Building a Shed on Concrete Pad

[Handyandy23]

Hi all, I'm going to be building a small shed soon, and I have some questions for those of you with more experience doing this than I do.

We're currently having an in ground pool put in our backyard, and once ready there will be concrete poured around it. That concrete pad will extend about 18' past the pool on one side to our fence, which gives me room to put a small shed.

This is just basically a storage shed, nothing fancy. Has to be under 100 sq ft. The pool equipment will be installed behind the shed, and the electrical panel will be housed inside the shed. Otherwise it's going to hold random pool stuff, lawn mower, etc.

What I'm wondering, is do I just frame the walls right on top of the concrete? I'm seeing that a lot online. And if I do so, would I seal the baseplate somehow so that water can't flow under it when it rains?

My initial thought was it would be best to build a base frame with a plywood floor on top, then walls on top of that. This keeps it directly off the ground and gives some level of airflow underneath.

However lots of online sources seem to feel this is a waste considering the concrete itself makes the best floor. And it certainly would save on material and my labor.

This is in Ontario, Canada, near Detroit, for reference. So we do get cold winters with snow, if that makes any difference.

 

[johnnyradiant]

I would consider framing off of a row of blocks but leaving the slab as my floor. If water ingress is an issue then you're left with either framing a floor above the slab and going up from there or placing a slab on top of the existing concrete that would raise everything up so that water on the floor won't be an issue till the roof leaks.

 

[bdbecker]

Since you mention the shed as to be under 100 square feet, I'm assuming you're building it this size to avoid permitting/zoning restrictions. If that is the case, I suspect that you also would have to have it be freestanding, meaning that you can't use the concrete below it as the floor (double check you local ordinance).

 

[Bretny]

Frame it right on the concrete with PT ground contact as the base plate of the wall. A concrete floor in a shed is really nice.

 

[NUTTSGT]

I would consider framing off of a row of blocks but leaving the slab as my floor. If water ingress is an issue then you're left with either framing a floor above the slab and going up from there or placing a slab on top of the existing concrete that would raise everything up so that water on the floor won't be an issue till the roof leaks.

This would be my issue as well.

Consider talking to the guys doing the concrete work to see if they can a small step up in the concrete for a small charge. basically a pad slightly above the other pad, just a couple of inches. It should be no different than pouring a set of steps.

A competent concrete guy should be able to handle it.

 

[nadogail]

IMHO, I would put a bead of caulk under the bottom plates of the walls and threshold. The bottom plate should be Ground Contact rated treated lumber.

I really don't know but knowledge is not a requirement for an opinion.

 

[Bretny]

Typically you run the siding down past the base plate to just under the concrete. How high your concrete is above grade and what type of siding your useing matters.

 

[Kevin54]

Build a frame with floor joist out of treated lumber and add a treated floor on top of that. Since you will be sitting on concrete the floor joist could be 2x4's. You'll have a small step up into the shed, but you won't have to worry about any water getting in like if you just built wall on top of the concrete.

 

[The Cobbler]

I would build the shed on 2 to 3" of xps foam under the bottom plate , or lay a course of 4" half blocks on the slab. you could also pour a stem wall a few inches thick after the pour has been done. many ways to skin the cat. I would use the concrete as the shed floor, no need to add anything to that.
you should ask the guys doing the concrete if they can do anything for you, for an extra cost.

Since you mention the shed as to be under 100 square feet, I'm assuming you're building it this size to avoid permitting/zoning restrictions. If that is the case, I suspect that you also would have to have it be freestanding, meaning that you can't use the concrete below it as the floor (double check you local ordinance).

not the case in Ontario, just limited to size without requiring a permit . a shed permit is no big deal either, depending on your lot size/footage under roof etc

 

[The Cobbler]

also should let the concrete guys know in any case, you don't want it in a low spot where they're running water off.

 

[LS6 Tommy]

Since you mention the shed as to be under 100 square feet, I'm assuming you're building it this size to avoid permitting/zoning restrictions. If that is the case, I suspect that you also would have to have it be freestanding, meaning that you can't use the concrete below it as the floor (double check you local ordinance).

X2. Usually any kind of poured slab is considered a foundation and makes it a permanent building.

Tommy

 

[The Cobbler]

Since you mention the shed as to be under 100 square feet, I'm assuming you're building it this size to avoid permitting/zoning restrictions. If that is the case, I suspect that you also would have to have it be freestanding, meaning that you can't use the concrete below it as the floor (double check you local ordinance).

X2. Usually any kind of poured slab is considered a foundation and makes it a permanent building.

Tommy

doesn't make any difference here. a shed is a shed is a shed. only requirement, over 110sqft you are required to get a permit.

 

[LS6 Tommy]

doesn't make any difference here. a shed is a shed is a shed. only requirement, over 110sqft you are required to get a permit.

Sorry, didn't see your location. Good to go.

Tommy

 

[The Cobbler]

^^^ that's what spurred my thread, Why do people build sheds on wood raised off the ground. something that made no sense to me , but being explained, it now does.
now, when you do go to build a structure, like a garage, you have to include the roofed portion of all buildings and they count towards total square footage allowed for the lot size.regardless if it's a built on concrete shed, a plastic one laying on a skid or a covered sunporch etc.

 

[James-W]

I have a small shed that I built many years ago, it is 10ft by 16ft with a wood floor and the shed is sitting up on blocks. The wife and I like the shed and it has served us well over the years. It has provided a place to put gardening tools, store boxes of stuff that we seldom use, and in general a place to put those items that we want to keep, but probably will never need.

