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Educate me - how to insulate the concrete slab for a new garage.

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MikeAmann
MikeAmann Member Posts: 998
I am planning for a prefab steel 2-car garage, 22' x 31' on a concrete slab with 2' tall knee walls. The following pictures do not show the knee walls. So imagine the building two feet taller with taller garage doors.










There will be double the normal amount of gravel under the slab with drainage taken into account. How do I insulate this slab so that the cold of the frozen ground in winter does not make me freeze my butt off? I plan to have heat via a propane Modine heater.


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  • dko
    dko Member Posts: 642
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    I see you intend to have a work area, so what about the summer and cooling?
    Was a mini-split a consideration?
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,241
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    This is a golden opportunity for radiant...Pex is cheap.  
    1) 2" Thick Polystyrene Boards on ground.
    2) 1" "                                        vertically on edge
    3) 6" Square reinforcement mesh.
    3a) lay tubing or don't- No brainer!
    4) Pour your normal Slab.
    You're going to save much more fuel.over the years AND be toasty.  

                           Mad Dog

    SuperTechhot_rodEdTheHeaterMan
  • SuperTech
    SuperTech Member Posts: 2,205
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    Mike I would recommend considering installing radiant heating as well.  Nothing beats a heated slab. At least install the tubing before the slab is poured....
    MikeAmannMad Dog_2
  • dko
    dko Member Posts: 642
    edited April 2023
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    His plan was a simple garage unit heater. Which is also the lowest upfront cost option. So we can get an idea of what he had in mind in terms of complexity. Not freezing your butt can be dealt with standard slab insulation. Cold climate slab insulation is nothing new. 

    I would agree if the garage was attached and it was as simple as adding another zone to what is in the home now. and work as if it was part of the system already.

    Anything else I don't think it would benefit over the upfront cost for just a garage. Especially if a new heat source is needed. But would love to hear other opinions
    MikeAmannTinman
  • Jamie Hall
    Jamie Hall Member Posts: 23,635
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    The simple answer is at least two, and preferably four inches of rigid foam insulation under the slab and over the gravel. Also, rigid foam insulation on the outside of the foundation walls.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    MikeAmann
  • hot_rod
    hot_rod Member Posts: 22,472
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    Slab on grade, or foundation walls?

    2" foam under slab, 2" edge with Z flashing to cover exposed edge of foam if it is on the exterior..

    Three rolls of 1/2 HePex would cost around 300 bucks. 6X6 wire mesh maybe another 300.

    Here is how I did my shop, about the same size. I used 8X20' flat sheets of mesh, much easier to work on. Foam chunks to hold it up in the slab.

    You only get one chance to install the tube in a slab.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Mad Dog_2CanuckerMikeAmann
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,166
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    You might want to look at building code and builder and general contractor sights that address this particular issue. https://www.finehomebuilding.com/project-guides/insulation/insulating-a-slab-on-grade. They will be more specific. I remember when we were adding a master bedroom to our home the contractor specified a crawlspace. When the masonry contractor looked at the site, he asked if he could change the specifications to a slab on grade. The grade of the property was much higher where the addition was going to be. This meant that there would be too much earth to excavate in order to have a crawl space. The Slab on Grade would be less expensive. I agreed and said I was going to place tubing in the slab for future radiant floor heat.

    When the mason arrived to set the forms for the slab he only brought enough insulation for the perimeter and about two foot of the slab edge. the rest of the slab would be poured directly on the gravel. This would be just fine if the floor was not going to have radiant floor heat. the part of the ground under the building would not be subject to the cold outdoor winter temperature. Only the perimeter would be exposed to the cold. So the standard 2 foot edge and perimeter was what the masonry contractor was going to do. This was normal. This was included in the price. But this would not be acceptable for radiant floor heat.

    I quickly ran out to purchase more insulation to cover all the gravel... and installed the insulation myself with vapor barrier tape, and the rebar grid and the tubing so it was ready for the cement truck the next day. This is a detail of how I installed my insulation.

