Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Building & Construction

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 05-10-2012, 02:45 PM   #1
Member
 
Join Date: Apr 2009
Location: KS
Posts: 430
Share |
Default

Deck Questions


I am trying to redisign an existing 2nd floor deck and I have a few questions. The problem is the current deck has part of it resting on the roof, both at the outside edge of the deck and where it meets up with the house, and I want to get it off of my roof for obvious reasons. So I plan to install a ledger board onto the house and then run the new joists off of that. In order to get the outside edge of the deck off the house, I plan on installing 6x6x14' cedar posts 8' out from the ledger board. I'd then like to cantilever the deck approx 2' over the beam, which I plan on using two 2x8x14' cedar beams sistered together to make and notch them into the top of the 6x6's.

I hope to this point, everything makes sense and that all sounds structurally sound.

My questions are this:
- Is 2"x8"x10' lumber sufficient to use for the floor joists, if they will be resting on the beam at approx 8' out from the ledger board? If I use 16" o/c spacing would 2x6 lumber be ok? I'm guessing I'm better with the 2x8's but curious.

- From an asthetic standpoint, would I be ok, using treated lumber for the floor joists if I use cedar beams and cedar lumber for the beam and outside skirting? On that note, is the cedar ok to use for the beam or would I be just as well off going with treated for that as well? Again, this is 14' up and I will actually have a pergola type structure under it to cover a patio area below.

- Should I double up the outside joists or is that not necessary? What about the Ledger board. I wouldn't think it would be necessary, but the current deck, which is 2x6 lumber and not as large doubled these up.

Master Brian is offline   Reply With Quote
Old 05-10-2012, 02:50 PM   #2
Member
 
Join Date: Apr 2009
Location: KS
Posts: 430
Default

Deck Questions


Ok, as soon as I finally hit send to the above message, I came across something saying not to use cedar for structure. Does that really hold true?

Based upon that, I am now kind of thinking I'll just use the cedar 6x6's, build the beam out of treated and use treated for all of the joist material and ledger board, then just skirt the framework with cedar. This would surely be a nice savings, but will it give the same look? Not sure what I'll use for the flooring or railing, but leaning towards cedar or the composite lumber for those....

On this subject would I be better off using pressure treated instead of cedar for the posts? The cedar does look much nicer, but I could easily live with either.


Last edited by Master Brian; 05-10-2012 at 02:53 PM.
Master Brian is offline   Reply With Quote
Old 05-10-2012, 03:50 PM   #3
Civil Engineer
 
Join Date: Mar 2009
Location: Boston
Posts: 4,141
Default

Deck Questions


You need to decide what your basis of design is going to be. Most people simply follow local code, thereby bypassing difficult mathematical computations. You just follow the rules. If you are building a deck that falls outside standard practice, you then have no choice but to perform the required structural computations, or of course hire someone to design and certify the design for you.

So the place to start is, what is your basis of design? In my town, we follow the 2006 International Residential Code for decks. Virtually everyone follows the standards set forth in the Prescriptive Residential Wood Deck Construction Guide, and in the rare case where someone wants to deviate (for example, build a two story deck, install a hot tub on the deck, install a cantilever greater the L/4), then they hire an engineer.

So you should start by telling us where you live, what code you intend to follow, or if you want to do custom design.
Daniel Holzman is offline   Reply With Quote
Old 05-10-2012, 04:05 PM   #4
Member
 
cortell's Avatar
 
Join Date: Nov 2010
Location: Austin, TX
Posts: 708
Default

Deck Questions


Quote:
Originally Posted by Master Brian View Post
Ok, as soon as I finally hit send to the above message, I came across something saying not to use cedar for structure. Does that really hold true?
It's recommended you don't use cedar for structure not because you can't or shouldn't, but because it's going to drastically increase the cost of your deck.

Cedar has the disadvantage of being weaker than PT lumber (which is usually pine), and it's typically much more expensive than PT. Double whammy particularly when you're talking about parts of the deck the eye isn't drawn to. The big advantage of cedar is its aesthetics. So, people typically use it for the visible parts of the deck, and use cedar veneers to wrap other parts which are not as prominent but still visible.

If you wanted to drop a lot of coin, you could build a deck 100% cedar, but not only is the wood significantly more expensive lb per lb, you're going to require more of it to meet a particular design strength.
cortell is offline   Reply With Quote
Old 05-10-2012, 04:11 PM   #5
Member
 
Join Date: Apr 2009
Location: KS
Posts: 430
Default

Deck Questions


Quote:
Originally Posted by Daniel Holzman View Post
You need to decide what your basis of design is going to be. Most people simply follow local code, thereby bypassing difficult mathematical computations. You just follow the rules. If you are building a deck that falls outside standard practice, you then have no choice but to perform the required structural computations, or of course hire someone to design and certify the design for you.

