[Greenbuilding] Anyone know about the Legalett Slab System

Sun Jul 16 22:32:45 CDT 2017

It can be – but heat is heat  - it transfers to materials (hopefully not the ground) and those details are generally just worked out in the design of the layers, resistance, flow etc. What is interesting is the less resistance the lower the water temperature has to be which makes thing more responsive – quickly heating and at less temperature (depending on insulation).

It is hard to deal with slope on sites (which is why they get dug up, blasted to hell and basements and crawlspaces get made). A crawlspace is not bad it is just an odd cold or heated space creating good habitat for neighbours.  If you have a good engineer remind them that a footing is a footing – has to resist frost upheaval (insulation), and that you like to save the planet from unnecessary concrete consumption.

Filling up 24” with rubble/rock is not bad. Rocks will always be rocks. The alternative for a crawlspace is putting in plastic and some concrete on the ground to seal it and then having to insulate and heat it and create access, etc. It is handy for wiring and plumbing if things are not all thought out before. 

Good luck

John

From: Lynelle Hamilton [mailto:lynelle at lahamilton.com] 
Sent: Sunday, July 16, 2017 8:21 PM
To: John Salmen; Green Building
Subject: Re: [Greenbuilding] Anyone know about the Legalett Slab System

Wow, thank you for the detail!

I will have to raise the house up 24-30" in order to be on grade with the septic at the south side. The other 3 sides will have some variant of a retaining wall or slope.  I have concerns about the Legalitt from that perspective as well. That and the level of insulation--I've traditionally done R34 under the slab. They do have a water system option, but I've not yet found the pipe diameter specs on the website for it.

I've always thought concrete to be a better transfer medium for radiant heat. Do you notice a difference with your floor system?

Lynelle

On 2017-07-16 10:58 PM, John Salmen wrote:

Interesting. If a slab is to be used I am a fan of frost protected foundations or integrated footing in a cold climate. A lot less ground invasive and a lot less concrete. Not so effective here on the west coast as we don’t need much depth.

Now ‘if a slab is to be used’ in a consistently cold place heating the slab makes sense if there is sufficient insulation below. The use of air has  a very ancient history – as does water. Air though only contains a tiny fraction of the energy storage potential of water. They will both transfer heat but what it means practically is that air will transfer heat quickly and water will transfer it more slowly. From here on it it gets more complicated looking at pumps and fans to figure out who is working more efficiently but strong suspicion would be that water flow would be drawing less energy (heated to a lower temperature, slow pumping velocity)

What is generally more important to me environmentally is both minimizing materials and being a bit qualitative about what the material is for the job it needs to do. We currently waste a lot of materials on buildings. What seems like a good idea is often bad design.

Look at the pictures on the lego slab site. A structural slab can be as thin as 3” and work well if reinforced properly. The buildup they have with what looks like 2-3” pvc pipe (or in another picture galvanized duct would probably require 6-8” of concrete. That is a lot of energy intensive material to no structural effect (simply contains pipe). Someone could try to make an argument about ‘mass’ but typically a well insulated drywalled house with a few tile floors has more than enough ‘mass’. 

Also a radiant water slab is typically ½” polyethylene pipe classed as either a type 1 or 2 plastic – a bit better on the scale than PVC which is a type 3 and has long been recognized as not the greatest – in comparison.

The most important element is insulation and they are using plastifab brand type 1 expanded polystyrene. About 98.8 percent air and 1.1 percent of some vinyl monomer (PVC) – expanded with pentane. I don’t have issues with that so much as it is effective for the job it is doing and can go having some life as it is a solid isolatable and recyclable material (for some uses). Its wholesale cost is generally abound 16 cents a board foot and retails for about 3 times that. There are better foams and monomers out there but guess what PVC is cheap – so industry uses it. What can we do but be efficient with what industry gives us thankful people.

I italicized ‘if you use a slab’ as I’ve eliminated concrete slabs in projects as only a footing is required for load bearing elements and have used the foam as the floor system with ply sheathing laminated over the foam supporting interior walls and finished floors. Radiant heating tubes are imbedded in the foam. An FPS footing can be done without an integrated slab. Check with your engineer. 

Thanks for the opportunity to comment on that.

Best
John

From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of Lynelle Hamilton
Sent: Sunday, July 16, 2017 6:23 PM
To: Green Building
Subject: [Greenbuilding] Anyone know about the Legalett Slab System

Has anyone had any experience with this?

Many thanks!

Lynelle

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