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Re: Covering fiberglass insulation in attic?

To: "Mike Lee - Team Banana Racing" <>,
Subject: Re: Covering fiberglass insulation in attic?
From: "Phil Ethier" <>
Date: Tue, 8 Feb 2000 22:17:46 -0600

-----Original Message-----
From: Mike Lee - Team Banana Racing <>
To: Shop Talk <>
Date: Tuesday, February 08, 2000 6:53 PM
Subject: Re: Covering fiberglass insulation in attic?

>Sorry for disappearing after sending the mail; d*mn work gets in the way
>About the insulation; yes, the fiberglass is on the angled underside of the
roof (the
>rafters?), and not the flat top of the sheetrock (joists?) which separate
the attic
>from the garage below.

I know you don't want to hear this, but I'd rip it all out and insulate the
ceiling instead.  I'm serious.  Some bozo had put insulation against the
roof on my house.  I went up in the attic and tore out some to check.  The
sheathing was wet from condensation.  I tore it all out and threw it out the
window into the back yard.  It was all nasty and moldy.  I bagged it all for
the trash-man.  Now my sheathing has dried nicely.

If you need to insulate a roof with fiberglass, you need to put in the
plastic separators which allow cold air to circulate between the insulation
and the roof sheathing.  This means that one end must be open to outside air
in the soffit and the other end open to outside air via ridge vents or gable
vents in a mini-attic.  Personally, I don't see it as worth it.

Here is what I would do (what I did to my garage shop, essentially):

Rip out all the roof insulation.  If it looks dry and clean, you can use it
again.  Otherwise, out it goes.

Make sure you have vents to outside air in the attic area.  Big louvered
gable vents are nice because you don't have to mess with your roof shingles.
Vents in your soffits are a good idea.  Put cheap plastic channels to
connect the soffit with the attic so the insulation does not close off the
soffits.  In my case, I have the attic open to the 20x20 parking garage
area.  It gets plenty of ventilation.

This is the time to put in all the electrical boxes and wire for your
lighting and outlets, unless you want to surface-wire later.

Put decking on the tops of the joists in the part of the attic you will want
to walk on.  This can be done from below while the joists are open.  Leave a
little gap between panels.  Leave space where the roof is too low to use
anyway.  If you can't get at the attic any other way, frame in a trap-door
now.  I can reach the "floored" part of my shop attic from a ladder in the
garage.  I have a trap door in the back of the shop because I don't want to
have to duck-walk 30 feet if I want to put in any stuff on the south wall,
like a gable vent perhaps.

Staple up fiberglass insulation from below.  I used stuff with kraft paper
because that was available and the paper made it easy to staple.  Remember
that the kraft paper goes towards the warm side.

Have you insulated the walls?  This is a good time.

Staple up poly sheet for a vapor barrier separating the heated area from the
insulation.  About twenty bucks worth of 6-mil covered the entire inside of
my 20x30 shop.  Get the clear stuff, not the black stuff.  It is much easier
to see what you are doing.

Cover the poly with whatever you like.  I used thin hardboard because
drywall was golden at that point in time.  Rent a drywall lift for like 30
bucks and you can do the ceiling by yourself in one day.

I painted it all semi-gloss  white.  Some folks on this list have paid the
big bucks for white melamine, which would be neat.

>The garage itself is heated =8^), what with the furnace and water heater in
>and does have it's own heating/ac ducts.  The temps don't get too low here
>but there is a lot of humidity and moisture, what with the constant rain.
It sounds
>as though putting up plastic sheeting to cover the fiberglass is generally
a no-no,
>and likely some sort of fire code violation, but the kraft paper sounds
like a good

Explain to me why poly is a fire-code violation and kraft paper is not.

>it will at least keep the 'glass dust from coming down.  I'm using some old
>paneling I got from a co-worker to go across the joists and form a floor.
I know
>the stuff isn't the strongest, but when nailed into the joists with only a
>unsupport spread, it seems sturdy enough to walk around on w/o a lot of

Your joists are on 6" centers?


Phil Ethier    Saint Paul  Minnesota  USA
1970 Lotus Europa, 1992 Saturn SL2, 1986 Chev Suburban

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