Replies

1. 
   Guest_ | Jul 09, 1999 06:47am | #1

   *
   Good Evening Brian,

   I'm assuming that you want to isolate the slab as much as possible from the cold exterior.

   I'm also assuming that you are installing rebar from the inside of the wall assembly, bent in a 90 and extending into your structural slab's rebar.

   Therefore the only place that you can make any kind of a thermal break would be where the slab edge is exposed to the exterior. Here you can simply set the edge of the slab back an inch and install styrofoam and then cover with whatever you had planned for the outside.

   Having said all this, I also assumed that you have consulted an engineer for this project of yours.

   Also, I question the need for radiant heat in the slab over a heated workshop. The garage slab should maintain a reasonable temperature with the heat loss from below. With garage doors openning all the time, radiant heat, in cold areas, wouldn't be that efficient to justify the cost.

   Gabe

1. 
   Guest_ | Jul 09, 1999 03:40pm | #2

   *Brian

   I would be interested in the details of this "suspended concrete floor."

   Joseph FuscoView Image

2. 
   Brian_Griffin | Jul 11, 1999 06:40am | #3

   *
   Gabe,
   Thanks for the information. The use of styrofoam was my plan.
   This project has been going smoothly so far. I have received all the proper permits, and had an engineer put his seal on the design. My plan is to finish the top concrete floor first, then do the basement. Next year I will continue with a frame structure on top.

   I don't know if radiant heat is the way to go here, but since I am doing most of the work myself, I thought I would try it.

   Thanks again for the advice.
   Brian Griffin

1. 
   Brian_Griffin | Jul 11, 1999 06:48am | #4

   *Hi Joe,The space underneath will serve mainly as storage and a workshop. The above floor will contain two car spots and a set of stairs to a loft (for storage). The building will set into a hill. Having access from the bottom front and right (upper) side. I will continue with a frame structure next year.Thanks Brian Griffin

3. 
   Guest_ | Jul 11, 1999 09:13pm | #5

   *
   Brian,

   I will offer you my perspective as an RFH designer.

   As Gabe suggested, using 1" insulation on the outside edge of your suspended slab an excellent solution to reducing edge losses. Edge losses typically makeup approximately 1/3 of the downward loss component. In your case (depending on your outdoor design temperature) the proportion is probably much higher.

   The RFH design for the lower level is fairly cut and dried. Do the heat loss and design with the amount and spacing of tubing appropriate to overcome the loss from the exterior exposed components PLUS the infiltration. Infiltration in a workshop area can vary drastically depending upon the method of mechanical air exchange employed. For example, if you are exhausting fumes from a woodworking finishing operation or collecting/disposing sawdust from machinery (outside the envelope) your infiltration factor component of the total load will be the largest single BTUH component in your heating load. Depending upon the frequency you run such equipment must be considered also. The higher the frequency of use, the more critical the effects. This frequency along with other factors may determine whether or not underslab insulation should be employed. In many instances the thermal sink below the slab can be used to compensate for close to 100% of the momentary infiltration losses. Such is the case when designing for the typical residential garage also. Keep in mind that radiant heats primary function is to warm the OBJECTS in the space, not the air.

   Addressing your suspended slab garage space:

   The major heat loss component in your garage space is not the infiltration. The load is instead heavily weighted in the edge losses and also the thermal load from moving 2000# of cold steel into the space(cars/trucks). Assuming you have reasonable insulation in the side walls and the garage doors, these components are minor (but constant losses). The underslab loss is almost nonexistant because the area below will be heated. If you don't want the suspended concrete above to contribute to the space below, insulate the underside of the slab with something as minimal as R5. Radiant ceilings are much more efficient in transferring radiant heat to a space than floors due to the fact that radiant heat is omnidirectional. Radiant heat does not rise. Rather it radiates to a cooler object. Much in the way the sun warms the earth. When the sun was given the responsibility to warm the earth, Dave Lennox and his group of convection/scorched air engineers never called back with a bid on the project. In essence, depending upon the particular circumstances of your structure the suspended slab *could* cover the load for both the garage and the workshop below. These factors all play into a good design strategy.

   Considering the slab edge loss (exposed thickness of the slab):

   I would tend to hold the tubing back at least 18" from the perimeter walls. I would also concentrate the tubing directly under the cars. I say this for a couple of reasons: The cold car/truck becomes the major heat attraction (again radiant heat transfer always moves toward a colder object). A garage not being necessarily a living space, your comfort will not be as affected by your body proximity to the outside walls. The fact that the slab edge insulation is minimal would be good enough reason not to transfer heat laterally to this colder surface only to be sucked out of the structure. The opposite strategy would be employed if I was designing the same space within the home OR if the slab edge insulation amounted to a figure such as R10.

