Support plan for deck

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Old 04-28-03, 07:39 PM
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Question Support plan for deck

I am planning to build a deck. The details are as follows:

21' length, 16' width
21' length is ledgered to house. 8' above ground.

My question is concerning the support post placement. Thus far I've had two ideas:

1. two rows of support posts (beams). First row at 7', second at 14', with 2' cantilever. I would use 2x8 joists.

2. one row of posts (beam) at 14', and use 2x10 joists.

From what I've read, a 2x10 can span ~15 ft. Am I correct in determining that my span for plan (2) is 14 foot, not 16 foot, due to the 2' cantilever?

Would plan (2) be too "bouncy"?

I am planning on using Trex 5/4 board for the decking, so there is an increase in weight over regular pressure treated.

It would be nice to use plan (2) because the slider for my walkout basement is directly underneath the center of the deck.

Any suggestions? Experiences? Obviously plan (1) would provide better support, but would be harder to implement. Are 2x8 joists effective in plan (1), which would have a maximum joist span of 7'?

I have the plans drawn up with both options, and have not yet submitted them to the township.

Thanks.
 
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Old 04-28-03, 08:53 PM
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creiter,

Well, since this is getting into spring time, I've just got done 4 decks this weekend, what's another right?

Here are the suggestions that I can give based upon what you described.

Option 1 - Things to think about - the 2x8 joist can span a maximum of 12'-2" @ 16" O.C. and for simple spans beams can be 2-2x10 but when you have an overhang the beam must be 2-2x12. With spacing at 7' intervals, this would be solid.

Option 2 - beam at 14' and use 2x10's @ 16" O.C. joist is dueable but not recommended by me. Again the beam size would be 3-2x12 as per code for the overhanging joists, 2 - 2x10's if there were no overhang.

This will be bouncy and if you were to reduce the effect, go 12" on center with solid blocking midway using 2x10's. If you prefer, use 2x12" at 16" O.C. and 2x12 beams for option 2 but with solid blocking. Fot those that think this is overkill...you're right but this guarantees a solid deck system. What is allowed by code doesn't mean it is a "No Bouncer"!

I would recommend option 1, placing a support post in the middle of the patio door. It's out 7 feet, so it won't bother anything. If need be, rethink your post placement at the door location and go from there. This deck is large and I would think that when you get all the guests on it, you want a solid unit.

Hope this helps!
 
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Old 04-29-03, 06:21 AM
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Doug,

Thank you, your response does help. My gut told me that it would be a better idea to place posts at the 7' mark, but my mind told me it would probably be easier to do it with just the 14' beam.

Just to be absolutely sure, do you think 2x8s are going to be adequate for the joists? I was also going to do them on 12" centers, not 16, to ensure that the Trex decking does not sag at all, since I've heard it can sag a bit. I figure that since I only have 7' spans, I may as well save a few dollars and go with the 2x8s vs 2x10s.
 
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Old 04-29-03, 06:28 AM
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creiter,

I won't deny that 12" O.C. would be better for 2x10's for the larger span to ensure no sag but 2x8's 16" O.C. will be fine for the 7 ft spans.

Hope this helped!
 
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Old 04-29-03, 06:59 AM
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creiter,

I've always heard that while the span tables for dimensional lumber (2x8 and larger) allow for spans well in excess of 10 feet, that most people will find such spans to be bouncy, even on larger 2x12 joists.

As for the joists 12" O.C. - hell, it doesn't require that much more effort and expense, so why not go for it, especially with the composites and the thinner hardwoods (1x Ipe).

How far apart do you plan to space the posts supporting the beams?

John P.
 
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Old 04-29-03, 09:35 AM
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Here is my current deck plan. I did the plan in Visio, but distilled it to a PDF since I figured not everybody has Visio. Some detail may have been lost in the translation, but I think it gives the general idea.

Take a look and let me know if anything jumps out as bad.

http://mywebpages.comcast.net/reiterch/deck_plan.pdf
 
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Old 04-29-03, 10:13 AM
petrsjo
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creiter,

I took a gander at your plans and, for starters, I think your support plan #2 is a no-go. 14 feet is just way too long a span in my opinion. While structurally feasible (with the right dimensional lumber), I think in the long run you would regret it because of the bounce.

With support plan #1, I have a suggestion and a question. The question relates to the triple window. Is there a ledger board attached to the house at that point? I'm pretty sure there is, but just wanted to verify.
 
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Old 04-29-03, 10:19 AM
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Sorry about that .... can't type straight.

My suggestion is to move the beam on the right hand side (the side with the sliding glass door) out from the house about a foot or so, if the post for that beam interferes with the slider on the basement level. The span from the house will not be excessive and you'lll have better access from that door (if I understand correctly).

