Cantilever joist repair

[CAF123]

New to forum. Have searched many threads and so apologies in advance if covered, but could not see anything.

I have a 1st floor (3m high) cantilever deck - 2m out from the house. 8.5m wide with 19 of 270 * 50 joists.

8 of the joists have rot in the top 50 - 100mm at the off side from the house.

Various advice to date from decking dudes;
[ul]
[li]Rip out the rot top sections and laminate in new 50 or 100mm sections, glued and clamped.[/li]
[li]Rip out the rot top sections use the remaining 170mm+ to sister in new joists.[/li]
[li]Cut off the joists to good wood and but join with new section, and add a 100*50 sister member on one side, bolted in x places. Ensuring the joins are staggered.[/li]
[li]Cut off all joists to near the brick skin wall, and place a ledger across the face of the cut end of the joists, and replace with new joists on joist hangers. And add posts and beam at the opposing side.[/li]
[/ul]

As always cost is a major factor, so am reluctant to go with the last one.. Alternatives appreciated Open to steel plates if such an option is beneficial. I'm not too worried about the look as the deck will be tiled above, and have a ceiling under. It is the structural strength to hold a tiled deck, and of course any live load.

If I do have to go for the last option of a ledger, what sort of fixing should I consider to the 19 joists.

 

[asixth]

I reckon point 4. Dry rot can appear good but affect more of the joists than what may appear visible.

That and I think trying to cut back and splice or sister new joists to the old with create a very weak point and not worth doing for an elevated deck.

 

[msquared48]

I take it that these cantilevered joists were not pressure treated?

I also take it that since these joists are cantilevered, they have a back span that extends into the building. Do you know how far they extend, and how they are connected to the existing floor structure?

Is the existing deck sloped? If so, was that achieved by tapering the top of the existing joists, or sloping the joists?

Mike McCann
MMC Engineering

 

[CAF123]

asixth - The old decking has been completely removed and the soft rot has been scrapped out, so we do have a reasonable view - albeit I take your point that until a joist is sawn back we really don't know.

msquared48 - correct the exiting joists are not pressure treated. There is a deep overhanging eve of about 600mm which has resulted in 'like new' timber on the majority of the joists for at least the first 500mm or so from the house. The back span is about 5m, being the existing floor structure. The existing deck is not sloped as it had timber decking on it. I do have the option of replacing with timber decking as opposed to a tiled deck - if so I'd go for 130mm Spotted Gum.

If the sister board idea has any merit, then how would one calculate the stresses involved with 2m 100*50 bolted section, as opposed to say 150 * 50 section?

 

[MikeHalloran]

Do apply some borax and/or ethylene glycol to kill the rot:

http://www.acbs-bslol.com/Gadgets/D97WoodRot.htm

Mike Halloran
Pembroke Pines, FL, USA