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The connection between your roof structure and the walls is one of the most
important structural connections in your house. It is also one of the things
that you may be able to strengthen with out too much disruption to the interior
of the house. If it is possible to gain access to the connection along the
eave either because there is no soffit (and consequently access is easy) or
through your soffit area (the flat bottom surface at the eaves that forms a
sort of ceiling where the roof overhangs the exterior wall) it may be possible
to install straps or clips that will anchor the roof structure to the top of the
wall and preferably directly to the wall studs. Another opportunity to strengthen
the roof-to-wall connection is when the house is being re-roofed. At that time,
removal or roof deck sheathing at the eaves, that exposes the roof to wall connection,
will allow the installation of brackets, clips or straps that will reinforce the
connection.
The first thing you need to do is determine how well your roof structure is attached
to the walls. In older wood frame construction, the connection of roof trusses or
rafters to walls is 2 or 3 sixteen penny (16d) nails driven at angles (toe nailed)
through the rafter or truss into the top plate of the wall. In newer construction,
metal straps are added that anchor the trusses or rafters to the top plate and
sometimes to the studs in the walls below. 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. In your attic or in an unfinished garage, 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.
If you see straps, check to see whether they are on every connection or every other
connection. Print out the checklist available by clicking on
Wood Frame Wall Checklist
and use it to record information about the roof-to-wall connection. Assessment
suggestions and some idea of the implications of what you find are included
on the checklist.
Retrofitting Roof to Wall Connections:
Areas where the roof framing meets the top of outside walls are normally hidden
by drywall on the inside, by wall cladding and soffit panels on the outside, and by
roof sheathing and the roof covering above. The following paragraphs outline some
ideas for how you may be able to strengthen the roof to wall connection.
Wind uplift forces on your roof tend to be highest at the ends and outside corners of
your roof and are higher for gable ends than for hip roof ends. Consequently, the most
important areas for retrofitting roof-to-wall connections are the 6- to 8-feet of the
outside walls, measured back from an exterior corner of the house, where the trusses or
rafters actually connect with the exterior wall. Similarly, retrofitting roof-to-wall
connections at gable ends are more important than retrofitting roof-to-wall connections
where you have a hip roof end.
From the inside, there are no really easy ways to install hurricane straps
because drywall will have to be removed and replaced. You can use the following tricks
to help make this process easier and less disruptive. Note that you only need to remove
a strip of drywall along the top of the wall and ceiling on the exterior walls where
trusses or rafters are supported.
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You can use a combination of straps to transfer uplift from the trusses or rafters through the double top plate and into the wall studs. The more structure you can engage in resisting the uplift, the better.
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- To limit the amount of drywall that has to be replaced use a ruler and
pencil or a chalk line to mark a straight uniformly wide strip of dry wall that
you can cut and remove from the wall and the ceiling. This will make it easier
to repair the drywall after you finish installing the straps.
- From the attic, use a small rake to pull any insulation back from the edge of the ceiling
so that it doesn't fall into the room when you remove the ceiling drywall.
- Using #8 1-1/2 long deck screws (not drywall screws they break
too easily under wind loads) instead of nails will minimize impacts to the
framing member that might cause the heads of nails holding drywall on
ceilings to become exposed (nail pops). If there are trusses, there will
likely be steel truss plates where you need to install screws or nails.
You will not weaken the connection by installing a screw or nail through the
plate, just drill a small hole in the plate so you can get a screw started.
Alternatively, you can use an air powered palm nailer to drive the nails into
the straps. This will avoid your trying to swing a hammer through a relatively
small gap and will really speed up the project. It should also allow you to
limit the width of the drywall that is removed to a strip about 8-inches wide
on the wall and 6-inches wide on the ceiling. Note that if you are driving
nails into a single 1-1/2 thick board (truss or rafter) you should use special
1-1/2 long 8d or 10d nails especially made for use with these straps and
available at home improvement stores.
