Span of roof without using a center beam

twmackey

I'm building a 16x10 foot roof over my deck I want to know if I need a center beam to hold up the ridge beam is needed. The beam is 4x8x16 feet. the span is 16 ft wide 10 ft long with a cable roof. I'm using 4x4 pressure treated post.

Yoyizit

Supply drawings and/or parts list and your location so we can calculate loads due to snow, etc.
If I made no arith. errors, for an L/D of 180 and E = 1 million PSI for the wood I get that this beam can hold a distributed load of 9 pounds per linear inch.

Bob Mariani

what is the roof pitch, the rafter sizes? And it you are using the ridge beam to hold up the roof you cannot use a pressure treated 4X4. It does not have the required strength and it twists too much in the wall space. I would use paralams for posts.

Wildie

You should state where you are located, as some locations require that snow load would be considered!

twmackey

Why can't I use presure treated posts? The width is only 14 ft after measuring and the snow load is not a problem. I'm using a metal roof. I'm using 2 x8 with 4x4's on both sides the 2x8's on both sides with bolts holding the 2x8 and 4x4's together.

Wildie

With no snow load, its not much of a problem! In my area, you could use 4X4's to support a snow load of 30# psf.
My roof uses a laminated beam constructed from 3-2X10's spanning 13 feet! The rafters are 8 feet from the ledger to the beam and are 2X8's. I could have used 2X6's but I may close the porch in and heat it! The 2X8's will allow R20 insulation to be installed!
Snow load in my area is a major consideration!

In your post you said its to be a CABLE roof! Did you really mean a GABLE roof?

twmackey

Yes I meant Gable roof. with a meatal roof the snow will slide off easy and should not create problem.

Wildie

My roof was built to replace a metal roof! The snow didn't slide off and bent the metal stringers!

Certain weather conditions can freeze the snow to the metal and then it will pile up!

Don't make the mistake of ignoring your local building requirements!

Daniel Holzman

I recommend that you discuss your project with the local building inspector. If you do not need a permit, you may still wish to comply with the IBC or your local code anyway. Without specific details of your roof design, and details about how the roof load will be supported, it is reckless for anyone on this site to offer opinions as to the adequacy of your "design".

Any roof structure should be designed to handle a reasonable combination of live and dead load, including the weight of the roof, snow load, wind load, seismic forces, and impact loading. That is one of the reasons the building code exists, to set minimum loading standards, connection details, and material standards for building construction. All structural elements must be analyzed for bending, shear, torsion, and buckling. This includes the posts. All connections must be checked for adequacy. If you build from pre-engineered plans that are approved by your local building official, you can have reasonable confidence that these factors have been considered. If you are designing this on your own, you need to check all these factors.

twmackey

twmackey

I kinda expected a reply either faverable or not, but just leave a guy hanging with out additional comment took me by suprise.

Wildie

Hmmm! A reply from me? From the looks of what I see in your photos, you have done an excellent job.

However, any criticism from me, would be worthless, as I have no structural engineering qualifications.

Besides, this, my wife has just spent the past summer recovering from a life threatening illness, so my internet time has been limited!

Gary in WA

Did you check with any officials to see if the structure meets with your location's minimum Code? The posts seem undersized, the double built-up beams near the rafter tails are not really built-up with the space between them. The rafters (1/2) the span plus the overhang load is resting on ONE header beam, I'm sure it is over-loaded. Around here, the entire structure would be required to be built with pressure treated wood for outdoor exposure. The use of OSB (rather than plywood) for the sheathing will absorb moisture from the underside and not fair as well. Need diagonal corner braces going at right angles on all posts. Need solid rafter blocking at the lower rafter bearing to prevent rotation. Don't know your location to comment on the 4x8 ridge beam, but the single beam near the tails will only carry a 25# live load per sq.ft. and 10# dead load, with no snow load.

What did the Inspector say about the posts?

ps. Glad to hear she is recovering, Wildie!

Gary

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Wildie

Thanks Gary, it was serious enough that her doctor didn't think that she would make it!

Joe Carola

Why don't you ask your building inspector what he/she thinks?

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Joe Carola