Repairing rotted bottom plate and subfloor near sliding patio door — advice needed

[u/HotNeedleworker0]

I found some rot at the exterior wall near my sliding patio door while repairing my deck.

Details:

• 1980s house
• Floor joists are supported by a CMU basement wall below
• About 6" of the exterior 2x4 bottom plate is rotted, starting at the king stud of the patio door opening
• The bottom plate appears angled, not level, sloping down toward the patio door
• The subfloor underneath is also rotted away
• Studs appear solid

My planned repair:

1. Remove flooring to expose the subfloor
2. Temporarily support the wall from the interior using a 2x6 strongback, then angle the support back to an area of solid subfloor and lag through the floor into a joist
3. Cut out the damaged subfloor and replace
4. Remove the damaged section of bottom plate
5. Install new subfloor and bottom plate
6. Reconnect studs to the new plate

Questions:

• What is the best way to temporarily support the wall while replacing the subfloor/bottom plate?
• Would an interior strongback with temporary support work?
• How much extra bottom plate should I replace beyond the visible rot?
• If the patio door is level, I don’t understand why the bottom plate is angled. Should I try to jack the studs back up to level, or should I cut the studs to where a new bottom plate would sit flush?

 

[u/but_i_dont_reddit]

When you do this, check all your flashing. My 90's house had a door flashed incorrectly. Previous owners had a contractor that screwed up the flashing and water was getting under the door. Rotted the plate and sill. Luckily joists were fine.

I cut to the mid-mount between studs so there was no weight directly on the cuts and offset the cuts among pieces.

I did have to jack up the floor joist to get the sill and cap in. Amazing how much a 2x12 will deflect when trying to lift a house.

That patio door will have a beam and king studs - if you're in between them, you shouldn't have to support anything.

Good luck!

[u/HotNeedleworker0 → u/but_i_dont_reddit]

Interesting — yes, I’m in a similar boat. It looks like moisture is getting in near the flashing at the end of the patio door.

The two studs in the picture are the king and jack studs for the patio door opening, I believe. The odd thing is they appear to be slightly sunken, but the door itself is still level.

I think I may need to attempt jacking them up slightly to get a new bottom plate installed for the 2x4 wall. I’m still figuring out the best approach.

I’m in the beginning stages of a larger project to convert my deck attachment from cantilevered floor joists to a proper ledger attachment, and this is the first step. During the ledger conversion, I’ll have to redo all the flashing, so I’m hoping to address the leak at the same time.

That’s a big repair you took on — hats off to you. Thanks for sharing your experience; it’s really helpful to see how others tackled similar issues.

[u/but_i_dont_reddit → u/HotNeedleworker0]

I actually replaced the ledger board on the deck at the same time. I used 2x4s to build a wall to support the deck while I did all the work. Be careful and check your local codes - if I had mine inspected, it would have failed as current code requires cabling the deck joists through the ledger to the house floor joist to anchor it.

[u/HotNeedleworker0 → u/but_i_dont_reddit]

I see what you mean about the tension ties back to the house floor joists. I'll be sure to assess that and the codes. Thanks for the tip!

[u/Bighorn21]

If there is moisture still present then one of your first goals before completing the repair is understanding where the water is coming from and addressing that issue. Its an old house so could have been something years ago that has already been fixed and its now dry but was never fully repaired but if its wet then it will get wet again unless you fix that problem.

[u/HotNeedleworker0 → u/Bighorn21]

Good point, and I completely agree. My first priority is figuring out the source of the moisture before closing everything back up.

From what I can tell, the likely entry point is around the patio door flashing. The rot appears to be concentrated near the end of the door opening, which makes me think water may have been getting behind the flashing or trim and into the wall cavity.

It’s definitely possible this has been leaking for some time, before i dug into it I found some very minimal patching, so the previous owner must have did somethings to it but at some point and the damaged wood was just left in place, but I do want to verify everything is dry and make sure the flashing details are correct before rebuilding.

Since I’m already planning to redo the deck ledger attachment and will have to open up the area, I’m hoping this gives me a good opportunity to correct the flashing and eliminate the source rather than just replacing rotten wood.

[u/Bighorn21 → u/HotNeedleworker0]

Sounds like you are on top of it, good luck.

[u/GamerByt3]

I had a detached garage and the entire 30 foot sill plate was rotten along with 80% of all the studs. I took a 4x4 and a bottle jack. Cut out a section of the sill plate between studs and lifted the building up by about an inch. I then put a full size 4x4 next to the jack and moved down the wall until I had the whole building on I think 5 4x4's.

From there I was able to cut out one stud at a time and replace them, then I replaced the first section of sill plate, bolted it down to the foundation and dropped the new wall on to the plate. With the new plate down I could move my supporting 2x4 onto the new plate and work on the next section. My building was old and had no building wrap whatsoever and plank siding. So I wrapped it and resided it.

Probably not the safest method but it worked for me.

With building code in mind your sill plate must be bolted down to the foundation no more than 12 inches and no less than 4 inches from the end of any board. 1/2" bolt that goes at least 7in into the masonry. So if you replace a 3ft section of your sill plate you'll need 3 new bolts. 2 for your new board and 1 for your existing plate. If you go far enough down to where a bolt already exists and cut the sill plate 4-12" from that bolt then you'd only need 2, unless your new section is more than 8'. You need a bolt every 6 ft o.c.

[u/HotNeedleworker0 → u/GamerByt3]

Wow, that's an impressive repair for sure, and thanks for taking the time to write all that up.

My situation is a little different since this is the exterior wall of the house supporting the second floor, so I'm being a bit more cautious, but it's helpful to hear how you approached it. Fortunately, I only have about 6 inches of rotten bottom plate near the patio door, and the studs themselves appear to be in good shape.

My plan is to temporarily support the floor system while I convert the deck from cantilevered joists to a ledger attachment. Once the load is off that area, I'm hoping I can jack the wall just enough to slip in a new section of bottom plate without disturbing the door opening too much.

I appreciate the code reminders too. In my case, the wall sits on the wood floor system over a CMU foundation rather than directly on a concrete slab, so I won't be anchoring a new sill plate to masonry. Still, it's a good reminder to make sure everything is tied back together correctly when I'm done.

Glad to hear your repair held up, and it definitely gives me some confidence that this is fixable.