[Greenbuilding] Hydronic Radiant Underfloor Heating

[John Straube]

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. This has been a serious problem in many houses. My consulting firm has been involved in investigating problems involving almost 1000 homes because of poly under a sand layer or under foam trapping water. poly on top of the foam directly under the concrete always.

Foil faced insulation only works when facing a gap. It does not matter which way the foil faces as you wont get any benefit. I have done real life field testing of foil under radiant slabs. No radiant exchange benefit if there is not 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