So the place to start is, what is your basis of design? In my town, we follow the 2006 International Residential Code for decks. Virtually everyone follows the standards set forth in the Prescriptive Residential Wood Deck Construction Guide, and in the rare case where someone wants to deviate (for example, build a two story deck, install a hot tub on the deck, install a cantilever greater the L/4), then they hire an engineer.

So you should start by telling us where you live, what code you intend to follow, or if you want to do custom design.
I live in central Kansas, it looks like we follow the 2006 Int Residential Code. So I guess I pretty much have to follow that. I feel I have a fairly good grasp of the job at hand, as I have several years of residential construction experience, but alas that was mainly 10+ years ago and it was more on the framing of houses, not decks. Though the two do kind of go hand in hand, I know things have changed and my mind is a bit rusty on the specifics, so I need to make certain I'm good to go before putting my plans together....

Thanks!!
Master Brian is offline   Reply With Quote
Old 05-10-2012, 04:22 PM   #6
Member
 
Join Date: Apr 2009
Location: KS
Posts: 430
Default

Deck Questions


Quote:
Originally Posted by cortell View Post
It's recommended you don't use cedar for structure not because you can't or shouldn't, but because it's going to drastically increase the cost of your deck.

Cedar has the disadvantage of being weaker than PT lumber (which is usually pine), and it's typically much more expensive than PT. Double whammy particularly when you're talking about parts of the deck the eye isn't drawn to. The big advantage of cedar is its aesthetics. So, people typically use it for the visible parts of the deck, and use cedar veneers to wrap other parts which are not as prominent but still visible.

If you wanted to drop a lot of coin, you could build a deck 100% cedar, but not only is the wood significantly more expensive lb per lb, you're going to require more of it to meet a particular design strength.
Yeah, I think I've pretty much talked myself out of cedar for most if not all of the framing. I liked the idea of the posts being cedar, but for half the cost and a stronger support structure I am currently leaning towards the PT, besides, I'll likely cover it in vines...
Master Brian is offline   Reply With Quote
Old 05-10-2012, 04:29 PM   #7
Civil Engineer
 
Join Date: Mar 2009
Location: Boston
Posts: 4,141
Default

Deck Questions


Unfortunately the IRC does not apply to two story decks, see paragraph 1 "This document applies to single level residential decks only." So you are immediately outside code, and the design becomes more difficult, and may require an engineer.
Daniel Holzman is offline   Reply With Quote
Old 05-10-2012, 05:05 PM   #8
Member
 
Join Date: Apr 2009
Location: KS
Posts: 430
Default

Deck Questions


Quote:
Originally Posted by Daniel Holzman View Post
Unfortunately the IRC does not apply to two story decks, see paragraph 1 "This document applies to single level residential decks only." So you are immediately outside code, and the design becomes more difficult, and may require an engineer.
Being as that may be, I don't see how the joist length and spacing would change. I can see how they might care about the support under the deck.

With that, should I be good planning on 2x8x10's or will that be spongy?

Based upon a search result I ended up at Lowes.com and they apparently have a deck builder program. I realize you get what you pay for on that one and it is pretty cookie cutter, but it actually gave load calculations, etc.... The problem is they don't allow you to dictate where you want the posts, but you can specify lumber dimensions and spacing. The other problem is I'm not sure how real world their program is.

The main problems I had with their site was mine will actually be a little bit of a split level deck, basically, the landing outside the door will be one step lower than the rest of the deck. I would like to use the same posts for it all, but the step out won't be cantilevered over the beam. The other problem was they place the cantilever with a 1' overhang and I prefer a 2'. The 2' appears to be well withing the guidelines of acceptable practice, but if all I can do is a 1' overhang, then I would just make the deck 9' deep vs 10'.
Master Brian is offline   Reply With Quote
Old 05-10-2012, 05:16 PM   #9
Member
 
cortell's Avatar
 
Join Date: Nov 2010
Location: Austin, TX
Posts: 708
Default

Deck Questions


Quote:
Originally Posted by Master Brian View Post
Being as that may be, I don't see how the joist length and spacing would change. I can see how they might care about the support under the deck.
The structural framing that holds up the deck floor is the most critical part of a deck. Get that wrong, and you're in for a world of hurt. If there is no prescriptive code for a multi story deck (which there typically isn't), then it must be engineered.

Quote:
With that, should I be good planning on 2x8x10's or will that be spongy?
No on hear could even begin to answer that. We'd need to know 20 different details about your deck and we know maybe two.

Quote:
Based upon a search result I ended up at Lowes.com and they apparently have a deck builder program. I realize you get what you pay for on that one and it is pretty cookie cutter, but it actually gave load calculations, etc.... The problem is they don't allow you to dictate where you want the posts, but you can specify lumber dimensions and spacing. The other problem is I'm not sure how real world their program is.
No company likes to be sued. I'd bet anything they're program is conservative. Also, it's in their financial interest for you to over-engineer the deck rather than under-engineer it. That said, I've never used the program and can't vouch for it.

