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Old 10-19-2012, 12:50 PM   #1
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Questions Regarding Ridge Beam


I am building a 16'x20' screen porch off the back of my home in NW Arkansas. This will be built with a gable roof perpendicular coming off a truss built home roof with a 4/12 pitch. Actual size of the porch slab is 15'-8" wide and 19'-7-1/2" long. There are 4x4 posts less than 46" on centers around the perimeter with two 2x4 top plates sandwiching a double 2x8 header. Rafters will be no more than 24" OC with 7/16" OSB and 3 tab shingles. The underside will be insulated (in case later we decide to enclose) and covered with 3/4" tounge and groove boards.

Will a 19'-7-1/2" double 2x12 beam do the job?

Second question, we have a sliding glass door coming out of the house onto the soon to be porch. How would you support the beam over this end of the house? Would I need to stack another header over the 7' header that already exists over the sliding door to support the beam?

The pitch will be 5/12 or 6/12 with 2x8 or 2x10 rafters with a 18" overhang all around.

Thanks in advance.

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Old 10-19-2012, 01:54 PM   #2
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Questions Regarding Ridge Beam


You don't need a ridge "beam" if your ceiling joists are sized properly and are structurally continuous from plate to plate.

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Old 10-19-2012, 02:31 PM   #3
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Its a vaulted ceiling and wont have ceiling joists.
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Old 10-19-2012, 02:50 PM   #4
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Questions Regarding Ridge Beam


AG is spot on.

from the 2009 International Residential Code (basis for most local and state building codes:

R802.3 Framing details. Rafters shall be framed to ridge board or to each other with a gusset plate as a tie. Ridge board shall be at least 1-inch (25 mm) nominal thickness and not less in depth than the cut end of the rafter. At all valleys and hips there shall be a valley or hip rafter not less than 2-inch (51 mm) nominal thickness and not less in depth than the cut end of the rafter. Hip and valley rafters shall be supported at the ridge by a brace to a bearing partition or be designed to carry and distribute the specific load at that point. Where the roof pitch is less than three units vertical in 12 units horizontal (25-percent slope), structural members that support rafters and ceiling joists, such as ridge beams, hips and valleys, shall be designed as beams.

R802.3.1 Ceiling joist and rafter connections.
Ceiling joists and rafters shall be nailed to each other in accordance with Table R802.5.1(9), and the rafter shall be nailed to the top wall plate in accordance with Table R602.3(1). Ceiling joists shall be continuous or securely joined in accordance with Table R802.5.1(9) where they meet over interior partitions and are nailed to adjacent rafters to provide a continuous tie across the building when such joists are parallel to the rafters.

Where ceiling joists are not connected to the rafters at the top wall plate, joists connected higher in the
attic shall be installed as rafter ties, or rafter ties shall be installed to provide a continuous tie. Where ceiling joists are not parallel to rafters, rafter ties shall be installed. Rafter ties shall be a minimum of 2-inch by 4-inch (51 mm by 102 mm) (nominal), installed in accordance with the connection requirements in Table R802.5.1(9), or connections of equivalent capacities shall be provided. Where ceiling joists or rafter ties are not provided, the ridge formed by these rafters shall be supported by a wall or girder designed in accordance with accepted engineering practice.

Collar ties or ridge straps to resist wind uplift shall be connected in the upper third of the
attic space in accordance with Table R602.3(1).

Collar ties shall be a minimum of 1-inch by 4-inch (25 mm by 102 mm) (nominal), spaced not more than 4 feet (1219 mm) on center.

if your ceiling joists are installed in the lower 1/3 (height from ridge to top of wall) then there are considered rafter ties and you do not need a structural ridge beam. Rafter ties prevents rafter thrust (weight of roof loads) from pushing out the tops of walls. So does a ridge beam.

Let's say you still want a structural ridge beam. to know whether the beam you state will work one would need to know the species of wood and the grade of the lumber. One would also need to know what your ground snow load would be, or your code required roof live load.