    2'' rigid foam boards were available in 10 ft x 2 ft x 2" sheets. I believe that you should consider insulating the entire floor even if you don't plan on radiant floor tubing in the future. But the bare minimum is a 2 ft perimeter of insulation and the side of the slab thickness vertical as pictured in the above detail

    Hope this helps

    Mr. Ed

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    PC7060MikeAmann
  • MikeAmann
    MikeAmann Member Posts: 998
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    Great answers guys. A few more questions tomorrow. Thanks.
  • leonz
    leonz Member Posts: 1,179
    edited April 2023
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    Jamie is correct in telling you to have 4 inches at least of foil backed rigid foam board insulation everywhere. You want to hold the heat in not let it leak away into the floor.

    Having 2 overhead doors will require more work, more door panels roller rails and framing than a single wide overhead door and will leak more heated air.

    No matter what heat you invest in you will lose heat it every time you open an overhead door.

    How is the building interior going to be insulated??

    Are you going to extend the end soffit eave over the garage door(s) to divert more rain water/snow away from the door apron???

    Is there any reason you would not consider a hydraulic single panel door with a man door as this is new construction?? Clearances would not be an issue as the hydraulic door opens out and up with a pair of hydraulic cylinders with a continuous hinge on top of the door and the center space is gained back and not wasted with more framing, steel and labor. These hydraulic doors are also easy to insulate heavily too.

    Is the knee wall going to be poured concrete or hollow block filled with vermiculite?
    How is the exposed knee wall going to be insulated? Are you going to back fill and tamp crushed bank run gravel against foam board glued to the knee walls??

    If you do not have drainage tubing carrying off ground water around the slab all the gravel in the world is not going to help you.

    You have to build according to the seasonal frost line depth too so keep that in mind.
    MikeAmann
  • psb75
    psb75 Member Posts: 863
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    We have a product manufactured in Burlington, Vermont called "Glavel" (recycled foam-glass aggregate) for BOTH sub-slab insulation and gravel replacement. A vapor barrier is also recommended. Compacted Glavel has an R value of 1.7 R/in. It is water, rot, pest proof. Weighs 9.8 lbs/cu.ft. A 6" compacted bed of Glavel offers R 10.2.
    EdTheHeaterManMikeAmann
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,241
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    Radiant....HANDS DOWN.. why are you going to go through ALL that trouble to insulate the slab and edge, pour a slab,, and NOT put in the pex which is much cheaper than the polystyrene itself??  You could heat that slab on a water heater....Very economical and inexpensive,no?
    If you WERE NOT doing the slab,, I'd suggest the Unit heater as simplest and least expensive option...Mad Dog
  • GroundUp
    GroundUp Member Posts: 1,956
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    hot_rod said:



    Three rolls of 1/2 HePex would cost around 300 bucks.

    Where are you finding HePex for $.33/ft? It's 2.5-3x that around here
  • hot_rod
    hot_rod Member Posts: 22,472
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    GroundUp said:

    hot_rod said:



    Three rolls of 1/2 HePex would cost around 300 bucks.

    Where are you finding HePex for $.33/ft? It's 2.5-3x that around here
    I grabbed this screenshot off of SupplyHouse.
    Name brand "A" pex is no doubt more $$
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Mad Dog_2
  • GroundUp
    GroundUp Member Posts: 1,956
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    hot_rod said:

    GroundUp said:

    hot_rod said:



    Three rolls of 1/2 HePex would cost around 300 bucks.

    Where are you finding HePex for $.33/ft? It's 2.5-3x that around here
    I grabbed this screenshot off of SupplyHouse.
    Name brand "A" pex is no doubt more $$
    You specified HePex, which is selling for $.80/ft on that same site.

  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,241
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    Let's not split hairs.. any pex will work.  We're trying to sell a radiant job here. Ha ha 😂  Mad Dog 
    SuperTechEdTheHeaterManPC7060
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,241
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    I concur.  Mad Dog 
    MikeAmann
  • hot_rod
    hot_rod Member Posts: 22,472
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    GroundUp said:

    hot_rod said:

    GroundUp said:

    hot_rod said:



    Three rolls of 1/2 HePex would cost around 300 bucks.

    Where are you finding HePex for $.33/ft? It's 2.5-3x that around here
    I grabbed this screenshot off of SupplyHouse.
    Name brand "A" pex is no doubt more $$
    You specified HePex, which is selling for $.80/ft on that same site.

    I use that to describe heating pex, not a specific brand. Barrier pex is a better term.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterManGroundUp
  • GroundUp
    GroundUp Member Posts: 1,956
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    hot_rod said:

    GroundUp said:

    hot_rod said:

    GroundUp said:

    hot_rod said:



    Three rolls of 1/2 HePex would cost around 300 bucks.

