Floor insulation for garage addition?

[KiltLifter]

So for 3 years now I've been tossing around the idea of adding 36 more feet to my existing 24x48 detached 4-car garage. The existing 4-car has insulated walls only. The grand plan is to remove the depressing 3:12 roof and add an insulated gambrel (barn) roof that will allow for attic storage (attic only, 2nd story not allowed). The addition will be vaulted for a lift and will be the only heated section.

SO, with overhead radiant heat, is it worth it to add insulation under the new addition slab? (weekend heat/cool only)?

Thanks

 

[ForceFed70]

The foam is costly. When faced with this decision, I chose to skip it. I only heat for a couple of days a week and it was never going to pay off.

 

[bczygan]

Ever stand on a floor with an unheated space below it? Even though you are in a heated room, the floor stays much colder.

 

[matt_i]

I wouldnt put it in unless I was doing a hydronic radiant heat that's going to be on 24x7.

I have boots and if I'm going to be standing in one place and not working physically very hard, running a lathe or programming a CNC, I have 2 120vac plug-in electric heating mats that do a fine job of keeping my feet toasty.

 

[toyotadriver]

It is nice in the spring when the slab is cold and humid air starts condensing on it. But, for your uses its not critical IMO.

Do it if you can afford it. Don't worry about it if you can't.

 

[walrus]

To me it depends on comfort more than saving cost. Want to be comfortable, insulate it

 

[KiltLifter]

The space will be maintained above freezing, with insulated ceiling and walls, but I didn't know if that was a loosing battle without the floor foam. Honestly, I wonder if the floor foam would STOP heat from coming up from the earth if my goal is just not to freeze?

 

[ForceFed70]

Honestly, I wonder if the floor foam would STOP heat from coming up from the earth if my goal is just not to freeze?

I don't know about that, but it could do the opposite of what you want in the summer. Having that nice cool floor below you helps keep you and the garage cool.

For me - a cold floor is a non-issue. My shop is detached - I'm not walking out there in my pajamas and bare feet. I've got at least a sweatshirt and proper shoes on. When I'm down on the floor - I always throw a sheet of old cardboard down anyway so I don't notice the floor being cold, etc.

Been 5 years and I have No regrets - I'd do the same thing all over again.

 

[Radix2]

The most critical area to insulate is the edge of the foundation- do you have frost walls or just a slab?

In any case, the ground is much better at transferring heat than air - so it is critical to insulate against the frozen earth outside. This is a major spot fir losing btus to the outside.

So insulate frost walls to keep frost from getting to your floor inside.

Or

Insulate at least the perimeter of your floor, but even better is to also insulate outside the foundation like a FPSF this will also protect the edge of your slab from frost heaving and cracking.

These measures will also help with spring condensation on your floors esp against the walls.

 

[KiltLifter]

I like the perimeter idea. I've been looking at greenhouses that put 4" air piprs 8feet deep below the greenhouse and move air thru them for winter heat (and summer cooling) and they use perimeter foam to lock that in.

 

[Richard Cranium]

I don't think it would be worth it

 

[KiltLifter]

I wasn't suggesting the greenhouse pipes, just showing an example of perimeter.
Or did you mean floor foam in general?

 

[Radix2]

I like the perimeter idea. I've been looking at greenhouses that put 4" air piprs 8feet deep below the greenhouse and move air thru them for winter heat (and summer cooling) and they use perimeter foam to lock that in.

If you are trying to stay frost free and want to use ground heat, then perimeter insulation is the method. You need a large space to get much benefit, large commercial sites do it. Perimeter insulation is a huge benefit to any heated structure -even above wall insulation on an areas basis.

 

[KiltLifter]

Yes, I would probably keep a heater out there just to keep it above freezing, but that may end up costing too much all winter, so I may end up backing off, not sure. My old garage was fully insulated and would stay above freezing with just the act of parking a warm car in there each night, but that was a 2-car attached.

 

[KiltLifter]

So if I'm pouring a simple foundation in an undisturbed trench, do you dig for the foam after or is it part of the initial trench, almost like a form?

 

[Radix2]

We used the foam as one wall of the footings and built the frost wall of ICF blocks on top, which have the insulation built in. You may want to consider it. How deep do you have to go?

 

[BadgerBoilerMN]

At a dollar a sq.ft. to save roughly 10% on the load it can't be recovered, but, if you value the extra comfort, and the ability to drop a tool on the floor or steel can without worrying about water vapor and rust, it makes good sense.

You could likely heat both sides with the output of the added floor if you chose to add radiant floor. The low-intensity tube heater is the next best choice. If located over the new floor, it should be insulated. More especially if don't keep the building warm full-time.

 

[Elginz]

You only get one chance to insulate the floor. Dad didn't and his sweats in the spring. My has never done that. I heat with electric overhead radiant, it makes the floor nice to be on.I don't like cold feet. Walls and attic you can add later, not the floor. Last year it cost me $275 for the year on my 24x24x10 keeping it at around 60 all winter.

 

[KiltLifter]

We used the foam as one wall of the footings and built the frost wall of ICF blocks on top, which have the insulation built in. You may want to consider it. How deep do you have to go?

My Plan was to copy the existing garage foundation which is fairly simple:


I hope this comes through. the total depth is 2 feet, with a monolithic slab. I think I would rather have separate foundation and slab so I may pursue that, but the 2' depth would probably carry over.

 

[KiltLifter]

Ahh yes, and it's upside down, lovely Iphone. Sorry.

 

[KiltLifter]

At a dollar a sq.ft. to save roughly 10% on the load it can't be recovered, but, if you value the extra comfort, and the ability to drop a tool on the floor or steel can without worrying about water vapor and rust, it makes good sense.

You could likely heat both sides with the output of the added floor if you chose to add radiant floor. The low-intensity tube heater is the next best choice. If located over the new floor, it should be insulated. More especially if don't keep the building warm full-time.

I would Love radiant, but probably wouldn't heat it often enough to make that cost effective.

When you say insulate if tube heater over floor, do you mean insulate the foundation or the slab?

 

[KiltLifter]

You only get one chance to insulate the floor. Dad didn't and his sweats in the spring. My has never done that. I heat with electric overhead radiant, it makes the floor nice to be on.I don't like cold feet. Walls and attic you can add later, not the floor. Last year it cost me $275 for the year on my 24x24x10 keeping it at around 60 all winter.

Same question here: Perimeter or Slab insulation?
I would pay $275 to have that space to just 40F all winter (I just walked out into a 10F garage to use the air hose, ouch!)

Never experienced sweat here in CO (way dry humidity), but did get rust on some tools at the old house using an exposed flame radiant heater - but that was the heater exhaust I think.

 

[KiltLifter]

I guess I need to get on the ball and post some better details about the garage plan. The area I'm adding will share a roof-line, but will be a separate space. They will not share heat (normally) so really I'm looking to heat a 24x36 space. a warm floor would be sooo nice...