Sorry guys, I searched and need more info. I picked up some 2" pink rigid insulation at our local big box store. It is 15psi. I'm cutting it in half length wise to do the apron so the insulation will be 30.5" below grade here in MI. Is this sufficient and can I use this same stuff under my 5" slab? Thanks. -MATT
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Slab and apron insulation
- Thread starter matt60j
- Start date
hyvolt
Active member
Yes. I have 6" under my 6-8 slab. Been 6 years now and not a crack.
petty4243
Well-known member
how far north in mi are you??? you might consider just layint the panels on their sides and have 4' of insulation below grade... I am in iowa and frost goes as far as 4-6 feet here(deepending on weather of course)... you might find if you talk to menards, home depot etc that you can purchase damaged pieces(corners broken or cracked etc) much cheaper... never hurts to ask and save a few bucks... as for placing the foam on the bottom of your slab??? how deep are your footings? is the slab a ground level or basment floor? should not have to worry about it unless you have a shallow footing that might enable the frost to go around the bottom.....
I'm just east of what would be considered central MI and this is for my pole barn which is already up(40x56x12) so no footing. Code is 42" of depth for footings. I don't think going 48" is an option. I was hoping that 30.5" would cut it so I don't have to do major excavating. Thanks. -MATT
Steve in Mi
Well-known member
Matt, are you saying you could go 30.5" vertical around the perimeter but not 48"?
I have footings and block foundation so it was easy to apply rigid foam both inside and outside my foundation wall prior to backfill. I know, not the same but I'll offer some comments anyway based on what I've seen used for insulating pole type construction slabs.
I'm going to assume you are insulating because you intend to heat this (BIG) space. Double up (or more) on the insulation at the edge of the slab. Sometimes the vertical foam is placed in a trench (narrow trench dug by a trenching machine - diy rental) about the perimeter as close to the slab as possible and a cap is layed (underground) from the slab to this verticle wall of foam. The cap is generally slopped/pitched somewhat to provide water shed away from the slab. In other installations where the vertical foam wall to the frostline was not employed I have seen the insulation under the slab doubled in thickness about the slab perimeter 4' to 8' (different strokes for different folks) in from the outer edge and again double or tripple thickness at the slabs edge. One of my brothers with in-floor heating did the double perimeter foam under the slab. BTW, take pictures of the installation, it's better than a guys memory.
I have footings and block foundation so it was easy to apply rigid foam both inside and outside my foundation wall prior to backfill. I know, not the same but I'll offer some comments anyway based on what I've seen used for insulating pole type construction slabs.
I'm going to assume you are insulating because you intend to heat this (BIG) space. Double up (or more) on the insulation at the edge of the slab. Sometimes the vertical foam is placed in a trench (narrow trench dug by a trenching machine - diy rental) about the perimeter as close to the slab as possible and a cap is layed (underground) from the slab to this verticle wall of foam. The cap is generally slopped/pitched somewhat to provide water shed away from the slab. In other installations where the vertical foam wall to the frostline was not employed I have seen the insulation under the slab doubled in thickness about the slab perimeter 4' to 8' (different strokes for different folks) in from the outer edge and again double or tripple thickness at the slabs edge. One of my brothers with in-floor heating did the double perimeter foam under the slab. BTW, take pictures of the installation, it's better than a guys memory.
Matt, are you saying you could go 30.5" vertical around the perimeter but not 48"?
I have footings and block foundation so it was easy to apply rigid foam both inside and outside my foundation wall prior to backfill. I know, not the same but I'll offer some comments anyway based on what I've seen used for insulating pole type construction slabs.
I'm going to assume you are insulating because you intend to heat this (BIG) space. Double up (or more) on the insulation at the edge of the slab. Sometimes the vertical foam is placed in a trench (narrow trench dug by a trenching machine - diy rental) about the perimeter as close to the slab as possible and a cap is layed (underground) from the slab to this verticle wall of foam. The cap is generally slopped/pitched somewhat to provide water shed away from the slab. In other installations where the vertical foam wall to the frostline was not employed I have seen the insulation under the slab doubled in thickness about the slab perimeter 4' to 8' (different strokes for different folks) in from the outer edge and again double or tripple thickness at the slabs edge. One of my brothers with in-floor heating did the double perimeter foam under the slab. BTW, take pictures of the installation, it's better than a guys memory.
Thanks Steve! Yes, 30.5 vertical around the perimeter. I started hand digging and it ain't gonna cut it. I'll probably go deeper since I'll rent a backhoe. -MATT