Joist stengthening options

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Old 09-18-17, 04:13 PM
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Joist stengthening options

I'm renovating my kitchen and as part of it I'm strengthen walls, rafters and joist's. I'd to increase the joist's strength by at least 50% and I'm wondering if anybody has tried to attach 2 layers of 3/8 ACX plywood glued and fastened with overlapping joints.
Some recommendations like 1 layer of 3/4 ACX plywood with ends butted up which is probably fine but I feel that 2 layers with staggered laps will be slightly better despite the added work.
A much simpler approach would be to just add a new joist and even though it would effectively double the strength of the roof structure, however it's important that I try to try to keep the weight down.
I'm curious if anyone's tried this aproach
 
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Old 09-18-17, 04:35 PM
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#1, Why, what's the real issue?
 
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Old 09-18-17, 05:00 PM
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You mention walls, rafters and joists. Then you say you want to increase the joist strength (read, FLOOR JOIST) by 50%. They you talk about adding a new joist (read, FLOOR JOIST), but in the next breath you mention doubling the strength of the ROOF.

So what exactly is it you are trying to do? Are you taking about adding plywood to the side of a floor joist to reduce deflection? Or across the tops of the joists? (As in SUBFLOOR). Or are you taking about the rafters (read, ROOF)?

At any rate, adding 3/8" plywood and glue is not recognized way to strengthen anything. You have to work within the building code, and what you're asking about goes beyond that.
 
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Old 09-18-17, 05:13 PM
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The home was built with quarter sawn redwood the roof joist's are tru 2 x 4 redwood, i'd like to increase the rigidity in the structure and improve the strength. The existing joist's are in suprisely excellent shape, but it is redwood, much softer than Douglas fir.
I would like to augment several of them while the ceilings are open since now would be the time.
 
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Old 09-18-17, 05:21 PM
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The only method that would be approved by a building inspector is to kick the rafters to a load bearing interior wall using strongbacks and purlins (refer to the images on this 2nd party page) or to sister (full length) with larger dimension lumber. Keep in mind that unorthodox methods of construction will be flagged someday by a home inspector if and when you put your home up for sale.
 
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Old 09-18-17, 05:22 PM
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I think it's acceptable to the authority having jurisdiction to exceed the building code provided you have a structural engineer provide detailed drawings and calculations stamped and submitted by the owner or engineer and the structural upgrades get installed per the details and are inspected and signed off by the AHJ.
 
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Old 09-18-17, 05:30 PM
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Well, sounds like you knew that all along... so get yourself a structural engineer to provide his recommendation, and get his plan approved by your local building inspector and you're golden. Since this question goes beyond the realm of the advice we can provide, I am recommending this thread be closed.
 
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