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Garage Slab Heat Loss

wyo
wyo Member Posts: 4
Hello. I’ve worked through the Slant Fin Hydronic Explorer heat loss calculation process several times for a variety of small jobs. I’m attempting to use it now for a small house with an attached garage/workshop located in NW Wyoming. The owner/builder intends to use ICFs for the foundation (including garage stem walls), and use 2” blueboard under the slab. What value should I use in the heat loss app for the “floor factor” variable for the slab?

I’ve been a daily reader/lurker here at Heating Help for several years and really appreciate the things I learn and the general brain stimulation provided by reading the discussions that take place. Thank you to the wonderful group of frequent-contributors.

Thank you in advance for your assistance.
Gram (:

Comments

  • neilc
    neilc Member Posts: 1,460
    I'm no expert here, so salt liberally,
    slab on grade, with R or U value of your 2" of blue,
    and still add a slab perimeter isolation/insulation strip,
    right?
  • GroundUp
    GroundUp Member Posts: 1,281
    Is the ICF going to be only the outer layer of the slab edge, or is the stem wall actually coming up to slab surface height with both sides of the ICF block separating the slab from the outdoors? Some make an L so the slab comes to the exterior wall, some use a 4" ICF on the top course to set a 6" wall on, some run 6-8" all the way up which is then exposed in the finished space. I don't use the Slant Fin calculator, but the one I use has an input of "R value of slab perimeter insulation" or something like that which you'd just add whatever values your actual thermal barrier is
  • Gordy
    Gordy Member Posts: 9,514
    There is no way to “accurately” plug in what you want in the slantfin app.
  • neilc
    neilc Member Posts: 1,460
    Gordy said:

    There is no way to “accurately” plug in what you want in the slantfin app.

    could one assume an alternate floor assembly?
    say 6(?) inches insulation, wood floor, over unheated open crawlspace?
    or sumthin ?
  • Gordy
    Gordy Member Posts: 9,514
    Sure you could pick a “similar floor assembly ” selection from the drop downs. But it won’t be any where near as accurate compared to a slab on grade that is going to be warmer than a vented crawl space . Especially once operational.
    kcopp
  • neilc
    neilc Member Posts: 1,460
    well, ok,
    maybe similar floor assembly is a wrong or incomplete term,
    let's try fake it till we make it,
    do a separate floor calc using floor assembly with a unreasonable deign temp, 55(~)* ?
    spitballing here.
  • neilc
    neilc Member Posts: 1,460
    or pay a professional service / designer / contractor / engineer for the real answer
  • Gordy
    Gordy Member Posts: 9,514
    Well I most certainly can say 1/2” pex, 12” OC , and 6-8” OC three feet in from garage door, 100-110* SWT would work😁
  • neilc
    neilc Member Posts: 1,460
    200, or 2000 ft runs ?
  • hot_rod
    hot_rod Member Posts: 15,019
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Gordy
    Gordy Member Posts: 9,514
    neilc said:

    200, or 2000 ft runs ?

    Installer preference. Good luck with 2000’ loops......
  • wyo
    wyo Member Posts: 4
    The decision about the edge detail hasn’t been made, but at this point I am assuming the ICF with insulation left on after pouring will run full height and stay at full concrete thickness to that height. Full height will likely be around 6” above finished outside grade. Uncertain about slab elevation, but let’s assume top will be at or below stem wall height with full insulation left around the slab (both inner and outer insulation isolating slab from exterior condition). Door apron area tbd???? Each of the possible details here has its compromise.

    > @Gordy said:
    > There is no way to “accurately” plug in what you want in the slantfin app.

    In each field that has a drop down list, you can manually enter a value. For wall and roof assemblies, this time around, I used ResCheck to figure out a full assembly u value for each envelope condition to be built. Difficult finding info for calculating value for a slab, seems to be not much discussed and the essays out there seem speculative.

    @GroundUp
    I’ve had the heat loss calculator you suggested in another thread open in my browser for the last week. Maybe I should take the time to try it (;


    > @Gordy said:
    > Well I most certainly can say 1/2” pex, 12” OC , and 6-8” OC three feet in from garage door, 100-110* SWT would work😁

    (; Seems like a very safe bet, just trying to work through the math for the sake of sizing the boiler, etc.

