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Slab on grade perimeter insulation

I

Inspector 102

Silver Member
Joined
Oct 22, 2009
Messages
356
Location
N/E Indiana
Here in the great state of Indiana, we are about to adopt a modified version of the 2009 International Residential Code, Chapter 11. Typically our foundations are 36" deep with R-10 foam placed in a trenched footing to the bottom of the slab. This leaves 4" of concrete without a thermal break. Now the energy code wants foam all the way to the top of the slab. I have concerns on the structural break this is creating around the structure instead of tying the stem wall into the slab. Does anyone have pictures on how other areas are accomplishing this method? I find it hard to believe that the trade off of energy conservation vs. slab integrity is a good thing. I understand the insualtion can be placed outside the stem wall, but that creates a whole list of other issues with protecting the foam from damage. Any comments approceiated, supposed to start enforcing this on April 5th.
 
In Oregon,

You either put it on the outside or they will allow the foam to be beveled off at the top so that the slab edge comes to the inside of the framed wall.

Bill
 
i dont have the 2009 to access right now, what is the concern. the foam can be "protected" on the upper 4 or 6" via a mortar like compound ( i used it years ago, forgot the name) that you apply like blockbond or stucco. af the stem walls arte placed first, are there not reinforcing steel dowels left at the top of the wall to bend over and tie intop the slab rebar prior to placing that slab. in northern vermont, we also insulate under the slab with foam, depending on owners/designers preference. sometimes 4 feet in from the outside edge, sometimes under the whole slab.
 
We are getting ready to adopt the 2009 Energy Code. I went to training last week and they said it was OK to bevel the top of the insulation. That way it's not visible from the inside.
 
kyhowey said:
We are getting ready to adopt the 2009 Energy Code. I went to training last week and they said it was OK to bevel the top of the insulation. That way it's not visible from the inside.
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The beveled insulation is a typical detail here as well.
 
Francis Vineyard said:
Contractors complained when installing carpet strips it broke off the concrete because of the thin beveled edge; I suggested they not put the strip close to the edge, haven't had any more feedback on that problem.Here's the link; Perimeter Slab Insulation FAQ

Francis
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Yes that would be a real problem. With the concrete that thin at the edge you'd have to drill the holes for the tackstrip nails. The last project I designed incorporated exterior insulation and an elaborate flashing to prevent termites from gaining access.

Foggy
 
Or you can insulate the interior, and not put any insulation on any exterior surfaces of the concrete. In other words, insulate above the slab (below the subfloor) and inside the walls; do not insulate below the slab. This produces comfortable floors that are easy on the knees.
 
Francis Vineyard said:
Contractors complained when installing carpet strips it broke off the concrete because of the thin beveled edge; I suggested they not put the strip close to the edge, haven't had any more feedback on that problem.Here's the link; Perimeter Slab Insulation FAQ

Francis
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Good link, illustrations I can use to help explain this issue to the folks around here who have never had to do anything like this.
 
Here in the great state of Washington, we have our very own energy code. More restrictive than the IECC. (Although we are going in 2012 to the IECC (heavily modified)).

The link that Francis posted was good. Here is another link that has some decent information. It is published by the people that write the energy code and is called the "Builder's Field Guide". Slab insulation is covered among many other things.

http://www.energy.wsu.edu/Documents/entire_guide.pdf

Our regs have been getting stricter and stricter. Some of it seems downright silly to me. They are whittling the U Values down on the windows quite a bit.
 
Jasper said:
Or you can insulate the interior, and not put any insulation on any exterior surfaces of the concrete. In other words, insulate above the slab (below the subfloor) and inside the walls; do not insulate below the slab. This produces comfortable floors that are easy on the knees.
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Jasper, I think you mayhave just solved a problem i am having with garage to living space conversions and un-insulated slabs on grade. Can someone else chime in and tell me whether or not they think this insulation on the slab surface under the finshed flooring is a viable alternative?
 
Darren and gbhammer,

Your responses are ill informed. Adopt the energy code and enforce it properly or the Federal Government will do it for you. You may not like it but that is what will happen. Insulate it tight and ventilate it right and the energy code works well, but you can't do it halfway or skip any of it or you create an awful mess.
 
Thanks for the input. I am considering advising the individual to install 2 layers of 1" extruded polystyrene with seams offset and then re-installing the laminate wood flooring over that. Creating a "floating floor" more or less. This will prevent him from having to excavate 2 feet around the perimeter including the concrete driveway side to get the required perimeter insulation and this method will also enable the garage to living conversion to be returned back to a garage easier than sleepers and subfloor someday when the current owner goes belly up and has to sell the place knowing that the new owners will be looking for a place with a garage. (Sad but, I see it happen around here)
 
On a not entirely related note....watch for PT everything at the garage door infill....unless they are building up 8" concrete or masonry first....
 
steveray said:
On a not entirely related note....watch for PT everything at the garage door infill....unless they are building up 8" concrete or masonry first....
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Everything is going to have to be inspected "after the fact" since they did all the work without a permit and behind the scenes. They thought they were going to get away with it. Ha! :inspctr I am going to have them cut holes in the sheetrock to check for insulation and PT sill plates. they are hoping it goes in their favor. Otherwise, rip it out and start over! At that point the cheapskates will most likely (hopefully) decide it is not worth it and turn them back into garages. Should have never been done in the first place as far as their HOA is concerned. Takes away from their off street parking and is cluttering up what is supposed to be a fire lane with vehicles.
 
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