    Where are you finding HePex for $.33/ft? It's 2.5-3x that around here
    I grabbed this screenshot off of SupplyHouse.
    Name brand "A" pex is no doubt more $$
    You specified HePex, which is selling for $.80/ft on that same site.

    I use that to describe heating pex, not a specific brand. Barrier pex is a better term.
    Which was the source of my confusion, as HePex is a specific product made by Uponor. Just another Kleenex/Skil Saw/Sawzall type of thing I suppose. I'd never heard it referred to that way before. Thanks for the clarification.
  • MikeAmann
    MikeAmann Member Posts: 998
    edited April 2023
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    This info is awesome guys. Now let me fill in some of the missing information / limitations.
    I am now 56, and common sense says that I have 20 good years left. Beyond that, who knows.
    That's why the choice for the steel building - they are good for 20+ years.
    And I have been told that wood stick framing would cost $80K for this, I could be all in with the steel for $30-35K. A few of you have commented about my attention to detail, and that's what got me in this situation to begin with. That and the load that my parents unintentionally dumped on me. I will skip all of that story. The bottom line is that I put 20 years of work into my house and it's still far from being done. I could keep working on it for another 20 years and still not be finished. I have no choice now but to bail out. Attention to detail takes time - LOTS of time. I am a perfectionist. The work that I was doing to my house was done with the mindset that whatever I touched would never break and last forever. I was trying to insulate myself against TIME. OK, life just forced me to come to the realization that that will never work. Things change - period. At least I will learn this the first time and not continue to keep making that same mistake. INSANITY - doing the same thing over and over and expecting a different result.

    I am the only child, not married, no kids. But that leaves me with ALL the load.
    So now I am living back at my parents house and I have just spent the last year making the house functional again for Mom to live out her years there. But now she is in a memory care facility. Dad died 1 month ago. So I now have 2 houses to deal with. Hers is now functional - mine is far from it. The smart choice is to make her house mine. Cleaning out both will take at least a year. And my thinking is now changed - all I care about is functional from this point on. I no longer care about perfect, or 100% complete, or if two pieces of furniture match. And I will no longer build anything with the "last forever" mindset.

    Let's do some simple math -
    Mom's house is a 5# bag filled with 5# of sheet accumulated over 60 years.
    My house is a 10# bag of sheet.
    If I completely clean out Mom's bag, I still need another 5# bag for my sheet.
    That's where the 2-car garage comes in.
    I don't need to build this to last for 5 generations after I am gone.
    It doesn't need to have all the bells and whistles.
    It doesn't need to be anymore than a functional garage.
    I can't have this garage be a 20 year project.
    This will not be living space, just a garage.
    The KISS method is what is needed here.

    My neighbor directly across the street has a 2-car garage that is built into a bank.
    Drainage was not taken into account before hand. And the floor/walls were not insulated.
    He has a propane heater like I mentioned above, making the garage functional in the winter.
    No AC either - a fan does the job. The bottom line - his garage is functional.

    In my case, Mom's house has a 1-car garage under the house (ranch).
    And my father built an oversized 4 ft wide door between the basement and garage for moving large equipment between the two. The basement is unheated, but I am able to work in the garage in winter just by opening that door. It was great while we had the wood-burning stove. But I can work in there without freezing.

    For my situation, radiant floor heat would be nice, but not necessary.
    Besides, what if I wanted to install a lift at a later date? Or mount things to the concrete floor?
    For cooling, a couple of window A/Cs will do the job. And I have some big fans.
    All I really need to do is to make sure that there is a really good thermal break between the ground and the concrete floor. The knee walls must be solid concrete - no blocks.
    For water drainage, that will be easy. What will be the right-hand side of this garage, rolls off into a downward bank into the back yard. I plan to have the earth dug with a pitch towards that bank and a drain pipe at the base of that RH foundation wall.
    Let's stop here for now.

    See the pool and shed. That is the proposed area for the garage. The pool is already gone and the garage doors will be on the end where the shed is. I will add more pics.


