thermal break around existing slab?

[beakie]

been in this house for over a year now, and while I enjoy having the 26x34' shop, I have noticed a few things;

1. slab is wet in summer, so assuming no vapour barrier
2. slab is cold (unless dead of summer heat), so assuming it's not insulated
3. grading allows water in (spring I had 2+" of standing water in middle)

So I plan on improving the grading, and running weeper around it to move standing water (and spring thaw) away. This should improve water seeping up, and sweating this time of year.

Main question here

I was curious/thinking that while digging down 1-2' around perimeter for weeper, why not put 2" rigid around the slab to try and give a thermal break.
This should help direct moisture to weeper (as opposed to under slab), and hopefully help slab stay a bit warmer in winter months.


This sound like it's worth it, for the reasons I've stated... or any others?

 

[MagKarl]

Yes you need to fix the drainage problems first and foremost.

Whether or not foam would be worth it depends on what heat flow you are trying to slow down.

What do you have for insulation, ventilation, and heat?

 

[beakie]

insulation is 2x6 walls, so R15?
attic is blown in, 8" deep
ventilation is 2 windows, 2 garage doors, have thought of adding ceiling fans, but 9' ceilings limit options
heat is woodstove in corner & MrHeater propane ceiling mounted 80k btu


I will be fixing drainage issue, but while I have the excavator there I could add this foam.

In winter the garage is never quite as cold as outside (IE. -25*C outside, garage is -10*C) Windchill may play a large part of that, windy as heck here.

Garage is NOT heated all the time. I start a fire & turn on heater on cold days when I want to work in there, maybe leave heater going overnight if using garage for a few days straight.
But no matter how warm I keep the garage, the floor will always be cold. Figured a thermal break "might" help. I know it's not going to change things into a heatbox... but figured it can't hurt, and I'm digging there anyway, so why not.

 

[MagKarl]

Up to you but I don't think the foam is going to help you much. In your climate, your slab will likely be cold no matter what. My thinking is your heat source is heating the air, you have floor, ceiling, and 4 walls losing that heat. Of the heat going into the floor, a lot of that is going right through to the ground, and a small portion would conduct out the edges of the slab if it's colder outside than under the slab. Only that portion of your total heat loss would be influenced by the foam. If you had in floor heat on all the time, that would be a different situation.

 

[beakie]

that makes sense, thanks.

 

[BadgerBoilerMN]

Insulated the perimeter of any slab-on-ground building in nearly any climate is a must. It is the fastest route for heat conduction and can contribute significantly to the heat or cooling loads and allowing frost to form at the edges and increasing indoor rH.

2" -- 2 feet down and 4' out if you can, with special attention to the corners.

If the slab were heated or infrared used above perimeter insulation would not be an option.

 

[TractorJeff]

I've read this before and here seems a good place to ask. I know 2 feet down (vertical), so 4 feet out means on a Horizontal Plane?
I'm having a tough time grasping the theory on that?

 

[dfiler2]

I've read this before and here seems a good place to ask. I know 2 feet down (vertical), so 4 feet out means on a Horizontal Plane?
I'm having a tough time grasping the theory on that?

Yes, insulation horizontally, keeps the frost from going under the slab.

 

[beakie]

Yes, insulation horizontally, keeps the frost from going under the slab.

ok, so since I'm curious, do you see any value in doing as I first asked?

IE, 2" of foamboard, 2' down, around perimeter. on an slab that IS NOT kept heated, but is sometimes heated for hours/days by wood stove & a MrHeater propane ceiling furnace.

 

[BadgerBoilerMN]

The heat loss to the perimeter can be substantial, and frost coming in 3-4' on the slab is not good. Insulate while you can.

 

[dfiler2]

ok, so since I'm curious, do you see any value in doing as I first asked?

IE, 2" of foamboard, 2' down, around perimeter. on an slab that IS NOT kept heated, but is sometimes heated for hours/days by wood stove & a MrHeater propane ceiling furnace.

Yes, you will save energy doing that.

 

[jives]

Vertical or horizontal perimeter insulation will work and will benefit the garage -- heated or not. Read these:

http://www.buildingscience.com/documents/insights/bsi-059-slab-happy

http://web.ornl.gov/sci/buildingsfoundations/handbook/section4-1.shtml

www.huduser.org/Publications/PDF/FPSFguide.pdfHUD USER

 

[beakie]

well thanks folks, it seemed to make sense in my head (that doesn't happen often).

when the time comes to do some excavating work, I will add this insulating project to the list of things to do.

 

[theoldwizard1]

Insulated the perimeter of any slab-on-ground building in nearly any climate is a must. It is the fastest route for heat conduction and can contribute significantly to the heat or cooling loads and allowing frost to form at the edges and increasing indoor rH.

2" -- 2 feet down and 4' out if you can, with special attention to the corners.

If the slab were heated or infrared used above perimeter insulation would not be an option.

You are probably have to go deeper than 2' if you are adding a weeping system around the perimeter (put a sock on the pipe and cover with gravel; no dirt).

You should also put vertical foam against the footing of the slab, especially if you go deeper.


Also check your bottom plates on your walls. Mine rotted out completely from too much spring flooding.