[Strawbale] PEX, Concrete Slab, Fear of Death (by contractor)

[Speireag Alden]

On 2008, Jan 02, at 00:59, Shody Ryon wrote:

> Does anyone install more than 4” of XPS rigid
> insulation under a concrete floor?

     Almost no one.  I think that Rob Tom did.

> If it has an R
> value of 5 that would be R 20. Wouldn't problem with
> that be that being in direct contact with the ground
> which is cooler than the desired air temp inside would
> put a constant load on the heating system?

     Well, there's going to be *something* on the other side of the  
insulation.  If it's cooler than the house, then there will be a load  
on the heating system.  The question is, what is the effective R- 
value of this insulation assembly versus that insulation assembly?

> Wood may be easier on the
> body for standing and walking.

     This is true, though I've often felt that this could be  
mitigated with carpets and throw rugs.  This is one of the things I  
like about our earthen floor, though; it feels easier on the feet to  
me, versus concrete or pavers.

> Leaks in a hydronic
> system in concrete may be hard to find and deal with.

     At this point, leaks in a hydronic system are almost unheard- 
of.  Keep your PEX joints out of the pour, and the PEX itself should  
last pretty much indefinitely within the slab.

> I was advised to use the 15 mil
> comercial grade plastic under concrete as the normal 6
> mil will degrade quickly if subjected to pH extremes
> such as concrete.

     I have never heard this before.  It could be true, but I've  
never heard it.  Can anyone else shed any light on this?

> I am currently deciding if I should install a wood
> below grade in my current project because of all these
> advantages over concrete.

     Make sure that you understand exactly how that wood needs to be  
detailed.  Wood below grade is not as forgiving as concrete below grade.

-Speireag.