web info on sistering a floor beam?
edwardh1
| Posted in Construction Techniques on
Anyone know of a good web reference for sistering beams? I looked.
Thinking home floor joist, like above a crawl space, say 2×8 beams
goal is to reduce vibration some , not make it supestrong
If you sistered with a 2×4
1. would it matter if the 2×4 when attached to the side of the 2×8, was flat against
– the bottom 1/2 of the beam,
-or the top half (up under the floor itself) ??
which location is stronger- the bottom?
2. if the sistered 2×4 does not reach quite to the ends where the 2×8 is supported , is there any strength gain? seems there would be?
Replies
The first thing that comes to my mind is "why is there vibration?" Then, it's "what do you mean by vibration?".
How long is the 2x8? What's the span length for that species? Is there any blocking?
Under what circumstances is there vibration? How much?
Are there termites? What's over the joists? How are they attached?
Questions, questions.
Quality repairs for your home.
AaronR Construction
Vancouver, Canada
I doubt you'd notice any improvement by merely adding a 2X4 as a sistered element. However, you may be able to get some improvement by simply fastening the 2X4 to the bottom of the joists, perpendicular to the direction of the joists and center span, tying them together. You should also make sure, as suggested above, that the span has proper bridging or blocking.
Further, if you are dealing with a crawl space, you might consider instead supporting the center of the joist span with a perpendicular 2X8 that is supported on posts to the floor/footers.
Either of these methods may be easier to do than sistering if you have plumbing &/or electric lines to deal with.
Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.
Edited 9/9/2009 7:20 am ET by MikeHennessy
A 2x8 is not a beam, it is a floor joist.
I have seen and used the 2x4 added to the bottom on the flat, prescribed by an engineer to increase the stiffness of floor joists.
As a matter of fact, we did this on a section of the job I am renovating now. It had 2x6s spanning 9 feet. We turned them into mini i-joists in place by adding the 2x4 flatwise on the bottom. Good results.
Use glue and screws. Can do with nails, but it is usually easier to operate the screw gun when laying on your back in a 16" deep crawl
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was the 2x4 used as a flange on a I beam?
Yes flat to bottom like bottom flange on a steel I-beam, so you are screwing up into the 1-1/2" edge of the existing fraaming. These were sittin on a 6x6 sill beam so they abutt that,If you are correcting a sag too, and not just dealing with vibration, you want to jack up in center to take the sag out, and then run the screws home. But if the floor is flat just apply to existing.
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Piffin's suggestion is the way to go. By placing the 2"x4" on the bottom, unlike sistering it, you are effectively increasing the depth of the floor joists, and it is the depth that determines stiffness. Plus you are putting all that new wood where it is most effective: acting as a large bottom chord in tension.
(Make sure to use Piffin glue but not Piffin screws)
You didn't state the span but solid blocking/bridging at midspan would help.
Jeff
Thanks to all!I had to side sister one of the joists since Mr drain pipe, telephone wire, HVAC duct boot, hot water cold water pipe etc all were in the area.I will use the "add a 2x4 to the bottom and make a beam method in two other places thoOdd that builders dont do that in a few select areas like where you first walk into a crawl space home- would be relatively easy to do.
"Odd that builders dont do that in a few select areas like where you first walk into a crawl space home- would be relatively easy to do."
The hope is that good builders size their floor joists appropriately in the first place so that there is no need for remedial action. Then people like you don't have to spend time monkeying around on their backs down in the crawlspace :)