sizing microlams - Contractor Talk - Professional Construction and Remodeling Forum

mroldstyle · 10-21-2009, 09:29 AM

I have an agricultural pole building that needs a lean to roof put on the side. Poles are spaced on 8 ft. centers but customer wants 16 ft. clear span on one bay. What size microlam will I need to carry that section of roof. The span is 10 ft., 4/12 pitch, purlins spaced on 2 ft. centers with joist at 8 ft. centers. Central Wisconsin so snow load needs to be considered. Galvanized metal roofing. Floor to ceiling clearance somewhat of issue, so would rather go 2ply than deeper on microlam if possible.
Thanks

Framer53 · 10-21-2009, 12:26 PM

Quote:

Originally Posted by mroldstyle

I have an agricultural pole building that needs a lean to roof put on the side. Poles are spaced on 8 ft. centers but customer wants 16 ft. clear span on one bay. What size microlam will I need to carry that section of roof. The span is 10 ft., 4/12 pitch, purlins spaced on 2 ft. centers with joist at 8 ft. centers. Central Wisconsin so snow load needs to be considered. Galvanized metal roofing. Floor to ceiling clearance somewhat of issue, so would rather go 2ply than deeper on microlam if possible.
Thanks

Call your local lumber yard where you will buy the materials from, they can help you. Or call an engineer

rjconstructs · 10-21-2009, 09:03 PM

Yeah have them sized properly. I'm using 3-1 3/4 " x 11 3/4 " on a porch with a span of 18' between posts. Your situation might be different.

WNYcarpenter · 10-21-2009, 09:09 PM

Quote:

Originally Posted by rjconstructs

Yeah have them sized properly. I'm using 3-1 3/4 " x 11 3/4 " on a porch with a span of 18' between posts. Your situation might be different.

Why can't they send them out the same size as dimensional lumber?...11 7/8" How about 11 1/4"?

Rio · 10-21-2009, 11:15 PM

Use an engineer or an architect who does calcs.................

frankdog · 11-11-2009, 04:20 PM

iLevel has great free software for calculating and sizing microlam and parallam lumber.

The reason that the lumber is not usually made to dimensional sizes is twofold: first, laminated lumber uses special fasteners and hardware connectors that are engineered specifically for the loads the member is intended to support. Use of dimensional lumber connectors would not be adequate (or too much) for those loads.

Second, engineered wood is just that: engineered. It's designed for specific conditions and loads (shear, torsion, etc.), and as such, is made only as large as it needs to be to adequately handle those loads. There is no waste. Dimensional lumber is a little larger to compensate for the checks, knots and other natural "imperfections" that affect it's loading abilities.

I guess there's a third, and that's the dummy factor. I don't know if this is intentional (probably not, and covered by the first condition I mentioned), and that's simply that if you try to use a dimensional lumber connector on engineered wood, it just won't fit (in most cases, not all), hence, most people would go get the correct connector (one would hope...we've all seen some amazing things done in residential construction... :-D).

Hope this info helps.