Under slab insulation - overkill for VA?

[jpcjguy]

Hi all,

In the final stages of my 48x30x12 detached planning. Trying to determine if I should insulate under the slab. This is footer/block construction and our frost line 18" here (Richmond, VA).
2x6 wall construction and I will insulate/drywall the building. Building use is for working on my Jeep/Excursion and kids quads/buggies. I will have a gym area in one corner and a 1/2 bath. 1-2 mini-splits are planned down the road.
It appears that most of the people that insulate under the slab are way north compared to me. Wondering if it is worth it based on my location?
Or should I insulate on the outside of the footer with 2" xps and call it a day?
As is typical on this forum - Overkill! and while I can appreciate that - this mentality is really starting to creep my costs up!

 

[ConCretin]

The short answer is 'yes'. If the standard is cost vs benefit, it will take a long time for the energy energy savings to cover the cost of installation. I'm don't think you'd notice a difference in comfort either. I'd spend the money on a good quality vapor barrier to protect that new epoxy floor you'll put down some day.

 

[jpcjguy]

The short answer is 'yes'. If the standard is cost vs benefit, it will take a long time for the energy energy savings to cover the cost of installation. I'm don't think you'd notice a difference in comfort either. I'd spend the money on a good quality vapor barrier to protect that new epoxy floor you'll put down some day.

Thanks - that is what I was thinking - but this being one of those "you have one chance" items, I want to make sure I do it right!
As for epoxy floor, I think I will skip that - thinking ghostshield because I will do some welding and dragging axles, truck transmissions, etc will tear up any coating!

oh - and what about doing any insulation around the block? Inside/outside? or don't waste the time?

 

[ConCretin]

Thanks - that is what I was thinking - but this being one of those "you have one chance" items, I want to make sure I do it right!
As for epoxy floor, I think I will skip that - thinking ghostshield because I will do some welding and dragging axles, truck transmissions, etc will tear up any coating!

oh - and what about doing any insulation around the block? Inside/outside? or don't waste the time?

A good quality vapor barrier definitely falls into the "I have one chance" category. Maybe one of the garage floor experts will weigh in but any floor treatment whose bond can be compromised by water vapor pressure will benefit from a vapor barrier. I don't think Ghostshield falls into this category but limiting moisture intrusion into finished spaces is always a good idea.

Perimeter insulation is a different calculation because the difference in temps from interior to exterior is more extreme than the conditions under a slab on grade so I'll leave the answer to your question to others more knowledgeable than myself.

 

[machsnell]

I fortunately had a bunch of 3" 60 psi sheets left over from a job.

I used it under my garage slab and on the edges of slab in No va.

Along with the vapor barrier I love it. For climate controlled garage I would absolutely advise to do.

Concrete is a huge heat/cold sink. I dont like getting down on a cold concrete floor and when heating in the winter you are constantly fighting a huge radiator that wants to be at 55 degrees.

Installing vertically on the edges is key also. This is where most of your loss occurs. Try and go down a foot or 2 if you can.

Also I believe it helps with the contraction of the slab and random cracks. It provides a smooth surface underneath that allows the slab to slide and not want to crack as easily when contracting. Just a hunch.

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