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gaber6
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# Posted: 8 Oct 2025 08:06pm - Edited by: gaber6
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The 4"x10" joist spans on the cantilever deck are 3 feet and four feet on my deck. They protrude from the house about 5 feet across the 25 foot width. They used 2x6 boards on the build in the 80s and I want more support when I replace the rotten boards. I don't want to add more joists, but want to get 2.5" x 6" dimensional lumber milled.
Does this seem like the most reasonable solution?
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gaber6
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# Posted: 8 Oct 2025 09:10pm - Edited by: gaber6
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This is the deck I am talking about.
Roughly 120 sq. ft.
Just over 12.5 feet lengths
I got a quote from a lumber company to mill down 24 larger beams to 2.5 x 6 x 13 boards at @ $75 per board for pine. It is milled down with no scrap as it goes to waste. Roughly $1700. Crazy being standard 2x6x16 redwood boards are only $35 max at the box store.
Exotics start at $4000 for other quotes I got.
I could probably buy an old band saw and mill down 3x6 or 4x6 beams and have the rest to use as trim if I can't find anything.
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DRP
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# Posted: 9 Oct 2025 06:45am
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Just to clean up the description. The joist spacing is 3-4 feet, the cantilever span is 5'.
Are the 4x10 joists treated? and even if so... they are 40 years old, that's pretty much about best case service life.
To rag on that detail.. the company my Dad worked for in the 60's did that. The heavy timber floor joists extended through the wall to form the cantilevered deck. Flashing the large timbers poking through the wall in a splash zone is not easy, the timbers move. Through the 70's and 80's most were cut off, the wall rot repaired and freestanding decks on posts were built to replace them. Do due diligence looking the problem over, poke a moisture meter into the wall framing after a rain if possible.
From the oak overhead and southern pine below, I'm guessing hot/humid climate. The wood needs to be treated. It is a custom size very small run so expect to pay dearly. I'd work it from the other end, find the treater and have them use one of their supplying mills fill the order, order a healthy amount extra. If you mill down treated lumber, often it exposes untreated wood. We are supposed to dress field cuts with copper naphthenate, a brush gets the goodies in about one cell deep, don't fool yourself.
I don't know the species and grade used for decking before, it is likely overspanned. The design value of most interest would be "E" or Modulus of Elasticity. Some species , like Redwood, naturally have a lower E range, they are not very stiff woods. Happily Southern pine and dougfir are regularly treated, SYP most commonly, and they have some of the highest E numbers. E numbers also go up as the grade goes up. Using #1 in any species is going to be stiffer than #2. Select Structural is the top grade with better numbers yet, and prices reflect that.
Anyway, just some stuff to mull over.
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Brettny
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# Posted: 9 Oct 2025 11:19am
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Not a chance I would build it like that again. How much bounc did that have? Just because it was done like this 40yrs ago and you "never had a problem" dosnt mean it should be built like that again.
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gcrank1
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# Posted: 9 Oct 2025 11:56am
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Ever watch those movies where they cross the Old suspension bridge?
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gaber6
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# Posted: 9 Oct 2025 12:12pm - Edited by: gaber6
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Thanks for the replies.
This home is inherited and I plan on keeping it in the family.
As far as moisture goes, I am in the mountains in Southern California. Very little rain. The beams are presumably just pine and the structure of the house walls is fantastic. The flashing extends all the way beneath the first board and the roof hangs over half the deck.
The idea of cutting the beams off and starting new would be ideal, but I am not there financially. That would make the deck $20k or more and I am struggling with finding DIY solutions under $4k (not counting rebuilding the railings as well). No chance I am building a deck from scratch 14 feet off the ground. There is 5 foot crawlspace under the first floor.
I do fear there may be some rot on the top of the center beam where there are sistered 2x10s, but the rest have structure. The bounce on the deck boards is not as much as you would think for such a span but it still isn't right for sure. Most of the movement is from the rotten boards moving around the nail holes. Yea. Super safe currently.
I suppose if I check beneath that center beam and it is junk then my only solution is to rebuild.
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gaber6
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# Posted: 9 Oct 2025 12:29pm
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Here is a closer shot of the beams. They painted the whole house and deck probably 15 years ago likely right before my family purchased it. The peeling paint makes the boards look worse than they do in person.
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gaber6
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# Posted: 9 Oct 2025 01:28pm
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Quoting: gcrank1 Ever watch those movies where they cross the Old suspension bridge?
You aren't wrong.
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Upper
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# Posted: 9 Oct 2025 02:03pm
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Come to Fresno, I will mill you whatever you want.
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gaber6
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# Posted: 9 Oct 2025 03:34pm
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Quoting: Upper Come to Fresno, I will mill you whatever you want
Appreciate the offer. I am near San Bernardino so that would be a hike up some mountains with a loaded trailer. I got the number of a local guy so we shall see what that works out to be.
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Grizzlyman
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# Posted: 9 Oct 2025 04:07pm
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Would it be easier to just support the deck with long posts?
