Shed build advice

Good afternoon all! Long time lurker, first time poster and I have a specific question for those more knowledgeable than I.

I have a small 9ish x 10ish shed in the backyard that I want to take down and instead build a 12x~20 in it's place. (It's a tight backyard as you'll see in the pictures and I haven't confirmed yet how close this building can be to the house per code yadda yadda)

My question is, however, what do I do about the fact that I want to butt this shed up against an already existing, taller, patio slab that is not level (for water runoff).? The shed currently sits on a concrete slab but it's way too low and as it is floods when it rains heavily. My plan is to make the shed floor with treated material on top of the concrete that will then run over the dirt as it gets closer to the house (basically forget that an existing slab is even there. I have to be 5 feet off of the fence that's behind the shed which is why I need the new one to butt up against the patio slab.. here are some pictures.

Again, just looking for advice for the unevenness of the existing patio.. let's try some pictures:









Here's a little drawing of what I'm envisioning using one of these photos...

 

Welcome to the forums!
Ideally you don't want the slab draining toward the new bldg. I'd consider laying block to support the end of the shed that faces or meets the existing slab. You don't want a wood framed floor too close to the ground as it needs air circulation under it to keep the wood dry.

 

I'd say don't do it. I think water will be an ongoing problem. You've got a concrete slab directing water right into your shed. If you really want to do it I would build the new shed 6-12" away from your slab and bridge the gap steel grating so the water can fall through.

 

I would pour a footing, lay a concrete block perimeter, and frame the shed on that. Houses and sheds shouldn't be built right on grade for drainage reasons and siding should be kept a minimum of 6" above grade. (Most siding mfg's say so) Putting the shed up on a concrete block foundation solves that. No wood floor.

An 8" concrete block foundation filled with 4" of sand and 4" of concrete would make a real nice floor. 8" above the existing grade. Or skip the sand and pour the concrete on grade so that the top of it is 4" above grade. If the existing pad is in the way of the footprint of the new shed, cut it out and remove it! The top of your block wall foundation and your bottom plate for your shed will be several inches higher than the surrounding preexisting pad. No water problems there.

You have a lot of water coming off the roof and no gutters, so adding gutters to dump that water on the other end of the house would seem to make sense either way.

 

Ok so I believe I butchered my original post sorry, bear with me here..

The existing porch slab flows water perpendicular to the shed, directly away from the house to the back of the property. Not towards the shed. What I’m trying to convey about slope is that the pad isn’t level meaning at one end of this “new shed” there would be no transition stepping into the shed from the pad but at the other end there would be a step up, albeit not a big step. I was more after whether I should attach a 2x6 footer (?) directly to the pad or leave it unattached. Here’s a couple sketches to try to explain..

Can you tell yet that I have superior communication skills 😂😭

 

You don't build on top of the pad.

Like I said... if the new shed is going to overlap the sloped pad you would cut the pad out and remove what would otherwise be under the shed. Put in a concrete block foundation on a footing that raises the shed up exactly as you have it drawn... and build the shed. The part where you have the left arrow "how do I build up this gap" is where the new concrete block foundation will be behind the pad.

The right corner of the shed (actually the top of the shed's concrete block foundation) should be at least 2" higher than the existing pad, at your right arrow.

 

 

I think you are on your own. Good luck.

 

Yes thank you very much for your advice!