need help understanding I-joist requirements..

[timmi]

So Im trying to learn the basics of using I-joists, BCIs, TJI, etc..

Im planning on building a 16' x 24' cabin for myself this summer. I was told by a friend to use 16 foot long BCI's, 16" on center, and I would need 19 of them to cover the span of 24 feet. This all makes sense, but how do I know what the deflections and live loads need to be? The cabin will be on adjustable concrete piers/post/jacks, with 24' glulam beams on the posts.

This cabin will be my residence for the next 5 years. It will also have an attic (12/12 pitch). Small kitchen, small bathroom, general living requirements and a bedroom in the loft.

What deflection and live loads will I be looking at? I think the span will be 16 foot, but I could put in more concrete piers and add another beam in the middle if I need to, halving the span to 8 foot.

Basically, what size of I-joists should I be looking at?
Thanks
Tim

[homebild]

No one here can help you.
Not even your friend.

BCIs, TJIs, glulams, microlams, etc....are engineered wood products and as such require engineering to use them.

Such products can only be sized by a designed professional like an engineer or architect who can assess all roof loads, based on wind, snow, or even seismic forces...and design the roof system using these type engineered wood products to resist the loads.

Sometimes, the engineering can be performed by the engineered wood product manufacturer themsleves, using staff engineers.

Other times, an on-site field designer must be used.

Permits typically cannot be issued for roof systems using engineered wood products without proper engineering documentation.

So start talking to a local engineer/architect/ and your code enforcement office...and the supplier of the engineered products to determine what you need.

[timmi]

OK, thanks for the reply.

I'll go talk to our wood supplier.
This is an out-of-pocket private residential build happening in Fairbanks, Alaska, and so there really isn't any codes that have to be followed. Its mostly do-as-you-wish if there isnt a bank loan involved.

[HDNord]

The manufacturer can provide you with load, deflection, etc.. information. Some even will have it on the web.

I provided this information to our structural engineer and he figured out sizing ,spacing and spans.

After the engineer called for 24" OC I-joists I had him change it for a slightly smaller ones that went 16" OC. Got better deflection (for tile floor) and a slightly higher ceiling.

Very happy with the results, no bounce at all.

[homebild]

OK, thanks for the reply.

I'll go talk to our wood supplier.
This is an out-of-pocket private residential build happening in Fairbanks, Alaska, and so there really isn't any codes that have to be followed. Its mostly do-as-you-wish if there isnt a bank loan involved.


There may be no regulative codes where you live, but physics is the same world-wide.

A roof assembly needs to be engineered for snow loads, wind loads, structural loads, spans and other issues...and cannot be haphazardly 'guessed' at or the result can be catastrophic.

In your case, I would do nothing without first consulting a local structural engineer or local architect for your roof construction.

Luck.

[Don_P]

Homebild is correct. There is nothing wrong with educating yourself though, it's never a bad idea to understand what you're doing. There's a fair amount of info and construction details on the site below. Your supplier will be able to get you all the specific information for their products and either provide or refer you to an engineer if necessary.
http://www.gp.com/build/product.aspx?pid=1392

You'll need to know design snow load for your area to size the rafters and girders.

No larger than this is it could likely be built using conventional prescriptive practices and dimensional lumber also. For instance at a 70psf snow load a #2 SPF 2x6 can span 8' 5" measured horizontally on 16" centers. For floors #2 SPF 2x12's can span 17'10" on 16" centers at a 40 pound per square foot live load/10 psf dead load and still have less than a l/360 deflection.