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gaber6
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# Posted: 9 Oct 2025 04:25pm - Edited by: gaber6
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Quoting: Grizzlyman Would it be easier to just support the deck with long posts?
I have considered that as an alternative to add support if really necessary. I have water and gas lines and existing deck steps where 2 or 3 supports would have to go.
The main support cantilever beams aren't the problem though, it is the 3 and 4 foot spans that the decking go across. That is why I want thicker 2x6s milled.
Another option would be to add ledgers, cap the end of the deck beams with a 2x10 and add 2x10 joists inbetween the cantilevers from the house to the new end board making the joist spacing 16". Just adding some support, not so much structure. This option would allow me to stick with basic 2x6 boards.
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Atlincabin
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# Posted: 9 Oct 2025 09:24pm
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Depending on budget and availability, you might find 3x8 lumber around locally, or 4x6. Probably would have to at least finish one side to make it more walkable, but at least it would not likely have any significant spring.
At a minimum, to help with the bounciness you could screw a 2x4 flat on the bottom side of the deck midway between the timbers. That would transfer some of the load off of individual deck boards. It does introduce some additional spots for water to collect and rot.
Just a couple of thoughts.
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gaber6
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# Posted: 9 Oct 2025 09:58pm - Edited by: gaber6
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Quoting: Atlincabin At a minimum, to help with the bounciness you could screw a 2x4 flat on the bottom side of the deck midway between the timbers. That would transfer some of the load off of individual deck boards. It does introduce some additional spots for water to collect and rot.
I thought of this as well. Even considered if a few galvanized metal angle pieces every 16" would work the same function but screwed in from the bottom as sort of faux joists.
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Grizzlyman
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# Posted: 9 Oct 2025 10:26pm
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Quoting: gaber6 Another option would be to add ledgers, cap the end of the deck beams with a 2x10 and add 2x10 joists inbetween the cantilevers from the house to the new end board making the joist spacing 16". Just adding some support, not so much structure. This option would allow me to stick with basic 2x6 board
Got it. Yeah. Do that. That would be much simpler and probably the best solution.
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DRP
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# Posted: 10 Oct 2025 07:31am
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Dang, I was sure that was a white oak overhead. Another way to deck those was to use 2x4's on edge with creosoted little plywood spacers between boards. They were spiked together as well as toenailed down to the joists. Some had 4x decking as well... it has been a long time. If you look at decking direction on several there were joists perpendicular to the larger beams which allowed running the decking perpendicular to the house. That helps direct water away and reduces decking thickness.
If you want to see some really wide spacing... I think I remember up to 12' between "rafters" on a few roofs.
https://ncmodernist.org/deck.htm
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Brettny
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# Posted: 10 Oct 2025 07:44am
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You need a girder near the end of those joists and posts to the ground. Then theres a possibility to keep what you currently have.
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gaber6
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# Posted: 10 Oct 2025 02:34pm
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Quoting: DRP Another way to deck those was to use 2x4's on edge with creosoted little plywood spacers between boards.
Yeah i remember seeing decking like that at my zoo growing up. Seems like a lot more effort than cutting down a 3x6 to 2.5 thick.. that is about all the room I have beneath the patio door.
Quoting: Brettny You need a girder near the end of those joists and posts to the ground. Then there's a possibility to keep what you currently have.
I think the joists are plenty strong. My neighbor has the same setup and theirs goes out about 8 feet vs. my 5. There are a bunch of houses built like this here and some do the ledgers and some add a support girder with a few beams and some leave it. The girder isn't a horrible idea for future stability, but this post was mostly about the decking strategy.
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gaber6
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# Posted: 12 Oct 2025 12:06am - Edited by: gaber6
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Ok so how stupid is this idea?.. using 3x6 boards, I can just notch where the joists are down about 1/2 or so to get the depth I need vs. milling the entire boards. That's if the thickness is more that 2.5" off the shelf.
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DRP
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# Posted: 12 Oct 2025 07:45am
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It would be stiffer. It also traps more moisture and concentrates splitting stress to the inside corners of the notches (if that matters). It would also be quite a job. I'd personally plane the entire board down. Wider planks will also deflect less. I have some scaffold planks that are just rough sawn boards, roughly 2x12+. The scaffold has the planks spanning about 7'. Not unusual to have a couple of guys and materials on one.
The deflection on this is also coming from those cantilevered beams.
On planing, I looked over the oak trim material on the job. With cupping and warps, by the time I get it surfaced, it will be too thin to get stair treads out of. I went up in the shop yesterday and pulled down some 2" thick that I'll plane about half off of to get pleasing looking treads. I could saw new stock closer to dimension and wait for it to dry. Or I can plane treads tomorrow. The premium here is to use a stock dimension and grind away wood to save time and a special run
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gaber6
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# Posted: 12 Oct 2025 05:12pm
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Quoting: DRP would be stiffer. It also traps more moisture and concentrates splitting stress to the inside corners of the notches (if that matters
Thought about that after i drew it up as it would create more end grains on each notch. Thanks for the input
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