This ios actually for my house instead of my garage but im hoping that you all can give me some advice here. One bedroom on my house is harder to heat and cool than the rest. Im planning to add some more attic insulation as it only has R19. Ive also been insulating the edge of my house as its built on a slab. I started to insulate this room and found out that it doesnt have a footer. Im guessing that it was added on at a later date as a porch, then was closed in for a room. It partially sticks out from the house. Will insulating the edge of this 4 inch slab do any good? My only thoughts are to insulate the slab and fill dirt around it pretty good. Any other ideas on what I can do to help it? Thanks.
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Insulate slab edge without footer
- Thread starter derekeh
- Start date
In my opinion, no. I think it is a waste of time.
The slab presumably is not insulated underneath so you won't be able to bring it "in the envelope" by insulating the edge. I think your best option is to try to address the thermal bridge between the slab and your flooring.
The slab presumably is not insulated underneath so you won't be able to bring it "in the envelope" by insulating the edge. I think your best option is to try to address the thermal bridge between the slab and your flooring.
billconner
Well-known member
IMHO yes. Is slab edge.gool in winter? Ditch witch around and put as deep of 2" foam board vertically. It will definitely warm slab edge.
The edge of the slab is usually close to the same temp as the outside.IMHO yes. Is slab edge.gool in winter? Ditch witch around and put as deep of 2" foam board vertically. It will definitely warm slab edge.
billconner
Well-known member
I think it's same as a SFPF (shallow frost protected foundation) where the heat of the earth is trapped to keep the exterior cold away.
I've only read of the ditch witch idea and sounds clever but probably just as effective to go down 10-12" and then outward for 2 to 3'.
I've only read of the ditch witch idea and sounds clever but probably just as effective to go down 10-12" and then outward for 2 to 3'.
Don't do anything that would weaken the soil's bearing capacity under the edge of that 4" slab. You could remove the siding and window moldings, and install continuous exterior insulation. XPS board would need to be the correct minimum thickness, and mineral wool board could be any thickness.
racecougar
Well-known member
Agreed that it's prudent to be very careful not to undermine the 4" slab supporting this addition. I'm surprised that frost heave hasn't caused issues between the addition and the house, assuming the house is on a full foundation below frost depth. Carefully insulating around the slab may help prevent that from happening in the future, but then again, if it's made it as is however many years thus far...
finn
Well-known member
Depends on the underlying soil conditions.Agreed that it's prudent to be very careful not to undermine the 4" slab supporting this addition. I'm surprised that frost heave hasn't caused issues between the addition and the house, assuming the house is on a full foundation below frost depth. Carefully insulating around the slab may help prevent that from happening in the future, but then again, if it's made it as is however many years thus far...
We’re on sand at least fifteen feet deep, so drainage is good, with no frost heaving. Lots of gravel around, which would be the same.
The roads cross a lot of marshy areas, which is where one runs into frost heaving.
racecougar
Well-known member
The OP might be down south, too. Who knows.
CraigStu
Well-known member
I am C-S-H and racecougar, concerned about undermining the edge of the slab if you start digging around it. Another concern is do you want to build up the ground around it because you will then have the wood walls at close to the same height as the new lawn or whatever.
Right now, the ground is at the bottom of the slab edge leaving the entire edge exposed. I was going to fill up to halfway or so on the slab edge unless that's a bad idea.I am C-S-H and racecougar, concerned about undermining the edge of the slab if you start digging around it. Another concern is do you want to build up the ground around it because you will then have the wood walls at close to the same height as the new lawn or whatever.
racecougar
Well-known member
It's just a 4" slab, no turned down edge or anything? The rest of the house has a proper foundation below frost line? Frost depth over there is at least 24", right?I'm located in Southern Kentucky. This slab is over 20 years old and doesn't appear to have had any issues.
If it's worked thus far, I'm in the "don't touch it" camp. Insulate between the slab and flooring.
Is there much/any grade falling away from the slab? As CraigStu said, bringing the soil level up very close to your framing/siding isn't ideal either.Right now, the ground is at the bottom of the slab edge leaving the entire edge exposed. I was going to fill up to halfway or so on the slab edge unless that's a bad idea.
Are you able to post a pic or two to illustrate exactly what you're dealing with?
I cab try to post a Pic later when I'm home. It does have a bit of a slope running away from the slab. The rest of the house does have a footer, although I'm not sure how deep. Insulating above the slab isn't an option now. I'd have to do the whole house or have a step up. For now, I'd like to try other stuff to see if it gets the room holding a temperature closer to the other rooms first.It's just a 4" slab, no turned down edge or anything? The rest of the house has a proper foundation below frost line? Frost depth over there is at least 24", right?
If it's worked thus far, I'm in the "don't touch it" camp. Insulate between the slab and flooring.
Is there much/any grade falling away from the slab? As CraigStu said, bringing the soil level up very close to your framing/siding isn't ideal either.
Are you able to post a pic or two to illustrate exactly what you're dealing with?
nmk_61802
Well-known member
I think it's same as a SFPF (shallow frost protected foundation) where the heat of the earth is trapped to keep the exterior cold away.
I've only read of the ditch witch idea and sounds clever but probably just as effective to go down 10-12" and then outward for 2 to 3'.
Further info on SFPF:
If the slab is only 4" thick, it probably won't help much as it would if it's 12-18" thick...you may not be getting much insulation value but are creating a thermal break.
billconner
Well-known member
Cutting a "slot" to put rigid foam in. I think a ditch witch will work for 24" vertical. I believe that will make a noticable difference.I'm located in Southern Kentucky. This slab is over 20 years old and doesn't appear to have had any issues. When you say dig down 10-12 inches and out 2-3ft, what do I need to fill with?
CraigStu
Well-known member
I don't think you can do much to insulate this. Unless it's set on clay any digging is sure to have some of the soil under the edge fall out leaving it somewhat unsupported. And since the wall is built right to the edge, it loses support too. I'd rather forget insulation and fill in half way up the 4" just to maintain slab edge support. C-S-H mentioned xps on the outside which I think could help. Also if it is currently vinyl siding, that could be replaced w/ insulated vinyl siding. Another option might be the appropriate type of foam board insulation added inside. Or even an additional layer of drywall. Is there a drywall that offers better than standard insulation properties? It would be really nice to add some type of insulation to the floor but than you would have to deal w/ a short step which code probably doesn't allow..
The insulated siding does interest me but just thinking... it currently hasmaybe 7/16 osb on the outside. Would adding a layer of 1/2in xps over the top of it and covering the slab edge possibly work? And then add 2inch osb over the edge of the slab. I would have to retrim out my windows but thats honestly not a big deal. Insulated siding sounds okay but im afraid it might not color match my existing siding.
CraigStu
Well-known member
I like the xps over the osb bit I'd look at 1" if you are going to go to all that trouble. One concern, since it is now colder fall weather, would be removing the existing siding w/o damaging it. Vinyl cracks more easily at lower temps.
Id definitely work around the cooler temps for working with the siding.I like the xps over the osb bit I'd look at 1" if you are going to go to all that trouble. One concern, since it is now colder fall weather, would be removing the existing siding w/o damaging it. Vinyl cracks more easily at lower temps.