[Greenbuilding] Anyone know about the Legalett Slab System

[John Salmen]

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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