Partition Wall Actually Load Bearing

[Mitch Martin 120]

I have a question as to whether an intended "non-load bearing" wall actually bears some load and how (or whether) to determine how much. Here are the facts:

1. Roof=gabled and stick built
2. Two story house 29' x 38'. Beam in the basement divides the 29' span into roughly 16' and 13'.
3. First floor joists - span 16' from foundation to beam. Douglas Fir 2x10 and double every other one 16" OC.
4. Second Floor joists - 2x10 Douglas Fir double joists 16" OC that span almost 17' and run between the exterior wall and an interior load bearing wall. This interior load bearing wall almost sits on top of the beam (the wall actually sits on the 13' first floor joists "just on the other side of the beam").

A contractor installed a small wall to create a closet. The new wall runs perpendicular to the floor joists and is about 4 feet from the interior load bearing wall (and parallel to such wall) and is just over 2.5 feet long. It was built with a double top plate and 2x4 studs. There is no gap between the top plate and the joists (all of this from pics from the time). At the time it was built, the second floor joists were essentially fully loaded and the first floor joists were somewhat loaded but additional cabinets/quartz countertops have loaded the first floor joists around the margins. Four second floor joists (2 sets of double joists) run over this wall and continue on to the load bearing wall.

The question is whether this wall is taking a load for purposes of determining whether the first floor is overspanned given some additional live and deal load that is planned. If the 17' second floor joists were not continuous but cut and terminated on the closet wall (which is NOT the factset), the wall would take a load approximated as about 1,100-1,300 pounds. Even with this load, however, the first floor would be less than 40psf dead and live load after taking into account the planned changes. It seems to me, however, that actual wall load will only result from marginal deflection in the second floor joists. I'm inclined not to worry about this since the first floor can handle the "worst case" load but I'm not sure I'm thinking about this the correct way.

 

[Tomfh]

If the second floor joists are cut at the closet wall (do you know this for sure?) then it’s likely the first floor joists are now load bearing.

Check deflection, including localised deflection due to the wall load.

We have a similar scenario in our house where some of the first floor joists support the roof load via an internal wall. Whilst the joists still work, there is extra floor sag at that location, which I find annoying.

 

[Mitch Martin 120]

Sorry for the confusion. None of the joists have been cut or will be cut. Since I don't know how to compute the actual load on the intervening wall, I had hypothetically assumed the joists were cut to compute what I believe would be the max load on the wall. The relevant joists above the wall are 17' and are 2x10 Douglas Fir No. 1 according to the old house plans. They span between two load bearing walls and this small wall is in between and I believe it will accept load only to the extent of further deflection in the second floor joists above (which I believe will be minimal since they were fully loaded when the wall was installed). I am just not sure I am thinking about this the right way or if there is another way to think about it.

 

[phamENG]

The real question is why? Is this an academic effort, or do you have an end goal? The goal usually informs the requisite method.

 

[SWComposites]

Hmm, so in summary:
- there have been no changes to the original framing, except
- addition of small closet wall
- now you want to add more live and dead load (why? what for? where?)

Frankly I can't imagine that the added closet wall is currently carrying much load unless the contractor somehow jammed it in / jacked up the 2nd floor joists to take load off the original interior load bearing wall (which is highly unlikely).

 

[Mitch Martin 120]

Right. No changes to original framing except this 2.5 long wall in question. This is just informal analysis to make sure the first floor isn't overspanned after adding some floor tile, bigger countertops and some other live and dead loads which sit on the same joists as the wall. Also want to consider whether local deflection is a concern under this short wall. Unless I can demonstrate a problem, I don't think I should ask the contractor to rebuild the wall with a gap since it isn't usual building practice here. Contractor did not jack up the 2nd floor joists to build this wall although it's possible he took a little load by jamming the studs in. I'm concluding that this wall isn't carrying much load since the wall was built with full load already existing on the second floor and since the first floor deflection has likely increased somewhat. If the second floor was going to see material additional loads then I might change my tune but the load on the second floor is very unlikely to change in any material way. I've done the math to confirm that the joists aren't overspanned even if this wall was carrying full weight but the "local deflection" analysis is trickier because it may be bearing some weight and the wall sits on only three joists (one set of double joists and a single joist).

 

[Tomfh]

If both floors are self supporting and the wall links them then that’s your structure, a linked set of beams. Depending on how well fastened the wall is the floors will either move/deflect together or the wall will pull away/crack (perhaps at the ceiling)

If both floors are self supporting I wouldn’t be too fussed.

Do a local deflection analysis if you’re curious. Model a point load on the joists and see how much extra deflection occurs. I reality you’ll get a few extra joists too as the flooring spreads the deflection out.

 

[gte447f]

Ignore the closet wall and don't worry about it. The only way this could cause problems is if the 2nd floor had significant live load relative to the 1st floor. Then the closet wall would pick up that load and distribute it to the 1st floor as a line load. But, this is true with all interior non-load-nearing walls in multi-story construction, so your situation does not sound unique. Like Tomfh said, the floors are basically linked beams. If the loading on each floor is similar, then the floors basically have no effect on one another. If the loading is different, then they start to effect one another, but unless the loading is significantly different the effect is probably negligible for all intents and purposes.

 

[Mitch Martin 120]

Thanks all. I did some local deflection analysis for fun. If I assume the new wall carries the max load (which isn't a valid assumption but I have no method to calc the actual smaller load) and I only take into account the weight on the span of three joists under this new wall (basically a 32" by 16' area), I still barely meet L/360 deflection BUT if I assume the closest adjacent joist (about 9-10 inches from the end of the wall) shares some load it looks substantially better. The adjacent joists have virtually zero live load (mostly open space) and very little dead load on them. Thus, seems that all is well.

 

[Tomfh]

I still barely meet L/360 deflection

Is that along the joists, or perpendicular to them?

Perpendicular is where you see the effect. The difference in deflection between the loaded and unloaded joists.