Hot Topics: Sister Floor Joist

a ceiling joist connecting an incomplete beam

Over 250,000 experts and novices discuss 120+ DIY categories in the Forums, so each week we highlight a conversation that may help with your next project. This transcript has been lightly edited.

Original Post: Sister Floor Joist

Spinny24 - Member

I have a second story floor joist that was originally cut to accommodate a brick chimney. I removed chimney and need to sister the joist. Floor joists are redwood full dimension 2"x8"x14' on 16" centers. Do I need to sister full length, partial length, single side, or both sides? What type wood, or maybe Microllam LLV?

a patched wooden floor joist from below

XSleeper - Group Moderator

Is that an attic floor above those joists? It makes a difference, because your joists are currently overspanned.

Spinny24 - Thread Starter

Not the attic floor. This is the second floor of a 1892 built home in Northern California.

XSleeper - Group Moderator

Yikes. Do you have to stick with 8" or could you use 9 1/2"? A single 9 1/2" LVL sistered onto one side would do it. Yes, full span (from bearing wall to bearing wall).

Build a temporary wall under that broken joist and jack it up until it's straight, or even a little crowned. PL those joists and the subfloor once you are sure it's going to fit. Then put the LVL in, and crown it a little with a jack to match as you fasten it all together.

Spinny24 - Thread Starter

Not able to go with 9 1/2". Would have to raise the complete second floor which is about 2000 square feet. Even with the cut out in the joist, the joist is still completely level after 100 years. Home is constructed with balloon framing.

XSleeper - Group Moderator

Well, you will probably need to get a 9 1/2" LVL and rip it to 8" then. I assumed it was balloon framing in a house that old. You will just need to sister the studs under the ends of the LVL.

Amazing it's still level. That says something about that old growth lumber—far superior to the junk they sell us nowadays.

Spinny24 - Thread Starter

Thanks. What is amazing is the living room with the same framing dimensions is 18 feet wide by 18 feet long.

Added a couple of additional photos of the studs on each end. Which side of the studs should I sister? One stud has cross bracing at the top.

wooden floor joists from below

a wooden floor joist from below

XSleeper - Group Moderator

In the right photo it looks like you would want to do it on the left side.

In the left photo, it looks like you would need to pad out the whole right side 1 1/2" so that your LVL slides beside that stud on the right, but will that cross bracing be in the way if you do that?

Spinny24 - Thread Starter

What about just boxing out the cut out section to the adjacent joists?

XSleeper - Group Moderator

You certainly could, but that's asking a lot since they are already overspanned by today's standards. Since you say everything is still straight and level despite the hack job, that would probably be easy to do.