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.

 

[LD1]

Good info so far.

New favor to ask.

Those of you that have 40' spans or close do it, can you post some detail of your trusses? What size cords, spacing, span etc. Perhaps even a pic if visible. And if you happen to know the load ratings....

Any all all info is helpful in me making my descions about what to do.

 

[LD1]

Another possible change now.

I am considering 12' truss spacing. Need to call and get some quotes. But fewer poles, and I would drop to 12' doors on the eaves instead of a 16', and save having to do a large header.

Can't really find any tables for purlin spacing. But would think a 2x6,on edge would work. Probably stronger than 2x4's spanning 8' on edge.

The 8' oc trusses were $161. If 12' trusses are $290 or less, it will be less money overall.

 

[PoorPlowboy]

12ft OC trusses never saved me any money because I was always instructed to use no less than 2x8 No2 purlins on edge, on 24" centers with spans that far.

 

[s219]

Can you run the load calculations to see what the deflection is of a 2x6 over 12' with your design psf?

Anecdote: when building carrying beams for my boat house roof system, I used triple-bolted pressure-treated 2x6s over a 12' span (they only support load near the ends, not in the middle). Anyway, when assembling the beams with through bolts, for which I had pre-drilled ahead of time, I noticed the single boards slightly sagged under their own weight when hanging over the 12' span. I had to wrestle them a bit to get the holes to line up. These were fresh/wet pressure treated boards, so they were much heavier than a dry 2x6 should be, but it impressed upon me how little stiffness a single 2x6 has over 12'. A sopping wet 2x6 would have about 3# per foot of loading from the liquid, which isn't a lot.

Another factor to consider is uplift. You should be able to start with the roofing metal and get a requirement for purlin spacing, then work your uplift loads down to fasteners for the purlins to the trusses, then trusses to header beams, etc. What I found with my boat house roof is that there was a manageable spacing for which I could properly attach purlins to rafters, and then rafters to headers with readily available screws and hurricane straps. I needed two #10 3-1/2" star drive screws for each purlin/rafter attachment (that's for a 2x4 purlin laid flat), and then each rafter needed about 600# of uplift resistance at it's seat (which I got by putting two hurricane straps at every rafter/header attachment).

When you start spacing out the rafters or trusses farther, it means each will carry more of the uplift load. And it could reach a point where you can't properly attach them to the headers with readily available hardware. Or you may run out of places to nail the straps on if you need more than one. Just something to consider.

How were you planning to attach the 2x6 purlins standing on edge to the trusses? When I have seen 2x6 and 2x8 purlins used, they were sitting between trusses supported by hanger brackets. Seemed like a lot of extra hassle.

 

[LD1]

Weather I go 8' with 2x4's or 12' with 2x6 purlins, the plan is to go between trusses with the hangers.

I am not a fan of on edge on top with a huge nail. Just don't like it.

 

[GPintheMitten]

Wow. 12 foot O.C. trusses. Just make sure you do the calculation s for the purlins. Angle bracing of trusses will be harder.

There will be some handling and assembly challenges. I don't remember if you're building this yourself or having a contractor do it.

Personally, I wouldn't do it to avoid the need for a beam or two.

 

[LD1]

No I am doing it.

Will probably call one of them metal truss companies. I know they go 12' OC frequently. Weather or not I buy their trusses, I will ask them what size they use for purlins.

12' OC isnt just to avoid a beam or two.

12' trusses would take 7

8' would take 10

So fewer trusses = less $$
Fewer posts = less $$$
Fewer holes to dig and concrete = less money
Fewer purlin hangers = less money.

Now weather or not all of that savings is offsets the larger and longer purlins and heavier more expensive trusses...depends on just what size is needed. If 2x6's will span the distance, it should be a good bit less, just depends on how much the trusses are.

Should go up quicker too.

 

[s219]

At some point, fewer trusses and posts will begin to drive up the sizing of the trusses, posts, headers, and footings, as well as drive uplift resistance requirements of them all. That also starts to place more importance on individual structural elements as failure points. Typically, we design away from those fringe situations by distributing the load as much as possible, with closer spacings and lighter materials.

There is obviously an optimum with regards to managing loads from purlins all the way down to footings, and the associated costs. Might take a lot of calculating and pricing to sniff out that optimum. I bet the easy way is to copy whatever some of the better Amish barn builders have done. I had CHA Polebarns put up my barn, and they had it all down to a science, from design/plans to fabrication (I learned a lot of new tricks watching them, and this after 30+ years around the construction industry).

 

[GPintheMitten]

No I am doing it.

Will probably call one of them metal truss companies. I know they go 12' OC frequently. Weather or not I buy their trusses, I will ask them what size they use for purlins.

12' OC isnt just to avoid a beam or two.

12' trusses would take 7

8' would take 10

So fewer trusses = less $$
Fewer posts = less $$$
Fewer holes to dig and concrete = less money
Fewer purlin hangers = less money.

Now weather or not all of that savings is offsets the larger and longer purlins and heavier more expensive trusses...depends on just what size is needed. If 2x6's will span the distance, it should be a good bit less, just depends on how much the trusses are.

Should go up quicker too.

Good points LD1. You're putting a lot of good thought into this. It will be good to hear what you finally decide on... and of course, to see your build thread too.

 

[LD1]

Got a quote on some 12' OC trusses.

$270 ea Using 2x10 2400msr tops and 2x8 2400msr bottoms

The program actually gave using a 2x8 top cord. But I requested an upsize as the CSI was at 94% max capacity with the 2x8. The 8' OC trusses were also in the 90% range, so not much room for error or that ocassional heavier than designed snowfall.

Upping to the 2x10's gave 64% max load @ 12' OC. And at $270 per truss, desiging everything else around that, will save ~150 bucks and make a stronger roof too:thumbsup: