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Help! How to Measure for Level and Stiffen Bouncy Floors.

miataman2001's Avatar

Join Date: Sep 2013
Posts: 3

02-27-18, 09:10 AM   #1  
Help! How to Measure for Level and Stiffen Bouncy Floors.

This is a two part question.

1. What is the most cost effective way of checking the center beam in a crawlspace for level along its entire length? Is it possible to do this with mason line and a line level somehow and measuring down from the floor? If so, please explain exactly how and where to attach the line. There doesnt seem to be any detailed videos on this. My house is approximately 30 x 40 and is a single story built in 1977. The beam runs in the center along the 40 length. Its a triple 2x10 beam (so about 4.5 x 9.25) and it sits on a total of 7 concrete block piers. Two built in to each end of the foundation wall and five spaced evenly in between.

2. My floors are incredibly bouncy! Standing on my toes and then dropping down onto my heels next to the perimeter walls and the walls along the center beam feels solid, but moving that test toward the center of the room a few feet, or in the center itself, results in the entire floor and everything on it shaking/rattling. Even just walking down my hallway, which is about 3 feet wide and runs parallel to a portion of the center beam, results in squeaks/creaks and shakingand I only weigh 130 pounds! Additionally, Ive noticed some small cracks starting to form at the top corners of doorways that are in non-load-bearing walls perpendicular to the length of the house and parallel with the joist runs, as well as some out-of-square doorways. Im wondering if this is happening because of the movement of the floors and possible joist sag.
My floor joists are approximately 16 long 2 x 8s (1.5 x 7.25) installed 16 on center. They sit on the sill about 6 inches or so and continue to the center beam where they sit on that for its 4.5 width and overhang past it for 2. So the joist span in between the sill plate and the center beam is about 134. From what I understand, this is over the max span for a 2x8 joist 16 on center. Also, there is plywood subfloor (if I recall that size correctly) installed perpendicular to the joists and particle board installed throughout the house over top of that (that particle board is awful stuff, and I hope to replace it with plywood or OSB at some point in the future throughout). Would it be better to sister each joist with another 2x8 or to run two more beams, each centered between the main beam and the outside foundation for the length of the house, effectively cutting the joist span in half. Additionally, what would be the best, most cost effective method to check the joists for level in the center? Id also like to add solid blocking between all of the joists. Where would be the best location for these?

I apologize for the long post, but Im trying to be as detailed as possible. Im planning to install all new doors and trim in the house (theres only 5) and new flooring. Before I do that, though, Id like to stiffen up and level everything out as much as possible. The crawlspace is pretty clear. The majority of wiring was run up to and then down from the attic and the plumbing is confined to one area under the house. Looking forward to any helpful replies. Thanks!

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Pilot Dane's Avatar
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Join Date: Mar 2003
Posts: 16,675

02-27-18, 09:22 AM   #2  
1. Yes, you can use a masons level and piece of string. Drive a couple nails in the bottom of the beam. Stretch the string across and tie to the nails. Slide the string down 1" on each end or whatever. It just needs to be the same on both ends. Then hang your masons level. Or, you can just hold a level up to the bottom of the beam. Check it at each end and in the middle in case it's sagging.

2. You asked the same question about measuring level in #1. You can add blocking wherever you want. It's commonly done in the center or by breaking the joists up into thirds.

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