[Greenbuilding] Hydronic Radiant Underfloor Heating

[Clarke Olsen]

       I would underline that part about compacting the gravel. Making  
the base firm and level
       will assure that the slab is close to a consistent thickness,  
reducing it's need to crack.
       I have used 2 layers of 1" foam in the hope of conforming closer  
to the base (and to
       stagger the joints).
       Don't forget to cut (or embed) control joints in the concrete as  
soon as you can.
       More joints = less cracks. Sealing or covering the curing slab  
will make a harder surface.
       ClarkeOlsen
       Spencertown, NY

    On Oct 14, 2007, at 9:36 AM, John Straube wrote:
> Good advice Mr Green, but I would like to add a few details:
> The poly should always be directly under the concrete topping  
> otherwise water can and likely will be trapped between the foam and  
> the concrete.
> Foil faced insulation only works when facing a gap.Chris Green wrote:
>> Gary Viljoen wrote:
>>> Hi all,
>>> I am about to install an under floor hydronic system into the home I  
>>> am
>>> building, and face two options given to me by ‘experts’:
>>>
>>> 1.	Lay the concrete surface bed.  Place polystyrene insulation on  
>>> top.
>>> Lay the piping in the screed above this.
>>> 2.	Insulate below the surface bed with the piping in the concrete
>>> surface bed.
>>>
>>> Any recommendations based on experience?
>>>
>> Either way, but the first way just adds extra work and probably uses
>> more concrete.
>>
>> My experience recommends this way:
>>
>> 1: Level and compact the soil/ gravel as best you can. You want to get
>> it quite close to flat so there aren't any big voids underneath the
>> rigid insulation. Also, getting the bed flat as possible cuts down on
>> the amount of concrete you'll need.
>> 2: Place 5 1/2"/ 140mm strips of 25 mm rigid insulation along the  
>> inside
>> of the exterior wall footings or foundation to prevent heat flowing  
>> from
>> the slab to the foundation and out into the great beyond.
>> 3: lay down the poly and seal the joints and any big rips that might
>> show up in it. A few little ones are okay. The poly can run up the  
>> side
>> of the footings a ways. Also tape the poly to any plumbing pipes which
>> stick up above the surface. I also use the tape to seal any open  pipe
>> ends and prevent concrete from splashing into them (that can happen  
>> when
>> pumping the stuff with a pumper truck...)
>> 4: Place the rigid insulation. On one job we even taped the joints
>> between the insulation, possibly because we didn't put poly down under
>> it...or at least I don't recall doing that...
>> ---if you're using foil covered insulation, the foil faces upwards.
>> 5: place and tie the rebar as per the specifications. The rebar should
>> be between 1 to 1 1/2" or 25 to 40mm above the insulation. There's
>> little plastic risers that will set the rebar at the right height but
>> chunks of broken concrete patio tiles work just as well.
>> 6: lay out and tie the hydronics tubing to the rebar grid.
>> 7: do a walkabout to inspect and adjust everything before the cement
>> crew starts working. Repair any punctures the rebar has made in the  
>> poly...
>> 8: pour and screed the concrete.
>>
>> ***If I think some patches of the compacted soil aren't quite up to my
>> standards, I'll ask the rebar guys to throw an extra run or two in,
>> reducing the spacing
>> from 2' to 1'. I had to do that on one job this spring.
>>
>>
>> Cheers,
>>
>> Chris Green.
>>
>>
>>
>>
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>
> -- 
> Dr John Straube, P.Eng.
> Associate Professor
> Dept of Civil Engineering & School of Architecture
> University of Waterloo
> Waterloo, ON Canada
>
>
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