Repair damaged floor joists

[VictorAK]

Does anyone have any advice on how to repair existing floor joists? The floor joists are 2x8" over 70 years old in generally good shape except for those under the bathroom floor. The plumber cut 2-3" diameter holes aboout 12" from the end, approximately in the middle of the joist. I'm thinking I can splice a 2x6" joist on both sides just not sure how long. Does 4 feet on either side of the hole, or any other areas of the joist that is damaged, sound sufficient?

 

[jhoulette]

Since the holes are located near the end, shear should be your only concern. Check the remaining cross section area. If they are 70 years old I'm assuming rough sawn timber.
Area of 2x8 = 2" x 8" = 16in^2 - hole x 2"x3" = 10in^2 x shear strength 85psi (conservative value) = 850lb capacity
I guessed that the holes are side by side, not stocked. If stacked then you only have 4in^2. Also, verify the joists dimensions, I used 2" x 8" to make the example easier.

A quick stab at your loads 2x8 joist spanning 14ft at 16"o.c. would have a end shear/reaction of 467lb (40psf live/10psf dead) You may not need to reinforce the joist.

If you determine you do need to reinforce the joist I recommend cutting a 7/16" section of OSB to fit around the openings (U shape) glue and clinch nails in a pattern that meets your needs.

Jim Houlette PE
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