    Thank you all for your ongoing help. (:
  • nibs
    nibs Member Posts: 462
    Part of our slab abuts ICF, we just poured against it with no issues then or now.
  • nibs
    nibs Member Posts: 462
    Should have mentioned, If we were building today, all our exterior walls would be ICF right up to the roof line.
  • Gordy
    Gordy Member Posts: 9,514
    Icf is a very expensive alternative of construction in my opinion for the gain.
    kcopp
  • nibs
    nibs Member Posts: 462
    @Gordy , In this area 5 years ago the material cost of ICF forms was about the same as single use plywood forms, and the forming labor time perhaps 1/3 that of plywood. I have not done a comparative estimate of ICF concrete walls with stick framed walls but the longevity, strength, ease of applying interior and exterior finishes, and a host of other advantages seem to me to make an insulated concrete structure a front runner for modern construction.
    In the last few years cost of ICF forms has come down considerably thus changing the equation.
  • GroundUp
    GroundUp Member Posts: 1,281
    Gordy said:

    Icf is a very expensive alternative of construction in my opinion for the gain.

    Depends. I did a radiant job for an acquaintance last fall in a 1500 sq ft 1.5 story house, very similar to what I would build when that day comes, so I was picking his brain about costs and whatnot. He ended up doing 2x6 stick frame with loose fill fiberglass with fanfold on the exterior because it was $3500 cheaper than full 6" ICF walls with the same R value but zero chance of thermal bridging or air infiltration and no chance of the structure burning down. For $3500, the insurance savings alone would pay for the added cost in only 7 years not to mention the utility savings and soundproofing that comes with ICF. I wouldn't even consider wood frame for that cost difference, personally.
  • hot_rod
    hot_rod Member Posts: 15,019
    Some of my shop and office is IFC

    Bugs are getting to the below grade sections, I did treat the forms before the pour. I also added a perforated odd to add additional borate

    Underslab foam gets buggy around here also
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Gordy
    Gordy Member Posts: 9,514
    Don’t be deceived by the fireproof feature boasted. That foam burns, and burns hot, and toxic. Concrete will lose its strength when heated to that degree. Around here if a house burns down you are not allowed to rebuild on the existing foundation.

    I can’t imagine how applying finish layers would be “easier”.

    What I don’t care for is no one will ever know if proper consolidation is achieved since the forms are not stripped. I’ve seen a few horror videos in that aspect with ICF.

    I also go by what I see as prevalent construction techniques in a geographic area. If it were comparable, or cheaper to stick built you would see a lot more ICF.

    Concrete pumping, or conveying isn’t cheap either. There would be several mobs on the placing at various stages in the ICF construction. They usually have 8hour minimums unless there is a good contractor relationship in using them a lot.


    What I do see as an advantage is a DIY who doesn’t own concrete forms, or a concrete contractor who doesn’t want to deal with the storing,mobilization,stripping, and demobilization of the forms.






  • nibs
    nibs Member Posts: 462
    @Gordy
    Gordy, the ICF we used has strips at 8" O/C that will take screws, I screw drywall directly onto them. You can take a blow torch to the drywall and all you will get is smoke, granted it is very toxic smoke but it wont burn, I did a tiger torch burn test and it is not easy to light. We will screw siding on the outside when that time comes. The stuff we used is monocellular so we get no water penetration. Can't speak to bugs as it is not a problem here.
    We only used ICF on one wall 45ft long, and only one course (16") above the slab (4ft high), then went stick built. I have built more lineal feet of formed concrete wall than I care to think about and trust me, ICF is a maidens dream in comparison.
    GroundUp
  • Gordy
    Gordy Member Posts: 9,514
    To each their own I suppose.

    I go by market share as a tell tale more than anything. If icfs were that great you’d see more market share. You just don’t.
  • rick in Alaska
    rick in Alaska Member Posts: 1,242
    Gordy said:

    To each their own I suppose.

    I go by market share as a tell tale more than anything. If icfs were that great you’d see more market share. You just don’t.

