Lean-to/Shed Construction input desired

I need to construct a storage shed. One of the few viable places is where we have some concrete slab immediately adjacent to our house.  I'd basically like to construct a tall lean-to structure. For ease of access reasons, and to avoid creating a cavity for critters right off the house, I'd like to leave the floor open as possible and just be the existing slab.

I can't decide how exactly to do the wall/sill plate build up (was thinking 2x8/10 sill w/ a 2x6 wall plate on top). Easy answer is to put down an insulating barrier between PT lumber and the concrete, but I worry about that wood long term.

Here's a pic of the area w/ the rough idea sketched in. I might want to add a non-skinned wall between the two door openings. The footprint is very close to exactly 4'x11' (slightly less).

view from a different angle:

Why do you want an insulating layer between concrete and pressure treated lumber?

Why the back wall too?

If it was me i would do a 2x6 wall in front with a header all the way thru, Find the rim joist on the house and lag in to it. Stack the roof joists on top of both and build a side wall underneath

You can buy lean-to sheds from Home Depot that may be your easiest option.

Are you ok with pulling siding and attaching it right to the house? That would be the best way, but is quite a lot more permanent than a freestanding structure. It (probably) needs to be attached either to the house or the slab, so somebody is getting holes. 

Antihero said:

Why do you want an insulating layer between concrete and pressure treated lumber?

Trying to keep storm water from running into the "shed" area to keep out moisture. I saw a seal along the bottom, and back against the exterior wall of the house.

Why the back wall too?

I saw the back wall as being framed, but not necessarily, or completely, skinned. I figured it would be necessary for structure and so I could use it to hang things from.

Keith Tanner said:

You can buy lean-to sheds from Home Depot that may be your easiest option.

I've looked, but everything isn't as tall as I'd like.  I really want to be able to store things above as well (think wheels).

mazdeuce - Seth said:

Are you ok with pulling siding and attaching it right to the house? That would be the best way, but is quite a lot more permanent than a freestanding structure. It (probably) needs to be attached either to the house or the slab, so somebody is getting holes. 

Totally fine with holes in the slab.  I'd rather avoid pulling siding, but I'm ok with securing lightly to/through it.

Your primary water intrusion spot is gonna be where the roof meets the wall of the house. If you don’t pull the siding and flash it properly, it will definitely leak badly. 

Don't know what you are storing- water intrusion may not be an issue. 

bluej said:

Keith Tanner said:

You can buy lean-to sheds from Home Depot that may be your easiest option.

I've looked, but everything isn't as tall as I'd like.  I really want to be able to store things above as well (think wheels).

Fair enough. Don't forget to take the weight of the wheels (especially with tires, if applicable) into account when designing the rack and what it's attached to. They can be pretty heavy. My first tire rack was too weak.

If you are gonna have a back wall, just go ahead and skin it, and let the shed be fully free standing. 

Then you won’t have to worry about water intrusion OR attaching to the house. 

Cover it with T-111 or PT plywood, and slap some paint on it before you stand it up. Then shove it against the wall, and built from there. 

In reply to SVreX :

Agree, if it is not going to be attached to the house properly (remove siding, etc) it should be free standing.

You should either cut the siding and attach it to the house for real or build a separate free standing structure.  Halfway attaching it to the house is a recipe for water intrusion and all the bad stuff that goes with it.

Personally, I'd build a completely separate structure with block piers and a wooden floor somewhere else so I didn't have to deal with the artificial constraint of that narrow pad.

SVreX said:

If you are gonna have a back wall, just go ahead and skin it, and let the shed be fully free standing. 

Then you won’t have to worry about water intrusion OR attaching to the house. 

Cover it with T-111 or PT plywood, and slap some paint on it before you stand it up. Then shove it against the wall, and built from there. 

Sounds like this is the best option, and I saw it not really relying on the house for structure anyway. Wouldn't I still want to do something where the upper peak edge if the "lean-to" is right adjacent to the house to prevent water from the side of the house running behind the new (skinned) structure? Something as simple as a bit of caulk, flashing, and small fasteners into the siding?

There really isn't anywhere else I can build a shed on our property, unless we want to make some big compromises. We're in the city, so not a ton of exterior space.

Thanks for input so far, all!

In reply to bluej :

Why?

If the back of the shed is treated like the exterior of a structure, who cares if water runs down??

Sure, you can throw a little caulk at it if it makes you feel good. 

I probably would. Just because I would like to minimize how much water gets trapped between the 2 structures that is then unable to properly dry out. 

You could tuck some flashing into the vinyl siding joint with no nails without damaging or removing the siding at all. It would stop 98% of the water intrusion. 

I don't know if you have frost conditions in the winter, but assuming the house is on a foundation and the slab is floating you may have issues - a slab will move up and down as the ground freezes and thaws, while the house and its foundation will not, so each spring and fall the structure will be heaving up and down against the house framing.

For that matter, putting a freestanding shed up against the side of the house could create a moisture issue on the house siding (as well as a nice place for critters to hide.)

SVreX said:

In reply to bluej :

Why?

If the back of the shed is treated like the exterior of a structure, who cares if water runs down??

Sure, you can throw a little caulk at it if it makes you feel good. 

I probably would. Just because I would like to minimize how much water gets trapped between the 2 structures that is then unable to properly dry out. 

You could tuck some flashing into the vinyl siding joint with no nails without damaging or removing the siding at all. It would stop 98% of the water intrusion. 

I should have mentioned earlier that the siding is hardieplank, not vinyl.

You can tuck it into the Hardi- even better.