Reducing Floor Bounce And Sag With A Suspended Wall Or Partition

Reducing Floor Bounce And Sag With A Suspended Wall Or Partition

Reducing Floor Bounce And Sag

Skill Level: 4-5 (Advanced to Professional)

Time Taken: 8 Hours

During our old house bathroom remodel project, we were faced with a structural problem: the second floor was not stiff enough. It would bounce badly whenever somebody would take a step. When the house was built in the early 1900’s, the builders used 2×8 floor joists to span 16 feet. On the first floor the used 2×10 joists (which current codes require for a span of 16 feet). The 2×8 joists may be strong enough to prevent collapse (they measure 1-3/4 by 7-5/8, a little bigger than today’s 1-1/2 x 7-1/4 standard size) but the floor shaking was downright annoying.

Furthermore, the homeowner wanted to install marble floor tiles. Rigid tiles such as stone or ceramic require a rigid floor structure. So we knew we had to do everything we could to strengthen and stiffen the floor.

Our approach had two parts: sister the floor joists with additional framing lumber, and reduce the joists span by supporting the floor near the middle. See our article on sistering floor joists for the first part of this approach.

To support the floor in the middle of it’s span, we could have built a beam underneath the joists, since we were simultaneously remodeling the bedroom directly below. But such a beam would have been hard to hide. But the attic above the bathroom had plenty of space, and the large room was going to be divided by a wall. (The project is actually two bathrooms.) Normally a dividing wall (usually called a partition ) would add to the weight on the floor, causing further sag. I reasoned that I could devise a way to transfer part of the floor’s load onto the partition, and then let that load hang from the ceiling joists. But the ceiling joist are only 2×6, although they don’t span the full 16 feet width of the room because of the sloping ceilings on the second story. My experience crawling around the attic told me that the ceiling joists were just strong enough to carry the weight of the ceiling plaster, and not any additional weight.

So I had to somehow transfer the load to the walls at the edge of the bath room. I decided to employ a beam of double 2×10’s, that would bear upon the outside gable-end wall, and on an interior wall. And the 2×10 beam would sandwich the wall studs to securely hold them without needing fancy metal brackets.

By doing this we would take the the load of the floor and pass the forces onto existing wall studs in a way that spread the load out over as many studs as possible. Overall, the house has no extra load (except for the marble floor tiles, about 700 pounds), but some studs have slightly less load and some have more. I felt that it would be a safe bet.

Reducing Floor Bounce And Sag With A Suspended Wall Or Partition

Now, I admit that my mechanical engineering education gives me an advantage over a lot of people. But this is not rocket science. Some simple and sound principles are at work here:

  • Do no harm. Only add to the structure, do not take away material from the structure.
  • Envision the load path, or what framing members will be carrying the weight of the floor. The load has to be carried all the way to the foundation, always bearing on appropriate framing materials.
  • Calculate the loads involved to see if there are any large and unreasonable loads applied to any individual framing members. (See notes at the end of article)

A View From The Outside:

  1. Location of the 2×10 plate attached to the wall studs, in the attic.
  2. Location of the new wall.

Note the rectangular attic vent at the peak of the gable. It is visible in photos from inside the attic, such as the next shot.

Leave a Reply