run-in shed rafter advice needed

[gregfender]

I have decided to go ahead and build my tractor shed this summer in anticipation of picking up my machine in the fall. Its going to be a fairly simple structure - 20x30, 2 open bays, one closed for secure storage.

I don't have to worry much about snow load so I am going with a shed roof and center poles instead of clear span trusses. I have a few questions for you veterans, however:

Rafters: 2x8 or 2x6? And does it matter if they are treated if they are covered?

Drainage: Planning on putting a french drain along the back wall...is it necessary to put one on the sides as well...and maybe even the front?

Roof: Planning on simple metal roof...what type of spacing recommended for purlins on a shed roof?

Any other advice would be appreciated.

thanks!

 

[s78wingrider]

Rafter size and spacing depends on how they are built :confused2: :thumbsup:

 

[gregfender]

I am going to run the rafters 24" OC

 

[farmall40]

What is the span and pitch of the roof? No, they don't need to be treated.

 

[dmay]

I have decided to go ahead and build my tractor shed this summer in anticipation of picking up my machine in the fall. Its going to be a fairly simple structure - 20x30, 2 open bays, one closed for secure storage.

I don't have to worry much about snow load so I am going with a shed roof and center poles instead of clear span trusses. I have a few questions for you veterans, however:

Rafters: 2x8 or 2x6? And does it matter if they are treated if they are covered?

Drainage: Planning on putting a french drain along the back wall...is it necessary to put one on the sides as well...and maybe even the front?

Roof: Planning on simple metal roof...what type of spacing recommended for purlins on a shed roof?

Any other advice would be appreciated.

thanks!

Your 20' x 30' shed sounds similar to my 18' x 24' horse run-in shed I just had built. I've attached an engineer stamped drawing for you to review.

Roof joists 2x10, 16" OC. Roof purlons 2x4, 24" OC over and 1x4 strapping under.

 

[LD1]

Definatally need to know the span and spacing to figure rafter sizes.

But if memory serves me correctly, 2x6's will span just shy of 10' on 16" centers. The tables for rafter spans are easy to look up online to verify the sizes.

But more important than that is going to be your headers and mid support beams that are going to support the rafters. These need to be pretty hefty. But that will depend on post spacing and knee bracing as well.

For the purlins, if you are just using standard metal roofing, I wouldn't go more than 2' on them. Otherwise they get a bit soft to walk on. And since you are going rafters, which will be closer together than trusses, you can lay the 2x4 purlins on their side. This gives you a 3-1/2 wide board to nail the roofing to. Less chance of missing as opposed to when the 2x4's are on end.

 

[Scrambler82]

I am not a carpenter but I have built a few buildings including the house I now live in and my rule of thumb is Always space 16” OC w/ 4” up for each 12”s out for the angle of the pitch and size the Rafter based on length of span… 2x6 for 6 ft, 2x8 for 8 ft, etc, etc.
Some may say this is over-kill but it has always worked for me.

 

[LD1]

I am not a carpenter but I have built a few buildings including the house I now live in and my rule of thumb is Always space 16 OC w/ 4 up for each 12敗 out for the angle of the pitch and size the Rafter based on length of span 2x6 for 6 ft, 2x8 for 8 ft, etc, etc.
Some may say this is over-kill but it has always worked for me.

Definatally overkill:laughing: but it sure beats going too small:thumbsup:

But your rule of thumb is not too bad for floor joists, which must be a little more stout than rafters.

Their is pleanty that go into sizing rafters. First thing to consider is the deflection limitations. L/360, L/240, and L/180. Which is simply how much the joist/rafter is allowed to bend/deflect. L is in inches. L/360 is typically floor joists. L/240 is typically ceiling/rafters that are going to be finished on the underside. L/180 is just typical rafters. So using L/180, a 15' span (180") would be allowed to deflect 1" at its mid point and still be considered within limits. Same span in a floor joist would only be allowed to deflect .5", thus a larger beam is required for the same span.

Loading is another variable. Measured in pounds per square foot. Their is a dead load and a live load. Dead is the weight of the beams and structure itself. Typically allowed 10psf. Live load is anything added, like wind, snow, funature, people, etc. Can be anything from 20psf up.

So, it sounds like the OP is only spanning 10' on 24" centers. Given minimal snow load, using L/180 and a 10psf dead and 30psf live load, and white pine lumber, he would need 2x8's which are good to 11' on 24" centers. But he could also use 2x6's if he dropped down to 16" centers. 2x6's are cheaper but more are required. Personally I'd see which way would be cheaper overall.

 

[flusher]

I have decided to go ahead and build my tractor shed this summer in anticipation of picking up my machine in the fall. Its going to be a fairly simple structure - 20x30, 2 open bays, one closed for secure storage.

I don't have to worry much about snow load so I am going with a shed roof and center poles instead of clear span trusses. I have a few questions for you veterans, however:

Rafters: 2x8 or 2x6? And does it matter if they are treated if they are covered?

Drainage: Planning on putting a french drain along the back wall...is it necessary to put one on the sides as well...and maybe even the front?

Roof: Planning on simple metal roof...what type of spacing recommended for purlins on a shed roof?

Any other advice would be appreciated.

thanks!

I used 2x8s on 16" centers for my 20x28 ft shed, roof slanted 10 ft high in front to 9 ft in rear. Common DF dimensioned lumber painted with Behr outdoor solid color stain (I like to paint the lumber before installation--hate to stand on a ladder with a paint brush in my hand). Posts are PT 4x6s. Beams are doubled 2x12s (front row) and 2x10s (middle and rear rows). Siding and roof are 29 ga R-panel.



Roof purlins on 24" centers

 

[smstonypoint]

Greg,

Because you are in NC, I suspect you will be using southern yellow pine (SYP) for your lumber. Here are span tables that may be of use.

Span Tables :: Southern Yellow Pine

Steve