    I guess it just depends on location. Up here, they are the norm. It is rare in my area to find a house that is not put together with icfs, unless it is more than about 25 years old. One contractor in town is building entire houses out of them right up to the roof line.
    My foundation is built from them to a point where it is above grade, and then has conventional framing. I am on a sloped lot, so my entire back wall winds up being about 10 feet from footing to top, as my basement is 9 foot inside.
    I guess a lot depends on where you live, and whether your supplier carries them, and is willing to deliver.
    Personally, with the ease of installation, the structural value,and the insulation on both sides, I would not go any other way.
    Rick
  • hot_rod
    hot_rod Member Posts: 15,019
    They come and go in my area, along with SIPs
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Gordy
    Gordy Member Posts: 9,514
    R value is a bit different also. Play on numbers using the mass of the concrete wall, depending on its thickness. I will say it is where fly wheel can really work in your favor for short duration outdoor temperature swings. My focus was cost which is usually the controlling element in construction.
  • nibs
    nibs Member Posts: 462
    Am 20 years out of date on construction costs, and rusty as a bent nail when it comes to estimating buildings (used to be my profession) but am pretty sure that when all the costs are in, as well as the lifetime cost, ICF's probably are pretty even during building, and much less expensive to heat and maintain.
    My main quibble with ICF's is the insulation on the inside of the structure, which moderates the effect of thermal mass.
    Build properly with concrete and you have a 500 year house.
    GroundUp
  • GroundUp
    GroundUp Member Posts: 1,281
    As we all know, cost is a huge factor for most people. Any clown can stick frame a house and make a business out of it, but not just any clown has the experience or means to build with ICF so it cuts down the available contractor list by a very large margin (unless DIY, but most aren't into that) which limits the cost factor too. You could find a scabby carpenter a lot faster and easier than a scabby ICF guy around here, and you could also find a top shelf carpenter a lot faster and easier than a top shelf ICF guy. As is the case with most new builds, as most of us are familiar with, a few hundred bucks is a deal breaker for a lot of folks with any aspect of the build. Adding 5-10% to your build just to have concrete walls doesn't appeal to most people because their previous stick frame homes have been "fine", but what they don't see is the extra labor and room for error with all steps of the build especially air sealing. I'd say 5-10% in energy savings would be pretty easily attainable and forever, with no risk of movement or deterioration over time like wood frame. It doesn't fit every bill of course, but I'm of the "do it right or do it twice" mentality and the older I get, the more appealing maintenance free items are getting.
  • Gordy
    Gordy Member Posts: 9,514
    Don’t be so sure. I’ve seen plenty of foundations alone crack to hell. Let alone stacking ICF on top.

    I’d also like to see what happens when the foam disintegrates in x years. Don’t bank on a structure lasting 500 years because it’s concrete........especially in freeze thaw zones.

    ICF does lend itself to the DIY since most don’t own concrete forms. Just stack, and go right? Many incidentals not included in a full blown ICF build. Those get left out when comparing.
  • nibs
    nibs Member Posts: 462
    @Gordy
    As Buckminster Fuller pointed out, it takes the building industry 20 years to adopt a new technology, ICFs, and SIP's are beginning to become more commonplace.
    When we started our build, 10 yrs ago, ICF costs were prohibitive, today they are much more reasonable. Now I would build all my walls, interior & exterior with ICF.
    It would be the height of negligence to build concrete walls on a foundation engineered for stick frame, so that is not a relevant argument. Cracked foundations result from poor work on somebody's part, engineer form builder, cement plant or?.
    If & when the exterior insulation becomes degraded it can be replaced, every 50 or 100 years, for much less than a new building.
    In the 70's & 80's when I was a union carpenter, I built many CIP forms for walls and foundations, ICF's are childs play in comparison, and voids are a result of lack of care with vibrators, and are just as frequent in CIP or ICF pours.
    Years ago built many stick homes.
    My house Concrete where possible.

    PS. Our thinslab radiant floor does not overshoot temp wise, possibly due to the massive amount of concrete in the walls, both interior and exterior.

    10 years to build so far, started when I was in my late 60's now in my late 70's it takes me a while to scamper up the scaffold, so it may take another 10 before interior is all done.
    rick in Alaska