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Beam Size

Beam Size

Beam Size

I am working with a four car garage 35'X 20'The building was built in 1919.  The roof is flat with 1" pine sheeting and rolled roofing. (Approx.7.5 psf)  There is a wall between each garage.  The owner wants to open the garage up into one space.  The 2X6 Roof joists (24"oc) run parallel (the 35'length) to the building and overlap on top of each garage seperating wall.  When I remove these load bearing walls and install a beam to replace them, What size wood beam do I need? Steel beam?  

RE: Beam Size

You can't really size the beam until you know the location of the garage to determine applicable snow or roof live loads.  The applicable code for your area could also require particular loads on the roof.  Are there adjacent, higher buildings to the garage?  This may cause snow drifting if you are in snow country.

Also, by adding the beams, you are directing much of the roof loading to each end where there would be a concentrated load on the supporting walls.  These may need to be beefed up with additional studs.  

There would also be some concern on the footings at those concentrated load locations, although a continuous spread footing may be adequate to support the new concentrated load.  You may experience some new settlement of the wall footing in these locations.

RE: Beam Size

Hi tim,

As told by jae if u could specify the loads on roof at site(as per local code) it would be much simpler to determine the beam size.
Also specify is the structure a wooden or of any other material.
If wooden then the post supporting steel beam need to be steel post thus some connections required at beam post junction aswellas there might be some existing footing provided for the wall. But as now we would be dealing with concenterated load a seperate isolated footing would be needed(i,e some modifications to existing footing can be done but seems not feasible as it is more than 80yrs old so it would be wise to ignore strength of existing footing)
As far steel beam is concerened W8X18 should be OK for a roof load of 37psf(as per UBC)

PL elaborate the conditions at ur location so that any remedy can be suggested.

RE: Beam Size

This is a wooden structure in Southern California so snow is not a problem.  

RE: Beam Size

tim -
Not to make your issue worse, but in S. CA. you've also got the seismic considerations.  By removing these walls, you are altering the way the garage resists the lateral forces (assuming the walls are sheathed and behave as lateral shearwalls.

The beam you install can be a microLam wood beam.  Using an estimate of 15 psf for the dead load (assuming light roofing) and a roof live load of 20 psf (per code), you would have a total load of 35 psf on the roof.

With beams at 8.75' o.c. (35' divided by 4 car spaces) you would have a load on your beam of 8.75 x 35 = 306.25 plf.

A triple 1 3/4" x 11 7/8" microlam should work.  (total width = 3 x 1.75 = 5.25").  A steel beam, probably an 8" wide flange, would also be very feasible.  The steel beam could rest on built-up wood studs, designed for the new load.

I would, though, have an engineer look at the actual dead loads and lateral stability of the garage before doing any of this work.  If the roof deck is not adequate to carry the lateral seismic to the side walls, and if the two side walls cannot resist the lateral, you would have an unstable garage.

RE: Beam Size


can u let me know what connection/hardware u would prefer for resting steel beam over lumber studs?

RE: Beam Size

Many different details are possible.  Usually, we use a bearing plate with either bolts, or lag bolts extending down through a built-up double or triple wood plate atop the studs.  You need to check bearing on the wood, as well as the required number of studs to build-up under the beam.  The studs must be sheathed to work together as a unit.  Simpson Co. and others also have many connectors that work with steel beams.

Normally, steel beams on wood are limited in size due to the constraints on wood bearing.

RE: Beam Size

I am planning to constructed a garage that 26 feet long and 23 feet wide.  The beam will run the length of the garage and the walls will support the roof with a pitch 10/12. I plan on using 2X10 for the ceiling rafters supported by the i-beam in the middle. I want to have some storage over the garage but nothing heavy.

What size wood beam or steel beam should I use?

RE: Beam Size

You need first to evaluate the loads.
Evaluation of the loads is the most important task in the design of any structure.

So indicate

Span=26 ft?

dead and live loads acting on the beam, then we can do something.

RE: Beam Size

If it is a lightweight roof, wind uplift might be an important load case.

RE: Beam Size

this is my e-mail


if you draw one schematic structure I may advise afterwards

RE: Beam Size

Beam loading for a 26 ft span. Dead load 40 lb per ft live load 100 per foot.

What size beam should I use.

RE: Beam Size

Tim's garage project caught my attention and I found the replies informative; however I would like some input on my "do-it-yourself" post and beam carport project.  I have prepared the basic plans required by the Kern County (CA)building department but need some advice on selecting the sawn lumber.  I have a little span table book and a couple calculators but both were developed for conventional frame buildings, thus not much help for 6" dimension timber.  Here are the details: 20 ft clear span, 20 by 40 structure. Garage header is 20 ft 6x16 DF#1 on 6x6 12 ft posts with simpson post caps.  Other three sides are 6x8 beams on 6x6 posts, spaced 10 ft.  The front 20x20 structure has a sloping roof from 14 ft to 12 ft at the entrance.  The rear 20x20 structure slopes from 10 ft to 6 ft.  Rafters are 2x12's spaced 24".  Snow load is 30# by code, and roof will be light roof (5/8" CDX covered with corrugated steel.

Please comment on my beam and rafter selections.  Do I need to go heavier timber?

Thanks, Russ

RE: Beam Size

Hi, in my oppinion you have to study the problems as all. First the real condition of existing building, wall, foundation, etc. next, the loads ( dead, live, wind, eartquake, after next, analyzes the structural model that you will create and then design the beam of steel, woods or whatever you wish

RE: Beam Size

Check your deflection limits on that 20 foot 6x16 DFL.

RE: Beam Size

Thanks pylko, I was concerned about the 6x16 DFL 20 ft span however, I don't have enough information. No span table for heavy timber and looking at the Parallam catalog, I don't know which cell value applies to the 20 ft span for the ROOF PLF snow load area.  My load is 30+15 or 45 psf. Preferred beam if I used engineered lumber, would be the 5 1/4" wide to lay on top of a 6x6 post.  Oh, by the way the structure is detached.  Can you help some more?


RE: Beam Size

whats your roof joist span?  if its 16', then your PLF on your 20' DFL is 45 psf X 16'/2.  Abour 360 plf.  (3)-1 3/4" x 16" LVL's would probably work fine.  Of course, all depends on your actual loading

RE: Beam Size

A lot of questions have been asked that question the what and how of the works. Would it not be best to contact your nearest consulting engineer and get an accurate answer from some one who can fully appreciate what you want to do and look at the problem on site!!

To the engineers that reponded I think you need to reconsider the advice you give and consider the implications (legal liability, professional liability, etc) and your responsibilty in providing fully informed advice.


RE: Beam Size

While the main concern so far has been with the gravity loading on this structure, one has to also look at the effect of the seismic/lateral load on the posts, and on the connection of these posts to the beams and roof framing. The relative flexibility of the post-and-beam type of construction, as opposed to shear wall, could significantly affect your column design.

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