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When the roof sheathing on the gable end was torn off, the top of the gable end wall was left un-supported and broke over above the bond beam.
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Modern reinforced masonry wall houses have been found to perform quite
well in hurricanes. However, un-reinforced masonry houses can be dangerous
because they tend to fail suddenly and catastrophically. Masonry houses make
use of both the reinforcing steel and their roof diaphragms to preserve their
structural integrity. Keeping the roof in tact is very important for all houses,
both because it keeps the wind and rain out and because it provides critical
support for the top of the walls. Masonry walls that are not braced at the top of
the wall are notorious for blowing over in strong winds.
Roof to wall connections and what you can do to strengthen them: In houses with
masonry walls, it is common to find a wood plate that is bolted or strapped to the top
of the masonry wall. The trusses or rafters are then connected to this plate using toe
nails and, in wind resistant construction, metal straps. In newer wind resistant masonry
construction, the board may be missing and the straps may be embedded directly into the top
of the concrete wall (in a bond or tie beam) and the trusses and rafters will be set
directly on the walls with a metal plate or some other sort of moisture barrier between the
top of the wall and the wood. In early applications of straps, it was considered sufficient
to use straps on every other truss or rafter. Today, every truss or rafter is anchored
with a strap if the builder is following high wind construction guidelines. For guidance in
determining how well your roof is attached to your masonry walls, click on
Masonry Wall Roof-to-Wall Connection.
Concrete masonry block walls and what you can do to strengthen them: If you have a
concrete masonry block home there are a couple of techniques for determining how well the
exterior walls are reinforced and anchored to the foundation. These are described in the
Masonry Wall Checklist.
What you want to find is steel in the top row of blocks, steel coming down the wall at
least at corners and openings for doors and windows over 5' wide, and steel going down
to the foundation. Older homes may have very little or no vertical reinforcing. The
evolution of vertical reinforcing in masonry walls is from no vertical steel; to the
use of steel in the outside corners; to adding steel at one or both sides of wide
openings such as sliding glass doors or garage doors; to steel at one side of even more
openings and occasionally interspersed along long walls; to today's standards of steel
at every opening and regular spacing on all exterior walls. In many cases, the steel
bolts holding a top plate to the wall are just grouted into the top one or two blocks
in the wall. We have seen roofs lift off with a few blocks left attached to the J bolts
and the rest of the walls just a pile of rubble.
If your masonry walls are un-reinforced, click on
Masonry Wall Reinforcement to explore ideas
about how you can strengthen the walls.
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