Heated Slab Installation

Submitted by Ana White on Wed, 09/14/2011 - 20:55
Most days we are pretty thankful to be working up on top of the Momplex hill.
And we are usually pretty happy to just keep right on working into the evening.
And sometimes we even run back up to enjoy a beautiful sunset.
But beauty has it's price.
And after three days of wind, especially terrible hilltop and with no barrier, gusting upwards of 60MPH on the top of the Momplex hill, we were downright frightened as we drove to assess the damage.
Imagine holding a sheet of blueboard out the window as you drive the car down the interstate.  Now imagine holding 72 sheets down for three days.  
In the woods, foam pieces are scattered - but thankfully these are the scraps for the door bucks, not the insulation for the slab.
There's ARXX blocks that we have leftover, waiting to be stacked on the second story floor, undamaged, but deep in the woods.
And our wheelbarrow, is blown over.
But thankfully inside the Momplex, the foam is still there.  We had covered the windows and doors to keep drafts out, and also layed rebar and pex tubing for the radiant heat floor to keep the foam in place.

Pop Quiz!!!

Before we get to that process, I want to see if you all are just as clueless as me about how radiant heat floor goes in.  So a fun little pop quiz!

Question #1

What are these called?

Question #2

How much do you think this thing cost?

Question #3

How many feet of pipes do we need for the Momplex floor?
When we started talking about the slab and putting radiant heat in, I did not know the answer to any of these questions.  So you are probably three questions brighter than me  :)  and for those of you as clueless as me, read on . . .

Insulating the Slab

So back to foam.  Remember we layed foam blueboard down on the compacted gravel, with a layer of plastic paper in between to act as a vapor barrier. The foam does two things - keeps the slab warm and minimizes heat loss through the floor.  You can read about that step in this post.

Planning Zones

The first step in figuring out how to put the radiant heat floor in the slab is to find zones.  We decided that each garage needed to be on it's own zone.  So that means each bonus room/stair area is also on it's own zone.  And because the Momplex is a perfect square, with the garage taking up half of that square, we've got four equal zones to work with.  Man, building square definitely makes life easier!
But each zone is about 440 square feet, and with loops on 12" centers, plus extra for the runs and sides . . . we'd need about 450 feet of tubing per zone.  Length of loops needs to be less than 300 feet total, and all loops need to be the same.

Planning Loops

So we determined we would need to run two loops, at 250 feet maximum per loop, in each zone, as shown above.  

Pex Stapler

We could not afford to buy this stapler that does not even plug in for $1100 (to be fair, we were offered it for $600 if we bought the tubing there as well) so we rented it.  I tell you what, I'm in the wrong business.  I need to start selling these!

Special Staples

Coupled with these also ultra expensive staples, the tubing is stapled right to the foam blueboard.  Sounds too simple to be right, doesn't it? 

Pretty Simple

But that is exactly what you do.  You run your preplanned loops, knowing each sheet of blueboard is exactly four feet wide, you can easily gauge how big to make your loops and quickly staple down.
And we just kept going with the loops until the entire floor is covered in tubing. 
The loops all begin and end at the same spot . . . where the boiler is going to go of course!
It's funny to think, for this slab we put on a layer of fat (the foam) then the blood vessels for heating (the tubes), and now we just need the bones! The bones of course are more rebar.  
Rebar is layed in a grid over the tubing.  And while this is what was recommended for our slab, we felt like the rebar needed to be raised just a tiny bit to be centered inside our slab pour.
They really are called concrete dobbies.  
Perfect for holding the rebar up!
The rebar is tied everywhere to keep it in place for the next concrete pour.
And rebar is placed in the center footer for the load bearing wall.
And all these steps, these odd building materials put together in order, have created the main heat system for the Momplex.  
Time to call the concrete truck!


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