Add radiant Heat to existing Slab w/Topping mix and XPS
I will be adding an addition and second floor to my house. The current house is slab on grade. I currenlty have a base board heating system and will be changing it to radiant when done. The house was built in 1977 and I have no idea if there is insulation under the slab. I live in south eastern michigan.
The old area of the house I plan to convert to radiant also. I will be replacing the walls/doors due to a floor plan layout change so knocking off a couple of inches really is not a problem.
I want to know if any one has any thoughts on my plan.
1. I plan to glue 1″ XPS to the floor taped at the seams. and put 2″ foam around the perimiter.
2. Than I will put my pex with a mesh reinforcement .
3. Pour 1.5″ Sand/Topping mix
4. Install ceramic tile
I cannot use Gypcrete due to wanting to use tile.
Would it help if I added 1″ holes on a 12″ x 12″ grid to act as riser through the foam? (this is what Gypcrete recomends)
Replies
If you can add sufficient insulation around the perimeter of the foundation this will reduce the need for under slab insulation. Both will reduce heat loss with the perimeter approach giving you a less complicated floor system.
It can work
I'm no authority in this but I'll offer a few thoughts for you to mull over.
Consider the need for control joints. Even with fibermesh, a large thin slab of concrete subjected to the Delta-t's of a RFH system can stress the concrete. You don't want significant tenting, fracturing, cracks, etc.
Where you think you might have large dead loads; refrigerators, a heavy built-in bookcase, etc, the 1" holes for risers might help support those large loads and minimize the foam compressing over time. If you think it might need more help, you could add in ripped down 2-by sleepers. PT wood if they'll be in contact with the slab.
Baseboard hydronic heat usually circulates water a lot hotter than you'd want in a RFH system. If you haven't already, consider adding a mixing valve to knock the temp down.
Consider tiling on a membrane over the slab instead of directly on the new slab. The membrane will isolate the tile from the slab and minimize chances that the heated slab will pass thermal movement on to the thinset and tile. Prevent popping tiles, etc.
If your building inspector is a stickler, watch your window elevations in terms of how far the bottom of the window is above the new finish floor. You're raising your floor a few inches, make sure that doesn't force you towards the requirement for tempered glass, etc.
Same with stairs. Equal riser heights, any handrail heights, etc.
Edited for spelling