2019 Wrench Foundation

[Sung]

On 2019 built wrench house, things on the table severely rattles when someone walk on the floor between supporting points.

Supporting point has concrete structures in a crawl space. Distance between supporting points is about 15 ft. lying parallel to each others.

Engineer inspected and didn't find any structural issues.

Vibration is out of reasonable range, I think.

Please let me know your professional opinion.

[Mike Lamb]

Joist size and spacing? 16 O.C.? 

[BADAIR]

7 hours ago, Sung said:

On 2019 built wrench house, things on the table severely rattles when someone walk on the floor between supporting points.

Supporting point has concrete structures in a crawl space. Distance between supporting points is about 15 ft. lying parallel to each others.

Engineer inspected and didn't find any structural issues.

Vibration is out of reasonable range, I think.

Please let me know your professional opinion.

without pictures i can only hazard a guess

wrench house? or did you mean ranch-house 

possibly bridging, blocking or strip could help: R502.7.1 Joists exceeding a nominal 2 inches by 12 inches (51 mm by 305 mm) shall be supported laterally by solid blocking, diagonal bridging (wood or metal), or a continuous 1 inch by 3 inch (25.4 mm by 76 mm) strip nailed across the bottom of joists perpendicular to joists at intervals not exceeding 8 feet (2438 mm).

Edited February 4, 2021 by BADAIR

[Bill Kibbel]

We need sss - size, spacing, species of the joists.

Trampoline floors are common.  You can have a beam added to cut the span in half.  There'll be much less bouncy-bouncy.

If it even bothered me, I would  just put a pad or thicker tablecloth under the dishes.

[Jim Katen]

14 hours ago, Sung said:

On 2019 built wrench house, things on the table severely rattles when someone walk on the floor between supporting points.

Supporting point has concrete structures in a crawl space. Distance between supporting points is about 15 ft. lying parallel to each others.

Engineer inspected and didn't find any structural issues.

Vibration is out of reasonable range, I think.

Please let me know your professional opinion.

Welcome to the world of wooden floor framing. If you're accustomed to concrete or masonry construction, wood-framed construction can often seem flimsy, but it's surprisingly resilient. Floors that flex a bit underfoot are *very* common.  Many years ago, there was a TV commercial for a special kind of floor framing in which a china cabinet rattled when a little chihuahua walked by. Most viewers understood the reference because bouncy floors are so common. 

Flex in floor framing has nothing whatsoever to do with the floor's strength. If an engineer looked at your floor and said that it's fine, it almost certainly is fine. If the bounce bothers you, any carpenter can add supports to eliminate it. 

Just don't confuse deflection with strength. 

[Jim Baird]

This post reads like a google translation from another language, ergo "wrench" instead of ranch.

As an AHJ I inspected a home where new owners jumped the gun and moved in prior to final inspect.

It was one of these "kit" homes where everything is engineered and parts are shipped for on site assembly.  It used wood manufactured I-joists that bounced so much the newly moved in and loaded china cabinet rattled when you passed it.

[John Kogel]

I inspected a home where the owner had added a beam in the middle of the long span under the dining room table.

The beam was held up by two screw jacks resting on the concrete floor of the crawlspace.

I mentioned it with a picture in my report, because if the foot of a jack punched thru the concrete maybe 2" thick, it would be coming back to bite me. Not a concern, so just making my client aware.

The owner offered to remove the beam and the jacks. He said his wife walked around the table every day and didn't want the floor to bounce, made her feel heavy. My client said no, leave it there. 😃

Edited February 7, 2021 by John Kogel

[hausdok]

Is the floor platform constructed with I-joists? I joists sometimes exhibit a lot of bounce and vibration while still being perfectly functional from an engineering standpoint - as Jim already pointed out.

The Engineered Wood Association has published a paper about how to stiffen up I joists in order to reduce floor vibration. Click on the attachment.

I-Joists Vibration Retrofit.pdf