if the site was safe to walk through. It is their property until closing, and without there permission it is tresspass.

Its totally different when its your land, your construction loan, and you picked the GC and are making progress payments to them.

 

[premis]

I decided to bite the bullet. I'm just going to have the builder's HVAC guy bury the pipe in the slabs.

Thanks for all the feedback!

 

[stingry]

I decided to bite the bullet. I'm just going to have the builder's HVAC guy bury the pipe in the slabs.

Thanks for all the feedback!

I don’t think that you will be sorry, Radiant heat is fantastic!!

 

[rebelranger]

Premis - I put in 1.5in foam without PEX and then 1.5 foam around the footer covered with soil. My house basement does not have foam under it, just a vapor barrier. My shop concrete is MUCH warmer without a heat source vice my house concrete. It is worth it.

A. I am installing a minisplit but will only heat/cool as needed.
B. I have 1.5in closed cell spray foam and R11 batts in walls. I have R30 blown insulation in ceiling floor.
C. The insulation seems to really slow the heat/cooling of the concrete so late evening the concrete is still warm to touch even now in winter here in Southern Mo.
D. If I did over I would go 3in foam instead of 1.5in.

 

[imjustdave]

I decided to bite the bullet. I'm just going to have the builder's HVAC guy bury the pipe in the slabs.

Thanks for all the feedback!

My home has it and it's 30 outside and I havent' put socks on in over a week. Nice and warm walking on the the floor inside carpet, tile, fake wood floor... then I walk into my unheated attached garage to get a beer Burr as all can be...

I agree you will enjoy it and I plan to install it in my new garage once it starts going up.

In terms of pricing I would start pushing back a little on the crazy costs on change orders with the builder.

 

[TractorJeff]

My Shop is heated to a minimum of 50 degrees all winter. You can see the snow creep away from the concrete slightly. Biggest mistake I made was not budgeting for at least vertical insulation to stop Frost Creep / Heat Loss. Best would have been to go Whole Hog and set up for Radiant! Live and Learn!

 

[BKB]

40x64x16 i installed rigid foam 2' down around the barn and nothing under the slab. I have forced hot air and the slab is only 2-3' colder than the air. It does get colder 3' to the wall. I have had the system running 4 years now and the benefits of forced hot air to me are i can run large set backs if i want, air filtration this is a big one for me, Cost, i was broke and could not afford to insulate my slab. I burn maybe 350-400 gallons of waste oil a year keeping it 55-65 and that is t-shirt weather when im working. I also have a boiler running some baseboard heat in 3 rooms in the barn so in floor would have been very easy for me. I probably should have just ran the pex since it would have been so cheap but every time i put an anchor bolt in my floor its nice not worrying about hitting a pex.