Rafter size for 16ft Span

[nickel plate]

Thanks for the feedback, I knew I could count on you guys :thumbsup:.

I am thinking I am going to go with 2x10 on 24 oc or maybe even 2x12 (for the extra insulation space)--though hauling 85 lbs rafters onto the studs is not exciting me.

I was going to pursue a truss or an engineered rafter, but the nearest lumber yard near me just closed. Since I am not in the tradesm, I am left with big box stores, unless I am willing to go 30-50 miles.

While the 2x8 might work, if the structure of this building has issues, the wife will NEVER let me hear the end of it.

Just to be clear, I am planning on sheathing with radiant foil backed OSB, tar paper, drip edge and metal roofing.

Try working with 19.2" oc. A 4x8 sheet of roof sheathing will have 5 rafters under it instead of 6 rafters at 16" oc. Your run isn't really enough to warrant any real savings but just wanted to let you know. 19.2" oc????-Look at your tape measure and it should have a black diamond on all 19.2" intervals so layout is a snap.

 

[nickel plate]

FWIW...

#1 dense yellow pine is (pound for pound) stronger than steel...

Almost all structural members used in trusses of any kind in the S.E. US are made with #1 dense SYP...

Can you give me your reference data source that documents #1 dense yellow pine is (pound for pound) stronger than steel?

 

[/pine]

Can you give me your reference data source that documents #1 dense yellow pine is (pound for pound) stronger than steel?

why do you need me to provide documentation? try Google...

The key word is "strength" and the orientation of applied forces...

Actually there are a lot of woods (and many other softer materials) that are stronger than steel (by weight) in the correct orientation to the grain...

also if you're the doubting type...I guess you won't believe that (common silica) glass is one of the most "elastic" materials on the planet...

 

[herd]

Can you give me your reference data source that documents #1 dense yellow pine is (pound for pound) stronger than steel?

Southern Yellow Pine is one of the hardest softwoods there are, it is harder than some hardwoods, poplar comes to mind. In these parts, no one would use spruce over 2x6 for framing. Douglas Fir maybe, but avialiable and cost is an issue.

The lumber yards here (not bigboxes) normally stock 2x8's up to 20' and can get up to 28' on order.

I would use a 2x8 by whatever to get the total span including the eave, or overhang. I would use 2x6 joists laterally and tie it all together with bracing. I would definitelty not build @ 2/12 pitch, the min I would build is 4/12.

I am not suggesting this to you but I have found that a very sturdy and strong method of building a roof is to use 2x6' or 2x8's, depending on span, for the rafters at 32'' OC, along with same joists and then use 2x4 as purlins at 32'' OC. Secure every rafter with a collar tie and cross-brace back to the center, both sides. Screw your metal directly to the 2x4 purlins. Have had very good success with two outbuildings on my property with this method. We get no snow but lots and lots of wind, esp during hurrican season.

I would never use the 32'' OC with shingles and OSB, but with metal it's good to go.

 

[Charlesaf3]

another vote against 2/12 - do yourself a favor and go 4/12

 

[Duffster]

There is nothing wrong with 2/12 if done properly.

 

[ustmd]

another vote against 2/12 - do yourself a favor and go 4/12

I hear you about the higher pitch, but for out buildings, shallow pitches are very common in this part of Texas. For example, most prefab metal buildings (ex Mueller Steel) default to a 1/12 pitch

 

[MarkV]

Just my opinion but I think using 2x12 or even 2x10 ceiling joist for a 16' span is way over kill and very expensive. Also with 2x10 or 2x12's if you draw out the angles of a 2/12 roof pitch I think you will see how much of the joist you will be cutting to fit at the wall plate. A 2x12 that ends up being 3 to 5" at the wall hasn't added any real strength to the ceiling. I'll be surprised if you don't find engineered trusses the cheapest way to go and it will also save time.

MarkV

 

[/pine]

IMO, engineered members make no sense on such a flat roof unless there is an exceptional live load (which according to the OP there is not)...

The only problem I see with a such a low pitch is...if the span requires a lap in the metal...high winds in down-pours can sometimes force water up under the laps...(which is why I originally thought of a torch down bitumen membrane

 

[nickel plate]

why do you need me to provide documentation? try Google...

The key word is "strength" and the orientation of applied forces...

Actually there are a lot of woods (and many other softer materials) that are stronger than steel (by weight) in the correct orientation to the grain...

also if you're the doubting type...I guess you won't believe that (common silica) glass is one of the most "elastic" materials on the planet...

I asked you for documentation on your statement, not your attitude.