Another Porch Rafter Span Question....

[jjtrou2072]

I know this question should be answered by a simple span chart but I'm getting conflicting information in my web searches.

Basic question is can I use pressure-treated 2x6 rafters from the local big box store to span 11' from the ledger board on my building to the top of the Posts/Beams for my porch build?

Plan is to space rafters on 16" centers and sheath with plywood, then metal.
The ledger is 2x8.

 

[mike93lx]

I'd use 2x6 when there is no snow load issue.

 

[billconner]

Depends on snow load. 11' seems long for a 2x6 here, but I have 60 psf snow load.

By IRC 2x6 16 o.c. will span 11-2 at 30 pound snow load. At 50 pounds, 9'-2" span. Need 2x8. I'm using #2 so southern pine.

It's often amended by local jurisdiction, but if I know approx where you are, I can see what code says for snow load.

 

[readhead]

What is the ledger attached to?

 

[jjtrou2072]

Depends on snow load. 11' seems long for a 2x6 here, but I have 60 psf snow load.

By IRC 2x6 16 o.c. will span 11-2 at 30 pound snow load. At 50 pounds, 9'-2" span. Need 2x8. I'm using #2 so southern pine.

It's often amended by local jurisdiction, but if I know approx where you are, I can see what code says for snow load.

I'm in North Georgia, basically Gainesville Ga. I doubt snow load will be a concern but it'd be good to know what the code says.

 

[jjtrou2072]

What is the ledger attached to?

I put a pressure treated 2x8 Rim Board on the inside of the metal all along the perimeter of the building where I anticipated the porch ceiling would attach.

Used 4x6 posts to span distance between the girts to give the load a path to ground.

I'm also thinking about adding a few posts on the exterior of the building to give some additional support.

If I could do it again I would bite the bullet and pay the ridiculous price the building supplier wanted to engineer a porch into the structure.

 

[Firebrick43]

Georgia minimum building code says 10 lbs unless special areas. I don't suppose your in the high elevation of the mountains if your in Gainsville proper.

Why use pressure treated rafters????

They will just warp and twist more and provide nothing if you are putting a roof over them?

Also I don't see a slot cut in the metal for your flashing. Its a lot easier to cut it before the ledger is up than after.

 

[billconner]

I'm in North Georgia, basically Gainesville Ga. I doubt snow load will be a concern but it'd be good to know what the code says.

I think your 2x6s will be fine. In fact, southern pine no. 2 will work on 24" centers by my read - just - in your area. SPF for sure.

 

[jjtrou2072]

@readhead
Do you have a recommended cutting tool for cutting a slit in the siding for the flashing? Just trying to cut a straight line all the way down the building.

 

[readhead]

Diablo sells a blade for sheet metal to fit a circular saw. Should be available at Home Depot.
You can cut above the new roof and then have a flashing bent to come out over the wall sheets, down over the wall sheets and then out over the roof sheets.

 

[OccupantRJ]

I am in NC and have a shed room that I used 2x6 to span 10 feet at 24” centers. It has 7/16” OSB ceiling underneath, with a low slope asphalt shingle roof, and it has done fine For 12 years.

 

[jjtrou2072]

Diablo sells a blade for sheet metal to fit a circular saw. Should be available at Home Depot.
You can cut above the new roof and then have a flashing bent to come out over the wall sheets, down over the wall sheets and then out over the roof sheets.

Ok thanks. I will look into a metal cutting diablo blade at my local home depot.

Any tips for making a cut this long (approx. 90ft total) straight? I'm thinking I should rip a board to the right height, set it on the ledger board, and use it as a guide to rest the circular saw against as I work my way down the building?

 

[mike93lx]

Ok thanks. I will look into a metal cutting diablo blade at my local home depot.

Any tips for making a cut this long (approx. 90ft total) straight? I'm thinking I should rip a board to the right height, set it on the ledger board, and use it as a guide to rest the circular saw against as I work my way down the building?

Yes, I would put up a guide board.

Its Going to be loud and there will be chips flying everywhere. Use a face shield and be careful.

other options are a nibbler or power shears

 

[readhead]

That is an excellent idea. It will be loud and it will make lots of hot chips but it is the least worst tool for the job. A nibbler will be slow and leave a zillion little hooks that will get tracked into the truck and house and worse may make a trip to the vet when one gets into a paw. A customer experience I would like to forget. Shears will also be slow, hard to keep straight and I have yet to use one that wants to get over the ribs. Great for straight flat cuts.

