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Click here to download a PDF version of this checklist.
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Investigating the Roof-to-Wall Connection:
Inspection: In your attic, use a flashlight to look at the connection
between the trusses or rafters and the outside walls of the house. Try
to determine whether you can see any indication of metal straps. Don't
be confused by metal plates that rest on the top of the wall under trusses
and rafters that were used in older construction to seperate the wood from
the concrete. If you see straps, check to see whether they are on every
connection or every other connection. Look for the following:
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- Is there any sign of a metal strap connecting the roof rafters or trusses
to the wood plate or directly to the top of the wall?
[ ] Yes
[ ] No
- If there are straps, are they installed at the end of every truss or
rafter or to the end of every other truss or rafter?
[ ] Yes - Every Truss/Rafter
[ ] No - Every Other Truss/Rafter
- Are nails installed in every hole in the strap?
[ ] Yes
[ ] No
- Do the straps wrap over the top of the rafters?
[ ] Yes - I have trusses or the straps wrap over rafters
[ ] No - I have rafters and the straps do not wrap over the top of the rafters.
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Assessment:
If you answered "No" to question 1, your home is a candidate for
installing hurricane straps. The least expensive thing you can do (as
a start) that will reduce your risk of loss of the roof is to protect all
large windows and doors because this will reduce the chance that wind forces
will also be pushing up and out from the inside of your house. You should
make sure that your garage door is protected or replaced with an appropriate
wind rated one if you don't already have one. Protecting your windows
and doors could mean the difference between the home keeping its roof on
or loosing it when the winds climb above category 1 strength. You should
definitely plan on evacuating if a category 2 or above storm is threatening
your area, even if you protect the windows. You may want to consider adding
straps as described below, if it can be done inexpensively and you have
a bond beam at the top of the wall. A bond/ tie beam is a beam at the
top of a wall made by having concrete and ideally steel reinforcing placed
into the top row of concrete blocks. It may be that the tie beam was made
by pouring concrete into forms at the top of the wall thus not using blocks
for the beam.
If the answers to all of the questions are "Yes", your roof is reasonably
well strapped to the walls and you should concentrate on other areas of
vulnerability, including determining the amount of reinforcing in the walls
as outlined below.
If the answer to question 1 is "Yes" but the answers to either the 2nd
or 3rd question is "No", you may want to consider additional work on
connecting the roof to the walls if it can be done inexpensively. Retrofitting
the roof to wall connection is particularly important if your roof has
a fairly low slope, the home is more than about 30 feet wide, you have
open areas around your house, and you live in an area where the 3-second
gust design wind speed is greater than or equal to 120 mph. Again, the
least expensive thing you can do (as a start) that will reduce your risk
of loss of the roof is to protect all large windows and doors because this
will reduce the chance that wind forces will also be pushing up and out
from the inside of your house. You should make sure that your garage door
is protected or replaced with an appropriate wind rated one if you don't
already have one. Protecting your windows and doors could mean the difference
between the home keeping its roof on or loosing it when the winds climb
above category 2 strength. You should definitely plan on evacuating if
a category 3 or above storm is threatening your area, even if you protect
the windows. You may want to consider adding straps as described below,
if it can be done inexpensively and you have a bond or tie beam at the
top of the wall.
Investigating the Reinforcing of your Block Walls - Vertical Steel and Concrete Filled Cells:
Background and Suggestions: 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. If you have installed
permanent anchors for shutter on your windows and found that the blocks
on both sides of your windows are hollow, you probably have un-reinforced
or at least under-reinforced walls and some additional checks would be
a good idea. In addition, just because a few holes you made indicated
solid concrete does not mean that the blocks are necessarily reinforced
with steel and concrete. It is possible that you hit a concrete partition
within the concrete block. Some blocks have two cells so they have one
interior partition of block that goes from front to back of the block while
some blocks have three cells and have 2 partitions. Because concrete blocks
are easier to drill into than solid concrete, you may be able to distinguish
between the partitions of a block and solid concrete simply by how hard
your drill has to work. Un- or under-reinforced means that the cells of
blocks did not have steel placed in them and were not poured with concrete
at corners and beside each door and window. If you have not installed
permanent anchors for shutters, you can use a small masonry bit and drill
holes in the wall on both sides of the window opening, in an inconspicuous
location about 3-inches outside the line formed by the vertical edges of
the window. In newer wind resistant construction, you should find solid
concrete on one side or the other of the window. If you find hollow blocks
on both sides, you probably have un-reinforced or at least under-reinforced
walls and additional checks would be a good idea. You can patch your little
exploratory holes using a little dab of exterior caulk after you have blown
off the concrete dust.