   In essence Brian, you will spend less on materials using this strategy and much less on operating costs while at the same time achieving your objectives ie: warming the objects within the envelope.

   There are many ways to approach RFH design. This just happens to appeal to me based upon the results I have encountered in actual operating projects.

   With all due respect I must disagree with the statement in Gabe's post:

   ""Also, I question the need for radiant heat in the slab over a heated workshop. The garage slab should maintain a reasonable temperature with
   the heat loss from below. With garage doors openning all the time, radiant heat, in cold areas, wouldn't be that efficient to justify the cost.""

   I do not believe the basement slab will contribute substantially to the suspended slab above, mainly because the suspended slab will probably be at least 8 feet above the radiant surface of the basement slab, most of this radiant energy will have already been absorbed by the objects closer to the floor. The temperature differential between the slab surface and the ambient air temperature will not be large enough to create a convective atmosphere ( as evidenced by the lack of "stacking"). The ceiling of your basement contains more mass than the floor of your basement could reasonably be expected to cover.

   I also doubt that your garage doors will be opened that often or for a duration of time necessary to deplete the stored energy within the slab to any appreciable extent. Granted, a garage door open for 2 or 3 minutes at a time will create a very uncomfortable air temperature but will not waste as much energy as would be consumed if one was only warming the air (forced air systems). The air temperature, mean radiant temperature, will recover very fast with the recovery being affected of course by the cold mass of the vehicle.

   Your project should be very reasonably priced. Depending upon the total load, you could possibly use a simple gas fired water heater with a minimum of ancillary piping and zone control expense.

   Other than the issues above, I am in agreement with the rest of Gabe's post.(grin)

   Jeff

1. 
   Guest_ | Jul 11, 1999 09:59pm | #6

   *Morning Jeff,I'm a little bias, I guess, on the subject of radiant heat in garages.You have to remember, most of my work is commercial and I do live in Ontario, Canada, which means a lot of salt and calcium is brought into garages in the winter time along with minus 45 C winds.When I was thinking about Brian's slab, I thought of the worst case scenerio. Being that it is a structural, suspended slab, over a work or living area, you tend to only put in structural components and minimize the items that add nothing to the strength. (plastic piping being one of them.)Your probably right with the heating aspects, my expertise is in the structural.Nice to read your comments.Gabe

1. 
   Guest_ | Jul 11, 1999 10:37pm | #7

   *Good Afternoon to you to Gabe.I was a little concerned about how you would react to my post. I commend your attitude."Bias"?? LOL....I may be a bit biased myself considering that the design and supply of these systems is my livelihood.What does salt and calcium have to do with RFH?Thanks,Jeff

1. 
   Guest_ | Jul 11, 1999 10:49pm | #8

   *Hi Jeff,Modern structures are a collaboration of different perspectives with a common focal point. A better building.Salt and calcium have nothing to do with RFH. But it has a lot to do with rebar. Concrete developes a lot of micro shrinkage and stress cracking. The salt enters these tiny cracks and corrodes the rebar. If you lay plastic piping over rebar, there is a tendency for shinkage cracks to appear at those locations.Gabe

1. 
   Guest_ | Jul 11, 1999 11:14pm | #9

   *I understand what you are saying here Gabe. Much the same shrinkage situation as is sometimes seen in thin lightweight pours. I have often explained this to contractors in the context/comparison to a "cold joint". It would appear as if the use of a stiffer mix (with super-plasticisers for workability), micro-fibers and proper curing practices might lessen the effects of curing shrinkage. I don't think I have ever seen a suspended slab that did not develop at least a few shrinkage cracks. Seems as if the proper elastomeric crack filler(caulk) and a good surface sealer would be called for to prevent the leaching of corrosive chlorides into the plane of the re-bar. Thanks for bringing this to my attention Gabe. I have only designed for a couple of structural/suspended garage floors. I have however designed a couple of suspended/structural bridge snowmelt projects on private residences. What you tell me was never brought to my attention in those instances. I will certainly address this factor in my future designs. Do you think coated rebar would be satisfactory to prevent this corrossion?Where else but the internet could one carry on such an important and interesting conversation on a Sunday afternoon??Jeff

2. 
   Guest_ | Jul 11, 1999 11:55pm | #10

   *Back to you Jeff,Epoxy coated rebar would excalate the residential cost outside most budgets. For parking garages and bridges/overpasses, its a requirement.There's no reason why, a compromise couldn't be reached by strategically locating the RFH along side the lower layer of rebar and filling it with water at the same temperature as the rest of the structure.Just a thought.Gabe

