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installing hold downs for existing windows with no return panels

PNW_phil

Registered User
Joined
Jul 2, 2022
Messages
4
Location
Seattle WA
Hi,

I'm looking into how I could retrofit my existing wall bracing to comply with "the spirit" of current code on my old house built somewhere around the 1960's. The house has a pair of windows at two corners that don't look like they comply with current wall bracing requirements. I saw figure R602.10.7 says to add 800lbs capable hold-downs in this situation and was planning to install Simpson DTT1Z at the two points in my sketch.
When I looked in the crawl space, I found existing anchor bolts in the mudsill, but there is a 4x8 beam sitting on top of the mudsill, and I can't tell how (or if) the 4x8 and mudsill are attached together. I made a sketch of my wall/foundation in this room. (The rest of the house has conventional anchor bolts visible from the main floor and does not have this 4x8 beam along the foundations inside the crawl space.)
Do you think I could shim the 4x8 with the foundation (would be approximately 2" depth difference to shim) and then add straps (maybe HRS12 or ST2122) near where the DTT1Z's will screw into the 4x8 beams? Since the 4x8 beam is continuous, I wonder if it would be better to put straps at the ends instead of near the hold-down device.

Another question: does anyone have a guess about how old shiplap used as sheathing compares to plywood/OSB sheathing? Would it be worth adding 'Let in Braces' in an 'X' pattern on the interior walls to try and strengthen the wall if I plan to keep the existing shiplap in place? If the shiplap doesn't function very well as a shear wall, then adding the hold-downs too could be altogether pointless! Somehow the house has survived ~60 years though.
 
In process of re-wiring and removing textured drywall, I'm going to tear out all the interior drywall. My thought is if the wall structure is going to be accessible, it should be relatively easy to add some wall straps and a couple hold down devices.
 
What you propose is a lot of work for not a lot of benefit. You're liable to knock things loose in the process.
 
& * & * &

PNW_phil, ...is there some reason or reasons that
you want to add bracing ?........When you remove
the existing drywall, do the currently adopted
Codes, in your location, "require" bracing to be
installed ?.......If not, what is the purpose ?


& * & * &
 
& * & * &

PNW_phil, ...is there some reason or reasons that
you want to add bracing ?........When you remove
the existing drywall, do the currently adopted
Codes, in your location, "require" bracing to be
installed ?.......If not, what is the purpose ?


& * & * &
Comparing between shiplap and OSB panel, the OSB looks like it will have stronger shear capability? I feel like OSB/plywood shear wall is just a better material than the existing old/brittle shiplap boards and wonder if there's any reinforcement possible that I could add? There's no code requirement in my local jurisdiction to add any bracing, I just wonder if I could add any improvement short of rebuilding the whole wall with OSB/plywood.

Here are some reasons I think the existing shiplap might be an inferior material:
  • The shiplap has a gap between each board. It can't transmit forces vertically to the next board above it, unlike a whole OSB panel that can transfer shear load through a continuous panel in both X & Y directions.
  • The nailing schedule of OSB/plywood looks better than whatever was used on the shiplap. From having previously ripped out some of this shiplap, it has maybe 2 fasteners into each stud at each end of the board and sometimes those fasteners are folded over or missing. An OSB panel that has many fasteners along all edges that may backup the others if some fasteners are compromised or overdriven? I can see some shiplap boards are butted up with no blocking/stud between the butt joint, so they're effectively "free floating' ends with no shear strength.
 
The shiplap is not providing much bracing...if any at all. Replacing the shiplap with OSB would certainly add bracing but something to consider is the anchorage to the foundation. It might work against you to stiffen the walls without providing sufficient anchorage to the foundation. In other words, a ridged box that is not held down can jump off the foundation.

Of course I don't know what your earthquake exposure is so I could be plumb full of ... well you get the idea.
 
Is there no let in bracing? Typically 1x4 at each end/corner of the wall?

I lived in two balloon framed houses with 1x12 horizontal sheathing, 3 nails each board each stud, no headers above openings, and after 140 years and 115 respectively no sags or leaning. I don't know how thick your ship lap is but my 1x12s we're a full inch, and I'll take that over 7/16" OSB any day.

You'd get more return if you spray foamed the sheathing and studs - both structurally and energy wise.
 
According to Fema Hazard Map I'm in a D2 seismic design category area.

The shiplap is 0.75" x 7.25" (actual). When I've replaced it in other areas of my house (adding/replacing windows), I just used 11/16 plywood, which I think is a better material. I agree that the 7/16 OSB looks like garbage.

I still have concern with how the two corner windows don't seem to comply with the bracing requirements for 2ft shear wall returns. My existing wall has a pair of windows in both corners; that is part of the reason I'm tearing out those two 3ft wide windows (they are nearly full wall height - almost 8 ft tall) and replacing with plywood. At least that existing wall has a 48" long section of shiplap wall in between the pairs of windows. I've seen some old houses in my neighborhood that are chock full of windows/doors filling the entire lengths of walls/corners and I doubt they have any hold-downs or ABW panels whatsoever.

I do think I should try adding some sort of hold-downs for my walls into the foundation. The existing construction looks like it's missing that. I also considered adding threaded rods by drilling down from above, through the 4x8 beams and into the foundation. Having clearance to angle the drill would be an issue with the existing shiplap in the way.
 
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