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Subject Author Date
Joist selection Wayne Whitney 02-15-2008
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Posted by DanG on February 18, 2008, 2:40 am
You might be ahead to explain what it is you are doing. I don't
think I would mess around sistering a bunch of joists. If the
existing 2x4 have worked fore years, I would spend the time
designing a beam to carry the load for the wall you are yanking.
It would seem much more simple to me to install one beam and the
carrying ties. By the time you sister the joists in question, you
will have the existing ceiling on the ground.

Just where were you going to special order those 17 foot 2x8/s?

--
______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)
dgriff237@7cox.net



>
>> What sort of deflection are you getting with a 2x8 sistered on?
>
> From the awc.org calculator, the span rating for a 2x8 SS DF
> with a
> 20psf live load and L/360 deflection is 17' 2" and is deflection
> controlled. So ignoring any end taper, the deflection at 16' 5"
> will
> be L/360 * (16'5/17'2)^3 = L/412, or 0.47".
>
> I'm ignoring the existing joists when doing this calculation,
> since
> they are 2x4s. Most of the house has 2x6 ceiling joists, so I
> was
> quite surprised to find the 2x4s in the area I'm working on.
>
> Cheers, Wayne



Posted by RicodJour on February 18, 2008, 7:56 am
> You might be ahead to explain what it is you are doing. I don't
> think I would mess around sistering a bunch of joists. If the
> existing 2x4 have worked fore years, I would spend the time
> designing a beam to carry the load for the wall you are yanking.
> It would seem much more simple to me to install one beam and the
> carrying ties. By the time you sister the joists in question, you
> will have the existing ceiling on the ground.

Dan's got a great point - it was bound to happen eventually! ;) A
flush beam supporting the joists with joist hangers would be much
simpler and cheaper. There's usually some surgery to create the beam
pocket and you have to plan the assembly (possibly installing beam,
then installing supporting studs), but it's a preferable way to go in
almost all aspects. You mentioned five joists needed sistering, so
that's about a 8' span. You wouldn't need much in the way of a beam
since it's only a ceiling load - you were surprised that the CJs were
2x4s so it's safe to assume that you hadn't been up in any attic
space. A couple of 9.25" LVL's would be more than enough.

> Just where were you going to special order those 17 foot 2x8/s?

They're not special order around here. Generally, depending on the
yard, they stock 18' or 20' 2x stuff.

R

Posted by Bobk207 on February 18, 2008, 10:37 am
>
> > You might be ahead to explain what it is you are doing. I don't
> > think I would mess around sistering a bunch of joists. If the
> > existing 2x4 have worked fore years, I would spend the time
> > designing a beam to carry the load for the wall you are yanking.
> > It would seem much more simple to me to install one beam and the
> > carrying ties. By the time you sister the joists in question, you
> > will have the existing ceiling on the ground.
>
> Dan's got a great point - it was bound to happen eventually! ;) A
> flush beam supporting the joists with joist hangers would be much
> simpler and cheaper. There's usually some surgery to create the beam
> pocket and you have to plan the assembly (possibly installing beam,
> then installing supporting studs), but it's a preferable way to go in
> almost all aspects. You mentioned five joists needed sistering, so
> that's about a 8' span. You wouldn't need much in the way of a beam
> since it's only a ceiling load - you were surprised that the CJs were
> 2x4s so it's safe to assume that you hadn't been up in any attic
> space. A couple of 9.25" LVL's would be more than enough.
>
> > Just where were you going to special order those 17 foot 2x8/s?
>
> They're not special order around here. Generally, depending on the
> yard, they stock 18' or 20' 2x stuff.
>
> R

Rico-

If he's got the ceiling plaster down, wouldn't throwing five long
2x8's up there & nailing them in place be quicker than creating beam
pockets, cutting the joists, installing a beam with hangers?

cheers
Bob

Posted by RicodJour on February 18, 2008, 10:39 am
>
> > Dan's got a great point - it was bound to happen eventually! ;) A
> > flush beam supporting the joists with joist hangers would be much
> > simpler and cheaper. There's usually some surgery to create the beam
> > pocket and you have to plan the assembly (possibly installing beam,
> > then installing supporting studs), but it's a preferable way to go in
> > almost all aspects. You mentioned five joists needed sistering, so
> > that's about a 8' span. You wouldn't need much in the way of a beam
> > since it's only a ceiling load - you were surprised that the CJs were
> > 2x4s so it's safe to assume that you hadn't been up in any attic
> > space. A couple of 9.25" LVL's would be more than enough.
>
> If he's got the ceiling plaster down, wouldn't throwing five long
> 2x8's up there & nailing them in place be quicker than creating beam
> pockets, cutting the joists, installing a beam with hangers?



Posted by RicodJour on February 18, 2008, 10:46 am
>
> > Dan's got a great point - it was bound to happen eventually! ;) A
> > flush beam supporting the joists with joist hangers would be much
> > simpler and cheaper. There's usually some surgery to create the beam
> > pocket and you have to plan the assembly (possibly installing beam,
> > then installing supporting studs), but it's a preferable way to go in
> > almost all aspects. You mentioned five joists needed sistering, so
> > that's about a 8' span. You wouldn't need much in the way of a beam
> > since it's only a ceiling load - you were surprised that the CJs were
> > 2x4s so it's safe to assume that you hadn't been up in any attic
> > space. A couple of 9.25" LVL's would be more than enough.
>
>
> If he's got the ceiling plaster down, wouldn't throwing five long
> 2x8's up there & nailing them in place be quicker than creating beam
> pockets, cutting the joists, installing a beam with hangers?

Damn send button! Sorry about that.

Without pictures it's tough to tell what's the quickest solution.
There's room above the CJs, and the OP mentioned having to notch, but
he didn't say whether it was one or both ends. There might be room to
put the beam above the existing CJs without cutting them and hang 'em.

The sistering option seems to be throwing a lot of extra expense and
weight at the problem and getting a fairly large deflection as a
result. Sistering may be a bit faster, but I don't think a 1/2"
deflection is acceptable. It's definitely not necessary. Doesn't
seem like a great solution.

R

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