I've noticed that in my 1908 wood frame house, the roof rafters do not
bear directly on the exterior wall top plates. Instead, a 1x4 is run
along the top of the 2x6 ceiling joists, and the roof rafters bear on
this, usually over a ceiling joist. Is this a currently acceptable
I'm adding a (very) small addition with a separate roof, and I'm
wondering if I should use this detail. Repeating it would likely
facilitate matching the overhang, soffit and freize board details of
the original house. FWIW, the basic wind speed at my urban site is 85
mph, the design earthquake load is 0.17 W, and all roofs are 8:12
slope and hipped.
Very little of a 1908 house would conform to the current code.
They're still standing 100 years later, but they don't fit the code.
There's not reason to use such an odd detail. Any engineer or
building inspector would have you doing so much extra work to approve
that detail that it would cost you far more than any perceived
Place the rafter/truss on the top plates, raise the wall height if
necessary to match roof and soffit lines, build the ceiling and
soffits down to match existing.
The recommendations about the code issue is correct, but you can bring
it to code with Strongtie metal connectors easily enough. If the
ceiling joists are blocked on the ends, then really it will probably
satisfy the inspector for the seismic requirement, though not for the
wind. I would beef up the standards for the wind to 125mph
regardless. 85mph is just too low anywhere, really. I live in
California where wind requirments are low, and just two winters ago we
had storm winds as high as 65mph. I would feel uncomfortable with
just 85mph here. You certainly want to match the architectural
details of the original house to keep your property value high,
whichever way your plan the framing.
Is correct, raise the wall plates to the height of the ceiling. I would
recommend that you use manufactured roof trusses in lieu of conventional
framing. This way you won't have too many connections to be concerned with.
It will be cheaper and the trusses would be installed in one day. Make sure
you have a good, preferably, plywood sheathing for the roof so you can
develop a diaphragm to resist lateral forces i.e. wind and earthquake.
Don't worry about the 85 mph many code areas are using this value but you
need to follow the ASCE7-02 loading criteria which increases loads based on
location. The wind forces get greater the higher the structure, at corners
of buildings edges of roofs etc. This is required by the IBC 2003 building
code. You need to have a detail so that the sheathing can transfer the
lateral wind/eq force to the sheathing on the walls ( shear walls ). If
you are getting a local authority permit for this construction you will have
an inspector. Hopefully the inspector might not recognize a lack of
connection of the existing roof diaphragm to the exterior walls. But he/she
might, then, you will have to fix all edges of your roof. Luckily there are
exceptions to this. How is the connection between the roof sheathing to the
exterior walls in the existing construction? Blocking would do it which
would be at the ends of ceiling joists nailed to the joist plates and to the
roof sheathing. If, you don't have blocking at the ends of the ceiling
joists you might be able to fix your whole roof system by adding blocking
all around nailed to the existing wall plates and the sheathing ( if you
have any ) to take the wind/eq forces to the walls. Do you have wall
sheathing on the existing walls? Where are you located?
If you are going to need foundations for your project I guarantee you that
the permit authority will require a structural engineer to design foundation
and do the seismic and wind load design. If this does happen you should have
the engineer check your roofing sections and details so the permit process
will be smooth and easy. At this point you should check your costs and see
if it all is in your means.
Sorry, that this has taken so long but these are things that engineers and
architects go through quite often on many projects.
Hope this helps.
A reasonable suggestion, but my addition is quite small, only 50 ft^2
of (projected) roof area and a maximum span of 4'. So trusses seem
I see you suggest later on to do this with blocking connected to both
the sheathing and the wall top plate. Would a twist strap face nailed
to both the rafter and the top plate do this, assuming a tight nailing
pattern of the roof sheathing to the rafters? I'm referring to the
new construction, not the existing construction.
I'm not touching the existing roof and exterior wall top plates, and
my inspector hasn't raised the issue.
The existing roof seems pretty hopeless so I've not tried to upgrade
it. It consists of (full dimension) 2x4s 32" o.c. spanning 12.5'
plate to ridge. The original skip sheathing has been topped with a
layer of 1/2" plywood sheathing and composite shingles. There' no
blocking at the wall/roof intersection, and as I mentioned there's the
funny detail of the rafters bearing on a flat 1x4 on top of the 2x6
I'm in Berkeley, CA, and I've updated the house's lateral force
resisting system up to the exterior wall top plate. There's a new
engineered foundation as of 2004, and I've rebuilt each wall segment
without any openings as a shear wall: hold downs at each end, sheathed
with 1/2" Struct 1 plywood with a 4" 8d perimeter nailing pattern,
blocking between the floor joists, and tension straps connecting
stacked shear wall segments.
Actually, for my permits for my small addition, the building
department accepted my plans without any engineering. I used the
foundation detail from my engineered 2004 foundation replacement.
Thanks for the detailed response.
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