Static structures (e.g. – buildings) – Inclined top cover – Rafter tie-in at horizontal-type support
Reexamination Certificate
2001-06-20
2004-04-13
Mai, Lanna (Department: 3637)
Static structures (e.g., buildings)
Inclined top cover
Rafter tie-in at horizontal-type support
C052S167100, C052S712000, C403S403000
Reexamination Certificate
active
06718698
ABSTRACT:
BACKGROUND
Description of Prior Art
Recent studies of wildfires indicate that the flames entered the house by vents along the eaves or soffits of a house. Studies of hurricane damage on wood-frame buildings indicate that extensive damage was generated to a house by strong winds, when the roof rafters or roof trusses were torn from the outside wall. Earthquakes can shake the walls and roof at different rates, because of the weight difference, which can cause the roof and wall to separate.
Roof sheathing ties all the rafters 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 wind and rain to enter the house.
Roof 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.
Roof trusses can take tremendous compression pressure, but are usually weakly attached to the top plate of the wall by toe-nailing or prior art hurricane clips. During house construction, when a rafter or roof truss is attached to the erect wall, it is usually fastened by toe-nailing or driving a nail at an angle into a thin edge of the rafter and into the top plate.
Toe-nailing is a weak, but time honored way of constructing rafters and trusses. Driving a nail at an angle usually moves the rafter off it's correct location on the top plate. This invention forms a much stronger building connection without toe-nailing or fragile hurricane clips.
Wildfires
Studies of wildfires show that flames enter a house by vents along the eaves or soffits of a house. The ventilation spaces formed a chimney-effect that sucked the flames into the attic of the house. Even if the roof had fire-proof material on the outside, the flames were already inside the attic, burning from the inside. Spraying water or fire-fighting foam on the outside of the roof will not stop the flames after they have been sucked into the house through vents or other openings.
Some engineers feel that an attic does not have to be vented. The vent screens usually deteriorate over time, letting birds, bats, insects, and rodents into the attic. If a bush next to a house catches fire, even if only momentary, the flames can be sucked into the attic like a chimney. To prevent flames from entering the attic, the opening between the rafters, top plate, and roof sheathing must be tightly sealed off.
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. Roof sheathing can be improperly attached to the rafter, and is usually covered by the roofing material. If the roof sheathing becomes detached from the underlying rafter, the house will be severely weakened, and rain will ruin everything inside.
A hurricane's wind and pressure can push in a wall, suck out a wall, push a wall laterally, lift the rafter from the top plate, and separate the roof sheathing and roofing material from the rafter.
A Federal Emergency Management Agency (FEMA) Publication, FIA-23, “Building Performance: Hurricane Iniki-in Hawaii” shows undersized and improperly attached metal fasteners (FIGS. 26-27). Because of the shape of all roofs, wind blowing across a roof tends to lift the roof off the walls as shown in FIA-23, FIG. 48. 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.
Another problem with home construction is on mis-installation of prior art hurricane clips. 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.
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.
Steel connectors, between different components of a wood-frame buildings superstructure, provide continuity so the house will move as a unit in response to seismic activity (Yanev, 1974).
The outside wall sheathing provides lateral stability to the walls, preventing racking. The sheathing also absorbs and transfers earthquake forces by becoming a shear wall. In order for the wall to perform as a shear wall, it must stay upright and intact. This invention makes a strong and rigid connection between the roof rafters or trusses, top plate, and wall sheathing.
Construction
Many houses are still built with the time-honored method of toe-nailing the rafter or roof truss to the top plate of the wall. This weak method drives a nail at a steep angle through a thin edge of the rafter into the top plate. Any uplifting force splits the rafter or pulls the nail out. This method was used in most places until after Hurricane Andrew devastated southern Florida.
Exact measurements are usually performed to get the rafters in the correct location, but toe-nailing or striking the rafter at a steep angle shifts the rafter even when striking it again by nailing on the opposite side. Installing this invention can cut measuring time drastically and eliminates toe-nailing so rafters or trusses are exactly on-center. Hurricane clips have been used in the past, but they are thin, weak and only tie a thin edge of the rafter and top plate together, and don't tie adjacent rafters together.
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 the roof rafters together and to the wall top plate, exactly space out the distance between rafters, prevent chimney-effect of fires into the attic, tie into the roof sheathing, prevent lateral movement during an earthquake, prevent thrusting when heavy loads are placed on the roof, and prevent uplift during a hurricane.
My co-pending application, Ser. No. 09/794,998 shows a frieze board that is retrofit to the roof rafters, the top plate, and outside wall sheathing. It provides ventilation and prevents uplift, thrusting, and lateral movement. My co-pending application Ser. No. 09/516,655 and related applications show other roof plates for tying down the roof sheathing.
A leading manufacturer of wood construction connectors, the Simpson Strong-tie Company, shows no connectors in their catalog that tie the roof rafters to the wall top plate, while spacing out the distance between rafters, preventing fire from entering an attic, and tying into the roof sheathing to prevent lateral movement during an earthquake and uplift during a hurricane.
There are a number of connectors that block fires from spreading from one floor to the next, by blocking flames from rising between studs. Boscamp's U.S. Pat. No. 6,189,277 is a firestop for metallic stud framing.
There are several connectors for rafters that provide ventilation, but they don't prevent the chimney-effect of fire entry into the attic. Jonett, et al's U.S. Pat. No. 5,370,577, and Luckey's U.S. Pat. Nos. 3,777,649 and 4,126,973 vent the attic.
Hess's U.S. Pat. No. 5,412,920 spaces beams laterally. Pearson's U.S. Pat. No. 5,007,216
Mai Lanna
Tran Hanh Van
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