Should I insulate under new slab floor or not?

[DLausche]

I'm building a new garage stall that will be mostly my workshop. About 400 sq. ft total. Will have a forced air furnace to heat in the winter. Should I bother with the foam insulation board under the slab? If I did, would I need to go all the way to the edges with the foam board or just under the main work area where I would be standing, etc. ? I don't know how much difference in temp this would make on the concrete surface. I want it to be comfortable working out there in the cold winter months.



-Deon

 

[CJ8Rockcrawler]

Grid heaters in the concrete...

 

[BDanner]

Any place that you apply a thermal break there will be a payoff. Some areas of construction technology are greater. With energy costs at what they are, most insulating applications have enormous paybacks. A payback is the amont invested in insulation vs. the number of years to recoup the cost based on energy savings.



In Minnesota you can't over insulate a slab. Many insulate the perimeter of the foundation wall. Paybacks decrease after about 2' below grade on the exterior. Insulation around the inside perimeter of foundation wall before slab pour keeps the slab from getting a condensation problem in the summer if you cool!



As for under the slab, now is the time to do it. Be sure and get the high density stuff, blue or pink in color. Don't waste your time or money on the white beaded insulation, as it degrades and has very low r-values. Some are laying a reflective mat that is sandwiching bubble wrap type material.



Bruce in Northern Virginia

 

[tgbol]

Would you have to lie down on it during the winter?

 

[Island Dodge]

Some heavy mil plastic under the slab will make a huge difference but ridged insulation would be best.

 

[BDanner]

Some heavy mil plastic under the slab will make a huge difference but ridged insulation would be best.

That's right do not leave out the heavy mil plastic. If going all the way, first 4-6" of stone or gravel - this will help prevent some frost heave of slab. Next your insulation followed by plastic and steel mesh.



If you could find a roll of 1/2" PEX tubing laying around, just rough it in for later use. Leave the return and supply in a corner for later attatchment to a water heater.

 

[testraub]

I think the insulation idea is great. But I don't see any mention of the most imortant item that should be installed as well..... a drain!

 

[frankram]

In Soth Fayette Twp. Pa. You are not permitted to put a drain in a garage.

Please don't ask why.

 

[DLausche]

Thanks for the replies.



Yes, they are planning on insulating with the rigid board on the inside of the foundation wall before they backfill the inside. Will go all the way down to the footing. The plans also call for a 10 mil vapor barrier under the slab.



I'll probably have to lay down on it once in a while if I need to wrench under the truck or car. Probably won't have to sleep on it though unless I behave really badly and am sent out to the garage for the night without a pillow.



It is sounding like it would be a wise choice to put this down under the slab as well as inside perimiter of the foundation wall. Also looks like there may be more than one choice when it comes to compression rating of these blue and pink boards. I assume I want the higher rating since it will be supporting the weight of my truck.



Assuming this stuff comes in 4x8 sheets I'll need about 15 sheets. Am I looking at $20 per sheet or more like $40 or... Having a hard time finding a price for this anywhere on the net.



I also asked about the drain idea and the answer was a definite NO. Would be easy because the sump pump drain pipe going out to the storm sewer is 4 ft under the middle of the new garage. They will not let me tap into it because it drains to a local wetland area and they are afraid of oil and chemicals going down the drain.



Thanks

-Deon

 

[RKerner]

Thanks for the replies.



Yes, they are planning on insulating with the rigid board on the inside of the foundation wall before they backfill the inside. Will go all the way down to the footing. The plans also call for a 10 mil vapor barrier under the slab.



I'll probably have to lay down on it once in a while if I need to wrench under the truck or car. Probably won't have to sleep on it though unless I behave really badly and am sent out to the garage for the night without a pillow.



It is sounding like it would be a wise choice to put this down under the slab as well as inside perimiter of the foundation wall. Also looks like there may be more than one choice when it comes to compression rating of these blue and pink boards. I assume I want the higher rating since it will be supporting the weight of my truck.



Assuming this stuff comes in 4x8 sheets I'll need about 15 sheets. Am I looking at $20 per sheet or more like $40 or... Having a hard time finding a price for this anywhere on the net.



I also asked about the drain idea and the answer was a definite NO. Would be easy because the sump pump drain pipe going out to the storm sewer is 4 ft under the middle of the new garage. They will not let me tap into it because it drains to a local wetland area and they are afraid of oil and chemicals going down the drain.



Thanks

-Deon

BDanner's advice is golden. Also, one substitute for PEX tubing is KITEC. If you go to the expense of insulating the slab, finish it off with hydronic heating. Are you building 2x6 walls and insulating also? That would help in estimating the benefit from insulating the slab. Houses up here use 2x6 to get R19 in the walls to keep out the cold.





For the drain, don't tell anyone. By the time it travels a few hundred feet to the "wetland", it will be fine.

 

[Nate]

Weird... here the garage drains go right to the sewer pipe.



I would put some heat in the floor. It can be 80* in the garage, but lying down on the floor to work on something will have you wearing carhardts.