- When wall studs are directly below the truss or rafter, select straps that
are designed to connect rafters to studs. If these connectors cannot be used then
use connectors that tie the rafters to top plates and use additional connectors
that tie the top plates to the studs.
You may be able to cover the drywall openings with a large crown molding, covered strip
lighting along the wall, or you could replace the drywall in such a way that it adds a
beveled or tray ceiling look to the room. All of these options probably sound easier
than they actually are and may not produce an acceptable look for the room. Simply
replacing the drywall and having a professional drywall finisher complete the job may
be the easiest solution if you are undertaking a retrofit from the interior. However,
one of the two exterior access options will likely be more cost effective.
From the outside, it is frequently possible to get access to the connection
between the rafters or trusses and the top of the wall from the outside either
because they are exposed or by removing soffit panels. This is a fair amount of work,
but once one gets the hang of it, it isnt too difficult. The trick is to number the
soffit panels so that it is possible to put each of them back where they started.
This could be important if they were cut to fit the length of the overhang that might
well change even along the face of the wall. Removing vinyl or aluminum soffit panels
gives a great opportunity to better secure the soffit system to the house.
See Soffits
for more details about this. Once a couple of the soffit panels are removed, take
a close look at the top of the wall and the existing connection of the trusses or
rafters. Look to see whether there is plywood or OSB sheathing over the outside of
the wall studs and whether the sheathing goes all the way to the top of the top plate.
If there is brick on the outside of the wall, it is only a veneer that is not well
attached to the house and the bricks are not well attached to each other.
So strapping to the brick is ineffective and a waste of effort. However, the brick
veneer frequently stops short of the top of the wall and it may be possible to gain enough
access to strap the trusses or rafters to the wall framing behind the brick.
From the top, when your home is being re-roofed, there is a great opportunity to gain
access to the roof-to-wall connection by removing roof sheathing at the eaves of the house and
installing straps, clips or right angle brackets to reinforce the connection between the roof
structure and the walls. The following specific guidelines were developed for the Florida
Building Commission to support a mandate by the State Legislature that requires houses valued
at more than $300,000 to include some roof-to-wall retrofits as part of a re-roofing project.
Prescriptive method for gable roofs on a wood frame wall: Unless it is possible to verify
through non-destructive inspection or from plans prepared by a design professional that the roof
structure is anchored at least as well as outlined below, access shall be provided to a minimum
of 6-feet of framing members, measured from the corner, along the exterior wall on each side of
each gable end. Wherever a strap is missing or an
existing strap has fewer than four fasteners on each end, approved straps, ties or right angle
brackets with a minimum uplift capacity of 500 lbs shall be installed that connect each rafter
or truss to the top plate below. Adding fasteners to existing straps shall be allowed in lieu
of adding a new strap provided the strap is manufactured to accommodate at least 4 fasteners at
each end. Wherever access makes it possible (without damage of the wall finishes below the soffit),
both top plate members shall be connected to the stud below using a stud to plate connector
with a minimum uplift capacity of 500 lbs. Use of straps that connect directly from the rafter
or truss to the wall stud below shall be allowed as an alternate provided the two members align
with no more than 1-1/2 offset.
Prescriptive method for hip roofs on a wood frame wall: Unless it is possible to verify through
non-destructive inspection or from plans prepared by a design professional that the roof structure
is anchored at least as well as outlined below, access shall be provided at a minimum
to the hip rafter, to the hip girder and to one rafter/truss on each side of the hip girder at
each corner of the hip roof. The hip rafter, the hip girder and the
rafters/trusses adjacent to the hip girder that are not anchored with a strap having at least four
fasteners on each end, shall be connected to the top plate below using a strap or a right angle
gusset bracket having a minimum uplift capacity of 500 lbs. Adding fasteners to existing straps
shall be allowed in lieu of adding a new strap provided the strap is manufactured to accommodate
at least 4 fasteners at each end. Wherever access makes it possible (without damage of the wall
finishes below the soffit), both top plate members shall be connected to the stud below using a
stud to plate connector with a minimum uplift capacity of 500 lbs. Use of straps that connect
directly from the hip rafter, hip girder or adjacent rafters/trusses to the wall stud below shall
be allowed as an alternate provided the two members align with no more than 1-1/2 offset.
