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Heated Slab Installation

September 14, 2011 |

Missed a Momplex Post?

We are DIYing our moms a Duplex in Alaska! Check out our progress so far as we owner build a home, step by step. Read the Momplex blog here.

posted by Ana White

Momplex Stats

Money Spent So Far: 
$36,000 + Cost of Property
Time Spent So Far: 
600 Hours on Site + Tons of Planning and Prep work
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!

Heating Idea

Ana,

Are you planning to use your boiler for multiple heating uses or just the radiant floor?

I'd strongly suggest using it for multiple things as you get some economy of scale when you add your heating equipment loads together. You just have to loop them in priority according to temperature: heating water comes off first (~160F), water heater second (~140F), radiant floor last (~120F). Couple them to an uber-efficient condensing boiler and you've got a really efficient heating system that can be smaller in total capacity than the combo of all three elements individually. Put both sides of the Momplex on the same boiler, and you get even more economy!

Just a thought...

posted by Rhett Graves, P.E. (not verified) | on Thu, 2011-09-15 06:38
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Ana White's picture

Hi Rhett, thanks for the

Hi Rhett, thanks for the great suggestions! We definitely plan to do both sides on the same boiler. We will definitely be looking into your priority water heating suggestion! Thanks so much, Ana

posted by Ana White | on Thu, 2011-09-15 12:11

Wow!

Every time I read a new post about the Momplex I am so excited for you and inspired in my own life. I am so glad you are posting all of these steps because I am sure that at one point or another these things will come in very handy for me! Thank you! Sending prayers and good vibes from NC...

posted by Guest (not verified) | on Thu, 2011-09-15 07:45

Momplex

You know when the Momplex is completed, I am going to go into withdrawls! I watch every day for a post to read about what you are doing next. I am so enjoying watching this building process.
From North Louisiana where it was 102 degrees yesterday.

posted by Mary Falkner (not verified) | on Thu, 2011-09-15 08:19
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I'm a little confused

So you're heating the garage floor? I'm from the Southwest, so this is a totally foreign concept to me, we heat our bathroom floors for a luxury and that's about it. lol
So will this heat the whole home or just help stabilize a desired temperature for your climate?

posted by Veronica Gentry | on Thu, 2011-09-15 10:53
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Ana White's picture

Hi Veronica, up here in

Hi Veronica, up here in Alaska, the temperatures will drop below 50 degrees below zero. Sometimes we will see weeks of 20 below weather ... not looking forward to that!

Anyway, the heat tubes in the floor will be the main heat system for the lower level. The garages will get air handlers in addition to speed up recover for when the doors are opened. Upstairs, we may do more heat tubes in the floor or radiators.

But the cool thing is IF we are able to get the Momplex closed in by winter, we will be able to put a boiler in and turn on the heat as is to keep the building warm while we work!

posted by Ana White | on Thu, 2011-09-15 12:15
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stcarroll's picture

Here's hoping!

That would be awesome to have heat and be able to work through the winter to get it finished up! Good Luck, I hope you're able to get it done! We are having so much fun following your progress.

Cheers!

posted by stcarroll | on Fri, 2011-09-16 12:40
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dakotatransplant's picture

Pex stapler

Man, I cannot BELIEVE how expensive that stapler is up there! We have Menards here (primarily in the Midwest, I think) and the stapler for their staples ran $250. We just borrowed one from our contractor cousin though. And staples were $26 or something for about 200 or so. You will have to start ordering online and Menards and reselling cheaper! haha

posted by dakotatransplant | on Thu, 2011-09-15 11:21

stapler

We had never heard of the stapler when we did our floor last year. That would have saved some backs! We used zip ties to secure the pex to the rebar.

posted by June (not verified) | on Thu, 2011-09-15 17:11
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Ana White's picture

Bless you and your hard work!

Bless you and your hard work! The stapler certainly saved tons, and thank goodness we could rent it, otherwise we'd be thinking creatively like you too! Thanks for sharing commenting and reading! Ana

posted by Ana White | on Thu, 2011-09-15 18:46

I really enjoy watching this

I really enjoy watching this project come along. I'm looking at similar construction techniques for my place!

One thing to note, though, PEX shouldn't be left out in the sun. 3 days won't hurt it too badly, but the max time in the sun should be no more than 30 days. Especially considering where it's going.

Keep up the great work!

posted by Derek M (not verified) | on Thu, 2011-09-15 11:43
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Ana White's picture

Thanks for the tip! We are

Thanks for the tip! We are pouring the slab now, so should be fine on the 30 days. Good to know!

posted by Ana White | on Thu, 2011-09-15 12:25

Foam board?

