lumber grading: SPF vs SYP

[LD1]

On my never ending quest for more info about building my upcoming pole barn.

One of my concerns is the trusses. The only company that has gotten back to me so far on 8' OC trusses for 40' span is quoting 2x6 lumber for both top and bottom cords. They are quoting 2400-2.0e msr lumber though. However, it still seems a bit light to me. A similar building built by Morton that I looked at had 45' span trusses with a big 2x10 top and a 2x6 + 2x4 for the bottom.

I know the new "thing" seems to be MSR or MEL lumber as to know exactly what you are getting so you don't have to "over-build". But I am not sure I am sold on it.

So I was doing some research on lumber....considering building trusses (which I probably won't). Using the span calculator at Maximum Span Calculator for Joists & Rafters shows #2 SPF being able to span farther than #2 syp. I always thought grade for grade syp was stronger.

Now for #1 and select structural, syp is better, but not in #2?

Also seems syp isn't just #1, #2, #3 anymore. There is dense, and non dense, and selections for prior to 6-1-13, and selections for after 6-1-13??? And the grading prior to that date is stronger.

So what happened June of last year?

In the 18-22' lengths that I am looking, Menards, Lowes, etc only have #2 syp or #2 SPF for choices. And given the current span ratings for that commonly available lumber, SPF is stronger? Just don't seem right.

And using the current span tables, a simple SPF #2 2x8 will span farther for a given distance than the 2x6 2400 msr lumber the truss mfg was quoting. So why not use the 2x8 that is a little stronger vs the more expensive msr 2x6??

Anyone shed any light on the topic?

 

[newbury]

Can't shed any light but how closely did you investigate metal trusses?
When I had my 40'x60' shed roof raised and reskinned one quote (Lowes or HD) came in with metal truss replacement for my wooden trusses. The cost was only slightly more than wooden trusses.

 

[LD1]

not familiar with metal. Just assumed it would cost more. On top of that, it would be more difficult to finish the inside with insulation, and a ceiling. With added cost, and added work to finish, I just dont see the benefit.

But...if it is a cheaper way to go, I would be all for it.

Only prices I have found online though are for a free-standing roof. I think it includes posts, trusses, purlins, and metal roofing. But the 40x40 kit was $7500. I would assume to go about double the depth (somewhere around 40x70), I would be looking at close to 14k for posts and a roof. I would still have to add walls. And right now as I am figuring materials, I should be about 14k for everything with conventional wood trusses and siding. (Thats not counting doors, windows, etc).

 

[LD1]

not familiar with metal. Just assumed it would cost more. On top of that, it would be more difficult to finish the inside with insulation, and a ceiling. With added cost, and added work to finish, I just dont see the benefit.

But...if it is a cheaper way to go, I would be all for it.

Only prices I have found online though are for a free-standing roof. I think it includes posts, trusses, purlins, and metal roofing. But the 40x40 kit was $7500. I would assume to go about double the depth (somewhere around 40x70), I would be looking at close to 14k for posts and a roof. I would still have to add walls. And right now as I am figuring materials, I should be about 14k for everything with conventional wood trusses and siding. (Thats not counting doors, windows, etc).

 

[JimRB]

So I assume that visual inspected lumber had a span rating created years ago. First weakness in that system is visual inspection. One inspector may let some loose knots through while another may not. MSR and MEL appear to test each piece of lumber so you actually know it will perform at the rated spec. Kind of like a 200 hp 1970 car. Was it 200 hp gross or net? Was it 200 hp advertised for insurance reasons or was it really 330 gross hp? In 1971 or 1972 they started to rate net horsepower. I do not know how accurate that was but the same engine code in a Mopar had a lot less HP in in 1972 then in 1970. Same cam, same exhaust, same windage tray, same carb.

So your question was "Why not use the old span chart and choose visually inspected lumber versus using the new span chart for mechanically inspected lumber?" Or asked again sideways Why not build with scientifically known and tested materials versus lick and a promise materials and guesses? For a manufacturer I would imagine he would want to build a product that he believes will perform well versus building one that he hopes will perform well. If you want to get into the whole responsible stewardship of lumber you would build to spec and not overbuild and overuse resources. Why put in a 10" concrete slab when a 4" slab with a bit of rebar will work?

I learned years ago that Home Depot and Lowes are not lumber yards for the pros. If you want good answers and top grade products you usually have to go to a proper lumber yard. I have bought a lot of supplies from Home Depot but I have to go to the lumber yard when I want some things. Granted HD can order most anything but you have to know what it is you need, the lumber yard can often tell you what you need and has it in stock. Of course this also assumes that you are in a market where the lumberyard has decent sales and is not going out of business.

