Help me replace rotten joists in crawlspace

jamesbodellFebruary 18, 2009

I have a section of my house thats an old barn. The joists under it are nominal 2x7 pine timbers, probably about 100 years old, and 16" apart. These cover a 9' span, there is no weight other than the living room above. The subfloor is T&G 1 1/2 boards finished with wide pine floors.

The problem is rot. The beams show signs of old insect damage and rot. Many of the beams are just the shell of wood beams, and are actually a fine powder inside when you grab and break them apart. The floor is still structurally sound with no bounce, but I would like to clean them up. I have addressed the water and insects already to prevent further rot/damage.

I have installed a girder 6' from the exterior wall for support. I wish now to replace the joists and cut out the rot. I plan to do the following and am intersted in any feedback. Be aware that this is a crawlspace and space is very tight.

Rip down 2x8 to 7"x6' boards. I plan to install at 16" on center since its a 6' span. The span tables say I could do 24" on center but I feel better with 16"

I can do 2 things here. Since I will have to put the boards in flat and turn to vertical, I can either cut the edge at the ends to allow room to turn the boards, or rip them down to 6 1/2" and use shims on the girder and sill plate to lift the new joists up into position against the sub-floor. Does anyone have insight into the best way to do this?

After the boards are in place, I want to fasten to the subfloor. I imagine I could just toenail from the joist into the floor since they are so thick. Or I could use nailers or a metal tie of some kind. Thoughts?

Should I fasten the joists to the box of the house?

I will then cut and remove the rotten joists.

I imaging I would need some bridging?

Feedback and help appreciated.

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bus_driver

Just a wild thought: Consider having an exterminator treat the existing structure to prevent further rot, insect damage. deterioration. Then add whatever structural members are deemed necessary. Remove nothing.

    Bookmark   February 18, 2009 at 7:01PM
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jamesbodell

I am a bit of a perfectionist. Removing the old rotting members would make me feel better, but maybe your right, unnecessary work.

A far as the joists install, any thoughts to the method?

    Bookmark   February 19, 2009 at 8:02AM
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airqual_guy

I think you're better off ripping to slightly less than the vertical height and using shims. The height reduction will reduce the load-carrying capacity a bit but you've compensated for that by putting them closer than spec.

To fasten the joists to the decking, I would attach a piece of perforated angle bracket along the side of each joist at the top, so that when the joists are installed you can put fasteners up through the angle iron into the underside of the floor. Use screws, not nails. Nails will work loose over time and cause squeaks.

I assume by the "box of the house" you mean the rim joist. You definitely should attach the joist to the rim joist, I would use joist hangers.

Sounds like a fun project in the crawlspace, good luck.

    Bookmark   February 22, 2009 at 11:50PM
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