An item for the discussion of home insulation...

17 responses total.

As mentioned in the flooring item, I have to install some simple
flooring in the attic so that it can be used for long-term/seasonal
storage. If I'm going to be crawling around up there nailing down
boards, that would seem to be an appropriate time to improve the
insulation, which seems to be fibreglass over the garage and perhaps a
thin layer of cellulose over the house.

The problem is, the rafters over the house are only 5.5" tall.  Living
in Illinois, I'm supposed to aim for R60 insulation for the attic. 
Because I can't afford to have someone else install it, I'm looking at
something that comes in batts or rolls.  5" of insulation isn't likely
to give me more than R20.  I could raise the new floor, that would mean
adding even more weight to the rafters.

If the boards are horizontal they are ceiling and/or floor joists.  If they
form the structure of the slanted roof, rafters.  We have three sets of
rafters in our ceiling in order to put in 15 inches of insulation (still
probably not R60 - what part of Illinois is colder than Michigan?).  If there
is space in the attic you could add another set of 2x6" joists nailed parallel
or perpendicular to the existing ones.  If parallel, stagger them.  Nail the
ends to boards resting on the tops of the existing walls and no extra weight
goes on the current joists.

The existing boards are rafters. The living room is very roughly (I
paced it out) 12m long by 6m wide.  If I put beams on top of the
existing rafters (perpendicular to them), I can't depend on a supporting
wall.  I'm concerned about the extra weight of the beams and the
floorboards.

I'll consider bamboo when we have to replace the living room floor.

I went out to a hardware store today.  They had a huge isle
filled with fibreglass rolls and batts. They had some styro-
foam panels too.  Tucked away I found some bags of cellulose
loose-fill.  It's inexpensive, efficient and recycled.  The
main drawback seems to be that I'll need to install a
moisture barrier separately.

I meant we had three sets of ceiling joists.   Does your enormous living room
lack a ceiling and use the roof instead?  If so, you could add a ceiling with
2x10's and insulation between them.

You probably mean you have ceiling joists because it is unlikely you would
nail a floor to rafters.  The ends of the joists are resting on walls, and
you could add another set of joists if you nailed boards across the ends of
the existing joists.  Get a carpentry book from the library to see how.

You're right, they're joists ("ties", the diagram here calls them) and
not the rafters, which I see now are the sloped upper sides forming the
roof itself.  I may have to settle for ~= R20 for any floored section
and more insulation for other parts of the attic.

How high are your ceilings below?

I'm not sure, but I can touch them without standing on tip-toes.

If they are 8' and you can live with 7' 6" (assuming your building code
permits that) you could add insulation and vapor barrier below.

My attic has cellulose loose fill.  Except, my attic is mostly just roof
rafters.  Do I need to put a vapor barrier over the cellulose?

It would greatly increase the insulating value, since otherwise you have damp
insulation, which has fewer air spaces and insulates poorly.  Also it would
keep the under surface of the roof (sheathing) from getting wet from
condensation and rotting.  Vapor barrier should go up on a cold dry day (if
you have such things there) so that the absolute humidity is low.  We have
interior storm windows on two windows that were installed on rainy days and
it now condenses onto the outer pain, freezes, and then warms a bit and drips
onto the wood below, which is turning black.  
Instead of dealing with the rafters, can you add a real ceiling?  Then you
could have lots of insulation, and also less space to heat.

The vapor barrier should be on the *in side* of the insulation. Therefore 
you have to install the vapor barrier before installing loose attic 
insulation. Insulation between the rafters (usually paper-backed batting) 
should also have the vapor barrier side toward the attic.

We have loose attic fill (we added more when we moved in), but I don't 
think there is an additional vapor barrier except that of the ceiling 
board.

You can put the vapor barrier under the ceiling board, such as by using pints
with a high vapor barrier rating.  Latex probably won't do it.  Several coats
of oil paint would help some.

Perhaps batts for 2x6 (R19) in the attic floor.  Then you could put a
2x6 or 2x8 along as a rim where the roof gets too low to allow real use.
 Then you can pile the loose fill behind the rim and put down flooring
in the middle.  If you have eve and ridge vents be sure to leave a gap
between the pile and the roof sheeting so that air can move up to the
ridge vents.

And please do put the vapor barrier on the heated side as the
instructions say.  Otherwise you get higher absolute humidity warm air
migrating into the batt or pile, cooling off, and then dumping moisture
into the body of the insulation which will ruin it, and possibly create
a mold problem.  Sure would be a shame to condemn the house  because of
backwards insulation.

    Thanks for the tips arthurp.  The house has other issues
that could condemn it, but reducing the likelihood of mold
is a good thing in any case.

I hope things are progressing.  But plumbing/wiring/structure do have to
come first.

    We're off the well and on city water now.  That day
included the removal of our concrete driveway and someone
putting a backhoe through the gas line that feeds the house.
I may end up having to pay for a new driveway to replace the
one they tore up.

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