Need some help with rafter sizing and snow load calc

[maxspeed96ct]

Im going through some design details still for my 25x24 attached garage . It's currently a single carport and I'd like to save the existing carport and add onto it .
Went to pull my permit and my inspector had some douts about my snow load capablities of my design . Or he was busting my balls because i disnt have them . My plan was to use 2x6s 16" on center for a gable style roof . Pitch is 5 3/4 - 12 . That is how the existing part of my house and car port is and I'm just going to extend from it and attach the 2 car .

Anyone have a link or some details on rafter weight capabilities ?

I know myself 2x6 rafters will be fine since my house was built 50 years ago and there's no issues . But I need some kind of proof for the inspector .

I'm really trying to avoid going through a engineer to keep my build costs down. If anyone can help me out I'd appreciate it .

 

[K'ledgeBldr]

Anyone have a link or some details on rafter weight capabilities ?
Start here:
http://www.awc.org/technical/spantables/tutorial.html

I know myself 2x6 rafters will be fine since my house was built 50 years ago and there's no issues .
That is not true- lumber that was used 50 yrs ago had higher span capabilities than lumber used today.
I'm really trying to avoid going through a engineer to keep my build costs down. If anyone can help me out I'd appreciate it .

That tutorial should help you out- But knowing what the established snow load is for your area (or what is recognized by the AHJ) will help tremendously.

 

[Falcon67]

What he said - you'll need to know the loads, then they type of lumber you are using. Pitch doesn't matter, it's the load and the run. If you are in a 50 lb/sq ft area, you're probably looking at 2x8 or 2x10 for a 12' run.

I know myself 2x6 rafters will be fine since my house was built 50 years ago and there's no issues .

Our ex house was built 86 years ago and used 2x4 rafters and joists. You're not going to see that now, either. Sometimes there is a reason they don't build 'em like they used to.

 

[maxspeed96ct]

That tutorial should help you out- But knowing what the established snow load is for your area (or what is recognized by the AHJ) will help tremendously.

Thanks, this is a good read , hope it has what I need.

What he said - you'll need to know the loads, then they type of lumber you are using. Pitch doesn't matter, it's the load and the run. If you are in a 50 lb/sq ft area, you're probably looking at 2x8 or 2x10 for a 12' run.

Our ex house was built 86 years ago and used 2x4 rafters and joists. You're not going to see that now, either. Sometimes there is a reason they don't build 'em like they used to.

Snow load in my area in 35/sq ft according to the inspector. I think he was just busting on me for not knowing the load calcs.
At least I hope so because if I cant use the 14ft of roof from my existing carport It will require alot more money then I planned

 

[TommyK]

What he said - you'll need to know the loads, then they type of lumber you are using. Pitch doesn't matter, it's the load and the run. If you are in a 50 lb/sq ft area, you're probably looking at 2x8 or 2x10 for a 12' run.

Our ex house was built 86 years ago and used 2x4 rafters and joists. You're not going to see that now, either. Sometimes there is a reason they don't build 'em like they used to.

2 x 6's ain't gonna cut it.

BTW pitch does matter.

 

[BD1]

Your local building zoning department should have their own code book with
a table that will specify spans.

 

[maxspeed96ct]

2 x 6's ain't gonna cut it.

BTW pitch does matter.

Have any charts or info for me ?

Your local building zoning department should have their own code book with
a table that will specify spans.

He did , but wouldn't share much with me besides the fact hes looking for a 35lb snow load.


Looking at this chart - http://www.wclib.org/SpanCalc/SpanC...d=10&submit=Calculate+Maximum+Horizontal+Span, it says 2x6's are useable depending on the type of lumber....

But my next question is , what can I do to save the existing car port roof, would there be a formula or possible way I can sistor up the exsiting 2x6 rafters to get my desired load span ? or is this out of the question ? total distance is 24' so my span would be 12' correct ?

 

[Devildogs]

I remember the American wood council has span charts on the website. That should give you uniform loading capacity for a given span. Example: if center to center of joist is 2 foot. each joist supports 2 square foot per linear foot of joist length. @ 35lbs/sqft that is )70lbs per foot of joist span. Note that this is for a square or rectangular shape and that if the shape changes the loads will change. All joist should be braced to keep them from rolling under a load. This being said you will probably need a drawing and a PE stamp to pull a permit.

 

[Kevin C]

If your using the IRC ( IBC should be similar) A 30 PSF snow load , 10 PSF dead load requires a #1 Doug fir 2x6 16" OC. Southern Pine #2 or better.


A 20 PSF dead load 16" OC = #1 Doug fir 2 x 8 , #3 Doug fir 2x10, #1 2x6 Southern Pine or a #2 2x8 In southern Pine.

Getting a full load of #1 lumber can be challenging. #2 is a lot more common.

In my IRC book the next loading number is 50 psf. For that a #2 Doug fir or Southern Pine 2x8 would work. As long as you stick with the prescriptive charts you dont need a PE's stamp.

Same with trusses, as long as they are engineered by the truss company with a report that they meet the loading requirements you should be able to get a permit.