    Mad Dog_2PC7060
  • hot_rod
    hot_rod Member Posts: 22,472
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    Sounds like you need a massive garage sale. Par down all the stuff that you will never use.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Mad Dog_2
  • MikeAmann
    MikeAmann Member Posts: 998
    edited April 2023
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    That's the plan.
    When my parents retired, they should have cleaned out then.
    That never happened. Now I am stuck with the job.
    Mad Dog_2
  • hot_rod
    hot_rod Member Posts: 22,472
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    MikeAmann said:

    That's the plan.
    When my parents retired, they should have cleaned out then.
    That never happened. Now I am stuck with the job.

    Two Men and a Truck can make a pile of stuff disappear in a few hours time😳

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Mad Dog_2
  • MikeAmann
    MikeAmann Member Posts: 998
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    True, but I have to sort through all of this first to determine what is junk. That will take time.
    All while trying to go to work, and do all the ADLs myself. And visit Mom a couple of times per week.
    4 days after we buried Dad, she fell and broke her hip. She just went back to the assisted-living facility yesterday.
    They saved EVERYTHING. Not hoarders, we just always found second and third lives for things. 60 years later, you have 2 tons of stuff.
    Mad Dog_2PC7060
  • MikeAmann
    MikeAmann Member Posts: 998
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    psb75 said:

    We have a product manufactured in Burlington, Vermont called "Glavel" (recycled foam-glass aggregate) for BOTH sub-slab insulation and gravel replacement. A vapor barrier is also recommended. Compacted Glavel has an R value of 1.7 R/in. It is water, rot, pest proof. Weighs 9.8 lbs/cu.ft. A 6" compacted bed of Glavel offers R 10.2.

    This sounds great, but can I get it in Connecticut? Price?
    If I were to use this, then I would only 2" of rigid foam on top of the glavel.
  • psb75
    psb75 Member Posts: 863
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    The concept of using the Glavel is to NOT use foam board. It's probably not readily available in CT. It should be. Vermont is sufficiently progressive "in that way"--using recycled glass. There is no shortage of glass. Kind of like using ground-up paper as cellulose insulation in building envelopes.
  • hot_rod
    hot_rod Member Posts: 22,472
    edited April 2023
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    Spray foam is fairly common around here for underslab. It seals and stays down better than sheets. Should be about the same $$. The link Larry posted in another thread shows an installer spraying the ground with foam.

    https://www.cbc.ca/news/spray-foam-insulation-can-make-some-homes-unlivable-1.2224287
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • psb75
    psb75 Member Posts: 863
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    I see. Encapsulating our living spaces completely...in foam. Top-to-bottom--as it were.

    Another sustainable topic: Vermont is also leading-the-charge in "green burials"--in the Green Mountains.
    Look it up.
  • hot_rod
    hot_rod Member Posts: 22,472
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    This link seems believable, a foam applicator with hands on knowledge

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,241
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    I feel your PAIN...BEEN THERE still doing with THAT!. Try not to get to angry at them.  Its Rare the parent or grand parent that does "The Swedish Death Cleaning." (Paring down your life's junk). My father did it but the house is "cold" now.  
    1) Major 2 day Yard Sale.
    2) Very Cheap prices and FREE.
    3) save a few really dear things...
    4) Dumpsters. *The 1 800 Junk places are great for a quick fast and dirty clean out, but they are a FORTUNE...
    5) This will clear your loving area? Mind and soul....Go for it....Mad Dog



    MikeAmann
  • Erin Holohan Haskell
    Erin Holohan Haskell Member, Moderator, Administrator Posts: 2,345
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    I'm sorry for your loss @MikeAmann.

    President
    HeatingHelp.com

    MikeAmannSuperTech
  • MikeAmann
    MikeAmann Member Posts: 998
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    https://alansfactoryoutlet.com/2-car-garage/
    This is the site that I used for the pictures in the first post.
    They are the only site that has the designer program.