I'm just curious, is that a popular way to do floors up there in your neck of the woods? I've never heard of doing this. I think here we would have poured a layer of concrete first. This is so cool to watch in progress. We built our house ourselves as well. We did have some help because I was pregnant and things needed to move quickly. 2 days before giving birth, we moved in. What a rush! Keep up the good work, I can't wait to see what else you come up with. :)

posted by HomeSpun-Threads (not verified) | on Thu, 2011-09-15 12:08
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Ana White's picture

Up here in Alaska, you must

Up here in Alaska, you must insulate slabs or all your heat just goes out the ground! I'm sure the codes and recommendations change from climate to climate, but this is how it's done in Alaska!

Congrats on building your own home and the new baby! I hear ya on building while preggers - that's what happened to us with Grace too!

Thanks for reading and commenting!

posted by Ana White | on Thu, 2011-09-15 12:22

I'll be doing the same thing this weekend!

I've been following your progress closely as my husband and I are finished a house up in Breckenridge, CO. We'll be laying Pex in the basement this weekend. This was really helpful to see - thanks!

posted by Kate (not verified) | on Thu, 2011-09-15 12:11
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Ana White's picture

Hi Kate, best luck with the

Hi Kate, best luck with the heated floor installation! I lived in Breck a winter myself, beautiful place!

posted by Ana White | on Thu, 2011-09-15 12:17

Love the pex pics

We retrofitted radiant heat in our house reno (under the joist installation) and I'm in love with it. If we ever move or sell our house, being able to do radiant in a new house is a must!

posted by Pittsburgh momma of 3 (not verified) | on Thu, 2011-09-15 14:16

Home Heating

Ha isn't home construction wonderful Ana always learning new cost & things everyday. I know the feeling I'm still remodeling an older country home myself in MO and have seen just about everything. All those lovely speciality tools and fasteners that you will probably never use again unless you were in the business. I hired some people to help me on certain projects as they had the tools. I installed my floor radiant heat (electrical) myself and love it but it does have a few drawbacks. Last year one of my heating element failed not sure why nor the manufacturer but I sure wish these companies would do a little extra engineering and provide customers better options like a dual backup system. Why not just run (2 tubes or 2 heating coils together or next to each other) can't cost that much more? So if something should go wrong (and you know it probably will) you could easily just hook up to the other side without having to cry while tearing up your nice lovely wood or custom tile floors using a heavy duty jack hammer. I was admiring all those zones what a nightmare. It sure would help resolve the fears many have installing floor radiant heat. They should also take advantage of running off alternative energy sources like solar, wind, geothermal whatever is available in your area? Having options is better than just running your boiler, gas or electric all the time. Especially when you can't rely on just one source. Best to you guys!

posted by Tom M (not verified) | on Thu, 2011-09-15 14:30

Zones

Tom, I am certainly NOT an expert but we did have assistance from several friends (as well as a professional plan our zones) laying our pex radiant floor heat. If I remember correctly, one reason for the zones is that you can specifically heat one area (keep the bedroom cooler than the bathroom, for instance.) Also, if the zone or loop is too long, efficiency decreases .. the further away the water gets from the heating element, the cooler it gets, obviously, since it is heating the floor/room. We also pressure tested the hose multiple times (for leaks) prior to running the concrete.

We live in Kansas and have several friends that have had this system in their agriculture buildings (one for 16 years, before pex) and if installed properly, it's never needed replacement. If something goes wrong, it is usually an "above the concrete" problem OR someone has carelessly ran a nail or something through the concrete and into the pex. I took a TON of pictures and measurements so we know right where the tubing runs. And all new construction is glued to the floor, not nailed. :)

We can't wait until geo-thermal or wind energy become available at our price range. Currently, ours runs an antifreeze solution through a closed loop system heated by a gas water heater. We did not want the problem of "hard water" or anything else causing an issue in the future.

I love our heated floor ... and obviously love talking about it!

posted by June (not verified) | on Fri, 2011-09-16 17:17

Heat Exchanger for air exchange

Ana - With the long cold months, have you looked into running a heat exchanger ventilation system like they use in Scandinavia.

It lets you bring in outside air for freshness without losing much heat.

posted by Anonymous Coward (not verified) | on Fri, 2011-09-16 18:46

Radiant Floor Heat is Wonderful!!

We decided on radiant floor heat when we built our house a couple of years ago. I was very resistant when my husband first mentioned it, but I am now IN LOVE with the warm floors! I can't wait for winter! Radiant heat is so comfortable and quiet. We heat the water for the floors with an outside woodstove and pump system that also heats our water so that the water heater never has to kick on. Very economical if you are willing and able to cut firewood! The Moms are going to love their new home. What a wonderful gift you are giving them!

posted by Liz L (not verified) | on Mon, 2011-09-19 12:52

Love it

Ana, I am enjoying each of these posts so much. It's amazing to see a family build a house from scratch. I love reading about each decision and step along the way. I check every day for an update. Thanks for sharing.

posted by AmandaB (not verified) | on Tue, 2011-09-20 09:12

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