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Old 10-26-2012, 07:57 AM   #1
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long beams and 4x4 posts


I have a deck plan that is 28 ft x 48 ft around an oval pool. We wanted the decking to go the long way (48ft) so I need to have long beams. The posts are 4x4s and are set in place. I am questioning what is the best method to attach the beams to the 4x4 posts. My posts are at 8 ft spacing. Should / can I bolt to beam ends to a 4x4 post? Or should I use post cap? Or should I use a bracket that connects to the side of the post? My concern with using a post cap is making sure the beams remain vertical. Is the post cap strong enough?


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Old 10-26-2012, 08:11 AM   #2
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long beams and 4x4 posts


Got some pictures?
Post caps would be the strongest way. Most places code would not have allowed using 4 X 4's for a deck that high, and do not allow joist on the sides of 4 X 4 post.

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Old 10-26-2012, 08:55 AM   #3
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long beams and 4x4 posts


Your post was unclear what your basis of design is. Most people follow the prescriptive deck code in the International Building Code, which has been discussed repeatedly on this forum. The code is available at no cost on line. Many communities require that this code be followed in order to get a deck permit. Even if you do not require a permit, you may want to follow the code, as it pretty much tells you everything you need to know about how to building a deck, including sizing of lumber, methods of attachment of joists, beams and posts, how to attach a ledger, spacing etc. Unfortunately the code mandates a minimum post size of 6x6, and attachment methods for beams are based on that minimum.

Should you choose to stick with 4x4 posts, you cannot follow the code. Not saying your deck will fall down, but you will be outside of standard prescriptive code methods, so it would be important to decide what your basis of design is going to be, i.e. you could hire a professional to design your deck, you could follow design advice from a book, or you could wing it I suppose.

See http://www.awc.org/publications/dca/dca6/dca6-09.pdf
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Old 10-26-2012, 09:01 AM   #4
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long beams and 4x4 posts


Did you allow for railings and a spot for a self closing, self locking gate?
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Old 10-26-2012, 10:23 AM   #5
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long beams and 4x4 posts


I have not seen a deck built with 6x6s. It has always been 4x4s. I am not sure where most places are, but I do not know one person that has a deck built on 6x6s (Wisconsin, Illinois, Arkansas-metro areas). The deck design was done with Big Hammer - on line. It is the same program that is used at Home Depot. The guy at HD had great difficulty using it, so I found it online and did the design. What it does not show me is the way the beams should be attached to the posts. The posts are cemented in. We wanted the decking to go the long way with the pool, that is why the beams are that direction. The height of the deck is mostly between 2 feet and 5 feet to deck top of deck height. There is one corner that has a deep slope where the deck height is about 8 feet, but that is just one post. The width of the deck around the pool is 8 feet across. So pool side to outside of deck is only a span of 8 feet. I have 2x8s for the beams and 2x6s for the joists. I am not in violation of any beam or joist span chart I have looked at, and I have looked at many.
Where I am located, just outside of Little Rock, there is no permit required.
I have not found the IBC code online for free. Do you have a link?
The railing is going to be a wrought iron fence on top of the deck with gates. There is sufficient height around the deck to meet the pool gate requirements.
Thanks for any help you can provide.
Roger
Attached Thumbnails
long beams and 4x4 posts-beam-joist-layout.jpg   long beams and 4x4 posts-beam-direction-pic.jpg   long beams and 4x4 posts-posts-pool-porch.jpg  
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Old 10-26-2012, 11:29 AM   #6
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long beams and 4x4 posts


The code I was referring to is the International Residential Code (IRC), NOT the International Building Code (IBC), which I am not familiar with. I understand that many decks are built either according to a different code, or perhaps no code at all, however all decks built in compliance with IRC since 2006 require 6x6 posts minimum. The link I posted should take you to the code, it is about 25 pages, and you will see the full discussion on post size and method of attaching beams and joists.

The reason the code requires 6x6 posts is because the recommended method of attaching beams to the posts is by notching the post. There is an alternative for using a beam post bracket if the beam is installed above the post rather than flush with the post. Beams are in general built using doubled 2x members, the beams are approximately 3-1/4 inches wide, and you cannot notch a 4x4 to accept such a beam.

The code also requires that posts not be embedded in concrete, rather they be installed on top of a concrete pier using a galvanized bracket (commonly Simpson brackets are used).

Clearly it is not necessary that you follow the IRC code, since you do not need a permit. My main point was that if you do not follow IRC, you really should decide which code, if any, you plan to follow. Using an on line program such as Big Hammer obviously does not follow IRC, I have no idea what code, if any, it does follow. Since Big Hammer does not define the post/beam connection detail, you may want to consider using a post/beam connection bracket. Simpson and their competitors make many different types, depending on the dimensions of the pieces to be connected. My experience with Simpson has been very good, their products are well designed and nicely built. Make sure you follow their recommendations for nailing EXACTLY, many people fail to correctly read the instruction, and end up using 10d galvanized short nails for the diagonal nails rather than the required 10d standard length (3 inch nails) required by the manufacturer. This occurs because the directions have a small, easily overlooked footnote that allows use of short nails ONLY for the perpendicular nails attached to the joist, NOT the diagonal nails.
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Old 10-26-2012, 02:14 PM   #7
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Thank you for the information. I was leaning toward using the post / beam connector bracket that sits on top of the 4x4. I really feel that the move to have posts on top of a concrete pier is the wrong direction. I find it hard to believe that the time it takes to decay the post in concre is shorter than the time the fastner would loosen, or decay would occur on the exposed post. Not my concern any longer.
I do wish that big box stores would at least have the IRC handy to at least point to.
Again, thank you for your help and advice. I do appreciate it.
Roger
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Old 10-26-2012, 03:10 PM   #8
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long beams and 4x4 posts


roger,

here is a link that will provide you access to all International Code Council codes, including the IBC and IRC. http://publicecodes.cyberregs.com/icod/index.htm

The American Wood Council's " 2009 Prescriptive Residential Wood Deck Construction Guide" that Daniel provided you the link for is based upon prescriptive compliance with the 2009 International Residential Code."

The IRC requires that all joists and girders (beams) bear upon a minimum of 1-1/2" of wood or metal. The deck guide uses notched posts for the beams to bear upon and attachment of the beam to the notched post with bolts. you would not be able to notch a 4x4 with a 2-ply beam, thus one reason for a 6x6 post. You may use column caps under the deck guide, but again it specifies 6x6 posts.

Another reason is height of post. when putting together a prescriptive guide it must meet all typical types of deck construction. some decks are close to the ground, others have access from the 2nd story of home. as an unrestrained column becomes taller more material is needed in the column to resist the loads. also when the tributary load area that a column must support increases in area an increase in post size is required. thus when putting together a prescriptive guide 6x6 were determined to be the appropriate size column needed.

another issue is 4x4 pressure treated southern pine has a tendency to twist, especially the longer they area.

Another issue which is not part of the deck guide is there has been a reduction in the strength of southern pine lumber. This past summer the strength of visually graded southern pine was reduced approximately 30% for 4x4 and smaller lumber. this reduction was based upon actual machine testing of visually graded lumber (which is standard use in pressure treated wood).

So no one may be using 6x6 posts in areas you are familiar with, but now you can understand why everywhere else is transitioning to the 6x6 as it has become the industry standard.

please post back with any questions.

good luck!

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