3. 
   Guest_ | Jul 12, 1999 01:02am | #11

   *That would not be a problem at all Gabe. I would normally spec the tubing to be installed before the re-bar anyhow. Laying down a layer of 6x6 flat sheet mesh, securing the tube to the mesh with nylon ties prior to the placement of the re-bar is much easier than trying to configure the tube layout to the layout of the re-bar grid. In the case of a suspended slab without J-Deck or where we actually need the tube in the middle portion of the slab, we will have a couple of hands pulling the mesh up and securing it to the re-bar as the pour progresses. Much easier in a pumping or conveying delivery than a chute concrete delivery. We always pressure the tubing to at least 100# pressure during the pour just in case. Each loop has a valve on both the supply and return (closed off) so that in the remote possibility a loop is cut during the pour it shows up immediately and can be unioned, repressured real fast. Hasn't happened in a few years but we still take the precaution. I have a couple of problems with filling the tube with plain water during the pour: 1) In the event some schmuck on the pour crew does slam a shovel thru the tube, it makes one hell of a mess for the finishers 2) In most cases it is usually months before the tubing is actually connected to the boiler loop. In the meantime winter has come and we would then have to either evacuate all the water from the tube and/or replace it with a glycol mix to prevent freezing. Not that we fear damage from freezing but rather it never fails, we are called in to connect the boiler in the dead of winter. Tough to get circulation started thru frozen tube. I am not a fan of glycol in most cases because it presents inherent maintenance problems and necessitates an upgrade in the type of backflow preventer required. Once glycol has been introduced into the system the commitment to the more expensive BFP is a necessity even though the glycol is removed and replaced with straight water. I do see a few benefits and sometimes requisites for introducing water into the tubing during the pour: 1) Water does not compress. Theoretically if you could evacuate all the gases out of the tubing and place the water under say 120# of pressure, the likelihood of accidentally smashing the tubing flat would be reduced. Kinks? I don't think this practice would of much benefit.2) When placing hot asphalt over/or in proximity to the tubing the standard practice of running water thru the tubing during this operation is a prerequisite to prevent the tubing from reaching the amorphic state(meltdown).BTW, unless you are using a non-barrier tubing(with cast iron components) and/or are in a situation where the fuel source or electrical power to the boiler/pumps could be interrupted for an extended period of time (more than 1-3 days), I believe that glycol has too many disadvantages to be considered in an RFH situation. The consensus changes when we are talking about straight low mass systems or exterior applications (snow, ice control, etc.). Hence, another benefit to keeping the tubing back from the exposed perimeter of a meagerly insulated slab edge. I have some associates in the extreme temperature regions of the Yukon and BC who religiously follow this strategy even with the use of glycol. They reason that if you get chilled while looking out the window.....move your ass away from it!! Got a tad off subject with my rambling. You'll have that sometimes considering the specific passion of the subject. [grin agin]

4. 
   Guest_ | Jul 12, 1999 02:02am | #12

   *Pretty cool Jeff,We use glycol in plastic lines for ground defrost under insulated blankets but I never would have considered anyone using it in residential applications.Most of our structural pours would have no mesh and a top and bottom layer of rebar running right angles to each other. In order to ensure that the rebar does not touch the bottom form and stays at the mid point of the slab, we suspend it on chairs made of concrete.But having said that, these slabs typically wouldn't have any heating systems either. I can certainly understand the problems with workers and plastic pipes not being compatible.Gabe

5. 
   Guest_ | Jul 12, 1999 03:26am | #13

   *Gabe stated: "Most of our structural pours would have no mesh and a top and bottom layer of rebar running right angles to each other. In order to ensure that the rebar does not touch the bottom form and stays at the mid point of the slab, we suspend it on chairs made of concrete. ""I don't want to mislead anyone. The only function of the 6x6 mesh is for the convenience of securing the mesh prior to the placement of the rebar and offers an easy target for pulling the tube/mesh assembly to the bottom run of re-bar. In my opinion, wire mesh does not contribute to the ultimate strength of the assembly.You speak of using "concrete stairs" to suspend the lower run of re-bar. I have also suggeseted these. Prefer rough concrete pavers, hand split for the mechanical bond to the surrounding pour. Beats the hell out of those wimpy metal quad-pods which seem to collapse under foot traffic which then places a bearing point on the tube and ultimately allows the reinforcement to end up out of the proper plane. (I'm paranoid!!!). Along with creating a possibility of the foot traffic on the re-bar smashing the tube, it also concerns me that the tube would be in such close contact with the barbs on the re-bar as to cause an abrasive action over time. Hey Frank Lloyd Wright had the right idea (wrong material), he used the steel heating pipes for a dual purpose. Slab heat and structural reinforcement. Many of these innovations are still performing. Many of them have also failed do to corrosion from the inside-out.I will email you an interesting series of links to jpg.s that I came across this afternoon concerning RFH and radiant ceilings 30+ years ago. You may have come across some of these copper/plaster/concrete projects in older homes or commercial buildings. Anyone else wanting a "touch of history" on the "New Hydronics" [grin] is welcome to request same by email. I will only send the "links" as most of the jpg's are not compressed to less than 50K. They are currently posted on several aol sites and may be deleted without notice. In case they get deleted, I have them on my hard drive and can email them individually if your mail server allows you to receive files in the 450K or so capacity.Jeff

