# need help with size of lumber to use for lean to on deck



## walnut777 (Dec 9, 2010)

Hello. I'm getting all kinds of different info from friends for my diy project.
I have a 17ft x 14 ft deck. I want to put a lean to roof over it.I will not be attatching it to the house. It will be free standing. It will have a metal roof with no ply wood under it. One friend says this: the 17 ft pieces need to be 2x10's doubled together with 2x8's spanning the 14 ft every 16 inches with 1x4 to screw the metal roof to.. with 6 - 4x4's for support. 3 in the rear and 3 in the front.

My other friend says to use 2x8s with osb sandwhiched in the middle for the 17 feet sections and then 2x6's sandwiched with osb every 24 inches for the 14 foot span. with 1x4s to screw the metal roof to with 6 4x4's to hold it up.

One friend says the others is overkill the other says his is not enough. I live in S. carolina so there wil be no real load to it like snow. We rarely get snow and its not usually very much.

I personally wanted to build the frame with the steel they use to make those metal carports with but its as expensive as lumber, plus I cant weld.

Also. I there is concrete under half the deck. So the side closest to the house would have the 4x4's on concrete and the front side would have the 4x4s cemented in the dirt and I planned to use some type of lag bolts to secure them to the band of the deck.
Thanks in advance for your help.


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## JustinK (Oct 4, 2009)

Dont use osb for anything structure that will be exposed to elements even if its under a roof the humidity will still get to it. Stick with 2x8 24 oc. or 2x6 16 oc. for rafters. 
Im not sure how to calculate Porch roof beams so I just use house header spans charts which im sure is oversized. A header for that span would be double 2x10's with post in middle.


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## walnut777 (Dec 9, 2010)

JustinK said:


> Dont use osb for anything structure that will be exposed to elements even if its under a roof the humidity will still get to it. Stick with 2x8 24 oc. or 2x6 16 oc. for rafters.
> Im not sure how to calculate Porch roof beams so I just use house header spans charts which im sure is oversized. A header for that span would be double 2x10's with post in middle.


are you saying that i can do 2x8 - 24 in. oc and not double the 2x8s? or i can use 2x6 16 in. oc and not double the 2x6's? 
and you are suggesting 2x10's foor the 17 foot sections.are the 17 foot sections the header? sorry im new to this. also. and by post in the middle you mean a post in the middle of the 17 foot sections? also do i need to double the 2x10's? thanks


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## JustinK (Oct 4, 2009)

walnut777 said:


> are you saying that i can do 2x8 - 24 in. oc and not double the 2x8s? or i can use 2x6 16 in. oc and not double the 2x6's?
> and you are suggesting 2x10's foor the 17 foot sections.are the 17 foot sections the header? sorry im new to this. also. and by post in the middle you mean a post in the middle of the 17 foot sections? also do i need to double the 2x10's? thanks


You do not need to double rafters I am also assuming there is going to be a foot over hang (cantilever) to the rafters on each side. So that would make your span for rafters only 12' 
Yes double the beam (2x10) with a post in the middle


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## walnut777 (Dec 9, 2010)

no cantilever. i have very little space to work with from the decking boards to the metal roof on my house im trying to line up with is 8 ft. and im 6ft 4 so its cutting it close. i believe this is why my first friend said to use 2x8's because ( i think ) he said that 2x8's 16 oc could span 14 ft 1 inch. he said this was the best way he could think of since i cant cantilever


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## walnut777 (Dec 9, 2010)

in my head this is how it would be built. the second picture on this page: 
http://www.howtospecialist.com/outdoor/pergola/how-to-build-a-lean-to-carport/
thanks again for all your help. im sure this is aggravating


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## JustinK (Oct 4, 2009)

He is right. Since it is only a metal roof you could probably get away with a smaller rafter or larger oc but for the couple extra dollars it is not worth it.


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## fortunerestore (Mar 6, 2014)

This discussion is quite informative. Having a look at the picture I hope it is easy to make out the decision. He is right and the solution is implementable too. Thanks for the discussion.


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