[Ferro List] Thermal Breaks

[Walter Jeffries]

On Apr 30, 2008, at 10:14 PM, Peter Payne wrote:
> My foundations will all go down to bedrock (4-5 ft at most!) A concern
> is thermal break from the rock--as rock conducts pretty well, and  
> there
> is exposed rock at several places around the site, I think the rock  
> will
> get pretty cold in the winter.

Peter,

We cut keys into the ledge in a few places around the edges,  
particularly at the up hill corners. We then drilled holes into the  
rock ledge for rebar which we cemented in place. These became the  
attachment points to the mountain for our floating slab to keep it  
from sliding down hill or changing level. The ledge comes right to  
the surface. You can see a photo (#3) of one of the keys here:

http://sugarmtnfarm.com/blog/2006/11/first-window-frames.html

There is no significant thermal bleed, nothing noticeable even though  
I have lots of probe thermometers. The reason is likely that we get  
early deep snows. You're near us and also up on a mountain so  
probably get the same. Did your ground freeze this year? Ours did  
not. I lifted bales of hay up many times through the winter and the  
ground was soft every time. Snow is an amazingly good insulator. The  
ledge is buried below the snow all winter and well into the spring.

Wind and raw cold combined is the real issue. The first winter I left  
a corner exposed on the north east side where the wind hit it. We got  
a very nice thermal bleed in that spot. It was the wind and cold that  
did it - there was no protecting layer of snow. I simply put a piece  
of 2" foam over the spot loosely and then piled snow on it. For the  
rest of the winter it was fine. Read about that here:

http://sugarmtnfarm.com/blog/2007/04/cold-corner-thermal-bleed.html

Note the comment about the rebar _not_ acting as heat radiating fins.  
Quite surprising and contrary to my expectations.

For all of our footing concrete I used full strength, non-insulating  
concrete as I wanted it to be strong enough to hold a stone and  
concrete house for my lifetime (4 to 5 thousand years :) ).

Outside our concrete walls we insulated with 4" of pink foam board  
and then parged with fiber cement about 5/8" thick to protect the  
foam board. The foam and parge go all the way down to within an inch  
or so of the ground and then the concrete is below to protect the  
foam from mice, insects, etc.

We still have not insulated the roof but it did fine through the last  
two winters. Right now it just as a single sheet of foil-bubble- 
bubble-foil (FBBF) on it. A tin foil cap so to speak. I have  
temperature probes inside, halfway through the roof, on top of the  
concrete below the foil, above the foil below the snow (which was on  
the roof most of the time) and then an outdoor air temperature probe.  
I was impressed with how well just the thin 1.5" layer of concrete  
roof did and just how effective the FBBF is. I hope this fall to take  
the roof to the next stage where it will have both more insulation  
and more thermal mass.

On our old farm house, when I put in a new foundation I insulated at  
a downward angle for about 2' (width of a foam sheet) out from the  
foundation. Studies show that technique works to move any frost away  
from the foundation.

Like you we have water running along the bedrock in places. I simply  
put in many 4" diameter pipes through the gravel (6" to 18" to  
achieve level) pad under the slab insulation. The water flows away  
and the gravel stays dry keeping our floor dry and warm. Sometime I  
plan to play with building a _very_ _little_ pond, a kiddie pool  
really, further up the hill to trap and control that water. Fun stuff  
for a later date.

When you're doing your attachments to the ledge think of them as  
pillars. Create steel reinforced concrete beams between the pillars  
to support the slab and the house. (I like FC for what is good at and  
RC for what that is good at - each has its place as does stone,  
brick, block and wood.) The pillars amount to a very small surface  
area and bleed heat very little while still providing the structural  
support you need. I would not worry about thermally disconnecting  
between the pillars and the ledge - that is a place to focus on  
strength. I spent a huge amount of time thinking about this before  
doing it and came to the conclusion the heat loss was insignificant -  
experience of the last two winters has born out that conclusion.

Happy Birthday!
>

Cheers,

Walter Jeffries
Sugar Mountain Farm LLC
Orange, Vermont
Pastured Pigs & Sheep
http://SugarMtnFarm.com/blog
http://HollyGraphicArt.com
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