Exsisting 2x6 attic floor joist depression.

[JAZERUS]

I have an exsisting attic with 2 2x6's sistered 16" on center over a 12' span. I have used this area for storage and overtime the sheetrock nails have popped (in the ceiling below)from the depression when holding heavy loads in the middle of the span.

When I move the weight away I can see that the nails become flush again. Currently when jumping up and down the floor has very minimal bounce and the ceiling below is and looks level and straight.

The proposed fix: sister the Joists with 1/4" x 5.25" x 11.5' flintch plate, bolted with 1/2" carrige bolts every 16" and four bolts at each end. I know the typical construction of a finch plate calls for the steel plates to be sandwiched by the 2 2x6's but they are allready in place.

Any advise on a fix to stiffen up the exsisting 2x6's would be appriciated. Maintaining the demention of the 2x6's and not removing them is the goal.

 

[msquared48]

It would be a lot simpler to sister on an additional 2X6 to each existing one.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[JAZERUS]

Just to be clear, I have 2 2x6's sistered together 16" on center already. I am looking to add additional rigididy that the 2 sistered 2x6's have not provided. Are suggesting a 3rd 2X6.

 

[boo1]

The steel plate will be hard to install and is expensive.

The existing 2x6s joist depth is not ideal for loading. Creep can be an issue. Sistering additional wood joists or steel channels are easier solutions.

 

[Ron]

How much storage load have you been putting on there? How much do you want to put on there? Each combination of repair for the joist has a limit, both for capacity and deflection. You need to start there, with the capacity you want to achieve.

Once you've decided on that, and you have a repair scheme, you might consider jacking the joists up slightly in the center, make the flitch plate or sistering repairs, then release the jack.

 

[JAZERUS]

I was hoping to bring the floor up ro at least minimum live load capacity. = or > 40 lbs/sf would be the goal capacity. And a deflection limit of 360.

Jacking the joists up in the middle slightly while making the retorfit was something I was considering; thanks for the suggestion, I will most likely do that now.

How would steel channels do at stiffing the joists up?
Not much experience with using them structualy.


The floor is close to the capacity of 40lbs/sf according to the floor joist span chart I have referenced the span is about 16" to long. They are doubled up so i would think that would compansate for the loading the problem is the slight deflection in the middle.

 

[hokie66]

As your problem seems to be just deflection rather than strength, you might consider just dealing with the ceiling fastening. If you are always going to have stuff stored up there, you could put it back and then restore the ceiling support. Use sheetrock screws, then repair and repaint.

 

[msquared48]

"the sheetrock nails have popped (in the ceiling below)from the depression when holding heavy loads in the middle of the span.

When I move the weight away I can see that the nails become flush again."

Sounds like the nails have pulled down from the 2X6's and need to be re-nailed, preferably screwed. I would suggest additional screws to avoid pullout.

In order to add anything and not disturb the sheetrock, any additional strengthening will have to be done from the attic space. If two 2X6 are giving you this deflection, and you have to remove any boards used to support stored materials above the 2X6's anyway, why not sister on a 2X8 instead to the (2)2X6's? The I value would be about doubled. Deflections consequently cut in half.

As it stands now, assuming HF#2 for the 2X6's, they are gooe to 40 psf live load for the 12 foot span. So, as mentioned above, deflection is the problem, plus the fastening of the sheetrock to the ceiling members.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Rick90210]

You didn't mention if there is plywood fastened to the top of your ceiling joists. If not I suggest you add that (5/8" is good) with the long span perpendicular to your C.J.'s with full depth blocking at 1/3's of the C.J. span . Use 16d at 6" plywood to joists. This creates a de facto increase of the joists' "moment of inertia" which is the critical value in determining deflection. Also sister an additional 2x6 (microllam or similar would be ideal) at the middle 1/2 of each joist to be safe.

The steel options proposed will work also but I wouldn't forget the full depth blocking at 1/3 points of the C.J. span if you go that route.