6. 
   Guest_ | Jul 12, 1999 03:55am | #14

   *Thanks Jeff,Gabe

7. 
   Guest_ | Jul 12, 1999 04:11am | #15

   *You are most welcome Gabe.Do you mean to tell me that you have run out of objections to RFH in Brian's situation?or maybe I need to give you a "time out"?Meanwhile, back at the ranch.....I have had a bunch of fun conversing with you Gabe. You have given me some things to think about. The archives of BreakTime will forever embrace our banter this afternoon to the amusement or benefit of all who are hungry for the subject.Thanks, Jeffps: I was worn out too. I forgot about addressing/questioning the thawing of the sub-base before placing the slab. Works great!! Have seen it used in Minnesota. We have used it in Ohio for a winter shot-crete pool project.[Aaarrrgghhhhhh!]Another time, another day? I suppose.

8. 
   Guest_ | Jul 12, 1999 07:03am | #16

   *I have always wondered how many folks look in on Breaktime and never post. Try these links first. Please no more requests by email until at least Tuesday. My mailbox is full.http://members.aol.com/brewdog106/cover.jpghttp://members.aol.com/brewdog106/rfhpage1.jpghttp://members.aol.com/brewdog106/rfhpage2.jpghttp://members.aol.com/brewdog106/rfhpage3.jpghttp://members.aol.com/brewdog106/rfhpage4.jpghttp://members.aol.com/oneradiant/rfhpage5.jpghttp://members.aol.com/oneradiant/rfhpage6.jpghttp://members.aol.com/trinasmom/rfhpage7.jpghttp://members.aol.com/trinasmom/rfhpage8.jpghttp://members.aol.com/trinasmom/rfhpage9.jpghttp://members.aol.com/trinasmom/rfhpage10.jpghttp://members.aol.com/just luann/rfhpage11.jpghttp://members.aol.com/just luann/rfhpage12.jpghttp://members.aol.com/just luann/rfhpage13.jpghttp://members.aol.com/just luann/rfhpage14.jpgI want to credit Bill Nye and John F. for getting this publication to MEto post it on his aol home pages. Maybe you may recognize someone inthese early photographs?Jeff

9. 
   Guest_ | Jul 12, 1999 07:25am | #17

   *Hi Jeff,The links 11 to 14 have an error, the space between just and luann should be removed.I know what you mean with the visitors to breaktime. When I posted that notice that I had found some 3.5 gallon toilets, within 3 hours, all 70 were spoken for.The power of the internet.Gabe

10. 
    Guest_ | Jul 12, 1999 11:44am | #18

    *I know the space seems like a mistake(Netscape email thinks so too) but I swear it is legit. You must copy and paste, deliver it to your Browser window with kid gloves. AOL is a strange bird, eh?BTW, Do you realize Gabe the power that Sean now wields over your destiny? He could probably roll-over, turn states' evidence and convict you to 70 times 99 years for promoting and defecating[sp?] 2 gallons more per flush? I hear from the intestine[grapevine?] that these webmasters feed us cookies to track our whereabouts. Imagine that?? what a life? Tracking "flushers" through the wilds on the basis of moisture content. What would Daniel Boone think of our "tracking abilities" if he were alive in this day and age? I sure pray these young pokes we're whelping come up with more meat on the bones they've been tracking lately than I have. Otherwise, I'm gonna starve to death. This cyber-beef I been runnin' after don't smell to tasty.Jeff

4. 
   Brian_Griffin | Jul 12, 1999 11:51am | #19

   *
   I am building an unattached garage. The poured concrete floor will be suspended on a block foundation.My plan is to run tubing in the floor for heat. The room underneath will be used as a workshop. What is the best way ( or is there a way ) to insulate the concrete floor where it sits on the block foundation ?