Decks, Patios, Porches and Docks - deck repair engineering Q

I'm going to be replacing the 2x4 deck boards which are in poor condition, with 2x6 pressure treated boards. Also, some portions of the 2x10 joists are in poor condition. My problem is the following: the deck is 45' x 9', and the 9' joists are cantilevered, running out from the interior first floor of the house, so there are no posts under the deck. There are a total of 33 joists between the end joists of the deck, about 10 of which have a severely damaged 3 to 4' section at the outer end (the 6' section closest to the house is protected by a cantilevered 2nd floor and is in good condition). I am concerned about the extra weight involved in adding sister joists, because the deck is cantilevered and not supported by posts. Would it be best to:
1. Add 4 to 5' scabs on both sides of each damaged end, attached with nails or long screws and lag bolts (or, with 10 joists to be so repaired, will this add too much weight to the outer end?), or:
2. Add a 9' sister joist to each of the 10 damaged joists, supported at both ends with double joist hangers, or:
3. Cut off the 4' damaged section, add a 9' sister joist, with a new 4' section to replace the removed section, and secure with joist hangers. I am concerned about cutting off the damaged section, since that is on the main cantilevered joist, or will adding a new section with a sister joist and joist hangers sufficiently transfer support to the new sister joist and sufficiently stabilize everything despite the added weight?

Sorry about the length of this post, but those are my major concerns. Thanks in advance for your replies.

evesk

9' is a substantial cantilever for 2x10's on 16" centers. The strength comes from the joists extending into your interior. If you were sister 9' joists to the current damaged ones, all of the load would still be on the old joists, focused at the point where it comes through the wall. I'm no engineer, but I would expect that any solution that calls for additional weight without additional support extending into the interior is asking for trouble. I would suggest a call to your local building code department (they should have an engineer on staff), to see what they think (I would expect it would be free also).

Do you have access to the interior where the joists are attached? If so, since you will already have the deck boards removed, perhaps you can remove each damaged joist and replace it with a new one. I would expect that they are attached to interior floor joists with bolts or nails (possibly also construction adhesive which would complicate matters). It would be quite a task, but you might be able to separate them to remove the damaged joists. Since they were probably attached when the house was originally constructed, they might also be nailed to the subfloor which would make their removal very difficult. Hope this helps.

evesk,

Welcome to DoItYourself.com and the deck forum.

First, forget trying to maintain the cantilever. That would involve replacing the ENTIRE length of the joists, which means ripping out the subfloor of the house for as far back as the joists go. And you are opening up a much bigger can of worms than you realize if you attempt it.

Sistering on the the existing joists won't work -- too much weight and your existing joists have lost their strength.

You need to put in footings. posts and a beam to support your joists.

I would cut off all the joist and properly protect(put in rim joist and weatherproof) your floor joist if it's not too late. Then you will need to put in concrete pier pads and build a post and beam deck. More and more builders are being sued for their cantilever deck construction. moisture leaks in and wroughts your interior floor joist. Just a poor design in my opinion and only provides astetics to a home. Post and beam is the only way to go when you want a deck to last and feel sturdy.

Thank you Ubob, lefty, and Tony. After having reviewed your responses, and after having removed half of the deck boards (which revealed more rot in the joists than anticipated) and meeting with an architect, I've decided to heed your advice and replace the cantilevered deck with new post and beam construction. Thanks guys.
evesk

Even though this is an old thread, I wanted to thank those who contributed. A google search led me here and the initial problem described is EXACTLY the position I find myself in with a cantilevered deck with the ends of the cantilevers rotted.

I appreciate the advice - that will help me to negotiate with a deck contractor.

Cheers,

Dean

halfdone,

Welcome to the forums.

A 9' cantelever, as was talked about in the initial post, is just absolutely rediculous. Hopefully your's is nothing that stupid!!

When I answered this post originally, I had just come off of an estimate for a deck that was cantelevered about 6' or 8'. Needless to say the owner balked at my estimate of about $1/2 million for 600 sq. ft. of deck, plus contengencies for me to CMA. He was dead set on keeping the cantelever -- "it fit the architecture of the house". A VERY short conversation with the folks at the County Bldg. Dept. backed me up -- they would NEVER approve those plans. Obviously, I didn't get the job, and I have no clue what happened with it.

The lesson to be learned is that you don't cantelever. Repairs become outrageous!!

Well, unfortunately, mine is between 5-6 feet. A contractor looked at it last night and is going to work up some estimates for us - both to fully replace the joists (he said this would be the preferred method, so the cantilever must not be too outrageous) and to also move to a post/beam layout.

This is my first home and unfortunately, I didn't realize the inherent complexity associated with cantilevered decks before I bought the place.

Thanks for the input, and I may be back shortly to discuss my options!

Cheers,

Dean

halfdone,

Let's look at what you have and what your options may be. (remember, you can actually see it -- I CAN'T!)

The deck cantelevers 5 to 6 feet. The joists of the deck are an extension of your floor joists which go through the exterior wall to the first interior wall. In your case that should be at least another 10 to 12 feet. I'm betting that the joists are just doug fir -- not treated, but possibly painted under the deck. (How am I doing so far??)

To replace the joist, you are going to have to tear out the floor of the room or rooms that they go through, and if there's a ceiling below some or all of them, that has to come out as well. IT'S MAJOR!!

In the case of the one that I submitted a $1/2M bid on, I was dealing with both the floor on top of the joists and the ceiling under them. Replacing the ceiling meant resheetrocking the interior walls of the lower floor after the ceiling was 'rocked. So, new subfloor and flooring above them and new sheetrock from the floor to the ceiling in 2 rooms on the lower level, ...

And what do I use for joists?? The 2/3's that is in the interior can be doug fir. It's not exposed to the elements and will last at least 100 years. But under the deck, where they ARE exposed to the elements, they're going to last about 15 to 20 years, tops.

In my opinion the building codes regarding cantelevered decks neds to be changed so that the only joists allowed for them are steel, aluminum, or structural plastic -- something that's not going to rot.