Here is the link to the MSR Producers Council with some explanatory PDFs. MSR Lumber Producers Council - (888)848-5339 - Home Page for the Machine Stress Rated Lumber Producers Council

 

[LD1]

I understand the reason for MSR lumber. But it is very pricey.

There is still visually graded lumber. And visually graded lumber used by this truss company. So to respond to the comment about them wanting to use something they "know" will work vs something he hopes will work.......one of the quotes WAS with visually graded lumber.

I actually got quotes for 6 different trusses. Ranging from 4', 5', and 6' OC and both 36 and 40' spacing.

For his 40' span 4' OC trusses, were #1 (visually graded) SYP for top and bottom cords.

For 40' and 5' OC jumped up to 2400f-2.0e for both cords.

And for the 8' OC, same lumber, just heavier plates.

An 8' OC truss has to carry twice the load as a 4' OC truss. I guess I just have a hard time fathoming that going from #1 lumber to 2400MSR lumber and some heavier plates doubles its capacity.

And again, since truss mfg's DO use visually graded lumber, and 2x8's #2 SYP show that they can span farther according to the charts than the MSR 2x6's, I would think it would make for a stronger truss AND be cheaper. I bet even #1 2x8's are cheaper than 2x6 MSR lumber.

Again, just a little leary with 2x6 trusses on 8' centers spanning a 40' building. Not that I ever paid very close attention to specific detail, but in every larger building I have been in, they use much larger boards for trusses. 2x8's, 2x10's etc

 

[s219]

In general, SYP should be stronger than SPF by a notable amount, assuming all else equal. So if there is a case where you are seeing the opposite, I assume it's a non-equal comparison in grading, or maybe even an error. I have seen errors in some of the web calculators before, so I recommend using a handbook. There should be a free download of the "wood structural design data" handbook online, and I believe there is a southern pine association website with reliable data PDFs.

Design of production-built trusses factors in a lot of things, including repeatability and consistency of materials and fabrication, fastener retention, productivity, and installation labor. And they generally carry engineering certification. I would guess that all of those factors drive the construction approach they proposed for your trusses. I wouldn't fret over the lumber sizes if it's a reputable company. You could build a truss from popsicle sticks if it was designed and fabricated right.

 

[LD1]

In general, SYP should be stronger than SPF by a notable amount, assuming all else equal. So if there is a case where you are seeing the opposite, I assume it's a non-equal comparison in grading, or maybe even an error. I have seen errors in some of the web calculators before, so I recommend using a handbook. There should be a free download of the "wood structural design data" handbook online, and I believe there is a southern pine association website with reliable data PDFs.

It was on the AWC.org website. I linked the calculator earlier.

Comparing same loads, same deflection limits, same application, #2 SPF is now a stronger lumber than #2 SYP.

Anything higher, like #1, Select structural, DSS, etc and the SYP is stronger. But no longer so in #2 or lesser which is all that is commonly available at lowes, menards, etc in the longer lenghts.

There was a change in june 2013 (I did some more reading on it). And in a nutshell as far as I understand, lumber is evaluated from time to time in destructive testing, and design values like E, Fb, Fv, etc are changed as needed. And it lowered for #2 SYP dropping it below #2 SPF now.

So if you go to menards and compare a #2 SPF to a #2 SYP, according to the current tables and engineering calcs, the SPF can span father/carry more...

 

[GPintheMitten]

Why not bring up these questions with the truss company. Seems like they would be willing to explain their choices in general terms.

They claim they are engineered trussed, right? If they certify them then just go with them.

Or ask them what they would do for you if they failed.

 

[s219]

Interesting. I didn't realize the June 2013 changes de-rated SYP -- I have been using a design program when engineering my boat house structure, and selected the June 2013 SYP dataset since the wood being used was #2 pressure treated SYP (you also get dinged slightly for pressure treated, especially if the wood is perforated in any way). I had no idea the 2013 specs were making the SYP less capable, so it would have resulted in larger beam and rafter heights. I'll have to go back and see just what difference that caused, compared to the pre-June 2013 specs.

My biggest problem with #2 is watching out for knots and other irregularities and defects. It makes picking out lumber a little more involved, checking for iffy knots and defects in addition to looking for bowing and crowning (on top of that, pressure treated wants to hockey stick when it dries out, so it needs to be stored properly and fully nailed into place as soon as it comes off the stack). I hand pick the lumber myself, bring it home and stack in a logical order, and then strap it down. It's a chore. But delivered lumber would have to be #1 grade to be as reliable/usable, since most yards will not hand pick it before delivery. A delivery of typical #2 would have a lot of rejects.