Engineered lumber span chart

[ejb]

Can someone with a litle more building/engineering experience help me with a question regarding engineered lumber?

I am designing my addition/remodel, and one of the spaces that we end up with in order to get the look that we want is a second story space with a width of 33 feet from one outside wall to the other.

I am going to put a 12 pitch roof over the whole thing and am trying to figure out if there is engineered lumber that I can use as roof rafter that would allow me to not having any interior load bearing walls.

I found this document on the Georgia=Pacific website <A target="_blank" HREF=http://www.gp.com/englumber/pdf/10-11.pdf>http://www.gp.com/englumber/pdf/10-11.pdf</A> that seems to map it out but not sure what all the live/dead numbers mean.

Anyone interpret this for me??

Thanks.

PS: I live in a SNOW area so I think the second page od the PDF is the document I need.

EJB

 

[Cdash]

What the chart says, is that your out of luck! Yes, you'd need the second page. At the lightest snow load, 25psf, with 15 psf dead load, the largest one they make is just short of 33'. You would have to check your local building codes to determine the design loads. The live load, would count a snow load, and the dead load is the weight of the joist, sheeting and roofing. 15 psf is pretty standard for joist, sheeting, asphalt shingles. I can't remember typical snow loads, but it varies depending on where you are.

I would try a local lumber yard, they should be able to help you out. They will know the design loads, have the tables and may have access to different manufactures products to help you out.

Another thing thing to consider is trusses or truss joists, there are many different engineered products out there right now to choose from.

 

[ejb]

Maybe I wasn't clear, (or maybe I was and I am still out of luck) the fllor span is 33 feet, but the rafters would need to be about 24-25 feet from peek to the end.

(As a side note, anyone remember how to figure out the length of a isiclese triangle if you know the angle and the length of the third side??)

It looks to me like lumber is available to cover 25 feet, just not sure what the live and dead loads refer to...

 

[Soundguy]

When I built my house, there was a setion in the back, with a recessed lania, and I wanted regular roofing over it, not the vinyl or aluminum.
It was a bit tricky between code, and design, but I ended up using wood ibeams to help with the span. Trussing was a bit expensive though.

Soundguy

 

[Anonymous Poster]

You need to talk to an engineer or architect who is qualified to design your building. He will know the required dead and live load values for your area (wind, snow, etc.). What you want to do can probably be done, but I suspect you will wind up using engineered trusses rather than simple rafters.

 

[crb478]

On a 12/12 pitch you would need a rafter length 23.33 feet long. You would also need to add the length of any overhangs to that length. The formula is X squared + Y squared = Z squared.
33 feet divided by 2 = 16.5 feet. X 12 = 198 inches. 198 inches squared = 39204 + 39204 = 78408. The square root of 78408 = 280.01428 inches divided by 12 = 23.334523 Feet. I am not sure what yor snow loads are, but this is not a unreasonable span in my opinion. The timber thickness would have to be sized for your intended use.

 

[BB_TX]

<font color=blue>how to figure out the length of a isiclese triangle </font color=blue>
An isosceles triangle has 2 equal sides, but not necessarily a 90 degree angle included.
The formula is (a squared) = (b squared + c squared) if you are talking about a right angle triangle (45x45x90). If not, then it is much more complicated. You will probably need a set of trig formulas for that one. My book shows multiple formulas depending on the knowns and unknowns.

 

[TWINKLE_TOES]

ejb,

If the angle you know is either of the equal base angles, then the length of either of the equal sides is: L= (base/2)/ Cos angle

If the angle you know is the angle between the equal sides the the length of the side is: L = (Base/2)/(Sin angle/2)

Al

 

[Soundguy]

A bit off topic here, but I read many of the subs here on TBN, and have noticed something about the users here. It would seem that of the available user population, we seem to have a higher percentage of engineers than other occupations. Anyone else notice this?

Soundguy

 

[ejb]

crb478 and others:

Thanks for the formula...I suppose I could have tracked it down somewhere on the internet but this makes it easy.

The 23ft span does seem reasonable. Will setup an appointment with the engineer at the lumberyard to figure out what kind of engineered lumber I need for my loads and spans so I can frame in the new second story...my guess is it won't be cheap (the engineered lumber that is). Good thing I work for free/w3tcompact/icons/smile.gif

Thanks all/w3tcompact/icons/smile.gif