 

[CumminsAholic]

I'd highly reccommend putting tubes in the floor for heat. You'll kick yourself later if you don't. With them you can heat it with whatever you want, gas electric, wood, ect. Even if you don't use them right away you will want them down the road, for the cost it's well worth it. And on the foam, yeah put insulation under it, you don't need the poly with the pink or blue foam.

Corey

 

[DLausche]

OK, you guys have me convinced of the in floor heating tubes as well. Wirsbo mfg. and dist. center is less than 10 minute drive from my place. Can I just walk in and buy this PEX tubing and the twist-in anchors? One zone or two or... ? Expensive or cheap stuff? Floorplan pic is attached. Is it possible to use only radiant/hydronic heating and not do the forced air furnace thing??? Walls will be 2x6 construction and fully insulated all around. I was thinking forced air heat would be nice because then I could pump some heated air in the next garage stall and keep my Wife's minivan a bit warmer in the dead of winter. I suppose with radiant heat I could just leave the door open a bit and get some heat into the main garage.



Foundation block should be finished tomorrow... Oo.

 

[BDanner]

Really nice add-on! My neighbor just installed a radiant floor system in his garage (Vette museum) using the Wirsbo products. He took the course and became a tech rep. so he could save $ on purchasing the Wirsbo products direct. Plumbing suppliers should sell directly to you, though the warranty is you if you install. I have researched the radiant floor thing allot. It is really a do-it-yourself no brainer installation. Especially the rough-in.



A couple of searches on Google typing in radiant heat will provide you much knowledge. I am currently starting a project similar to yours. The heating temp of the water never goes much over 85* so look at available fuel choices and costs of boilers. Several new boilers are the instant on style like the Bosch Aquastar or Takagi. These are things you can add later. Right now just get your circulation lines in. The system will heat the garage if insulated properly. Insulation is what makes these systems work! A single zone is all you need for one room. What you have to work out is your manifold distribution needs. All of tthe distribution hardware can be done after the slab pour.



The tubing layout: the length of each tube run should all be of equal length. Example would be 4- 275' foot runs snaking from your manifold or distribution point. The length of runs is based on tube diameter/ run lengths. Too long of tubing runs cool quickly at the end, that is why you run several equal lengths. Tubing is spaced closer together near doors, walls and windows as these are heat loss areas that demand more radiant heat. My neighbor roughed in 2- 3"-4" PVC elbows and standpipes in a corner against the wall. This was in order to collect his supply & return lines. This is also where he plans to place his boiler. Also think of exhausting the boiler if needed in the layout design.



A quick peak at this site will give you some great do-it-yourself confidence for your project. http://www.aimradiantheating.com/

Hope this info helps!



____________________________________________

Bruce in Northern Virginia

 

[CumminsAholic]

You really wouldn't need more than one zone for a garage, unless you put up a wall and want one side warmer than the other. I'm not a heating guy, so i don't know how many feet of tubing you need, but you should be able to find that out where you get the tubing, I'd guess in a garage, maybe 16" to 2' apart, maybe 2 runs? Like you say, you won't be able to pump the heat into the other garage, but you can leave the dividing door open and that'll make a difference.

Corey

 

[Rotty]

Do multiple zones, reason, if one tube breaks/cracks, etc, you have backups.

I did this in seattle, but unfortunatly I have several tubes freeze over the winter and broke 3 out of five. My fault, not the product.

Use the pink or blue board. Use the bigger tubes, like 5/8" if you can get it.

Less resistance. When you lay the tubes, fill with water and pressurize while pouring the concrete. Check for leaks. After the concrete hardens, then drain it until you are ready the use for warming the floor.

Lay each tube in complete circuits with out splices. Less chance of leaks, besides how do you repair a spice buried in concrete?????

If you have any more questions, I have done several of these project with pix. PM me... .

Good luck.

 

[MKinner]

Gotta love Hydronic heating. Now if a guy could just extend it out into the driveway and sidewalks, fill with good 'ol 50/50 coolant, you would really have something... . #ad

 

[DLausche]

Thanks to all of you guys for the feedback. I am really looking forward to the hydronic heating in my new shop/garage. Yesterday I finished the foam insulation and laying out the wire mesh. This AM I am going to lay out the PEX piping. A buddy, one of the concrete guys, came and helped me with the wire mesh yesterday. Man, they really have a strong dislike for this wire mesh stuff. But, it really helps out with laying and securing the piping. Will use zip ties to attach to wire mesh. I think they are going to use rebar on top of the wire mesh/pipe layer.



-Deon

 

[Joe Mc]

Deon - as for the wife's side see if you can tap the in slab in your's to include a base board to her side. Or go w/2 zones one for your in slab and the other for her baseboard. MHO

 

[DLausche]

Deon - as for the wife's side see if you can tap the in slab in your's to include a base board to her side. Or go w/2 zones one for your in slab and the other for her baseboard. MHO

That is an excellent idea! And, I have plenty of extra PEX tubing because I had to run 3 fairly short circuits instead of 2 longer ones. I'll make sure to order a 2 zone setup when I go to order the boiler and so on. I could put one or two baseboard heaters on the wife's side (old garage) and turn it on when desired or off to save energy.



Pics attached show progress if anyone is interested. Slab is being poured tomorrow AM. Oo.



-Deon