There are some stud finders with metal detection that are capable of determining
the location of reinforcing bars in masonry walls. Typically they have
a "deep penetrating" metal detector option. Be sure to follow the manufacturer
's instructions for calibration when you turn them on. These metal detectors
can be used to conduct additional checks to determine how well your masonry
walls are reinforced and anchored to the foundations. The checks outlined
below are intended to help you make this determination. In older masonry
homes, conventional practice was to grout "J" bolts into the top of the
walls and anchor a wood plate to these "J" bolts. The trusses or rafters
are then connected to this wood plate. In these walls, there may not be
any reinforcing steel installed that runs from the top of the wall to the
foundation. In some cases, the top blocks in the wall have a "U" shaped
cutout and reinforcing steel is laid in that "U" shaped cradle and the
top blocks are filled with concrete to form a bond beam at the top of the
wall. In some cases, a header beam (also known as a lintel) installed
above the window and door opening is the only part that is reinforced and
no reinforcing is installed along the remainder of the top of the wall.
To determine how well your wall is reinforced, use the deep penetrating
metal detector setting on the stud finder / metal detector to search steel
in your walls. Some of the better metal detectors will also indicate if
both metal and electricity are detected. Consequently, be careful that
you don't pick up a false positive from an electrical cable. Also don'
t be confused when using a metal detector near metal from window frames
or downspouts. Make an effort to distinguish between steel in the wall
and other indications by trying to track the indication.
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Video: Checking for rebar
(click image to view video) |
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Inspection: Begin your search for reinforcing by checking for steel
at the outside corners of the house. Go to an outside corner of your house
and with the stud finder / metal detector in deep penetrate mode and placed
against the wall about head high at the corner, move the stud finder sideways
across the wall away from the corner. Repeat this on the other face of
the corner. If you detect metal, move the stud finder vertically along
a line that passes through the point where you detected the metal to make
sure that the metal runs from the top of the wall to the bottom. Note
the results on the checklist below. Then check along the top of the walls
to determine if there is reinforcing steel running along the top of the
wall. Note: if the block wall extends one or more block heights above
the soffit panels, you will not be able to check for this from the outside
of your house without removing the soffit where you want to make a test
. If you do remove soffit do not be confused by the metal detector finding
aluminum parts of the soffit system. Next, move the metal detector horizontally
along the outside wall of the house, sliding it along over a long stretch
of wall without openings to see if reinforcing bars are found. Determine
the distance between the reinforcing, if any is detected, and note the
results in the checklist below. Finally, check the location of anchor
bolts or straps embedded in the masonry wall from the attic and estimate
the distance of one of these from a corner of the house. Then go to that
location on the outside of the wall and from a ladder determine how far
down into the wall the metal is indicated. Most "J" hooks are about 16
-inches long and will engage the top couple of blocks when they are grouted
into the top of the wall. If you get an indication of metal running all
the way down through the wall, then it is likely that the cell below the
"J" hook contains reinforcing steel and that these cells have hopefully
been fully grouted throughout the height of the wall. Note the results
on the 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.
Masonry Wall Reinforcing Checklist - Vertical Steel and Concrete Filled Cells:
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- Is there a solid grouted cell on either side of the window or door
openings?
[ ] Yes
[ ] No
- Were you able to detect reinforcing steel near the outside corners
of the house?
[ ] Yes
[ ] No
- Is there reinforcing steel indicated along the top of the wall (indications
of a reinforced bond beam)?
[ ] Yes
[ ] No
- Is there vertical reinforcing in the wall of the house? If so, what is the typical spacing between the reinforcing and does it run the full height of the wall?
[ ] Yes [ ] No Vertical reinforcing
[ ] Yes [ ] No Typical Spacing less that or equal to 8-feet
[ ] Yes [ ] No Full height reinforcing?
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Assessment:
If you answered "no" to all of these questions, you have un-reinforced
masonry walls and, if your home faces a large open area or the water or
your house is 30' or wider, your home may be at risk of wall collapse or
loosing its roof in a Category 2 or stronger hurricane. The least expensive
thing you can do to reduce your risk of wall damage or loss of the roof
is to protect all large windows and doors. You should make sure that your
garage door is protected or replaced with an appropriate wind rated one
if you don't already have one. Protecting your windows and doors could
mean the difference between the home keeping its roof on or loosing it
when the winds climb above category 1 strength. You should definitely
plan on evacuating if a category 2 or above storm is threatening your area,
even if you protect the windows. You may want to consider adding reinforcing
as described in the following sub-section when you undertake a major re-modeling
job. If you decide to try and reinforce your walls, you should
get a design professional to help you find the best solution for your house.
If you answered "Yes" to all these questions, you have reinforced
masonry walls and you do not need to worry about retrofitting your walls.
Just to be clear that you found steel at the top of wall and down the
full height of the walls at the corners and at wide openings.
If you answered "yes" to some but "no" to other questions, you probably
have under-reinforced masonry walls. You should put a high priority on
protecting all large windows and doors, including garage doors. You may
also want to consider adding reinforcing as described in the following
sub-section when you undertake a major re-modeling job. If you decide
to try and reinforce your walls, you should get a design professional to
help you find the best solution for your house.
Back to Masonry Walls
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