Radiant Floor - Insulation Question

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Old 11-30-10, 08:40 AM
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Question Radiant Floor - Insulation Question

I've got a radiant floor in my home. We utilized the method where you secure aluminum plates to the subfloor and tap in the tubing. Link to photo:



Unfortunately we decided to go with floor trusses 2' on center and the floor is rather springy in areas. We have an area we would like to install tile and I'm not comfortable with the amount of deflection.

What I propose doing is applying spray foam insulation, in between the trusses and right over the plates/tubing and subflooring just in this area. I'm thinking that the added strength would significantly reduce the deflection, however I am concerned with the affect on heat transfer. I would think that the heat would still transfer from the piping to the aluminum and floor - or I am I perhaps chocking things down too much? Would appreciate opinions.
 
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Old 11-30-10, 11:12 AM
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Just an opinion as I'm not a pro in this field, but the foam would not be sufficient for added strength. Again, opinion.

As for the radiant heat, you would be isolating any air movement right under the floor, so all heat transfer would have to be through the wood in contact with the plates. In my experience, those cavities are usually very warm all across the bottom of the floor, allowing some heat to conduct through the entire floor surface.

Radiant heat is a challenge from the start, getting the floor warm enough to conduct up through wood, which is somewhat of an insulator, then up through all of the floor material used above it. When it is all added up, you are trying to force all of your heat up through something like an R-3 or 4.

IMO, I would look for a way to provide support from below that would allow access when needed.

Bud
 
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Old 11-30-10, 12:42 PM
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Originally Posted by Bud9051 View Post
Just an opinion as I'm not a pro in this field, but the foam would not be sufficient for added strength. Again, opinion.
You wouldn't think so, however they claim that it increases the strength of the applied surface by a factor of 2.

I have an insulated shop where I used steel roofing material as my ceiling mounted to strapped roof trusses. I had 3 inches of insulation sprayed to the back side of the steel and in-between the trusses and all 215 lbs of me can walk atop of that ceiling with no fear of busting through

As far as the heat goes, as it is the house heats nicely with the current tubing/plate configuration. I have 24" batts of insulation secured by friction fit wire rods between the trusses in a "cupped" fashion, such that there is an air gap between the insulation and the floor. It must work good because I only used 417 gallons of oil for an entire heating season.

I would think that with the heating components sandwiched between 3" of foam with an R-value of 21 vs. subflooring/tile with a combined R-value of maybe 2, the heat would transfer more readily to the materials above. Also, surface area of the aluminum heat plates are in contact with nearly 50% of every square foot subflooring.
 
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Old 11-30-10, 12:55 PM
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BS on increasing the strength. Have them spray 3 inches of foam on a 2' long piece of OSB like your floor. Put it on 2 bricks and stand on it...bet it deflects just the same.

Yes, you should have insulation to help with the heat..otherwise you are just helping heat the space below. Foam might make any repairs harder down the road though.
 
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Old 11-30-10, 01:44 PM
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Joey

The best way to solve a deflection issue between the joists such as what you have, is to add more plywood from above. I realize that you cannot do that, as you might compromise the tubing below. If your osb subfloor is at least 3/4" t&g, you could use Schluter Ditra XL over the current subfloor. That is provided that the I-joists themselves also meet deflection standards accross their length. Take a look at the Schluter website, you'll be looking for Ditra XL. It's a 1/4" thick uncoupling membrane that claims it can be used over 24" oc spacing with minimum 3/4" t&g subfloor.

What gunguy said about the spray foam, yep, it aint gonna make the floor any stiffer.
 
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Old 11-30-10, 02:37 PM
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I had glued and screwed a bunch of 3/4" x 12" plywood strips as "gussets" in a number of places where there were vertical members in the trusses to attach them. This actually seemed to make a big difference, however I think there is still some deflection - is there ever an acceptable amount? Anyhow, thanks - I'll take a look at that product. I'll only consider it if I can find a certified installer of that product and get a guarantee on my install if they are making that claim as I did use 3/4" T/G Advantech. These are not I-joists, they are engineered trusses that look like these:

 
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Old 11-30-10, 03:33 PM
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I didn't pay attention to your picture and was thinking I-joists. The latter doesn't allow for a lot of load in the wrong places, but a web truss might. Picture a piece of 2x4 glued into the space between the plates such that another support member run perpendicular to the trusses and attached to the top cord would provide support across the 24" span. With the top cord to attach to and glued into place, I think you could easily create some extra support to take care of the issue at hand.

Bud
 
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Old 11-30-10, 03:37 PM
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Why don't you just put plywood on both sides of the all trusses that are under your bathroom? That should stiffen it up quite a bit and for a lot less money than spray foam. Maybe you should ask your engineer why he your floor bounces so much.
 
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Old 11-30-10, 07:24 PM
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The issue here is the deflection of the subfloor between the trusses, not along the length of the trusses. Stiffening the trusses will not change that. Since you cannot add more plywood over the subfloor, you will need to use ditra xl or a similar membrane. The 3/4 t&g advantech meets Schluters requirements and you should be ok.
 
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