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kcinkc71

insulating the footings?

kcinkc71
10 years ago

I searched but can't find the exact answer on this.
Midwest USA, footings are in, foundation walls are poured.
drain tile going in and plumbing rough has begun.

our plan is to do rigid foam on interior foundation walls (9') before finish.

what about footings? can I make a thermal break by insulating the footings below basement floor? (insulate vertical face of footing and horizontally below basement slab/floor? I do not intend to insulate entirely under basement slab with 2" XPS. we will be using forced air heat for house. thanks

Comments (13)

  • worthy
    10 years ago

    No point that I can see. A capillary break should have been installed over the footing before the wall was poured. It's now Code in my jurisdiction. If that wasn't done, a strip of XPS would provide that at least on part of the footing.

    Illustration from Building Science Corp. RR-0202 Basement Insulation

    This post was edited by worthy on Wed, Jul 10, 13 at 13:13

  • kcinkc71
    Original Author
    10 years ago

    Thanks Worthy, that was the photo I looked at. so, by putting XPS on top of footer, then XPS sitting down on top of that, running up the wall..... seems might give me some better break? I know it is too late according to your photo, but if I can make it better now, I will

  • kcinkc71
    Original Author
    10 years ago

    sorry, last question. if I am not insulating under the entire basement floor, am I wasting my time insulating the footings?

  • PRO
    Epiarch Designs
    10 years ago

    his detail is what I did under my basement slab except my walls are ICF and used XPS (250) under the slab. I also put a 6 mil vapor barrier above the rock, taped and under the foam. I ran it up the side about 4" and taped it off to the ICF. There is no reason to insulate the footings under the slab. However I would highly recommend insulating under the entire slab, or at a min, 2' around the perimeter. Insulating under the slab will keep it warmer and drier, trust me. You can only do it once before you do concrete, so spend the extra money if you ever intend on finishing the basement. No one ever regrets adding more insulation, but always do if its not there.

  • kcinkc71
    Original Author
    10 years ago

    uugghhh. thanks. I am banging my head against the wall. In Kansas City area, NO ONE insulates under the slab, right or wrong, they just don't around here. I know I should, but trying to justify cost. Our climate hear seams to get more mild every year, and at 9' below grade, no one deems it necessary. beautiful foundation BTW.
    so, they can just pour 4" slab on top of xps?

  • renovator8
    10 years ago

    At 9 ft below grade the temperature of the ground below the floor slab will be approximately the temperature of local well water. The heat loss through the slab will be proportional to the temperature differential between the ground and the living space. Historically that was not considered enough to justify insulation but because the cost of energy continues to rise it is now a serious consideration and what has been done before is no longer relevant. As often happens these days it is a matter of pay now or pay later. Essentially the decision should be based on local energy cost, desired comfort and how long you plan to own the house. Eventually energy codes will require under slab insulation in all cold climates.

  • PRO
    Epiarch Designs
    10 years ago

    kc-
    there are a couple things to consider here. Obviously upfront costs and costs later. In KC, the loss is not has large as northern Iowa where I am, but I still think you should really consider it. You could drop to 1.5" too and save some upfront cost.
    In my field, I constantly hear "this is what we have always done" or "this is code". Right, I know what the codes are. But I always have to remind contractors and builders that code is the MINIMUM requirements you have to hit. Just think about that. If doing the least amount you have to do to get by is fine for your home, that is your call. There is only 1 area in your house that will give you a financial paybac, and its in your insulation. Not in granite counters or ornate trim (just generalizing). It may be 1 year or 10 years, it depends. Then again, your zone 4 so they are pretty light on energy code levels anyway. However 2012 code will increase values and not sure if it is enforced in your area yet. But things to note- again, 2012 code is the MIN. energy standards. For zone 4, it changes the insulation from r13 (probably what they are all doing currently) to r19 or r13+5. I would recommend the r13+5 as a min since the r5 will give you a better boost than a 2x6 stud wall will, however r19+5 is better yet. Again, these are min. requirements by code. Energy costs will always go up, so invest now and have a more comfortable home for years to come. You may be able to slightly reduce your hvac requirements as well by adding additional insulation which can result in an upfront cost reduction.

  • worthy
    10 years ago

    The XPS on the top of the footings not already under the foundtion wall will act as a good thermal and capillary break.

    The Passivhaus practitioners--who remind me so much of hot rodders looking for ultimate bragging rights but with no practical purpose--use 8"-16" of EPS under both the foundation and the footings.

    Under-basement floor/footing insulation isn't even close to making it into the International Energy Conservation Code.

    The only reasons I would consider it would be if I were building in the Arctic, had radiant basement heating, wanted to reduce moisture flow into the basement or wanted energy independence in the face of a breakdown in social order and infrastructure.

    the cost of energy continues to rise

    Not natural gas thanks to fracking. And electricity rises only due to politically motivated decisions of governments to subsidize "alternate" energy sources such as wind and solar by tacking the costs onto other energy usage.

  • Brian_Knight
    10 years ago

    Iam pretty sure IECC 2012 Climate zone 4 is calling for R10 2' around perimeter as the minimum (cheapest allowed by law). Not that its being enforced yet..

    Ive always considered insulation under slab somewhat of a waste in zones 4 and below but considering the permanence of it, its probably a good requirement especially considering the comfort and moisture benefits. Damp basements are expensive problems.

    We have been having spray foam contractors spray an average of 2" closed cell as an alternative to XPS under slab. This speeds things up for us and is very competitive in costs mainly due to the detailing around the pre-cast concrete panel or header block perimeter. Its also a much better air seal to soil gas and moisture compared to taped plastic or foam.

  • worthy
    10 years ago

    Iam pretty sure IECC 2012 Climate zone 4 is calling for R10 2'

    That's for slabs. There's no requirement anywhere for insulation under a basement floor.

  • PRO
    Epiarch Designs
    10 years ago

    correct, IECC does currently not require basement slab insulation and values in the chart are for slab on grade installations above the frost line.

    Again, code mins. assuming somewhere around a 1600 sqft slab, that is about $1500 installed 2" of XPS. Will you see a payback in zone 4? Probably not. But you will have a more comfortable, dryer basement floor. Example: I took temp readings of 2 projects. 1 where they took the advice and installed a vapor barrier and 2" XPS. The other they did neither. The temp of the insulated BARE concrete was closer to room temp by about 5 degrees compared to the uninsulated floor. The floor also had a 1/4" thick underlayment insulated pad and 5/8" engineered wood floor on it which is what I pulled the temp from. By putting the foam under, you are creating a thermal break and allowing the slab to absorb and regulate close to room temp. Will your wallet see the savings? Again, probably not. But your feet will feel it. Its a comfort thing, not too dissimilar from other tangible items such as all of your finishes in the house. One client stressed over an upgrade charge between fiberglass batts and blown insulating I recommended. The upgrade was about $400 and came with a payback. On the flip side, they elected to go with a unique granite counter that was about $2800 more than their budgeted granite without blinking an eye. Hopefully you get my point.

  • kcinkc71
    Original Author
    10 years ago

    Thanks and I get your point. Builder has some 1" xps from another job, but still pondering the 2",(which is what I am leaning towards) I wish I could get your pricing though, I am over $2K for just at 2000 sq ft, that is with me doing the install and taping. speaking of, what tape?

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