Insulation under a garage slab.
I guess this is where this question belongs.
The question came up today whether or not I would like to put an inslation under the garage floor slab. Most of the 1950 sqft garage is actually going to be a woodworking shop and I am hoping to use it regularly. Some of it will be used as a game room with a pool table in it. Only about 400sq’ will actually be for cars(or maybe no cars?) Anyway, I am In the PacNW and the soil is sand. Does the foam panel really work well as a thermal break when laid under the concrete. And, are there a problems of deterioration of the panels to cause the slab to crack/sink? Plus, does the foam panels tend to lose their energy efficincy after a few years. Anybody know any thing about this??
I have even thought about a rfh heat system, but at this time, the piggy bank has only pennies left in it. So, someday, I’ll be using a space heater
Thank you in advance, Brian
Replies
I'll be looking forward to answers on this one as I may be doing a slab job soon, but I have a thought. Perhaps you could put pex tubing in the floor now and hook it up to a hot water heat system when the budget allows.
Al Mollitor, Sharon MA
Infloor heat is great but I don't have it, however I do have detached garage with wood shop & pool table--highly recommended
Edited 12/12/2003 6:22:04 PM ET by BKHY
When I build my house I put in installation under the slab. At that time the recommendation was a vertical piece and only the first 2 ft horizontal. And we only used 3/4.
My first floor slab has the forced warm air ducts under the slab. While this is not "heated" by anymeans in the middle of a cold winter I can stand on it with sock feet and vinyl floor.
My basement slab also has it under it. The only heat that I have in their is an electric blower that is used only when I am in there. That floor is cold, but I am sure that it would be colder without the insulation.
And no problems with cracks are anything.
I would do it again.
we've put a lot of insulation board under our slabs over the years.. we are constantly researching cost effectiveness... and longevity.., ease of installation..
ancillary effects on other costs..
a lot of cement finishers balk at pouring over foam board.. they claim it retards the set..
anyways : if i was pouring your garage slab...
i'd use 2" EPS , much cheaper than polyiso... and scandinavian testing shows that eps has great longevity, and almost zero water absorption..
i'd put 6 mil poly on top ... and cast about 1" of sand ..
i'd tell my cement finisher i want a plasticizer, because i want him pouring a low water content mix... the plasticizer will give him the workability of a wetter mix without the water..
the insulation will make all the difference in the world in terms of both energy saved and comfort attained..
the pex for future RFH would be a nice added touch
Mike Smith Rhode Island : Design / Build / Repair / Restore
Mike: is this method only good for garage slabs which have a perimeter footing without foam insulation underneath? Or can you do a "slab on grade" entirely on top of foam insulation?
Mike -
How do you handle the carpenter ant problem with EPS? We have only a 2ft footing depth here in Oregon and I am guessing that in the carpenter ant convention center that is my lot, they will want to play games in any EPS - they will even tunnel through fiberglass batts that are left lying on the ground.
Casey,
Ask around about PerformGuard EPS, it's a 2# RFBI treated with borates.
casey...one of the main reasons i dropped polyiso is because of vermin..had some real scares in the past
in the chit-chat here i learned about Performguard EPS.... now all we use in anything connected to the foundation is PerformGuard ... they treat the EPS with borates in the manufacture..
in the south ... a lot of the jurisdictions require PerformGurard or the equivelent for ICF's
Mike Smith Rhode Island : Design / Build / Repair / Restore
I'll be pouring the 30x30 garage/shop slab in the spring and considered getting some prices to put plex tubing in the concrete but it occorded to me today .....what if the gargage gets so cold when the heat isn't on....will the tubing freeze and crack?My life is my practice!
http://CLIFFORDRENOVATIONS.COM
dats why you use pex ( it won't split... and has a memory )... and probably anti-freeze in the boiler Mike Smith Rhode Island : Design / Build / Repair / Restore
Andy -
One of the heating guys that worked on my place tried an experiment - he filled a short piece of PEX with water, put fittings on both ends to seal it up and left it in his freezer for a week. The tubing expanded with the water/ice as it froze but did not rupture. Took it out of the freezer, let it thaw out and it went back to it's original shape.
Now - the thing to worry about with freezing tubing in the slab isn't the tubing rupturing but the expansion caused but the freezing water to spall the concrete! I suspect some type of anti-freeze would be in order, something like the potable RV stuff they use for winterizing campers. But - in a well designed system your boiler is hooked to your domestic water system - with an anti-siphon valve to be sure. This is to provide for make-up water periodically. Thus the anti-freeze over time may become diluted and not be as effective as need be.
I should think it would depend on your locality. If it gets cold enough to freeze water in a concrete slab inside a garage where you live, I don't want to know how cold it must be outside! (grin)
...........
Dennis in Bellevue WA
[email protected]
Living here in the interior of Alaska I haven't heard of anyone having trouble with the Pex swelling and causing problems with the concrete floor slab.
Several replies from other people mentioned the use of antifreeze(glycol) in the heating system. That is how most of the plumbers here in interior Alaska (Fairbanks) set up garage slab tubing. However, they don't use straight glycol in the heating system. The plumbers use a mix of glycol and water to get the best of both worlds for heat transfer and freeze protection. Water is bettter than glycol for transfering heat, but straight glycol has a freezing point that's not much lower than water. Just like your car, you use a mix of glycol and water. Talk to a plumbing or mechanical contractor to figure out the specific mix needed for your area.
One final comment on the glycol. Be sure and use the non-toxic glycol in your system. This is especially important if you use your boiler to make your domestic hot water. A rupture in the boiler could allow glycol into your domestic water supply.
Good luck with the slab! It is a balmy -5F in Fairbanks today.