You can also find span table at wwpa.org.

Thanks,
John P.
 
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Old 04-29-03, 10:28 AM
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Yes, there is a ledger board already on the cantilever. That is actually a big question area right now. When I talked to the township initally, they said "no" to cantilever ledgering, but said that they would have to look at it to see if it would work or not. My response was that the builder put it on, and it obviously passed their inspection. I hope I can ledger it to there, because otherwise I'll have to do some funky joist work if I can't use it.
 
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Old 04-29-03, 11:21 AM
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creiter,

Hope you don't mind, but after looking at what you have, the township is correct...NO DECK CAN BE ATTACHED TO A CANTILEVERED AREA. This will mean additional joists to double header it outside of the cant which is no major issue.

Adjustments can be made to the suppoort post by the slider as well.

Just some thoughts
 
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Old 04-30-03, 07:08 AM
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Well, I stopped at the Township this morning with my plans, and believe it or not, I am going with support plan 2. The township said that a 14' span with 12" centers will be plenty strong. Especially if I put blocking up at the halfway point for the span. Another reason I'm going with the single beam at 14' is because it will be very tough to hit virgin soil so close to the house. At 14' out, it should be much easier.

They told me when my house was built they had to go down 9' (NINE FEET!) for the footers, since the development I am in used my lot as a temporary retention basin, and they backfilled it later on. This meant that they had to dig down like crazy through the backfilled soil to hit the virgin soil. Some crazy number like 100 cubic yards of concrete went into the footer for my house. Normal is somewhere around 30 cubic yards.

The township is going to find out for sure how far down I will have to go with my footers because of it, but they figured around 4-5 feet.

I'll let you guys know how it all turns out, and what my final take it for the bounciness of the deck.

Chris
 
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Old 04-30-03, 07:36 AM
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creiter,

So you are using 2x10's 12" O.C. with mid blocking that I recommended? I must be doing something right!

What about the cantilever issue? Are they allowing the connection?

Keep us informed and thanks for the update!
 
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Old 04-30-03, 09:09 AM
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No, can't connect to the cantilever. I have to double up the joists on both ends and hang a double header between them.

The big question is do I even try to recoup the ~$100 that the builder charged me to put a ledger board where I can't ledger a deck?
 
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Old 04-30-03, 09:18 AM
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creiter,

Double header isn't any problem. As far as the $100, I doubt you'll get it back. Surprised Builder didn't know that it's not approved at cantilever areas.

Any idea on cost for this project and permit cost for others to get an idea what is involved? I'm sure they would like to know.

Good Luck!
 
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Old 04-30-03, 10:45 AM
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The permit cost is based on the square footage of the deck. In my case, for ~680 ft2, the Towship gets $170 for the permit. They do an inspection of the footer holes, an inspection of the support structure, then a final inspection of the deck before they issue the occupancy permit, so there is some cost on their part.

Since I am using Trex decking and railing, the cost of the deck jumps up dramatically over PT. I estimate the materials cost is going to be in the neighborhood of $7000-$8000. I'm still working out the entire materials list, and looking for the best price on the Trex.

My neighbor is having a deck built right now and the contractor's prices were $11, $14, and $17 per square foot for PT, cedar, and Trex respectively. (materials and labor)

This is in Southeastern PA.
 
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Old 04-30-03, 10:10 PM
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creiter,

Unless I'm mistaken, a 16' X 21' deck is 336 sq. ft.

The neighbor's contractor does Trex for $17/ sq.ft. That works out to about $5712 -- he CAN'T be including a Trex railing system at that price!! (Those 4X4 newel posts, 54" long are almost $60 each.)

The 680 feet you mentioned is the LINEAR feet of Trex, NOT the SQUARE footage. And, if you only buy 680 feet of Trex, and gap it properly, you will come up short. Buy 740'. (You can thank me later!!)
 
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Old 05-01-03, 05:55 AM
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Actually, the dimension of 16'x21' I posted was just for simplicity. The deck is actually quite a bit bigger.

Around here the Trex 4x4x52 rail post runs about $26.

I'm not sure if the contractor uses PT 4x4's and then clads them with trex for the railings. He sure went to town with the cedar though! Did a hell of a job, and capped everything with cedar, including the support posts.


Originally posted by lefty
creiter,

Unless I'm mistaken, a 16' X 21' deck is 336 sq. ft.

The neighbor's contractor does Trex for $17/ sq.ft. That works out to about $5712 -- he CAN'T be including a Trex railing system at that price!! (Those 4X4 newel posts, 54" long are almost $60 each.)

The 680 feet you mentioned is the LINEAR feet of Trex, NOT the SQUARE footage. And, if you only buy 680 feet of Trex, and gap it properly, you will come up short. Buy 740'. (You can thank me later!!)
 
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