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 framing practice?
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 benefit.
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.
"RicodJour" wrote in message news: snipped-for-privacy@n60g2000hse.googlegroups.com...
R 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 like overkill.
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 ceiling joists.
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.
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