"But - in a well designed system your boiler is hooked to your domestic water system - with an anti-siphon valve to be sure. This is to provide for make-up water periodically."
Yes, but in a well installed system, you don't need make-up water because there aren't any leaks. ;-) That's my perspective, but I realize that my design and practice in that regard is in the minority. At least my gycol is never diluted without someone knowing it.
FrozenMark: I agree about the water/gycol mix. More water for heat capacity and lower cost. But more gycol if you need a lower freezing point. Look at the label for the perentages.
And to add to what you said about toxicity: Ethylene Gycol (Prestone, etc) is the highly poisonous stuff. Oxalate crystals forming in the kidney cause renal failure. Propylene Gycol (Sierra is one brand) is so non-toxic it is in a variety of food at the supermarket. I've only ever used propylene gycol in a residential setting - solar DHW or hydronic heat. 20 years ago, you had get it in drums from speciality suppliers. Now Wal-Mart has it in the automotive section.
Edit: it was, "in the kidney cause liver failure" Jeez! Well, "liver" looks almost completely like "renal" if you turn it upside down. In simpler langauge: hard chunks form in the kidney (which extracts urine). Chunks are bad.
David Thomas Overlooking Cook Inlet in Kenai, Alaska
Edited 12/15/2003 4:50:44 PM ET by David Thomas
Migraine -
Do the insulation thing! You won't be sorry. It won't help a great deal to keep the floor "warm" but will retard heat loss into the ground, of course.
With respect to the radiant heating - install the PEX tubing now while you can. You don't have to install the heating system 'til later when the piggy bank grows up a little. I did that for my new shop. It's not too terribly expensive - as I recall the tubing alone ran about $300 for a 24 x 48 slab. I installed it myself. Just use plastic ties to tie it to the rebar or mesh so it doesn't float up out of the concrete - it's full of air at the outset ya know! (grin)
I used 2" pink EPS under this slab which was in turn over 6" of pea gravel. No 'undesturbed' soil, either. Rough grade under the insulation was done with the pea gravel. The finisher just specified 1% calcium (an accelerator) in the mud to compensate for the lack of water absorption into the ground due to the rigid insulation.
But by all means, try to get the tubing in if you can possibly afford it. I have a price from my heating guy of about $1800 for a small on-demand type water heater he says will do the job once I get the money to have it installed. That's for a propane heater - I'll still have to purchase a small-ish tank separate from the house tank but ... sure will be nice once I can get some heat in that shop!
Dennis in Bellevue WA
[email protected]
I live up here in the frigid interior of Alaska. Radiant concrete slabs are very popular in new construction. The standard approach I have seen is grade the base of your excavation, lay down 6 mil poly then 2" of Extruded PolyStyrene (pink or blue board) and then securing the pex tubing on top of the foam with the handy little staples the manufacturer makes.
I've seen people use the tubes to support the slab reinforcement, but the reinforcement should really be centered in the slab to be most effective for stopping the concrete slab from cracking excessively.
All the plumbers I've talked to pressurize the pex tubing before placing the concrete. They claim that the tubing could collapse or get bent if the tubing is not pressurized during the placement of the concrete.
Adding the radiant tubing in the floor slab now makes the most sense. Don't forget you'll also want to have some kind of unit/cabinet heater for quick make up of lost warm air when you open the garage doors in the winter. The concrete slab takes awhile to adjust to the loss of the heated air. But I may be thinking in the extreme sense. Our high for almost a week was -20F in the first part of December. The low for that time period was -42F.
Good luck with your concrete slab!
Does anybody know what the life expentancy of the "pink or blue foam" is?? Is it 15,20,30,40,or 50 years? I don't want to be jack hammering a slab out now or in a few years when I'm older. I hate using ones of those things now and I'll hate it even worse later. Plus, by then, my boys will be up and gone and I won't have anyone to help me schlep the waste away.
Another Alaskan response: I mostly agree with FrozenMark, but I haven't missed not having aa additional heat source to quickly respond to opening the doors. The entire floor is at 72F and weighs 50 pounds per square foot. That much concrete has 11 BTUs per F. The 10-foot column of air above it only weighs 12 ounces. Needs only 0.17 BTU per F. Heat capacity-wise, the concrete is where it's at, 65 to 1.
I do try to close the doors quickly and it does take 5 to 10 minutes for the heat to bounce back. But that's okay with me.David Thomas Overlooking Cook Inlet in Kenai, Alaska
Guess I forgot to say in earlier post an obvious but important point:
RFH in a garage is a wonderful thing. Gets the snow and ice off the car quickly. Evaporates the snowmelt or rainwater off the floor. With many other heating systems, you can get boxes FROZEN to the floor while T-stat is happily at 70F five feet off the floor.
Ditto on the SOP for type of insulation under the slab here in Minnesota. 2" rigid extruded...pink or blue. If you're really concerned about durability and if you might be having something really heavy in there, the board comes in two densities..150 and 250 I think...get the 250 for really heavy stuff like tow trucks, big tractors, or something.
Don't forget to insulate the PERIMETER, down as far as you can, and/or horizontally 24 " or so out form the slab.
Panicked the other night 6 degrees F outside, opened the garage door to give my SAAB a treat, looked at the wall thermometer after closing the door. 38 degrees!
Thought maybe I had underdesigned and the water heater couldn't keep up, or something else. This is a new system this fall and uses a slab sensor to keep the slab at 55 - 60 degrees first time it's got really cold. Shrugged, went down to work on the house awhile...came back up 45 minutes later...air temp 58 degrees....what Dave said:
That slab is a BIG radiator, a little cold air doesn't even phase it.