Perimeter foam insulation

[gogolf0401]

If I plan to have in-floor heat in my concrete, how deep does the 2" perimeter down foam really need to be? If the building was not going to be heated, I see the importance to keep frost from raising the floor and cracking the concrete.
If I have the perimeter foam down only 1ft is that enough? I will have 2" foam under the slab to keep the heat from going down. Thoughts?

 

[WisJim]

I'm in western Wisconsin, so similar climate I think, and I have 2" foam under the slab and 2 inch perimeter foam 2 feet down and horizontal foam 2 feet out from the bottom of the perimeter foam. I think that was the code requirement for a slab with thickened edges instead of footings going down 4 feet. I look at the underslab foam to keep the floor warmer and the perimeter foam to prevent frost heave of the slab.

 

[gogolf0401]

I'm in western Wisconsin, so similar climate I think, and I have 2" foam under the slab and 2 inch perimeter foam 2 feet down and horizontal foam 2 feet out from the bottom of the perimeter foam. I think that was the code requirement for a slab with thickened edges instead of footings going down 4 feet. I look at the underslab foam to keep the floor warmer and the perimeter foam to prevent frost heave of the slab.

Thanks for the reply. I'd agree if the building is not heated. If the building is heated, and even better, if the slab is heated, the frost will not be very deep next to the building, regardless how deep your perimeter foam is.. maybe I'm wrong, just my thinking.

 

[ConCretin]

I'd extend it down to the frost line. The heated slab is isolated from the ground by a layer of insulation so it becomes a battle between the heat from the ground under the slab and the freezing temps and frost on the outside.

Vertical insulation is relatively cheap insurance to ensure the frost doesn't win and get under your slab. Another consideration is that the building may not always be heated and it's a lot more work to do it later.

 

[gogolf0401]

I'd extend it down to the frost line. The heated slab is isolated from the ground by a layer of insulation so it becomes a battle between the heat from the ground under the slab and the freezing temps and frost on the outside.

Vertical insulation is relatively cheap insurance to ensure the frost doesn't win and get under your slab. Another consideration is that the building may not always be heated and it's a lot more work to do it later.

Thanks. It's not cheap when you need to go down 5-6ft to get below the frost. I started this thinking I may not need to go down a full 2', now I think I better just do it. I'm certainly not going to below frost though.

 

[65ranchero]

2" foam, 4" to 6" poured floor radiant heat in the slab, 3" frost walls on 2 sides.
that all I need for here in VT not a strain on the boiler
micro cracks as they all do

 

[Adesn]

2" foam, 4" to 6" poured floor radiant heat in the slab, 3" frost walls on 2 sides.
that all I need for here in VT not a strain on the boiler
micro cracks as they all do

Sorry to hop on this thread guys, but I am planning a new shop in VT and deciding between a 4-6" insulated slab vs. full 4' frost wall and slab.

My shop is also going to have 12' tall walls so I'm thinking the frost walls will help with the weight of the building.

65ranchero, are you saying you had 3" or 3' frost walls poured?

 

[haugy]

I'd extend it down to the frost line. The heated slab is isolated from the ground by a layer of insulation so it becomes a battle between the heat from the ground under the slab and the freezing temps and frost on the outside.

Vertical insulation is relatively cheap insurance to ensure the frost doesn't win and get under your slab. Another consideration is that the building may not always be heated and it's a lot more work to do it later.

So yeah I'll jump in here to with a question. If I'm doing a pole barn, essentially my bottom girts will be my slab form (floating slab). I planned to put 2" under the slab, but what do I do about the sides? There are no concrete walls, just the girts. I'm in TN so my frost line isn't too deep. But I'm going to be building up my pad (slope) so I will be very exposed in terms of temps. I don't want my radiant floor heating to be pointless and not be effective.

 

[HaiKarate]

So yeah I'll jump in here to with a question. If I'm doing a pole barn, essentially my bottom girts will be my slab form (floating slab). I planned to put 2" under the slab, but what do I do about the sides? There are no concrete walls, just the girts. I'm in TN so my frost line isn't too deep. But I'm going to be building up my pad (slope) so I will be very exposed in terms of temps. I don't want my radiant floor heating to be pointless and not be effective.

I put about 18" vertical rigid foam insulation around the edge of my pole barn - put the foam against the girts on the inside before the pour.

 

[ConCretin]

Sorry to hop on this thread guys, but I am planning a new shop in VT and deciding between a 4-6" insulated slab vs. full 4' frost wall and slab.

My shop is also going to have 12' tall walls so I'm thinking the frost walls will help with the weight of the building.

65ranchero, are you saying you had 3" or 3' frost walls poured?

The choice of foundation system - Footing/wall/slab vs. Monolithic slab really isn't a matter of weight. The pressure applied tom the ground by a building and slab are very low. Reasonably decent soil can easily support it whether it's 6 inches down or 6 feet down. For a detached structure, its hard to beat the cost and simplicity of a mono-slab.

Furthermore, if you are building on a solid base that provides uniform support to the slab, a 4" slab is more than adequate for most uses. I think 5" is a good target because it provides a little insurance against any variations in base and finish elevations and helps ensure any thin spots aren't too thin.

So yeah I'll jump in here to with a question. If I'm doing a pole barn, essentially my bottom girts will be my slab form (floating slab). I planned to put 2" under the slab, but what do I do about the sides? There are no concrete walls, just the girts. I'm in TN so my frost line isn't too deep. But I'm going to be building up my pad (slope) I will be very exposed in terms of temps. I don't want my radiant floor heating to be pointless and not be effective.

Your heated slabs effectiveness won't change regardless of the type of structure around it. Since it's presumably sitting on insulation and therefor isolated from the ground below, it won't heat the soils underneath but it will trap the natural heat from the earth and help keep the frost from getting underneath the slab.

In colder climates, the frost can push in around the perimeter and freeze the soil under the slab edges. If you are concerned about this, you can extend the rigid insulation out or down a minimum distance equal to your frost depth. This will protect your structure from frost whether it's heated or not.