So I’ve been remodeling my basement over the past few months and sinse i have all the drywall off I’ve been earthquake retrofitting my basement guess thats what they call it. Anyways I live in San Francisco and my house was built in 1907 so I wanted to add some lateral suport to the perimiter walls because theres no plywood sheathing on the exterior walls just lap siding old victorian home. I was reading about reterofiiting your home and they say to add plywood to the inside of crawl space walls well I don’t have a crawl space my ceilings in my basment are 10 feet high so i guess you could call it the first floor. My problem with installing plywood is they say you should cut vent holes in the plywood in between the studs one in the top one in the bottom for ventilation well thats a ton of holes in my walls and this is a finshed basement so that would be ugly Do I really need the holes for ventilation? I mean as soon as i took off the drywall I could feel lots of air coming through the siding this house is definalty not air tight not even close but there was no mold and everything was dry. Does Plywood prevent the walls from breathing? I really don’t want to cut these holes if i go this route. Also could i have thin drywall installed over top of the plywood for looks or would that just add to the ventilation problem. Maybe there’s something besides plywood I could use on the walls to add the same strength as plywood. The house seems to be pretty strong and has some nice old wood holding it up it made it through the 1989 earthquake of 6.9 with no problems but who knows I’m no engineer just thought I’d try to help it survive the next big one and i know sheathing the exterior of the walls with plywood or osb adds lots of strengh. Any ideas or advice would be much apperiated.
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If you are remodeling this basement space you will probably want to try to tighten up the outside of the house a bit. I live in a very different climate, but I would want to insulate those walls and moisture would be a concern if you can't keep the outside air from entering your stud bays. If you solve your air leakage issues then your need to vent the plywood is diminshed. If you have a large enough budget, spray foam the walls then use plywood for shear strenghth/racking resistance and drywall over that. You shouldn't have moisture issues in the wall assembly assuming your basement is conditioned and dry.
Ok I'll look into the spray foam think I read somewhere not to spray foam but that's what i wanted to have done in the first place I forget what changed my mind about foaming. Yes the basement is dry and conditioned so hmm what did change my mind about the foam.
I wonder who "they" are that
I wonder who "they" are that say to cut ventilation holes into the shear ply? Sounds sort of like seat of the pants to me.
And speaking of seat of the pants...... You might do well to consult a local structural engineer regarding your earthquake mods. Your house survived previous quakes because it was able to sort of go with the flow. If you add shear ply to the lower floor it will become a rigid box. This could result in the whole shebang vibrating off of the foundation, or possibly breaking the foundation apart. You didn't mention adding foundation tie-downs. They usually go part and parcel with earthquake resistant construction.
I don't know that any of my concerns are a problem for your house because I don't know anything about your house. But I do know that there could be consequences to your home-grown (or, perhaps, internet-grown) retrofitting. Talking to a local engineer will be cheap insurance. Although he may suggest some rather expensive retrofitting of his own.
Don't beef up the shear etc. without increasing your hold downs. Hold downs are one of the most important elements in seismic design. If you look at the evolution of codes you see how important this is.