sistering joists... how to seal the top edge. - Contractor Talk - Professional Construction and Remodeling Forum

s. donato · 01-25-2009, 10:46 AM

Okay i have a repair job coming up.

i need to beef up all the joists b/c there are currently 2x6 spanning 8-10 feet i am going to come in with 2x8's to sister them on but now i am opening up a can of worms b/c i don't want water to get in between the layers. usually i would use vycor deck protector along the top edge but since this is a repair how can i seal that edge.

i was thinking of using some pl along the top edge before i sister the two together. do you think that would help or hinder?

any ideas?

rebuilding is not in the budjet for the HO this year.

Greg Di · 01-25-2009, 04:55 PM

Why can't you use Vycor? Are you doing it from the bottom?

I'm confused.

**BuiltByMAC** · 01-25-2009, 05:03 PM

I'm thinking the decking's already screwed/nailed to the existing joists -

How about instead of sistering the joists, just double them? If the original joists are 24" oc, install your 2x8s in the middle of each joist bay, not next to the originals. Your new joists would be 24" oc, total decking span would be 12" oc. You can Vycor the tops of the new joists before installation...

Mac

RobertCDF · 01-25-2009, 05:11 PM

I like mac idea... Just add another joist in between each joist bay. This should give you plenty of added strength.

s. donato · 01-25-2009, 05:44 PM

mac i like that idea too.

yeah the decking is in place. i just felt sistering was the logical solution at the time.
it is a historic porch and is only 3.5 feet deep and i believe it only has three bays already. i will have to look again when i go there next week.

i like mac's idea also b/c it will definitely not trap moisture as bad either.

**BuiltByMAC** · 01-26-2009, 02:30 AM

Thought about this a little more - by pre-installing your blocking to the 2x8s, there will be less monkeying around under the deck...just tap the blocking up into place on one end, that will hold while you tap up the other side.

The additional off-set blocking will help support the existing undersized joists by creating a bridged effect. Everything supports everything else.

Plus, building on sawhorses beats building in place most days of the week!

Mac

tom m · 01-26-2009, 09:21 AM

If you go back to your first idea I think using PL would also work.....Its supposed to be a water proof adhesive. Its truely great stuff.