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Old 04-17-2011, 08:49 AM   #1
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Reinforcing existing floor joists


Working on my basement remodel and I'm concerned about a possible problem. The house was built in the mid 60's. Obviously rewiring part the basement and I'm going to have to run wires through an area that was just butchered by some nut with a hole saw. One runs of the holes (1 inch in size) comes within an inch of the bottom of the joints and probably runs 2/3rds of the house. Never saw during inspection 7 years ago because the basement was finished at the time. If I wasn't drilling more holes I wouldn't be too concerned being it's been like that for at least 40 yrs but more holes has me little nervous.I have read about reinforcing with plywood but nobody mentions what type. Suggestions would be appreciated.

Ps joints are 2x10 on 24 inch center with 12 foot span and the are already diagonally braced with metal straps.

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Old 04-17-2011, 09:18 AM   #2
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Reinforcing existing floor joists


if you have room you can sister up some joists won't hurt and will give you some peace of mind. just don't use dimensional lumber, use a stronger material like micro lamb. construction adhesive between them and you can use zig-zag nailing pattern or better yet through bolt with UNC 5. overkill, but the costs are minimal and method is pretty straight forward.

are you going to try and level the floors at the same time? in that case, level all the floors simultaneously before sistering joists permanently.

the other issue for you to think about is that 24" OC is no longer code.

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Old 04-17-2011, 09:45 AM   #3
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Reinforcing existing floor joists


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Originally Posted by Knucklez View Post
if you have room you can sister up some joists won't hurt and will give you some peace of mind. just don't use dimensional lumber, use a stronger material like micro lamb. construction adhesive between them and you can use zig-zag nailing pattern or better yet through bolt with UNC 5. overkill, but the costs are minimal and method is pretty straight forward.

are you going to try and level the floors at the same time? in that case, level all the floors simultaneously before sistering joists permanently.

the other issue for you to think about is that 24" OC is no longer code.

Knucklez
Thanks, I did think about sistering (and have in places already by newly modelled bathrooms) in 2x10s and basically kicking the center from 24 to 12 but there is a lot of plumbing and electrical already there and that is extremely daunting if you know what I mean. Didn't want to have to tackle that if not necessary.

Didn't have any intention of trying to level the floor being that is a much more difficult proposition being the house is about 24 wide with a steel I beam running through the center and it sags at the beam through the entire length meaning the whole house dips in the center. From all I have figured it was built crooked IE never level from the get go based off how door jambs were cut etc also because its off the same over the whole house. The house uses trusses for the roof so the squareness of the exterior walls is more paramount.
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Old 04-17-2011, 10:27 AM   #4
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Reinforcing existing floor joists


The house was built in the 60's, and apparently the framing has not been modified since then. Therefore, if the house was built to code at the time, there is no code requirement that you modify the spacing of the joists to meet current requirements.

As for sistering, you could certainly do that, using either dimensional lumber or glulam. Conventional lumber would probably be less expensive.

You may want to run some calculations on the strength of the existing beams, given the holes that were put in them. You say that there has not been a problem over the years, it may turn out that the joists are strong enough even with the holes, in which case I would not do anything at all. Calculations are a bit complicated, since the effective moment of inertia of the beams has been reduced by the holes being drilled in the wrong place, but an engineer could run the calcs since you know the size of the beams, the size of the holes, and the location of the holes.

If the beams turn out to be undersized, you can then move on to determine how to strengthen them. Options would include sistering, steel strapping, or use of plywood laminations. The design would typically be done by a structural engineer or an architect, or you can do them if you have the knowledge. This type of strengthening is not going to covered in your code book, so you may need some professional advice, or the building inspector may be willing to work with you on a design.
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Old 04-17-2011, 11:43 AM   #5
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Reinforcing existing floor joists


Thanks Daniel. I actually initially goofed in my original post. The joists are on a 16" center (roof trusses are 24" why I was thinking that I have no idea, must not have had enough coffee in me yet) so that is better still I guess. The glulam or the microlam stuff that knucklez and you mentioned, what is that stuff normally packaged as from a manufacture like GP etc and can get this stuff at a Home Depot or a Lowes? I ask because I walked around there some this morning and didn't see anything labelled as a microlam or a glulam and most of the plywoods had voids in the layers which I imagine is not desirable. I did look at some LVL beams and noted it "looked" like 1/2" OSB but I suspect that isn't the case. Thanks a bunch.

Edit I actually looked up what you were talking about and what you call a glulam is typically called Rim Board or LSL correct?

Last edited by kossuth; 04-17-2011 at 11:51 AM. Reason: more info
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Old 04-17-2011, 01:22 PM   #6
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Reinforcing existing floor joists


Microlam, glulam, and LVL are different types of engineered lumber. Microlam stands for microlaminated, glulam stands for glue laminated, and LVL stands for laminated veneer lumber. The actual differences between the types of engineered lumber has to do with the type of wood fiber used, the method of orienting the fibers, the glue used, and some other exotic stuff that only an engineer cares about.

Regardless of the specific type, engineered lumber is generally stronger than conventional sawn lumber when comparing equal sized pieces. Engineered lumber is often available in long lengths not available in sawn lumber. In some cases, you can get engineered lumber that is pre-cambered. Engineered lumber is usually used when high strength, long length, or unusual geometry is required, as engineered lumber is generally more expensive than sawn lumber for standard sizes like a 2x4 stud.

For your case, I would probably not use engineered lumber to sister to the existing beams, if you even need to sister. Attachment details for engineered lumber are often different than the techniques used for sawn lumber, especially for the engineered shapes like I joists or T joists, which require very specific attachment techniques.

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