Cantilever Deck Problems - Rotten Wood

[Mark W Pugh]

So, I have this cantilever deck that was built in 1979. The deck floor joists extend from the interior, which also holds up the floor in two rooms and the gable end structure walls off the foundation/block. I have numerous exterior floor joist portions that have rotted and need replaced. It appears these joists/boards are NOT treated lumber, and were sealed and painted with something. I think I have a good plan to replace, but I don't know what kinds of boards to use. I have access to the full length of all boards, drive in garage ceiling is not finished.

Now, wondering how to attack this.

1. If I use treated lumber, it will shrink as it dries. Since the floor joists actually holds up interior gable end walls, and interior walls, do I need to worry about using pressure treated wood and it shrinking and causing problems?

2 - If I were to use interior wood, how would one treat the interior wood to prevent rotting on the exterior?

3. KDAT lumber - should this be a consideration? Expensive, but......?

4. How would you attack this?

5. I was thinking about sistering the floor joists. Coming in with the exterior joist by 6', then using 3' on either side of the the joist's butted ends. I would add a board on both sides of the joist's mating ends, and bolt together with the use of construction adhesive. Obviously, securing back to floor, bottom plates, etc.

What say you?

[Lee Schierer]

Your first step should probably check building codes to see if your cantilever deck is permitted. Then consult a good structural engineer for proper support sizing and materials.

[Mark W Pugh]

Your first step should probably check building codes to see if your cantilever deck is permitted. Then consult a good structural engineer for proper support sizing and materials.

First, the house was built in 1979 in an area that had no inspections. Today, the only inspection that are required, for a total house build, is for the septic system. The cantilever deck is already there.

So, I have a problem I must fix. I hold no one responsible/liable for the work I do. I'm not a contractor, but I can find my way around a shop and home construction.

So, I need advice on how others have done, or would do this. You can message me vs putting here on-line.

Thanks for any inputs

[Wayne Lomman]

Do you have time to buy your treated timber and let it dry? Otherwise, buy a dry durable species. It's generally a bad idea to try to protect a low grade timber. Cheers

[Tom M King]

The only cantilevered deck I ever built had steel that went from being bolted to interior floor joists, and had treated wood bolted to it on the outside. The exterior wood can be replaced without bothering any other part of the structure. I think it was 1979 when I built that house too.

[Dave Zellers]

Cantilevered decks are a bad idea. I was involved with a couple 30 years ago and both developed serious problems. They leak and invite bugs into the house.

My advice is to cut off the cantilever, seal the house, and if you want a deck there, build it independently from the house, supported on both ends.

[Mark W Pugh]

Cantilevered decks are a bad idea. I was involved with a couple 30 years ago and both developed serious problems. They leak and invite bugs into the house.

My advice is to cut off the cantilever, seal the house, and if you want a deck there, build it independently from the house, supported on both ends.

Can't do this. This is a huge access out of the house. The house is brick, so independent support from the brick is not an option.

[Mark W Pugh]

Do you have time to buy your treated timber and let it dry? Otherwise, buy a dry durable species. It's generally a bad idea to try to protect a low grade timber. Cheers

I agree with this. KDAT lumber is expensive, but may be my only option.

[Aaron Rosenthal]

I was a contractor for over 20 years, and built many a deck.
Is it possible for you to PM me a few pictures and I'll do what I can to help.

[Chuck Wintle]

Your first step should probably check building codes to see if your cantilever deck is permitted. Then consult a good structural engineer for proper support sizing and materials.

I would absolutely have an engineer provide input for this deck.

[Stephen Tashiro]

The deck floor joists extend from the interior, which also holds up the floor in two rooms and the gable end structure walls off the foundation/block.

My advice is to cut off the cantilever, seal the house, and if you want a deck there, build it independently from the house, supported on both ends.

Can't do this. This is a huge access out of the house. The house is brick, so independent support from the brick is not an option.

I suggest you post some pictures. From the verbal descriptions, it isn't clear why you can't independently support a deck with posts.

[Eric Keller]

I was thinking the deck was too far off the ground for posts, but if it provides access that doesn't sound quite right. AFAIK, most decks are built with a ledger board, and aren't completely independent. Flashing the ledger is well understood, but still a common site for water intrusion and house failure. Still have to fix the penetrations though.

[Scott Brader]

First, the house was built in 1979 in an area that had no inspections. Today, the only inspection that are required, for a total house build, is for the septic system. The cantilever deck is already there.

So, I have a problem I must fix. I hold no one responsible/liable for the work I do. I'm not a contractor, but I can find my way around a shop and home construction.

So, I need advice on how others have done, or would do this. You can message me vs putting here on-line.

Thanks for any inputs

My concern would be that whoever buys your house someday may hold you responsible for the work you do. That's why I would definitely get an engineer or at least a licensed contractor involved. You want to make sure whatever fix you do will not only support the deck without damaging the integrity of the house, but will also pass muster with a home inspector who may look at the house as part of a future sale.

Scott

[Al Launier]

LVL engineered lumber is very strong, yet unsuitable for typical pressure treatment due to the glue lines & materials. So, you might want to consider the use of Paralam Plus PSL. Reference https://www.weyerhaeuser.com/woodpro...llam-plus-psl/. Having that exterior preservation treatment would be very beneficial over the long term.

Sistering the internal joists, then bolting (lag bolts or through body bound bolts/washers/nuts, carriage bolts/washers/nuts) & using construction adhesive would certainly provide for a secure means of attaching the cantilevered joists. However, in our neck of the woods when cantilevering, the structural framing members typically has the internal length of the framing member twice the length of the exterior cantilevered portion. Example: For 4' exterior cantilever the interior length should be 8'. Depending on the size of the deck, these joists could be quite long to maintain the 2/1 ratio. Your proposed method, although strong, would result in only 1 1/2' on either side of the butt joint. I would suggest longer splice places, but confirm with the local building inspector.

Assuming the internal joists are still in good condition, and resting on a pressure treated sill plate on top of a sill seal, and are still in good condition, then sistering the joists, i.e. typically alongside of each other rather than butting together with splice plates, is typically the method used around here nailing them together.

You have a serious construction project on your hands, so check with the local building inspectors to conform to building codes.

[Robert Engel]

How wide are the joists?

I probably wouldn't worry too much about PT wood shrinking.

2x lam beams will work, too.

Sister on to existing joists using lag bolts w/glue even better.