[Cob] radiant floor tubes in clay floor: insulation?

[Shody Ryon]

--- On Thu, 2/5/09, Tys Sniffen <tys at ideamountain.com> wrote:

> From: Tys Sniffen <tys at ideamountain.com>
> Subject: RE: [Cob] radiant floor tubes in clay floor: insulation?
> To: qi4u at yahoo.com
> Date: Thursday, February 5, 2009, 1:57 PM
> I hear you on the 'more insulation would be more
> efficient', unless by
> insulating my floor away from my stem wall I'm cutting
> down on my total
> thermal mass I'll be heating up, thereby not storing as
> much when I'm
> putting heat in, thus losing more quickly when I'm not.

When I think of more insulation, I am thinking of including thermal mass. I think the best design of thermal mass is to have a lot, or even most of it, in it's own insulation envelope separate from the living space insulation envelope.
In a mild climate, this is less important and you mind as well use the thermal storage of the cob to it's advantage; insulate exterior to it and any and all other structures at the perimeter and create an insulation envelope, not just at the walls and roof, but under the floor, as you have indicated.
the straw under the floor has been debated on some other lists recently. There are some that think it is a bad idea to have straw below grade in a manor that allow it to get wet. This may seem obvious or easy to deal with but apparently it is difficult to do this well; in a way that preserves straw long term. Some insist that every time it has been documented it has failed, as I understood it. I did not really follow along with the posts that closely, but that is what I think some prolific posters were saying. So I think it is would be good to make sure, one way or the other.  


> I know I'm not going to put store-bought insulation
> under the entire floor;
> I will put a lot of straw in my sub-floor though. The only
> question is
> whether to put store-bought stuff maybe a foot in
> (horizontally) from the
> wall and whether to put some vertical or not.

I assume mixing the straw with the mud is a good strategy, especially obviously if it is a known subfloor technique. 
 
> Being the cheap, all-natural-wannabe that I am, I'd
> like to skip this step,
> but my wife is thinking differently. 

So there is a trade off, burning gas is not all that "natural" so you will apparently be using one or the other, one once and the other every time it gets cold, depending on the efficiency of the solar heating system/thermal storage.

> Our roof will be pretty strong: minimum R value for our
> area is 19, we'll
> have R28 insulation under a steel roof and a 2 inch air
> gap.  It'll be
> better insulation than our cob walls.
> Tys
code minimums are minimums based on not much. code minimums used to not address insulation at all. In the future they will be higher than they are now.
I wonder if are you ok being very hot? I think it gets very hot in some areas of northern california, if you are in a hot area R 28 seems like it might be low. Are you going to run an AC system? If so, you might use a heat pump for most of the heating. What if you could have insulation at a rate that eliminate the need for heating or cooling? Accept for the solar system for heating? I am not sure this is practical for a cob project.
If you wanted to have additional thermal storage for heating and cooling air in your house you might consider
http://thermalattic.com/
It doesn't show it yet but can be used to cool in hot weather.
Shody