I would have to say a (2)2x12 span 16' would not be sufficient as a structural ridge beam. I would expect that a (2) ply 11-1/4 1.9E LVL would be needed at a minimum. Your lumber yard should be able to evaluate the requirements for a LVL structural ridge beam.

As far as the header over the slider you would have to ensure that the header can handle all existing loads, plus the point load of the structural ridge beam would be around 2500 lbs to 3000 lbs depending on your required roof live load.

you would have to ensure you have sufficient number of studs on either side of the slider to transfer the loads from the header down to the sill plate on the foundation. This would require either solid blocking between the floor joists, if you have floor joists. If you do not have sufficient studs to transfer the load the end result will the crushing of the sill plate which in turn will cause the jack/kings studs to settle downward.

attempting to perform load calculations with all the proper information can difficult enough, without the proper information it is impossible.

I would recommend either consulting a professional engineer to evaluate your design or installing rafter ties to eliminate the need of a structural ridge beam. Rafter ties are typically installed at 48" o.c. minimum.

You would also need collar ties (installed int he upper 1/3) or ridge straps at each pair of opposing rafter to prevent separation of the rafter ends from the ridge.

Don't know if I've been much help, but hope at least I helped to point you in the right direction.

Good luck!
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Old 10-20-2012, 10:24 AM   #5
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Originally Posted by bobber66 View Post
I am building a 16'x20' screen porch off the back of my home in NW Arkansas. This will be built with a gable roof perpendicular coming off a truss built home roof with a 4/12 pitch. Actual size of the porch slab is 15'-8" wide and 19'-7-1/2" long. There are 4x4 posts less than 46" on centers around the perimeter with two 2x4 top plates sandwiching a double 2x8 header. Rafters will be no more than 24" OC with 7/16" OSB and 3 tab shingles. The underside will be insulated (in case later we decide to enclose) and covered with 3/4" tounge and groove boards.

Will a 19'-7-1/2" double 2x12 beam do the job?

Second question, we have a sliding glass door coming out of the house onto the soon to be porch. How would you support the beam over this end of the house? Would I need to stack another header over the 7' header that already exists over the sliding door to support the beam?

The pitch will be 5/12 or 6/12 with 2x8 or 2x10 rafters with a 18" overhang all around.

Thanks in advance.
for a vaulted ceiling you will need a heavy duty ridge beam that posts down onto the outer walls and you will not be able to put a header above the door header because your homes roof rafters will not allow it most likely.
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Old 10-20-2012, 02:12 PM   #6
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Questions Regarding Ridge Beam


most of the roofs i stick frame get a double ridge beam. which is generally 16" lvl
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Old 10-20-2012, 11:29 PM   #7
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Very nice looking job! They passed this without rafter ties? (different than higher-up collar ties that do nothing to keep the walls from spreading); http://publicecodes.cyberregs.com/ic...?bu2=undefined

You may have trouble converting to living space without a perimeter foundation or built-up perimeter joists. Any snow loads?

Too bad no one caught the ridge beam in the on-going framing pictures, or after it was done: Screened porch project

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Old 10-21-2012, 08:05 AM   #8
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most of the roofs i stick frame get a double ridge beam. which is generally 16" lvl

That is a serious ridge beam and with adequate post bearing support will hold up a lot of roof no doubt!
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Old 10-21-2012, 12:37 PM   #9
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they carry 2x10 x 16 `rafters generally 12" or 16" o.c
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Old 10-21-2012, 01:21 PM   #10
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Questions Regarding Ridge Beam


I believe what Gary is referring to in the other thread is that the home owner used a ridge board and not a ridge beam.
In using a ridge board the sun-room should have had either ceiling joists or rafter ties (not to be confused with collar ties) to resist the outward thrust of roof and/or snow loads.
No inspector (if one was involved) caught this.


At least according to IRC 2009.

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