Taking the bounce out of a floor?

[Jim Dwight]

Sorry, been in the shop making sawdust. I think the "I", moment of intertia, for bending calculations is the second moment. The formula for a simple rectangular cross section is 1/12 bh3 - 1/12th of the thickness times the height cubed. That is why the height of a joist makes so much difference (as has been mentioned). My degree is in mechanical engineering. I don't really do any design work but I remember how to use the equations (but I have to look them up).

[Jerome Sidley]

Sorry, I've been away, the original planned use of the upstairs was as an apartment. The story goes that the original owner built the garage in the 40's and was going to rent out the upstairs but to be able to do that it would have cost him a $20 tax which he was unwilling to pay. I'm still undecided as to what to do

[Al Launier]

Jerome, if you are intending to use the upper level over your garage as an apartment living space, then you'll most likely have to upgrade the structural integrity as a whole to comply with local building codes, especially when considering the location of focussed loading such as a filled bathtub, refrigerator/freezers, etc., plus plumbing, electrical, A/C, etc. To do this, you really should consult with the local building inspector before you commit to a plan and materials. The floor joist arrangement should be constructed for a 40 PSF live, 10 PSF Dead load and for a span of 12' should have 2x10 floor joists spaced at 16' intervals. 2x10 floor joists have a maximum allowable span that varies from 11' 11" - 17' 4" depending on the type and grade of wood used.

Upgrading the joists can be achieved different ways, as note above, but the deeper joists, i.e 10" will provide more rigidity. Regardless of the method for modifying the floor joists, you really should consider the best way to support these joists at their ends. A mid-span wall is great, but the balloon framing is a problem at this point, especially if the outer wall studs are 2x4s.

If the supporting ledger boards of the balloon framing are internal and flush with the inside of the 2x4 wall studs, and the studs sit on a 2x6 or wider sill plate, then you could place another 2x4 on top of the sill plate and perpendicular to the face of the wall stud to form a "T" that the floor joist could sit on top of. If the ledger board is external then the alternative above using 2x6s could be considered as well.Using the 2x4 concept would be less expensive. Either alternative would provide the needed end support. You should review the applicable concept with the building inspector for approval before proceeding.

If you go forward with the apartment concept you might also consider the liability aspect, i.e. insurance(s).

[Jerome Sidley]

I'm Not Thinking of making it an apartment that was the intended use in 1942 when it was built.

[Jerome Sidley]

As I have not yet started this project I was thinking last night about an I beam running down the center of each bay this would make the span only 6 feet. How do you size a 22' I beam?

[Tom M King]

Google "I beam span chart table" and you will find plenty.

[Steve Rozmiarek]

Beam height, web width, and thickness.

[Al Launier]

Instead of a steel I-Beam I'd recommend a LVL (Laminated Veneer Lumber) beam (AKA Gang-Lam) which is much lighter, much less expensive, is secured with nails/screws, yet very strong in the vertical direction it supports a load. You would still need to support each end with posts, wood or lally columns.
Please note the difference is whether the joists are continuous or not.

[Tom Bender]

Another approach

Add a 2x4 flat on the bottom of each 2x6. This combined with the flooring will look a little like an I beam. It will add a lot of stiffness and won't impact any blocking, wiring,ducts etc in the space. And it's easier to do.

You may want to add a horizontal 2x along the wall to support this new 2x4.

Blocking or cross bracing is important also. If it's not there, add it.

[Tom Bender]

Add a 2x4 flat on the bottom of each existing 2x6. This will not interfere with the existing wiring etc and will add a lot of stiffness. It's easy and relatively inexpensive. You may want to run a 2x along each wall to support the new 2x4.

[Jerome Stanek]

When I was working at a cabinet shop they had a floor above that had a lot of bounce and we didn't want to loose the clear span so what we did was this. we made a beam to span it length wise using 2 2 x 10s on the out side and a 2 x 6 in the center the we ran a cable from just under the 2 x6 end to end but in the center we had a 4x4 block that the cable ran under. We used turn buckles at the ends to tension the cable we could actually jack the center of that beam higher then the ends. No post to deal with. I showed the company that I did trade show exhibits how to do this and they ended up building a lot of their truss systems this way.

[Jerome Sidley]

Thanks, guys
All great ideas I thinking of a combo of 2X8 between the 2X6 with a 2X4 glued and screwed to the bottom of the 2X6 and a cable truss in the middle. I'll make sure the 2X8's and 6's are the same depth.

[Tom Bender]

Start with the 2x4s on the bottom and I think you'll be done.

[Jerome Sidley]

So I took the week off and have spent a couple of days on this. I found that putting up 12' long 2x8's by yourself is a lot of work. I started by tacking up the ledgers but I did not have enough space to get the 2x8 in so ripped off one side. My technique is like this fid the center of the joist bay drill a screw up through the floor at both ends. Go upstairs and find the screws and start a screw from the top. Go back down and remove the screw lift the 2x8 into place on the ledger and the other end onto a 2x4 that's on top of a hydraulic jack. climb down the ladder and jack the one end until its tight go upstairs and finish putting in the screw that was started and another for safety. go back downstairs and remove the jack and take it to the other side and repeat. measure and cut blocking and nail into place. Once one section is finished jack up the ledgers until tight and permanently nail into place. Even before nailing in the ledgers and with the joists just hanging from the screws at the end there was a huge difference. with the ledgers, in place, it is really solid.
I did not continue to put the 2x4 at the bottom of the existing 2x6 as getting screws into the old wood would take 2 or 3 tries in the same hole at it does not seem to be needed.
I still have to go back and screw down each plank and that should improve it even more.
thanks for all the help everyone.

[Al Launier]

It appears you have an opportunity to hurt yourself by doing this alone. An extra pair of hands would seem to be a big help. Any friends that could help you? A case of beer could go a long way.