    I have no idea which manufacturer to buy from.
    Apparently these steel buildings have BIG-TIME condensation problems.
    There are a bunch of youtube videos from people that have gone this route talking about their regrets and what they would do differently next time. I want to figure out how to do this right - the first time.
  • WMno57
    WMno57 Member Posts: 1,408
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    How about a pole barn? I have an FBI pole barn. Came with the property. About 30 years old. Holding up very well.
    https://www.fbibuildings.com/farm-buildings

  • The Steam Whisperer
    The Steam Whisperer Member Posts: 1,219
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    Just to throw another idea out there. If you are looking to keep the building about 55F, you may not want to insulate the bottom of the slab. In order to prevent the outdoor cold from getting under the building, you can insulate about 4 feet down and/or out to break that thermal connection, yes down and or out. Now if you keep the outdoor cold from getting under the slab, the heat from the ground will help heat the space up to about 55F, assuming you insulate and air tighten the building well. Maybe add some big windows to the south, you'll do even better. Geothermal/solar heating without all the equipment.
    To learn more about this professional, click here to visit their ad in Find A Contractor.
    realliveplumber
  • MikeAmann
    MikeAmann Member Posts: 998
    edited April 2023
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    What is the best vapor barrier and insulation for a metal building?
    Double Bubble Foil
    It repels moisture well, reflects up to 95% of radiant heat, and prevents mold and corrosion. Foil is the most reliable option for insulating metal buildings if the budget allows.

    How do I keep my metal building warm in the winter?
    Install Radiant Barrier Insulation
    This insulation should be installed in conjunction with constructing the structure on the exterior panels between the panels and support beams. If installed properly, it will help redirect heat into your metal building, helping to retain a warmer temperature.

    This guy added the insulation to an existing building. I would have it done BEFORE the panels are attached. https://www.youtube.com/watch?v=IFHLiK6NoWM&ab_channel=PatriotDIY
    GroundUp
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,387
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    Hi, Along the lines of what @The Steam Whisperer says, here's a link to a built idea Larry Kinney has developed: http://www.larryweingarten.com/uploads/1/0/7/3/107350339/snug_house_sustainability.pdf

    Yours, Larry
  • MikeAmann
    MikeAmann Member Posts: 998
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    Just to throw another idea out there. If you are looking to keep the building about 55F, you may not want to insulate the bottom of the slab. In order to prevent the outdoor cold from getting under the building, you can insulate about 4 feet down and/or out to break that thermal connection, yes down and or out. Now if you keep the outdoor cold from getting under the slab, the heat from the ground will help heat the space up to about 55F, assuming you insulate and air tighten the building well. Maybe add some big windows to the south, you'll do even better. Geothermal/solar heating without all the equipment.

    70 degrees would be nice.
    I can deal with sweating a lot easier than being frozen.
    Heck, I wear socks to bed. You can put on many layers of clothing, but if your feet are frozen from standing on that ice cold floor, then you are cold.
  • MikeAmann
    MikeAmann Member Posts: 998
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    Hi, Along the lines of what @The Steam Whisperer says, here's a link to a built idea Larry Kinney has developed: http://www.larryweingarten.com/uploads/1/0/7/3/107350339/snug_house_sustainability.pdf

    Yours, Larry

    Your site is marked as spyware/malware by the computer that I am on right now.
  • MikeAmann
    MikeAmann Member Posts: 998
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    WMno57 said:

    How about a pole barn? I have an FBI pole barn. Came with the property. About 30 years old. Holding up very well.
    https://www.fbibuildings.com/farm-buildings

    I am only looking for 22x31 feet. Pole barns are typically much larger.
    And the cost. 24x32 pole barn KIT starts at $18,656 and could increase in price depending on additional features and current material costs. And then I would have to hire a professional building crew.
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 1,219
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    MikeAmann said:

    Just to throw another idea out there. If you are looking to keep the building about 55F, you may not want to insulate the bottom of the slab. In order to prevent the outdoor cold from getting under the building, you can insulate about 4 feet down and/or out to break that thermal connection, yes down and or out. Now if you keep the outdoor cold from getting under the slab, the heat from the ground will help heat the space up to about 55F, assuming you insulate and air tighten the building well. Maybe add some big windows to the south, you'll do even better. Geothermal/solar heating without all the equipment.

    70 degrees would be nice.
    I can deal with sweating a lot easier than being frozen.
    Heck, I wear socks to bed. You can put on many layers of clothing, but if your feet are frozen from standing on that ice cold floor, then you are cold.
    To get an idea of the comfort level, just walk your basement floor for a few hours, ground temperature is about at its lowest this time of year. I've been working several 12 hour days on my feet in my basement with air temperature around 60F and I find it cool, but i don't find by feet are even close to being cold. However, this measure of comfort is very individual dependent.
    To learn more about this professional, click here to visit their ad in Find A Contractor.