metal straps -hurricane retrofit- long??
Has any one seen anything on the web about using 2 ft long metal straps like the Simpson brand to tie down existing roof rafters?
The simpson books all show use of small hurricane clips where the rafter end sits on the wall top plate. That area in my house is almost impossible to get to since the house is already built. I live about a mile from where Hugo came ashore with 120 MPH winds. web pix of Andrew results scare me!!
Examples in their web site say in a 130 MPH wind you can get 500 pounds uplift on each truss (I do not have trusses – it is stick built rafters, king rafters etc.)
I have started putting their straps about 1 ft back from the top plate and connecting one end to the rafter and the other to the ceiling joist. Ever seen this method used? Not as good as the top plate connection but seems it would add some tie down force?
Thoughts?
Replies
I guess my only concern, if I understand you correctly, is now that you've tied the rafters to the ceiling joists, what is holding the ceiling joists to the top of the walls?
Can you get to the rafter tails? Clips there will work just as well.
SamT
I have seen a few cases of hurricane straps being retofitted to existing buildings. If the studs are adequately attached to the top and bottom plates and these to the foundation the weak point seems to be most often the rafter, or truss, connection to the tops of the walls.
The crews I have seen handle this sometimes will gain access to this joint area by removing strips of spots in either the exterior sheathing or the interior drywall. Once open appropriate straps can be added and the sheithing or interior wall to ceiling joint patched.
In the later case I have seen them use some crown molding to cover the partches but a good drywall man could also patch it without the molding. Amazing what a good mud man can do. A little paint and none the wiser. Along these lines if you do retrofit straps be sure to contact your insurance company. If it is done within cretain guidelines and by a contractor you could get a substantial discount on your rates. A good thing as the rates look to be skyrocketing for most folks real soon.
Of course if the walls are poorly, or not, sheathed and the studs connected versus uplift by toenailed connections this too will have to be handled. Sheathing, as I inderstand it, is a grand reinforcer of homes. It lends outstanding rack resistance, good ballistic resistance and can act as a perfectly good reinforcment between the studs and the top and bottom plates. of course this is only true if it is nailed in properly. The roof, walls and foundations have to be examined as a system. Reinforcing one part while leaving the other parts weak will do you little good.
A local builder glues and nails using an all nail pattern. 4/6/12 with #8s if I remember right. He claims this can almost double the strength of the sheathing as a reinforcment to the stud to plate joints. In makes it harder to work on later if you wish to remodel but it does seem to make for a strong house.
What is the basic construction of your house? Frame with sheathing and siding? T1-11? Block?
If block, I would consider external attachment of Simpson FSA or FJA to each rafter tail and anchored to the tie beam. You could hide those with a decorative frieze.
If sheathing and siding, I would consider removing enough siding to use the Simpson LTS or longer MTS as shown in the catalog diagram, nailing through the sheathing into the studs and then replacing the siding. Don't use the 1 1/2" hanger nails through the sheathing.
If T1-11, I would consider the LTS,as long as you catch the studs with several nails and renail the top of the siding to the top plates and check the nailing pattern on the rest of the boards. Hide the straps under a wide decorative frieze.