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Thermal break at overhead doors

Ken_25
Ken_25 Member Posts: 14
 I have a contractor building me a new shop and a radiant installer doing the radiant heating.  My question relates to the thermal break at the garage overhead door locations.

  I have 42 feet of overhead door openings. The contractor has a thermal break everywhere else except here. The floor at the doors will be poured directly over the frost walls without a thermal break . The floors are being poured 4" thick.

  Is there a very thin thermal break which should be placed over the frost wall which will still reduce the heat loss but also stand up to vehicles entering the shop. These are only pickup truck sized vehicles.

 I used the wall for a lot of research about 10 years ago , and I seem to remember HotRod doing some studies on this.

  The contractor is also leaving a spot for a 10,000 lb 2 post hoist. He has cut out the 3" under slab insulation for a 4 ft square under the posts to allow an extra 3" of concrete. Am I best of to have this concrete poured directly onto the packed ground or is there a thin thermal break which would work well for this purpose.

 The concrete is being poured on Thursday so any speeding response would be greatly appreciated.



Ken

Comments

  • icesailor
    icesailor Member Posts: 7,265
    Snow melt:

    You didn't mention this and its probably too late, but did they suggest a heat zone for the brow/aprons into the shop bays for snow melt when you have snow and ice in front of the doors or an ice buildup?

    Added as a zone that you can turn off when there is no snow or ice on the ground. You're not heating the outside ground.

    I did some work in a airport crash building where they stored fire trucks. The front of the doors were protected with snow melt so they never had to shovel the snow or worry about ice build up in front of the door. Something to consider if you have gone to all the trouble. The fire equipment must be available 24/7 for emergencies.
  • Ken_25
    Ken_25 Member Posts: 14
    No aprons

    The building is on my acreage and will only have gravel up to the entrance. Thanks for the response.
  • MikeG
    MikeG Member Posts: 169
    How much loss is too much

    A local large farmer (NW Ohio) built a 150x80 shop, office, apartmen twith all 5/8" pex in the floor.  They did put a break around the perimeter only 1" extruded foam and a roll type foam and vapor barrier under the concrete.  I think that was only about 1".  I didn't think that was enough, but I'm not a contractor.  The pex is tied to wire mesh mats and is on the bottom.  He spent about 1.3 mil on the palce.  The contractor did not put any thermal break under the overhead doors.  There are three of them.  The floor extends out past the door over the footer for a short apron.  How much heat is being sucked out, who knows.  He is probably losing some around the perimeter and under the floor also.  This past winter was the first for the system.  One thing I can say.  The shop was comfortable for working on equipment.  Like everyplace else we had an unusulaly long period of sub-zero weather.  The doors definitely didn't freeze shut so that was a benefit, but at what loss of heat.  He said the propane usage wasn't bad, whatever that means.  He dries grain and has a 30k gallon propane tank for that operation.  His shop has separate tanks for the boilers but I wonder if he really knows.  In his case he would almost have to put in a separate slab with it's own footer that extends into the shop to make a thermal break. That transmits the cold in.  He is not running glycol.   I have seen cases where the apron cracks where it extends over the footer and the rest of the floor is free floating.  Usually where they skimped on the concrete thickness and have heavy equipment.
  • Ken_25
    Ken_25 Member Posts: 14
    Long leader lines.

    My concern is that the supply and return leader lines for the heated workshop end of the building are running past 25 feet of overhead door entry in the section of the shop which will usually be left unheated. If these door openings don't have a thermal break they will be sucking more heat than necessary from this loop before it even gets to my shop end.

     The building contractor feels they should be left without a thermal break because they will be stronger.I just wanted to know if their was a thermal break product that the experienced people on the wall new from working with it that I should consider using.

     If the common practice is to leave this without a thermal break then that would be good to know. I just didn't want to wait until after the pour to ask the question.



     Ken
  • MikeG
    MikeG Member Posts: 169
    Insulate or reroute

    Ken,

    Is it possible to reroute those S&R lines farther away from the entry door?   Can you insulate those lines to reduce the heatloss through them?  Make the thermal break between the lines and concrete instead of a section of floor.  Otherwise you may have to isolate that section of slab in front of the door, which as I indicated earlier will need it's own footer and be big enough to provide the support you need etc.  That's why the conmtractor is concerned about the strength.  Is there danger of freezing or will these lines be running all the time in cold weather?
  • SWEI
    SWEI Member Posts: 7,356
    Can you tie the apron to the main slab

    with a bunch of #7 bar that bridges the thermal break?  Heat transfer is all about area, and that might do the trick.
  • Ken_25
    Ken_25 Member Posts: 14
    No Apron

    There is no apron to the building. The floor is being poured over the frost wall without any thermal break. there will be just a gravel driveway up to the building.

      I think I will run the supply and return lines for the far end thru a garden hose as they pass the door bays on the way to the far end workshop.

     Any comment on this

     Ken
  • MikeG
    MikeG Member Posts: 169
    Apron

    Apron

    Ken,

    I probably didn't use the right terminology.  I am calling the apron the part of the floor that extends over the footer or frost wall or foundation under the door and extends outside the door a short distance.   My garage and shop are this way and the part outside the door about 8" is sloped an inch to shed water away from the door. Most would call the parking area in front of the doors an apron.  I don't have any heat in the floor and it does radiate cold into the buildings.  What about not extending the floor slab out over the frost wall.  Pour your floor slab inside the frost wall with a thermal break all around the perimeter like the rest of the building.  At the door the break could be foam like the rest of the building or an expansion type material.  This makes your floor a floating slab not resting on a part of the frost wall.   In this case you will have to raise the frost wall up to the floor level, but you could also slope it to shed water.  Drill and pin this pour with rebar to the frost wall.  Just have to make sure that you have a good seal so water cannot get into the the joint at the doors.  Maybe just putting some insulation around the pex to reduce the loss will work.  Just some ideas.
  • SWEI
    SWEI Member Posts: 7,356
    We call it an apron

    and you just described nicely what I was trying to convey.  Separate the part of the slab that is under (and just outside) the door from the main interior portion.  Heat it or not -- your choice -- but keep it isolated at least a bit.



    Personally, I'd run it at least 18" past the door and set it up for a separate snowmelt zone as ice described in his original reply.  It's really, really nice not to have to chip away at the door closure after a cold night.
  • MikeG
    MikeG Member Posts: 169
    Detail

    I attached a detail of what I was talking about.  I dont know your wall thickness or exactly how your door will hit the floor or apron.  In the detail it's important to have the door fall outside the thermal break and still have a good watertight flexible sealant.  Since the floor is floating it doesn't have a chance of cracking since it doesn't rest on the frost wall. Usually not a problem with decent floor thickness and matched to load potential.  Ideally the floor would be a little higher than the part under and outside the door.  Like Swei said, this is isolated, but  now you don't have any benefit of keeping the door bottom ice free.  Maybe not a problem with an unheated space.  The shop I referrd to earlier has the floor extending outside the door, but the whole floor is heated with a boatload of zones and thick floor which is high mass.  The doors were defintely ice free this past winter.
  • hot_rod
    hot_rod Member Posts: 18,194
    I agree

    With the detail Mike shows. There is a foam strip with a H shaped plastic cap to protect it. After the pour, zip the top portion and fill that space with a polyurethane caulk. I like the detail where the door sets down 1" from the slab. That keeps water from driving under the seal. If a tube is within 12" of the door it will not freeze closed
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream