I was wondering about the popularity of this combination.  We are doing Amdeck over crawlspace, and I was wondering if many people are doing the same thing.  We chose it because of the insulation factor versus hambro.  We wanted concrete for the radiant heat.  We wanted to go suspended because of the crawl space accessibility and limited contact with the ground.  Also, when we were getting quotes for slab on grade everyone wanted to do a matslab, and so cost wise, people weren't quoting big differences between the two options.  With the matslab, I was either heating 12-16 inches of concrete or I needed an additional step of pouring the slab, adding insulation, and then adding gypcrete for the radiant, and by then the cost was very similar.

We look like we will pour next week.  They have finished all of the rebar for the Amdeck.  I have supposedly 4,000 stirrups for the floor. They are working on the radiant layout.  We had a few addendums from the plan, so they want to make sure that they have the tubes in the correct places.  A slight wall movement and slightly different kitchen cabinet layout.

We are putting radiant under the raised vanities and underneath the cast iron tub and freestanding resin tub.  Do you think that will make any difference to the tub temperature or the bathroom temperature by adding one more loop.  The contractor doesn't think it will make any difference, but it was easy to do, so I asked him to add the extra loops.  If it doesn't help, no big deal, but if it does, then we will be glad we added it.

Just wanting to see what other people are doing, and how they came to their decision.

Posted By eugenep on 29 Nov 2013 01:55 PM
We are putting radiant under the raised vanities and underneath the cast iron tub and freestanding resin tub.  Do you think that will make any difference to the tub temperature or the bathroom temperature by adding one more loop.  The contractor doesn't think it will make any difference, but it was easy to do, so I asked him to add the extra loops.  If it doesn't help, no big deal, but if it does, then we will be glad we added it.

Boy, I sure hope you had a qualified HVAC contractor design your radiant layout. He's the one to guide you on what the impact of the additional loop will be. It's too late now I guess, but why couldn't you have put the radiant loops into a slab, and why would the concrete have been 12 - 16" thick?

Posted By dmaceld on 29 Nov 2013 03:26 PM

Posted By eugenep on 29 Nov 2013 01:55 PM
We are putting radiant under the raised vanities and underneath the cast iron tub and freestanding resin tub.  Do you think that will make any difference to the tub temperature or the bathroom temperature by adding one more loop.  The contractor doesn't think it will make any difference, but it was easy to do, so I asked him to add the extra loops.  If it doesn't help, no big deal, but if it does, then we will be glad we added it.

Boy, I sure hope you had a qualified HVAC contractor design your radiant layout. He's the one to guide you on what the impact of the additional loop will be. It's too late now I guess, but why couldn't you have put the radiant loops into a slab, and why would the concrete have been 12 - 16" thick?

The loops will be in the slab.  They actually haven't laid out any of the PEX tubing yet.  Currently, they blocked out sections like under cabinets, under the tubs, walls, etc.  I only asked them to put them under the vanities and under the tubs because I didn't see the harm in doing that, and I am hoping it adds some benefit.  So far, they have just spray painted the foam to identify all of the walls and cabinets and other important structures.  I presume they will have the PEX done sometime next week.

The contractor I believe is a qualified contractor who has designed many radiant systems, but I do not have his qualifications.  He is being hired by the GC.  When I say a loop, I just mean one extra pex line, so it would add maybe 6-8 ft to that particular loop length.  The most would be 3 times that, so maybe 20-25 ft extra.  They are designing the full loops now.  There are 6 zones, and I just asked him to add a few extra feet to each zone, so I don't think it would impact much in the total design.  I think all of the zones are very equal in length, and the designer didn't want to have any small zones, i.e. just a bathroom zone.

The matslab was a structural thing.  It is very popular here in California.  Instead of using a perimeter foundation, and then having a standard depth slab on the ground, they like to use a continuous slab which somehow gets spec'ed around 12-16".   The structural engineer and soils engineer don't care about the cost to the user.  They are just covering their ass.  I think it is way overdesigned.  I look at the size of my footings, and it has to hold up quite a bit of concrete floor, and the total footing size is not equivalent to a 12" matslab, so I think they just way over design it.

Posted By eugenep on 29 Nov 2013 09:32 PM
The matslab was a structural thing.  It is very popular here in California.  Instead of using a perimeter foundation, and then having a standard depth slab on the ground, they like to use a continuous slab which somehow gets spec'ed around 12-16".   The structural engineer and soils engineer don't care about the cost to the user.  They are just covering their ass.  I think it is way overdesigned.  I look at the size of my footings, and it has to hold up quite a bit of concrete floor, and the total footing size is not equivalent to a 12" matslab, so I think they just way over design it.

Is that maybe for earthquake resistance? If it is post-tensioned then I can see how it might stay together and float during an earthquake thus preventing all kinds of stresses in the walls during a quake. I can picture it now, a house bobbing on top of the ground like a houseboat on water!

Posted By dmaceld on 29 Nov 2013 09:42 PM

Posted By eugenep on 29 Nov 2013 09:32 PM
The matslab was a structural thing.  It is very popular here in California.  Instead of using a perimeter foundation, and then having a standard depth slab on the ground, they like to use a continuous slab which somehow gets spec'ed around 12-16".   The structural engineer and soils engineer don't care about the cost to the user.  They are just covering their ass.  I think it is way overdesigned.  I look at the size of my footings, and it has to hold up quite a bit of concrete floor, and the total footing size is not equivalent to a 12" matslab, so I think they just way over design it.

Is that maybe for earthquake resistance? If it is post-tensioned then I can see how it might stay together and float during an earthquake thus preventing all kinds of stresses in the walls during a quake. I can picture it now, a house bobbing on top of the ground like a houseboat on water!

i don't think they would do a post tension with the matslab, but I could be mistaken.  i know that my GC used two layers of rebar on the last house with a matslab.  i think that would've held together with all of the rebar.

12" - 16" overall depth for an Amdeck or InsulDeck system is pretty common. Initial engineering specs on my InsulDeck 2nd floor showed 10" I-Beam + 4" slab + 2" bottom foam or 16" overall depth.

There is always a 20-30% margin of error/safety factor built into these systems but better that than the floor collapsing.

Posted By Lbear on 30 Nov 2013 01:06 AM
12" - 16" overall depth for an Amdeck or InsulDeck system is pretty common. Initial engineering specs on my InsulDeck 2nd floor showed 10" I-Beam + 4" slab + 2" bottom foam or 16" overall depth.

There is always a 20-30% margin of error/safety factor built into these systems but better that than the floor collapsing.

when I was mentioning 12-16 inches, it was just the slab on grade, not the amdeck assembly.