I've been working on my garage project and I'm about to the point of
installing insulation on the garage ceiling. The joists between the
living space above and the garage are 22" inches tall and manufactured
from 2x4's. Inside them is the plumbing, electrical and most of the
hvac flex ducts for the room above. I also plan on insulating the
garage walls. I have insulated garage doors on the front and back but
the front one is big, 20x9. The subfloor above is tongued osb.
Does it really matter which way I put the facing on the insulation
between the garage ceiling and the floor above? I know the vapor
barrier is supposed to be against the floor but i's going to be a
whole lot easier to install it with the paper on the garage side as
that will let me staple the paper to the bottom of the joists.
Otherwise I have to figure a way to hold the insulation up while I
install wallboard on the ceiling.
Easier is not always better, or even acceptable. Vapor barrier to the
heated side or potential problems Thee are metal supports made for holding
insulation in place between joists. .
Better applications is to have someone come in and do spray foam.
Holding the insulation up while attaching foam board presents the same
problem as holding it up while installing wallboard.
I'm thinking maybe I'll use string and staple the string across the
joists after I put a batt up. Not any different amount of work from
stapling the batt paper. If I cut a couple dozen pieces of string the
width of the space I can just let them hang as I install batts and
staple the string to the next joist.
I never did that- but it sounds like a good idea. My technique
would be to keep a ball of string in my tool pouch- stapler in a
holster. Push the bat in- then staple a zig-zag pattern with the
string as I walk down the line.
I like the zigzag idea. I can work down one joist bay and then back
up the next.
My other hassle is my ceiling height is 10' so I'll be going up and
down the ladder a lot. No avoidng that though. At least I have a
pneumatic 3/8 stapler so I can staple from most angles with out having
to be under the stapler enough to push hard.
I have used fiberglass tape, self adhesive and about 1/2" wide. Use a
stapler to attach to the joist, don't rely on the tape except to hold it in
place until you can fire a staple into it. Strong, flexible and easy to use.
Putting insulation bats between truss joists made from 2x4s will leave lots
of spaces within the truss joists allowing cold air to penetrate and will
still provide no vapor barrier at the floor level to prevent water vapor
condensing on the cold side of the drywall. It is still better to pay the
cost and have spray foam installed on the underside of the floor, it will
insulate and provide the vapor barrier without interference with duct
anchors and other obstructions. The ducts can also be encapsulated to keep
heat and/or cool from being lost. One could add some bat insulation
afterwards to boost the insulation value if wanted.
This job has a budget and hiring someone to spray foam is not in it.
The location is on the NC/VA border so I don't expect serious extremes
and I'm trying to insulate the garage space as well as I can too.
I meant foam board in lieu of insulation batts. A few dabs of
construction adhesive on the bottom of the joists will hold them in
place long enough to get the screwed-up rock up under it to hold it in
How is it making more work if you no longer need the insulation batts? I
think you misunderstand him. You can cut the foam board for a snug fit and
have it stay in place with no mechanical fasteners at all. You can us it
alone or you can use it in addition to the batts and hold them with the
I think you are looking for a simple solution but fail to see it when
offered. You have a pre-conceived notion that it it going to be difficult
unless it is done the incorrect way you asked about the first time. Sorry,
we will not give the "seal of approval" to the wrong methods.
You're not hearing me- forget about the insulation batts entirely, and
JUST use the (thick) foamboard, with the fire-rock cover. Not like this
is an exterior wall- 2" foam panel is plenty of insulation for a sealed
insulated garage with heated space above. No cold stripes where there is
no insulation under the bottom of the trusses, and no cold little holes
to freeze pipes and such if somebody accidentally leaves garage door
open. A nice tight insulating barrier.
The insulation can be held up by stiff springy metal wires that are
sold at various supply stores. They are about the size of a coat
hanger and come in different lenghts. These wires will hold up the
insulation by being inserted between the floor joists. Easy to do, no
Yes, I know about insulation wire supports. These are open web
trusses centered on 24". That makes the open space between trusses 20
1/2". I'll have to cut 24" wires down a bit. And carefully place
them on the lower edge of the truss. I'm wondering if there might not
be a better solution than the wires. For what it's worth the
insulation is in 4' batts.
You could put some nails into the sides of the joists just above the
bottom of the joists, and then use string to hold the batts in place.
Maybe someone has a bunch of old metal clothes hangers you could
cut. How much is your time worth?
I have an old house with uneven joist spacing. What I do is
temporarily push up the insulation and zig zag (sort of, I run across
and zag) staple fence wire to keep up the insulation. You can staple the
wire to the inside of the joist. You can cut insulation to fit the gap.
It's a pain cutting it and I usually use a large paper cutter and chop
my way through.
Vapor barrier is supposed to go to the heated side. In a hot climate
that may change how it is installed.
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