First off I'm not an expert. WHY would you want to use green board?
My opinion is that gypsum is an INTERIOR product,(green board or
not). I recovered the back of my house in the Houston area a couple
of years ago, and simply stripped off the old masonite then went
with 30# felt overlapped 6" then Hardie over the top- I used
Hardy panels(4X8 sheets). Green board is only water
resistant not water proof, if it gets
wet which is a good bet in Houston, your begging for a mold MESS! I
wouldn't do it.
There is a gypsum board that is made for exterior sheathing under another
exterior finish. The paper coating the sheets is saturated in a tar
compound. I have seen it used in houses that are being built this year, and
was used on the exterior wall separating my garage (Covered with concrete
block), and this was built 35 years ago.
Back when I was a young kid, I lives in an area that was always under
construction. I used to go from house to house and (probably) drive
the builders nuts. I always had a fascination of building and home
repair and I really learned much of it as a kid just watching those
guys build. At that time I built a fort in my yard, and got all the
scrap wood from those guys. They would give it to me if I asked.
Anyhow, that was in the 1950s. I covered my fort with some black
gypsum type material that was a sort of tongue and groove (or concave
and convex) along the edges and came in 2 foot wide sheets about 8
feet long. It was about 1/2 or 5/8 inches thick. Those guys gave me a
bunch of pieces of that stuff, and I remember my dad cutting it for
me, because I was having a terrible time with it. Amazingly, it held
up well, and I never put anything over it. On another wall, I had
some brown sort of fuzzy stuff they used back then as sheathing, an
was about 3/4" thick. If I recall, that stuff was called Celotex.
However, I can not recall the name of that gypsum material.
Geezzzzz,,,,,, Now I will be awake all night trying to remember what
that black gypsum is called...
As far as using greenboard exterior, dont do it....
It's not made for that use. Besides, you want something to add
strength to the structure, such as plywood. Of course now a days they
use foam. Then they wonder why a minor windstorm rips the place
apart. While it saves money, I would not even consider building a
home without plywood or solid lumber over the studs. The foam can go
over that, and then the siding.
I agree, foam doesn't do anything. When you think of it, many modern houses
do NOT have any protection from a break-in. You could enter a house right
through the wall with a carton knife. Just cut through the vinyl siding,
then punch through the foam or fiberboard, pull out the insulation and with
one kick you are through the drywall, then you are in bypassing all the door
When I added an extension, I wanted strength plus insulation. The studs are
covered with 7/16" OSB overlaid with 1 1/2" of high density fiberglass
sheathing, could have used foam, then housewrap and finally covered with
brick. In-between the studs went regular insulation. It is really tight and
warm in the cold winters we have here.
Break in protection thru walls is meaningless, easier to break a window
or kick in a door. why mess with insulation, its itchy and time
thiefs want to get in and get out fast, not tear apart walls.
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