Static structures (e.g. – buildings) – Inclined top cover – Rafter tie-in at horizontal-type support
Reexamination Certificate
1998-12-15
2004-07-20
Canfield, Robert (Department: 3635)
Static structures (e.g., buildings)
Inclined top cover
Rafter tie-in at horizontal-type support
C052S093200, C052S167100, C052S713000
Reexamination Certificate
active
06763634
ABSTRACT:
BACKGROUND
1. Field of Invention
This invention relates to an innovative retrofit connector that permanently connects the roof to the outside wall to create buildings that are stronger and more resistant to hurricanes and earthquakes.
2. Description of Prior Art
Recent studies of hurricane damage on wood-frame buildings indicate that extensive damage was generated to a house by strong winds, when the roof rafters, roof trusses, and roof purlins twisted or were torn from the outside wall.
Roof sheathing ties all the rafters or purlins together on a wood frame house, and the roof sheathing ties all the roof trusses together when a masonry or wood-frame house is constructed with trusses. If the rafters or trusses rack or twist from the wind forces, the roof sheathing can detach from the roof allowing rain to enter the house.
Sheathing that is tightly secured to the rafters or trusses and subsequently fastened to the walls, helps transfer uplifting forces to the walls and henceforth to the foundation. If the roof sheathing fails, the trusses collapse, and the walls usually fall down as they can not stand by themselves against strong winds.
Failure of the outside wall sheathing is common during hurricanes, because of inadequate fastening of the sheathing to the underlying structural members. This invention helps prevent the wall sheathing from splitting, racking, and detaching from the wall. The extreme negative pressure of a hurricane blows out the sheathing from walls, but this invention holds the sheathing tight to the walls, as sheet metal joints perform better than nailed joints in high winds and during seismic activity.
Hurricanes
Studies of damage after Hurricane Andrew show several problems with the attachment of roof rafters and roof trusses that this invention solves.
Roof overhangs act like wings, creating huge uplifting forces during strong winds. This uplift tears apart the rafters that are toe-nailed to the header or top plate. The uplift can also twist rafters and roof trusses weakening the toenailed connections and causing detachment.
The one thing that ties together the top plate, studs, and sill plate is the outside sheathing. This invention effectively ties together the rafter, top plate, and outside sheathing to form a continuous load-path to the sill plate. Attaching my invention to the rafter and top plate junction puts the nails perpendicular to the uplifting force and would require shearing the nails in order to lift the rafter or truss.
One significant factor in building construction is precision framing, where the rafter is installed directly above the stud. Unfortunately, in existing houses this is rarely the case.
Post-and-beam construction is very common in older homes in mild-weather areas, and we have found that the wall studs, or in this case, posts, are only under every fourth rafter, and the rafters can be 4-feet on center. Usually, the posts are directly under where the top plate butts up against the top plate in the run. The rafter is to one side of this butt joint, so the rafter does not line up directly over the post.
On newer stud-wall construction, we have seen that studs rarely line up directly under the rafters. We saw a house where the walls have studs 16-inches on center, constructed with a roof that had rafters 24-inches on center. This means the only rafter and stud that will line up to form a continuous load-path is every fourth stud or every other rafter. What are the odds that they will exactly line up?
Another problem with home construction is on mis-installation of prior art hurricane clips that are made for new construction and covered by wall sheathing. After Hurricane Andrew, there were many examples of careless and inferior attachment of hurricane clips or they were entirely missing. One company has visited new construction sites and documented many examples of shoddy and incorrect application of their products.
To achieve a continuous load-path on existing houses the outside sheathing must be taken into account. The most important tie in an existing house is between the rafter and top plate or roof truss and top plate. Any uplifting wind force on the roof must be transferred to the walls. In tropical climates, the roof purlin, an intermediate structural member, may separate from the rafter with the roof sheathing.
My invention effectively ties together the rafter or roof truss, top plate, and outside sheathing (and indirectly, the wall studs) to form the most practical and economical continuous load path from the roof to the foundation.
Earthquakes
During an earthquake, the floor, wall, and roof diaphragms undergo shearing and bending. The shear forces from the roof boundary members are transferred to the top of the shear wall by way of toenails to the top plate. To withstand and transfer the shear loads, the connection between the roof and wall must be strong.
The outside sheathing provides lateral stability to the walls, preventing racking. The sheathing also absorbs and transfers earthquake forces by becoming a shear wall.
An earthquake can send motion into a house and separate the sheathing from the walls. The sheathing can come loose from the walls by the nails popping out or the plywood splitting away from the nails driven on it's edge. Some codes allow sheathing to be stapled to the wall studs, which is a weak connection. This invention helps prevent the sheathing from pulling away from the wall during earth movements.
Steel connectors, between different components of a wood-frame buildings superstructure, provide continuity so that the building will move as a unit in response to seismic activity (Yanev, 1974).
Prior Art
A number of connectors have been developed to tie together the structural members of a house under construction. Up until this invention, nobody had seen how to make a connector that could tie sheathing to the underlying structural members and connect to the side or “meat” of a rafter or roof truss without having material hanging down.
My co-pending application, Ser. No. 08/191,852, is a retrofit hurricane clip. Although it can be mounted on 2× rafters, it was designed for large timber rafters such as 4× stock, and has a web member that can be seen from the side. This invention uses a saddle and side webs for lateral support, and can not be seen from the side, hence it is stealth-like.
The leading manufacturer of wood construction connectors, the Simpson Strong-tie Company, shows no retrofit hurricane connectors in their catalog.
There are a number of ties that fasten the rafter to the top plate while a house is being constructed including: Knoth U.S. Pat. No. 5,561,949, McDonald U.S. Pat. No. 5,560,156, Colonias U.S. Pat. No. 5,380,115, Stuart U.S. Pat. No. 5,335,469, Colonias et al U.S. Pat. No. 5,109,646, Commins U.S. Pat. No. 4,714,372, Gilb U.S. Pat. No. 4,572,695, and Gilb et al U.S. Pat. No. 4,410,294.
These are good inventions, but they are difficult to retrofit onto existing houses without demolition of existing parts on a house. None were designed or patented to be retrofit on to an existing house.
The prior art hurricane clips provide little lateral strength, even when using a left and right. The prior art cannot tie the outside sheathing to the underlying top plate and roof rafter. They cannot clear frieze boards and prevent the outside sheathing from being sucked off during the extreme negative pressure of a hurricane.
The prior art inventions do not prevent the outside sheathing from splintering and disconnecting during earth tremors. They do not have multiple uses such as tieing the floor joists to the wall studs, the weakest parts of a wood-frame house in an earthquake.
Frye's anchor system, U.S. Pat. No. 5,311,708, is patented as a retrofit, but it does not tie the rafter to the top plate, cannot clear frieze boards, and ties into the weakest thin edge of the rafter while splitting it with bolts. Frye's 708 also provides no lateral support against side movements.
Netek's reinforcing tie, U.S. Pat. No. 5,257,483, is patented as a retrofit and may cl
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