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Another area where modern wind resistant construction is significantly
different from the typical ways homes have been built in the past, has
to do with the narrow side walls next to garage doors on garages that
stick out from the house. The walls being built today are much stronger
than those built in the past. Winds pushing on the side of the garage
will tend to try and push the end of the garage over. This has to be resisted
by the short walls and the action of the roof and ceiling diaphragms.
Typically, these walls are so short (less than 18 inches) that they are
not very effective in resisting these loads unless special care was taken
to make them extremely strong and well anchored to both the foundations
and to the beam running across the top of the garage door opening. Several
manufacturers make kits that can provide the kind of strength required
provided they can be properly anchored into a strong foundation and into
the framing above the door. This type of retrofit would require removing
the garage door and making significant modifications to the walls. This
should only be done by a professional contractor.
Instead of having one of the kits installed, it is possible to add some
extra strength to these narrow walls, and this is easiest if they are wood
frame walls. This can be done by strapping the existing framing together
if the strapping is not already there and installing a layer of ¾-inch
plywood (cut into an L shape) up the side of the wall and across the top
of the door opening, on each side of the door. You want to use a single
piece of plywood to form the L so that it is continuous around the corner
at the top of the door opening. This makes the plywood act like a large
angle bracket that helps keep the corner from distorting. Install some
form of hold downs to anchor the wall studs at the base of the wall to
the foundation. Then cover the bottom of the wall with additional pieces
of ¾ inch plywood. There is usually no need to install additional plywood
over the top of the garage door opening (beyond the end of the "L") since
there is a large beam over the door and the ends of the plywood "L's" will
be attached to that beam. Applying an AFG-01 approved wood adhesive and
attaching the plywood using nails or deck screws is a belt and suspenders
option.
For wood frame walls, all the plywood should be nailed around the
edges with 8d (2-1/2" long) nails [or a 2-1/2" #8 deck screw] at 3" spacing
and at 6" spacing along any framing members that fall in the middle of
the plywood sheets. If you try to install 3/4" plywood over the inside of
un-finished masonry walls, the sheathing should be attached to the
masonry using 3/16" diameter by 1-3/4" long masonry screws at about 6"
spacing around all of the edges of the plywood. A second layer of plywood
should be attached over all joints between the plywood sheathing installed
on masonry walls. This type of retrofit will not provide the strength
of the kits. However, on wood frame walls it has been shown to at least
double the capacity of the original wood frame wall to resist lateral loads.
It is not known what kind of increase will be provided in the masonry
wall case.
If there are enough full height and jack studs beside the garage door in
a wood frame house, it may not be necessary to have the garage door removed.
One could cut slots in the 3/4" plywood to facilitate installing the plywood
where the garage door track mounting brackets are located on the wall.
If the garage door is to be removed for this retrofit, and it has a coil
spring, the removal should NOT be attempted by anyone other than a professional
garage door mechanic. These coil springs are very powerful, dangerous,
and can kill.
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Preparation of a test specimen for testing at Clemson University - this is the baseline structure built the way many garage door openings are framed when conventional construction (not high wind construction) is followed.
(click image for larger version) |
Adding strapping to tie all of the framing members together was the first step in the retrofit
(click image for larger version) |
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An AFG-01 rated wood adhesive was applied to improve the connection of the sheathing to the wall studs
(click image for larger version) |
A plywood L was applied around the top of the garage door opening - plywood was added over the top of the opening for aesthetics but it was not needed to improve the structure.
(click image for larger version) |
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