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 2x8 floor joists to span 16 feet. On the first floor the used 2x10
joists (which current codes require for a span of 16 feet). The 2x8 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
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 2x6, 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.
had to somehow transfer the load to the walls at the edge of the bath room. I
decided to employ a beam of double 2x10's, that would bear upon the outside
gable-end wall, and on an interior wall. And the 2x10 beam would
"sandwich" the wall studs to securely hold them without needing fancy
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.
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:
- Location of the 2x10 plate attached to the wall studs, in the attic.
- 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...
||A view in the attic, looking toward the gable-end wall. The
pale board is the 2x10 plate that we attached to the existing wall studs. We
cleared away the cellulose insulation and removed the ceiling lath where
the new wall would go. We kept a stock of planks in the attic for crawling
on, to avoid crashing through. (We'll leave that to Tim Taylor.)
For almost all of the framing here we used 3" premium deck screws.
(Never rely on drywall screws, they are too brittle and their shear strength is
not adequate for load-bearing framing.)
||The other supporting end.
The pale lumber here is a pair of new 2x6's used to sandwich the
ceiling joist directly above the old interior wall. That wall is visible
through the hole.
These 2x6's run all the way to the ends of the original ceiling joist,
and were attached with 3" deck screws.
One advantage to using deck screws is the reduced amount of debris that falls
from the walls and ceiling. The wood lath on the ceiling allowed quite a bit of
dirt and cellulose insulation to fall through, and hammering only amplified the
|Another view of the new 2x6's. One board is higher than the
other because of the some backer boards used to hold the wood lath.
Note how the new boards extend all the way to the end of the old joist.
This beefing-up is necessary so the load from the new 2x10 beam is spread
out across as many studs as possible.
A few weeks prior to this we:
- Made a reinforced concrete pier in the basement, directly underneath the
middle of this wall.
- Jacked up the main-floor joists directly beneath this wall, using a 12 ton
bottle jack. We raised the joists about 1 inch in the middle of their span,
which removed about half of the floor's slope.
- Added a supporting column in the basement to help hold up this interior
wall. This is part of the "load path" that carries the load all
the way to the foundation.
||The double 2x10 beam, anchored at only one end. We had to
let one end float free until all the studs were installed between them.
|The methods used to anchor the 2x10's to the wall. The board
on the left was installed first, using a joist hanger. The second board
was too close to allow a joist hanger (there was no room to get a nail or
screw into the diagonal "toe-nail" holes), so we attached a pair
angle brackets to the board, and then screwed it to the wall with Simpson
Strong-Tie screws, which are meant for attaching framing anchors.
||The studs were inserted between the 2x10's, right at each
ceiling joist. Each stud was screwed to a ceiling joist and the 2x10's
were screwed to the stud.
|Another view of a stud-to-joist-to-beam connection.
Of course, getting to this stage meant that the studs had to penetrate the
floor deck in the bathroom. The holes were cut with a reciprocating saw, and the
studs were merely left dangling (although they were carefully aligned to be
plumb). Later we attached the lower end of the studs to the second-floor joists
at the same time that we installed the joist sisters.
The bathroom has a ceiling that is just over 8 feet high. We used 10 foot
2x4's for studs and their length was perfect, providing plenty of overlap at
||Notice how the gable-end 2x10 is a bit lower than the beam?
I assumed that all the ceiling joists were 2x6, but the joist against the
wall, (which is really just a cleat) was only a 2x4. Consequently, that board
sat a bit lower than expected. In hindsight, the extra money for a 2x12
board would have been well spent.
||The new "suspension studs" that support the middle
of the floor span. There were four such studs. One stud was omitted to
allow for a narrow connecting door between the two bath rooms. The total
length of the new wall was just under 8 feet.
|The studs simply dangled through holes cut in the floor.
They will be attached later.
||Later, while sistering the
floor joists, we connected the hanging studs to the second-floor
frame. We used 5/16" by 6 inch long hex bolts, with very large
washers to prevent crushing of the wood fibers.
Some Minor Details:
||Since all the walls were going to be covered with drywall,
we needed to provide nailing surfaces to support the wallboard.
The original bathroom remodel job, done about 10 years ago (the one that
converted a bedroom into two bath rooms), had simply fastened a stud wall
against the old and crumbling plaster.
|We attached blocking at the corners, so the new drywall
panels would have a surface to attach to. Attaching blocking in this
fashion is almost impossible with nails (because you can't hold the board
in behind the stud and nail into it) but is a snap with deck screws. We
just used a Quick-Grip clamp to hold the block in place and zipped in a
||A surprise. Later, we removed the lath on the outside
walls, and discovered that on the gable-end wall, the original carpenters
had scabbed together 2x4's to reach the highest points. Since gable-end
walls are normally not load-bearing, this was once considered an
We screwed the adjoining studs together, and also added numerous pieces
of blocking to cross-brace the studs.
This house uses a technique called "balloon" framing, where the
studs run continuous from the first floor deck all the way to the rafters. This
method was the norm until the early 20th century, when over-logging caused long,
clear lumber to become scarce and expensive. Today, almost all houses are framed
with the familiar "platform" method, where the first floor walls are
erected, then the second floor deck is built, then the second floor walls are
erected while using the second floor for a work platform.
Some additional notes:
I made a quick calculation of the loads involved in this project. The
suspension partition would bear at most half of the floor
- The total floor dimensions are about 8 feet by 16 feet, so the new
wall would carry at most 64 square feet of load.
- Using the standard 40 pounds per square foot live load for
residential structures, I arrived at a total load of 2560 pounds, at
most, carried by the new beam in the attic. In reality, the old
ceiling joists carry some of the load.
- Half of this would be carried by the gable-end wall and half by the
existing interior wall, the one that had a new column planted beneath
- That's 1280 pounds for each wall, and that load would be divided
amongst several studs, possibly 4 to 6 studs, although completely
uniform load-sharing is unlikely. Still, it's quite likely that any
given stud received no more than an additional 300 pounds of load.
That's the weight of a heavy man. Or two people the size of me. I have
no qualms whatsoever about adding that much load to a stud that is
part of a sturdy wall structure.
- Our method of framing will remove some loads from previously
load-bearing studs, shifting the load to other studs, including those
not intended to carry major loads, but nevertheless quite capable of
bearing some load.
- I had to make sure than the interior partition's studs were bearing
upon adequate structure. They were bearing on a second-floor joist
that in turn was resting on top of the first-floor partition, which
stood on the sub-floor, very close to a floor joist. (That main-floor
joist was doubled with a sister joist and then supported by a steel
- The costs for the materials used here was about $75
- Update: After almost 5 years this is holding up very well,
although I do sometimes hear a small clunk when I walk into the room.
I suspect that some of the framing lumber has shrunk and there is a
slight looseness in a connection somewhere. But there is no noticeable
deflection in the floor structure, and the marble floor tile has held
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