 

[SGKent]

when time isn't important just keep plugging away until you figure it out. Out here the county or city will want an engineer's stamp on the plans so it makes more sense to get what you are going to pay for anyway - at least out here.

 

[premierplayer]

If your using the IRC ( IBC should be similar) A 30 PSF snow load , 10 PSF dead load requires a #1 Doug fir 2x6 16" OC. Southern Pine #2 or better.


A 20 PSF dead load 16" OC = #1 Doug fir 2 x 8 , #3 Doug fir 2x10, #1 2x6 Southern Pine or a #2 2x8 In southern Pine.

Getting a full load of #1 lumber can be challenging. #2 is a lot more common.

In my IRC book the next loading number is 50 psf. For that a #2 Doug fir or Southern Pine 2x8 would work. As long as you stick with the prescriptive charts you dont need a PE's stamp.

Same with trusses, as long as they are engineered by the truss company with a report that they meet the loading requirements you should be able to get a permit.

Pressure treated #1 SYP should be available. Nothing says you can't use it indoors. In my area cost is generally a few cents less than than framing lumber. Could be an option.

 

[Kevin C]

http://www.awc.org/calculators/span/calc/timbercalcstyle.asp?species=Douglas+Fir-Larch&size=2x8&grade=No.+1&member=Rafters+%28Snow+Load%29&deflectionlimit=L%2F360&spacing=16&wet=No&incised=No&liveload=20&snowload=35&deadload=10&submit=Calculate+Maximum+Horizontal+Span

Handy span calculator

 

[maxspeed96ct]

What I dont understand is why the inspector said I May not be be able use the roof from my existing car port. Its been up since the house was build in 64 and has no sagging or signs of stress

Thats like If I was putting a addition on a house, I wouldnt have to make the existing roof meet the new codes right?

What can I do to get around him ? Have a engineer verify it?
Im in a small town , I just cant believe one grumpy old mans opinion has the power the make or break my project ....

 

[TommyK]

Have any charts or info for me ?


http://www.awc.org/pdf/STJR_2012.pdf

 

[5lima30]

Pressure treated #1 SYP should be available. Nothing says you can't use it indoors. In my area cost is generally a few cents less than than framing lumber. Could be an option.

+1 on what he said! ^^^

 

[maxspeed96ct]

Have any charts or info for me ?


http://www.awc.org/pdf/STJR_2012.pdf

Ya I looked through the charts , certain 2x6s will work since my rafter span is 12ft ,but what about my existing car port roof ? How can I argue to keep it as part of my garage roof ? It spans my house and shows no issues of sagging or anything. Can the inspector really make me tear it down ? Here's a pic of my house so you guys can understand why I want to save it .

 

[bigdav160]

Can the inspector really make me tear it down ?

I'm not going political, but that totally depends on your area.

Where I live, there is little to no government. I can, pretty much, build anything I want, the way I want.

 

[K'ledgeBldr]

Can the inspector really make me tear it down ?

In a word- yes.
Is it right? Hell no!
The only way you'll "legally" supersede the inspector is with an engineer's letter/diagram. And it HAS TO BE an approved engineer for the AHJ.

 

[Aussie damo]

What I dont understand is why the inspector said I May not be be able use the roof from my existing car port. Its been up since the house was build in 64 and has no sagging or signs of stress

Thats like If I was putting a addition on a house, I wouldnt have to make the existing roof meet the new codes right?

What can I do to get around him ? Have a engineer verify it?
Im in a small town , I just cant believe one grumpy old mans opinion has the power the make or break my project ....

Here in Australia the inspector that signs a. Project off is now liable for any personal and/or property damage.
He is no doubt covering himself.
I know of one inspector that did his inspection after a long lunch on a friday and the turned timber stair case was 6mm under height (1/4 inch) and someone fell off. He was prosucated and had to pay out a couple of mill $.
It might cost you more now but never have to worry about it ever again.
My 2cents worth.

 

[Devildogs]

I can see the inpectors point because if he agreed to sign off he would be signing something that does not meet code becuse you are tying in to that structure. Another way would be to make your addition a seprate structure all together. Here in Texas a PE is the top dog. If he says it will work, thats the end of the discussion. If the PE reviews the plans and signs off you are home free.

 

[maxspeed96ct]

I can see the inpectors point because if he agreed to sign off he would be signing something that does not meet code becuse you are tying in to that structure. Another way would be to make your addition a seprate structure all together. Here in Texas a PE is the top dog. If he says it will work, thats the end of the discussion. If the PE reviews the plans and signs off you are home free.

I know what you mean but the part I will be build will meet codes its the existing thats a problem, if you look at the picture my existing roof rafters span more then half of my house. Am I supposed to rebuild my entire home ?
Just seems ridiculous to me

Im sure it was built with quality 2x6 lumber since it hasnt caved or sagged since it was built 60+ years ago.


The inspector wants to come out and see my existing car port this week, Im trying to gather as much information as I can so I can back up my case.

Any information is appreciated