Deck construction question

[Iansaws]

I know this may not be the right place to ask this, but this forum has always been so helpful when I have asked a question. So here goes:

I am in the beginning stages of building a carport with a gabled roof-covered deck on top as an addition to my house. The stucture will be 24' wide running from the house and 22' deep, toward the back of the house and ideally I would like to have an open floor without a center support. This has however proved difficult to plan. I need to span the middle of the deck from front to back with a 22 ft beam, there will be 12 foot floor joist 16" on center attached to this beam on both sides and this is where I need the help. My plan is to use double treated 2x12's to construct the beam which will be supports in the middle by a single steel post which all my friends in constuction and some beam span tables say is fine (see www.decks.com/article40.aspx). But some tables I have seen say the maximum beam span for this set-up is just over 7 ft, which means i would need to change the beam or put 2 supports under the beam at 7 ft intervals running down the middle of the carport. Neither of these options is appealling, but I don't want my deck to colapse either. I have considered using a flitch plate inthe center of the beam to strengthen it, but I can't find any span tables fo rthat set-up.

I have also found a product called "Lite Steel Beams" (www.litesteelbeams.com) to span the entire 22' distance without a support member and I'm going to investigate this more tomorrow.

Does anyone have any thoughts on my plans or confussion or maybe other options I haven't considered yet? Yes, I have looked into LVL's and Glu Lam's and they are really expensive (especially for treated), very heavy and taller than I want. Please help!!

JT

[Mr__Bill]

Why not put the beam on the outside along the 22' edge, or use a load bearing wall, and use 24' floor trusses. This should eliminate any posts in the carport area and provide a solid floor in the covered deck.

It sounds like a nice project, looking forward to the in progress photos when it happens.

Bill
over here in the fog.

[drillman88]

If the beam is going to be completly out of the weather you can create a laminate using 5/8" osb glued with construction adhesive and lagged between your 2x12's. The osb adds a lot of stiffing and resistance to twisting. This is done alot aroound here when there is a wide, open span. You may be able to use treated plywood but I have not seen it myself so I cannot attest to it's strength. The engineers around here may be able to verify if its strong enough to cover the span you are looking for.

These http://www.gp.com/build/product.aspx?pid=1390 are used in construction of garages with bonus rooms around here. Again these need to be out of the weather, but they are very strong.

If I misiniterepreted your discription I am sorry. With the covered roof over the deck I thought these may be viable options.

[woodturner]

I need to span the middle of the deck from front to back with a 22 ft beam, there will be 12 foot floor joist 16" on center attached to this beam on both sides and this is where I need the help. My plan is to use double treated 2x12's to construct the beam which will be supports in the middle by a single steel post which all my friends in constuction and some beam span tables say is fine (see www.decks.com/article40.aspx). But some tables I have seen say the maximum beam span for this set-up is just over 7 ft, which means i would need to change the beam or put 2 supports under the beam at 7 ft intervals running down the middle of the carport.

Have you considered an LDL beam? The span you need can be obtained with a smaller LDL beam than achievable with built-up beams.

What load are you planning for? People often underestimate the load on a deck, and changes in the law and requirements in the last few years in many areas have further increased the required load. There have been a number of deck collapses, resulting in more realistic load factors and attachment requirements. I'd design for at least 100 psf.

How are you going to handle the roof/floor?

[jabe]

When it comes to building a large project that cost $$$$, I would ask my local government Building permit dept. Do not guess or take suggestions if it's not directly from your Local Building code. In my area what the local code calls for is the minimum requirement for any load/span. So knowing that, I would always go 1 size larger, it's not that much more in cost. As for light gauge steel beams, I would do the same 1 size/gauge larger/more. I taught residential light gauge steel framing @ the HS I retired from. 75% of all the new homes built in Hawaii are done with light gauge steel because of the termite problems. They have found that to eliminate bounce in the floor they needed to use 1 gauge/size larger for beams & floor joist and or stiffen it with engineered lumber screwed into the channel of the beam/joist. It was cheaper to go with a heavier gauge & 1 size larger instead of placing a engineered lumber into the channel. A plus for steel framing is you order all your material to exact size so little cutting or waste for the builder and all the framing member was color coded for easy assembly. You can get more information from North American Steel Framing Alliance, sorry do not know their web address but their physical address was
American Iron and Steel Institute
1101 17th St., NW
Suite 1300
Washington, DC 20036-4700
Hope this helps, good luck