Hip roof ceiling joist 1

[planesmooth]

I am designing a workshop (18x25) with a 4:12 hip roof. My question is what should I use for ceiling joists since the shortest span would be 18', and 2x(southern pine No.2) framing lumber only goes up to 16' in the big-box home improvement stores. Also, looking at span tables (for southern pine), I would need to use MEL (machine evaluated lumber)or MSR (machine stress rated) lumber for that kind of span. Are these specially rated lumber readily available? Or can I double-up some No.2 2x to make a 4x joists that's 18 feet long? Thanks!

 

[UcfSE]

Have you considered microllams (LVL) or parallams (PSL)? I would use that before the specially rated sawn lumber, or just double up your 2x lumber, but try to use what is most common. Of course, the best advice is when in doubt, hire a professional. See if you can find a local lumber yard that can supply the length you want. Splicing your beams to make them longer definitely requires a professional.

Trus Joist is a major LVL and PSL manufacturer and has some information in this pdf file. Engineered lumber is pretty expensive so we usually try to double or triple joists first, depending on the cost and whether it works.

http://www.trusjoist.com/PDFFiles/2015.pdf

 

[planesmooth]

As a follow-up to my previous post on a 18x25 hip roof, can I place an LVL beam (18' span) so that the ceiling is now essentially split into 2 sections, each one 18' wide and 12.5' long. Now, I can hang 2x6 ceiling joist (12.5' long) from the external wall to the LVL beam. Would this be sufficient to create the necessary "triangulation" of the rafters to support the horizontal load of the hip roof? See "drawing" below.

******* (external wall, 18'wide)
| | | | (joists, 12.5' long)
+++++++ (LVL beam, 18' wide)
| | | | (joist, 12.5' long)
******* (the other external wall, 18' wide)

 

[UcfSE]

You can if it is properly designed and a complete load path is provided to the properly designed foundation. We can't give you a "yes" or "no" on a forum however. Your idea is one possibility, but you'll have to have the proper size LVL - width and depth, joist hangers, columns, footings, and check for uplift and gravity load on all connections.

 

[bylar]

Try a different supplier.
In our area dimensioned lumber is available up to 24'
Look at a span table ie 2x10 @ 16" SPF can span 19'10"
ceiling joist with limited storage LL=20 psf

 

[FSS]

Before going to expense of LVL's for joists, consider I-joists instead (TJI has some as do other manufacturers). Have called for them over garages often due to long spans and higher loads for storage. And definitely check with building material suppliers as they carry longer lengths than the box stores.

 

[trussog]

use trusses: )