Quote:
The main problems I had with their site was mine will actually be a little bit of a split level deck, basically, the landing outside the door will be one step lower than the rest of the deck. I would like to use the same posts for it all, but the step out won't be cantilevered over the beam. The other problem was they place the cantilever with a 1' overhang and I prefer a 2'. The 2' appears to be well withing the guidelines of acceptable practice, but if all I can do is a 1' overhang, then I would just make the deck 9' deep vs 10'.
Most building jurisdictions permit 2' cantilevers. This is probably an example of the Lowes program being conservative. If you use the prescriptive deck code book, and check that your local building code allows 2', you should be able to adjust the Lowes deck design to get what you want.
cortell is offline   Reply With Quote
Old 05-10-2012, 06:10 PM   #10
Residential Designer
 
AndyGump's Avatar
 
Join Date: Sep 2010
Location: Orange County CA.
Posts: 1,258
Send a message via Skype™ to AndyGump
Default

Deck Questions


Wow, designing a two story deck using a free (or cheap) Lowe's provided, computer deck design program.

I am stunned.

Andy.
__________________
Residential Drafter/Designer
www.draftinginoc.com
AndyGump is offline   Reply With Quote
Old 05-10-2012, 06:23 PM   #11
Member
 
Join Date: Apr 2009
Location: KS
Posts: 430
Default

Deck Questions


I realize the structure under is the most critical part, not saying it isn't, just saying it isn't going to change the distance a 2x8 or a 2x6 can safely span as floor joists on a deck. Considering the minimal cost, I will plan on 2x8's vs the 2x6's, but I am curious what the spans are. I will back up a bit and say I realize that framing underneath could strengthen that, but isn't there a maximum distance to span certain lumber?

You make a good point on Lowes website and their layout actually gives a live load rating of 58psf, which is on the upper level of what I have found a deck should be. Their plan calls for sistering 2x8's on both sides of the posts to create the outer edge beam, but other searches seem to say sistering two 2x8's directly together and placing on top of a notched post to create the beam/girder is the proper way to do it. Obviously, I need to research that more.

Right now, I'm just trying to get some sort of plan together so I can be as close to correct/safe as I can be, then I plan to draw it up and have it checked by a contractor I know before progressing and getting approval to start.
Master Brian is offline   Reply With Quote
Old 05-10-2012, 06:42 PM   #12
Residential Designer
 
AndyGump's Avatar
 
Join Date: Sep 2010
Location: Orange County CA.
Posts: 1,258
Send a message via Skype™ to AndyGump
Default

Deck Questions


THIS link might be a good place to start.
It is the Prescriptive Residential wood deck design guide.



Andy.
__________________
Residential Drafter/Designer
www.draftinginoc.com
AndyGump is offline   Reply With Quote
Old 05-10-2012, 07:10 PM   #13
Member
 
robertcdf's Avatar
 
Join Date: Nov 2005
Location: Colorado Springs, Colorado
Posts: 655
Default

Deck Questions


Stay away from the morons at the box store, their stupid program in completely useless and they don't have a clue what they're talking about.

I find that people (DIY er's) RARELY fully account for all the materials required for a project, and of course they never count their time, sometimes hiring a pro is far more reasonable than most think because they have a warped view on costs of materials.
robertcdf is offline   Reply With Quote
Old 05-11-2012, 12:24 PM   #14
Member
 
Join Date: Apr 2009
Location: KS
Posts: 430
Default

Deck Questions


1st of all, I wasn't really designing a deck based soley on that program. I was looking for some info and came upon it, so I went there to see what it had to say, if nothing else than to get a quick rendering of what it would look like to show the wife as well as to get a quick general idea of a parts list and it was good for both of those.

The Prescriptive Guide is exactly what I was looking for. It gives me the spans that I was curioius about as well as many other little things like what it required to attach the beam to the posts, footer diameter and lag bolt pattern for ledger board. Bracing was another thing I hadn't thought much about, but would have picked up on when building/getting approval.

This really isn't that complex of a design, except for the fact that it's about 12-14' in the air and I want a little bit of a cantilever to add a bit more room. I do realize the height is a BIG safety issue, but nothing I couldn't believe three 6x6 posts spaced 6'-7' apart couldn't handle. My main concern was beam span/attachement and the joist span.

Thanks!

Master Brian is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Cedar deck help mickbiv Painting 11 08-08-2013 09:21 PM
Update on my deck rebuild...more questions... mgh-pa Building & Construction 6 07-01-2011 07:30 AM
Deck Staining thread but I am desperate- please help mickbiv Painting 3 09-08-2010 12:28 AM
some questions about ground level deck fabian Building & Construction 2 08-31-2010 07:24 AM
New deck staining questions sk8z Painting 7 11-14-2007 06:45 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.