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In any of the structural retrofits, we recommend screws as opposed to nails to avoid nail pops from existing wallboard - never use drywall screws, they are very brittle and will snap off - use the more ductile deck screws or specialty high strength screws.
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If you find plywood or OSB sheathing on the outside of the wall studs,
you are in pretty good shape for improving the anchorage of the roof to the walls.
If you have trusses, a Simpson H10 bracket or a USP RT16 bracket would be a good
choice. You can slightly bend the flanges where you attach to the truss so that
the H10 or RT16 will stay in place. Because of the possibility of drywall nails
showing (nail pops) it would be best to install the straps with #8 deck screws
(not drywall screws they break too easily). As an alternative, you could drive
nails into as many holes as possible using a palm nailer. Use 1-1/2 long #8 deck
screws or 8d nails to attach the straps to the truss but use 2-1/2 long #8 deck
screws or 8d nails to connect through the sheathing and into the top plate members.
If you find a double truss, you can use a Simpson H10-2 or USP RT16-2 bracket to go
around both trusses. Note that you will use 3 long #10 screws or 3 long 10d nails
in an H10-2 or RT16-2 bracket. If you have rafters with ceiling joists connected to
their sides, check to see if a Simpson H10-2 bracket or USP RT16-2 bracket will work
by determining how close the top nail hole for the rafter comes to the top of the
rafter. If that top hole is within about 1-inch of the top of the rafter, the H10-2
or RT16-2 is probably a reasonable choice. If not, we have seen lots of rafters split
along their length when the strap is only connected near the bottom of the rafter.
If you need more length up the side of the rafter, or if you can squeeze the end of a
strap over the top of the rafter, between the rafter and the sheathing, and put one
nail into the far side of the rafter, Simpsons MTS12 or LTS12 straps or USPs MTW12 or
LTW12 straps are good options. Try to position these straps to get as many nails into
the double top plate (top three inches of the wall) as possible. In addition to
installing connectors, nailing the plywood or OSB sheathing to the top plates will be
beneficial. Use 10d nails 4 on center, but no closer than 3 o.c. to improve the wall
sheathing connection to the top plate.
If you find fiberboard or foam sheathing on the outside of the wall
framing, it is very important to make a better connection between the
rafters or trusses and the wall. The key is to transfer the uplift into the
wall studs. The fiberboard or foam sheathing is useless for this. Consequently,
you need to strap the trusses and rafters directly to the tops of the wall studs
whenever they line up close enough. Otherwise, you will need to strap the trusses
or rafters to the top plate and the top plate to the wall studs. The MTS12 and
LTS12 straps are good choices for connecting the trusses or rafters to the wall
studs or top plates. The H2.5A and H8 brackets are good choices for connecting
the top plates to the wall studs if you have access to the sides of the wall studs
and the SP2 brackets are a good choice when access to the sides of the studs is
difficult. Note that you will probably have to remove some of the fiberboard or
foam sheathing at the tops of the walls in order to connect any of these straps.
A razor knife might be a handy tool to cut away material. If you only end up
connecting the rafters or trusses to the top plate, you may not improve the strength
of the connection very much as the wind may just lift the roof off along with that
top plate. If you can determine that the wall has plywood or OSB sheathing, you can
get some extra uplift resistance by just connecting the rafters or trusses to the top
plate. The amount of benefit will depend on how well you anchor the rafter or truss
to the top plate and how well the wall sheathing (including the drywall) is nailed to
the top plate and to the wall studs.
Another approach that can be used when rafter tails are exposed and there are no soffits
to hide brackets is to add a frieze board on the outside wall to hide the straps. In
some circumstances, one might consider using pre-finished boards like synthetic trim
boards. Alternatively one could paint frieze boards a trim color (i.e. a contrasting
color to the walls) in order to minimize painting more of the wall.
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