[Greenbuilding] Block Wall Insulation

[Speireag Alden]

Sgrìobh Keith Winston:

>I thought Speireg's approach was pretty clever (though maybe I'm
>mangling it, and I hope he doesn't mind me sharing)

     I don't mind.  I don't own it, though we did come up with the 
water bottle part all by ourselves.

>insulate the outside to bring your thermal mass inside,

     Frankly, this is the key part.  When you insulate on the outside, 
you avoid all of the condensation-and-mold-behind-the-insulation 
problems.  The concrete wall itself is your vapor and air barrier, no 
detailing necessary after one wet-applied layer of surface-bond 
cement (or something weaker, if you mortared the wall as you laid 
it).  You don't have to worry about interior walls or piping.  Put a 
layer of poly plastic down the outside of the insulation and make 
sure you drain to daylight at the bottom, and you don't have to be 
paranoid about sealing pipe penetrations, because there should never 
be any water pressure against the wall.

     So you isolate the flammable insulation underground, where fire 
can't get at it, and the insulation is continuous, and you use the 
cement as your vapor and air barrier, and you have the thermal mass 
on the inside.

     I can't think of a single reason to put insulation on the inside, 
except for retrofit.

     Even then, I can make a strong argument for trenching around the 
house.  Years ago, some friends of mine bought a log house with an 
uninsulated basement (originally built in 1975 as a summer vacation 
home).  This being New Hampshire, it came as no surprise that they 
were unhappy with how cold the basement got in the winter, and how 
much wood they burned.  They wanted to insulate, and I begged them to 
trench around the outside insulate on the outside.  They did, and are 
very happy with the results.

>build on a rubble trench
>foundation, and fill the cavities full of 2 liter water-filled soda
>bottles. Big thermal mass, leaks drain harmlessly, continuous foam
>exterior insulation bridges band joists and other troublesome areas.
>Water control strategies become crucial.

     I think water control strategies are always crucial.  Every 
foundation should always have a footer drain to daylight, embedded in 
gravel, with landscape fabric on top to prevent sedimentation.  If 
you can't do that, then the plan needs alteration, because you're 
probably building in a flood zone.

     But I'm just a knowledgeable amateur, not a pro.

-Speireag.

-- 
Anger, if not restrained, is frequently more hurtful to us than the 
injury that provokes it.
--Lucius Annaeus Seneca, philosopher (BCE 3-65 CE)