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Building a lean to on a shed

D

dhermesc

Well-known Member
I have a 30X40 shed that has naturally been outgrown. The exterior walls are 10'6" tall. I would like to add a 11' leanto on one (40') side. The plan is a 2' 6" drop in 11' of roofing. Common 29 guage tin.

Two questions:

If I use Douglas Fir or some other better wood - can I use 2X4s on 5' spacing (no truss) for rafters or should I split the difference?

If I have 8' poles for support - how much should be in ground? (plan on using 4X6 or 6X6 for posts).
 
I don't know what your snow load or wind conditions are but I say no on the 2x4 go to 2x6 space them 16 on center. I have seen many buildings built out of 2x4 wide space and the building develops "rickets" I hope I understood your post correctly.
 
How much snow do you get, if any? 2x4's will sag without snow, break with very much. I have always built for snow so I have a tendency to overbuild, with shade tree engineering, but none of my building have ever fallen down. I would go 2x6 on 4 foot centers.
 
Do NOT use 2x4 for rafters!! If you use 2x6 even, they should be pretty close together, 16 or 24 inch spacing. If I was building it I would use 2x12 3 or 4 feet apart.

You will want the posts at least 3-1/2 feet in the ground so it is below the frost line.
 
I would go 2x6 on 4' centers BUT, do not use the "white wood" sold at box lumber companies. Find some made of yellow pine or go to your local sawmill and get 2x6,s made of good wood. If you go with department store "white wood" I would go one size bigger (2x8). Looks are deceiving.
 
What is the frost line in your area?? Where I am it is said to be 18 inches so I go 24 inch for the post so as to stop frost heave. So what ever frost line is go at least 6 inches deeper on the posts. As for 2X4s maybe not strong enough unless you space them say 12 inches or so apart and even then if you get a snow load if over 24 inches they are not strong enough
 
Here I use 6x6 placed 36" in the ground and full dimension (rough cut) 2x8s on 24" centers. These have held 4 or 5 feet of snow on some occasions. I use 1x rough cut lumber for furring strips to screw the roofing to. If you were using 2x4s for furring strips I guess you would be fine with 36" OC rafters but then I would want them to be at least 2x10 if not 2x12. 2x4 rafters is not going to hold up under any snow load at all, and I would not want to walk on furring strips that were only supported every 5 feet unless they were 3x6 or something ridiculous. Anything smaller is going to sag on a 5' span when you put your weight on it.
Zach
 
If you look up a load bearing / span chart I'm pretty sure you need a 2x8 at 24 inch centers max.
Also, you aren't going to have 8 feet clear at your post. You have to put something there to carry the rafters. So your going to end up with about 7 feet clear
 

2x4s would be plenty for a four foot span. for 11 foot I would be using 2x10s. They could go on 24 inch centers.
 
2x6 rafters of yellow pine or equivalent on four foot spacing, then use 2x4 purlins. If snow is a big concern, then go with 2x8 rafters
 
My framing table does not list 2x4 for low slope (<3/12) rafters. It looks like 2x6 white pine is good for an 8' span, 2x8 for about 11'. That's 24" OC. You could probably get by with 2x6 Douglas fir or yellow pine IF you go 16" OC.

If it was my shed, I'd go with 2x8s, 24" OC. 2x4 purlins every 4'. And I'd go with a pair of 2x8s for headers (aka girders) between the posts to support the rafters. Secure the rafters to the headers with "hurricane" clips.

Your posts should be treated for ground contact. The 4x4s sold at the big box stores are ALMOST NEVER treated for ground contact. Go to a lumberyard. I recommend you go with 4x6 posts rather than 4x4; they're generally of better quality.

In most parts of the country, 42 inches is deep enough to get below the frost line. Dig your holes at least 8 inches deeper than you need, and pour a concrete plug in the bottom to support the posts.
 
first of all check all building codes and snow loads 2' 6'' is not a lot of drop in 11'... second get a permit, they may tell you how to build.....third 11' 2x8, 2'oc for rafters, 2x8 face board, then 2x6 perlins 2' oc......post,posthole 44'' deep 8'' of concrete and 36'' of 4x6 post, .....tin warranty may be void if you don't run 2' centers, only 2x4 in this building should be for braceing
 
As everybody else says, depends on where you are. In Oklahoma, pole barns are built with rafters on 5 ft centers, an 11 ft span could be 2x6, 2x8 for 15 ft. Use 2x4 purlins spaced based the metal you are using. 29 ga we put purlins on 2 ft centers. We only have about 1 ft snow load but lots of wind load. If posts are 10 ft on center, run a 2x6 on each side of the posts and put a stub post at the 5 ft mark to nail that rafter to. This design is good for Oklahoma but will not be good for 4 ft of snow load.
 
I have several old garage size buildings with 2x4 rafters in snow country.

But they are quit peaked, and this is old growth, tight grain, few knots, full dimension wood. On 2 foot centers.

You'd have to be half off to use 2x4 for a shallow rafter of 11 foot with modern wood. And spaced that far apart?

Yikes.

Paul
 
>Good rule of the thumb on post depth. A least 1/3 of post length should be in the ground.

That's OK for fence posts, but posts for post-frame buildings are normally only 4' longer than their exposed height, regardless of how long they are. That allows them to be set in a 42" deep hole with 6" to spare. Obviously if the frost line is lower than 42 inches the post must be longer.
 
Yeah, 8 ft poles are pretty short if you want any headroom. I wouldn't try it and I'm pretty conservative when it comes to materials. And no, 2x4s would carry the roof. 2x6s on 24" should be fine unless you need a heavy snow load.
 
The lean to on the far side of the large barn won't meet any codes. It is 13'x48' with about 12" of fall and a shingle roof. It been there since 2002 and still doesn't leak. I have never shoveled it off in the winter(SE MI). Because it's not heated, snow doesn't seem to stay on it. That being said, it has 2x10 rafters 2' on center. No way would I use 2x4s.
 
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