In floor heating vs. radiant vs. forced air in shop??

[Raspy]

Raspy - any comments on my question regarding the suitability of poly-isocyanate .... as opposed to extruded polystyrene ?

And thanks for the answers/clarifications on the layout/tiedowns.

rswyan,

Any insulation you put down that supports a structural or topping slab must have the integrity to support that slab for the life of the building. It must also not absorb moisture or it's value is gone.

These two requirements severly limit the types and make me question their usefullness. The isocyanerate I've seen will absorb water. The blue board poly insulation is probably the best, but you should be sure it will hold the floor up for the life of the building. Another way might be void forming where the insulation is not bearing the load or you are relying on open space as a non conducting barrier.

Remember, insulation does not stop heat flow, it only increases the resistance to the heat flow. Resistance can also be accomplished by the length of the path, so keeping the tubing away from the perimeter also reduces heat loss. Loss to the ground is only a problem if there is air or water flow under the floor. Conduction to the ground below is not heat loss, but an increase in floor mass. A foil radiant barrier only works if the foil is not in contact with either the slab or the ground. Radiant barrier means no contact, but heat transfer through radiation. Contact heat transfer is conduction. I've seem people use foil in direct contact with the concrete and proudly say they had an insulation barrier. Foil also comes between layers of bubble wrap. In this case we are relying on the integrity of bubbles to hold up the concrete forever and prevent contact with the foil.

Just do the best you can and look at the various methods. In the long run, blue board only around the perimeter, both horizontally and vertically, and holding the tubing back from the edges, away from the perimeter, is probably the best. I also like the insulation to be inside the footing as opposed to outside. In mild climates don't bother with it if you have thoughtful tube placement and concerns about insulation failure over time.

 

[DRL]

Raspy,
Interesting thoughts. I used R-10 pink foam vertically inside the foundation walls 3' deep. Then compacted gravel then sand, but the codes still required R-10 under the whole slab. I had wondered about the need but did not have the choice.

DRL

 

[Raspy]

DRL,

I'm using verticle insulation inside the foundation wall like you. In my case the foundation and the slab are about 4 feet above ground in one area. At the most I'll use insulation only around the perimeter under the slab for about two feet or so. The slab will sit on compacted 1 1/2 inch gravel up to that point and then span to the top of the stem wall over the insulation. If it fails it will not affect the integrity of the slab. No insulation in the middle of the area. I'm on dry decomposing granite under the gravel.


I see a lot of projects use perimeter insulation on the outside of the footing. This seems like it will get damaged and wet and will be of little benefit. It usually gets a sheet metal covering, but it also makes a pocket for water to collect and might be worse than not having it.