 

[jaw22w]

I just added a lean-to onto my pole barn. 2x6 rafters on 2 foot centers @ 10' span on the gable end in northern Indiana. I have to do the flashing just like yours. The structure is up and the roof is on. I have not made the cut into the barn metal for that flashing yet. It got too cold for me to work outside. I decided to wait until last thinking that I could use the roof for a work platform. I will straight edge up the roof to the barn wall at each end and run a chalk line to cut to it. That cut location is pretty critical. I was afraid I wouldn't hit it if I cut it first due to the stack up of rafters and purlins and sheet metal and installation variances.
I intend to use a Metabo with a .040" cutting wheel. Yes. Lots of sparks and flying chips. The Metabo is very controllable. I can run a straight line with it. We did all the cutting of the metal liner panel on the ceiling with it. A guy could use a cutting wheel on a 90 degree die grinder. I don't like to use the die grinder though. They don't call them death wheels for nothing. Metabo is much safer. The wheel is clutched in case it sticks.
A sheet metal supplier can provide a piece of flashing, probably to match colors even.
I think doing the flashing on mine will be a little easier than yours. The sheets above the lean to are 3' down to 1' tall. I intend to just remove them, place the flashing and put the sheets back up.
Good luck!

 

[KenC]

Another question regarding the use of treated material. It is almost never found as kiln dried after treatment and this will warp badly. Locally at least it is ungraded and most seems to be #3 at best. And last, it is protected from water and shouldn't need treatment. #2 kiln dried SYP would be my choice given your location. Further West and/or North where douglas fir is more available that's what I'd use. Either in 2x6 should do the job.

 

[mike93lx]

Another question regarding the use of treated material. It is almost never found as kiln dried after treatment and this will warp badly. Locally at least it is ungraded and most seems to be #3 at best. And last, it is protected from water and shouldn't need treatment. #2 kiln dried SYP would be my choice given your location. Further West and/or North where douglas fir is more available that's what I'd use. Either in 2x6 should do the job.

You can easily buy ungraded PT lumber? I don't think I've ever come across it, and I've never had any significant warping issues on PT once installed. But if you can get it, kdat is nice just for the weight savings while handling

 

[KenC]

You can easily buy ungraded PT lumber? I don't think I've ever come across it, and I've never had any significant warping issues on PT once installed. But if you can get it, kdat is nice just for the weight savings while handling

Guess I wasn't clear as I meant to say I wouldn't use PT lumber for rafters but substitute a higher grade fo KD material.

 

[mike93lx]

Guess I wasn't clear as I meant to say I wouldn't use PT lumber for rafters but substitute a higher grade fo KD material.

No argument there. I would run kd for anything protected as well

 

[jjtrou2072]

My logic is probably flawed but part of my reasoning for using PT is that the price difference is minimal when comparing PT #2 southern pine at $11.18 vs. $10.73 for KD-HT SPF at my local Home Depot (2x6x12).

I know PT will warp I have learned that the hard way on this project. If I do wind up using it I just plan on adding blocking in a couple places to hopefully lock it in place once they are up there. Other than weight and the potential to warp is there any other reason not to use PT?

Not sure what I'm going to use yet. Still waiting on my Simpson LRUZ brackets to come in before I buy the lumber.....

 

[Firebrick43]

My logic is probably flawed but part of my reasoning for using PT is that the price difference is minimal when comparing PT #2 southern pine at $11.18 vs. $10.73 for KD-HT SPF at my local Home Depot (2x6x12).

I know PT will warp I have learned that the hard way on this project. If I do wind up using it I just plan on adding blocking in a couple places to hopefully lock it in place once they are up there. Other than weight and the potential to warp is there any other reason not to use PT?

Not sure what I'm going to use yet. Still waiting on my Simpson LRUZ brackets to come in before I buy the lumber.....

It’s more corrosive to fasteners and even the steel roof panels.

I has literally no favorable characteristics for the application you are building.

And it might poison people if you have rafter lickers around.

 

[mike93lx]

Corrosion is a huge factor.

Rafter lickers ruin everything and are the main reason why we can't have nice things

 

[73fxe]

You should use stainless steel fasteners with PT wood.

 

[mike93lx]

You should use stainless steel fasteners with PT wood.

Hot dipped galv is fine