Framing a lean to questions

[KathyInVa]

Hello all! I'm hoping someone can help me with some general info. I have very solid general construction skills... all the tools and know how to use them.... but never have built a lean to before. I'm single and have no help so no choice but to go at this alone, but I know I can do it! Just need a bit of guidance! I have a barn, 24x24 where my goats are housed, I want to add to one side of it - a lean to which will come out an additional 6.5 feet (that is as far as I can come out with the existing pitch of the roof and still have enough headroom to walk under the top plate where the entrance will be. The new portion will be the entire length 24ft x 6.5ft. I will use (4) 6x6s (I happen to already have) which I will dig holes and set with two bags of concrete each. I think this will be the hardest part and maybe could use some tips here... I am planning on setting them and laying 2x4 across top with level and just playing around with each one (in dry concrete) until I have them completely level across the top. I don't think I could ever cut them off completely flat/strait on the top so I do not think that is an option (although, I've seen where some people notch them out on the sides and attach their headers that way. The way the header is on the end of the existing barn is it sits on top of the vertical end posts, so if I do it that way and copy what is already there, I need to get those posts exactly right... so for this step I have a few questions:

1. I have these 6x6 posts on hand, free... 3 are not pressure treated, but if they will be completely surrounded by concrete, and remember this is for animals... could I get at least 30 years out of them???
2. should I do as I'm planning on and just work with the posts to get them set completely level (across the top)? I feel like spending the time to do that will make everything else easy.

The existing barn uses 2x4s 24" on center for the rafters. My neighbor tells me I have to use 2x6s or it'll never hold snow load... however I'm keeping same pitch of roof and the existing one has been there, and still in GREAT condition for 100 YEARS!!! I was planning on "scabbing" (not sure if that is right terminology) the new rafters onto the existing rafters, that'll make it easier to ensure I have correct pitch too. Questions about this step:

1. are the 2x4s as rafters ok? I can't imagine they aren't when they have lasted on existing barn for 100 years with no problems.
2. they didn't use joist hangers (didn't have them back then!)... and I don't think I would either with how I'm planning on doing it, but this step I'm not so sure about. Was thinking I'd notch the rafter where it hits the header that runs across the top of the beams that make up the new supporting side (not the existing supporting side) of the lean to.

Anything else y'all can think of? I'm using metal roofing, tucking it under the existing metal roofing, putting it on top of OSB sheathing.

Thanks so much for your help!!!
Kathy

 

[pattenp]

The post need to be treated for in ground use. Untreated in concrete will not last but a few years. The header across the post tops should be at least a double 2X6. The rafters can be 2X4's but need to be on 12" centers.

 

[NUTTSGT]

Gathering what I have read from your post, I would use 2x6s for the rafters. I'd put a birds mouth on both ends, one on the upper end under the roof and on top of the header for the wall. The second one at the bottom over the header that sits on top of your 6x6 posts.

Now that I say that, they may not work as there may not be enough room since the old roof used 2x4s. What you might need to do is actually measure the old rafters, generally, the old stuff will be native lumber. It's probably different dimensions that the modern kiln dried lumber.

 

[lilredex]

Here is something similar, added to my garage, about fifteen years ago.

All 2 X 4 walls and rafters. The rafters sit on a 2 X 4 ledge lagged into the existing garage studs and bird mouthed (notched) at the wall's top. The rafters were planed to sit squarely on the ledge and are held there with shop made "T" brackets. The wall sits on a footing (low wall) that was poured on top of an existing slab.

If you want to use those 6 X 6's for posts, make up some 3" pipes with a top saddle and put them in the ground. Similar to those pound in "stakes" that DIY fencers use to avoid digging holes.

Here are the best pictures I can find.


screen grab


image hosting websites

 

[HoosierMark]

When you are thinking of 2x4s you need to remember what species of wood they used for the original building. If those are "hard" woods such as oak that is a big difference then pine wood. I have old barns that you cannot drive a nail into the wood. Make sure you are comparing apples to apples.

 

[jkwilson]

You want your posts to be taller than you need. Then you mark a level line across the posts and hang your beam level and go back and cut the excess off of the posts. About an impossible job to level them as you install them.

I like to drill a hole crossways in the bottom of the post about 6" from the bottom of the post and drive a piece of rebar slightly shorter than the hole diameter through. With a bell shaped hole, this makes the lean-to much more resistant to wind lift.