However, having said all that, if I had to do it over again I would not hesitate to pour a concrete floor with a stem wall. With what we have now, small animals get under the shed and build nests. Then other animals try to get to them and they start digging. The wife and I came home from the grocery store one time and two dogs were digging trying to get under the shed. They had a large area ripped up in our lawn. I scared them off and put the dirt back with a shovel and planted grass seed, so, in time all was well. But the point is, a shed up on blocks is not exactly an ideal situation.

I realize there is a "penalty" for having a concrete floor in a shed, you have to pay property taxes on the shed because it is considered a permanent structure and in some locations you may need a building permit. But the cost of a permit and the amount of property tax you will pay on a small shed is very minor when compared to the benefits you get from having a concrete floor.

 

[CoogarXR]

When I bought my house it had a shed with a slab floor. It was just a couple rows of treated 2x4s along the bottom, bolted to the slab, then studs on top of those. That shed always was wet. I don't know if the concrete wicked moisture up or what (I'm not a construction guy, I have no idea). All I know is, everything in there ended up moldy.

I tore it down and had a prefab shed put in it's place, set on the same slab. But the new shed has a wood floor and sits up off the slab 4" or so. It's all good now.

 

[MushCreek]

I would either have them pour a raised pad above the rest of the deck, or put a PT wood floor down. You could even lay the 2X4's flat to minimize the step up. If you attach the walls directly to the pool deck, water will eventually find a way in. Regardless of what you build, you need to use PT lumber wherever the framing touches concrete. Concrete sweats under certain conditions, such as a warm humid spell right after cold weather. A PT plywood floor will actually feel dryer than concrete, but you want it elevated on framing.

 

[mike93lx]

Ground contact pt bottom plate with a couple beads of silicone underneath is what I would do. Set the PT plate, then add a framed wall on top. Keep the sheathing off the ground by a couple inches and trim with pvc trim at ground level.

There is no need to form a step or add block or frame a floor on top of the concrete. A couple tubes of silicone is plenty.

Canada doesn't require ground rods, but I would install two anyway considering the equipment and added ground potential of the pool

 

[Bretny]

If you guys are relying on a few beads of silicone to to keep water out of your building your building wrong. Gravity always works and dosnt dry up and crack when the wood shrinks.

 

[mike93lx]

If you guys are relying on a few beads of silicone to to keep water out of your building your building wrong. Gravity always works and dosnt dry up and crack when the wood shrinks.

It is a shed, not a house. If the silicone under the plate isn't enough, a bead on the exterior will do it

 

[yeldogt]

^^^ that's what spurred my thread, Why do people build sheds on wood raised off the ground. something that made no sense to me , but being explained, it now does.
now, when you do go to build a structure, like a garage, you have to include the roofed portion of all buildings and they count towards total square footage allowed for the lot size.regardless if it's a built on concrete shed, a plastic one laying on a skid or a covered sunporch etc.

A wood shed up on blocks will stay dry -- if it's just sitting on a slab .. it will rot.

I have done both and it't actually better w/o a slab

 

[yeldogt]

I'm a little confused -- so the shed is holding the panel .. but, not the pool equipment ?

If you frame the shed on top of the concrete it is going to leak -- no amount of caulk is going to stop the water and it's going to stay wet ... it's a bad idea.

IMO -- find a place for the shed to sit as a typical shed does on simple blocks -- over open ground.

I have never had any issues with concrete under a shed as long as the shed did not exceed the typical 120sf limit. But --again ... unless the shed can dry it will rot ... so a typical shed needs to be elevated ... so spending for the concrete under it is a waste. I have done it -- I know.

Also -- putting the panel in the shed may cause an issue .. did you check this out?

Personally -- I like to make a small "shed" .. to hide the equipment. I have never run into this being a problem and counting towards the one shed rule on the property. Same with making something to hide trash cans. It's nice to have the equipment hidden and it keeps it out of the sun and rain .... it need to have lots of ventilation. Every pool panel I have ever had was weather proof and rated for outside.

On last thing ... you can't store CL and pool shock w/ CL in an area with the equipment or other metal items. I store mine in a small rubbermaid "shed" ... I think it's rubbermaid -- it's for a trash can.

If you want to move forward with the shed on the concrete -- you need to have them pour a curb .. otherwise it's going to allow water to get inside.

Don't lock in all your pipes ...make sure you have some wiggle room in case you have issues and make sure the conduit is oversized if you have a LED pool light.

 

[didit]

I have mostly always poured concrete slabs for my personal sheds. I make sure they are elevated enough and crowned sufficiently not allowing any runoff to enter. A good bead of silicone certainly is cheap insurance as well.
The last vinyl shed I bought came with a plastic floor so I used limestone screenings, compacted, crowned and elevated, the same as a concrete pad. Worked out great.

 

[NUTTSGT]

If you guys are relying on a few beads of silicone to to keep water out of your building your building wrong. Gravity always works and dosnt dry up and crack when the wood shrinks.

I'm with Bret on this one and why I suggested a raised section of the pad.

It is a shed, not a house. If the silicone under the plate isn't enough, a bead on the exterior will do it

Don't matter if it's a shed or a house, water will get in under wall and ruin stuff.

 

[yeldogt]

I'm with Bret on this one and why I suggested a raised section of the pad.




Don't matter if it's a shed or a house, water will get in under wall and ruin stuff.

I think people are mixing up if the shed has a floor .... if using the concrete for the floor it's going to leak. If the shed has a floor -- and it's wood without any air under it ... the bottom will eventually rot from the underside.

A plastic one will not care ... and as I have said an elevated on over a pad will work ... but having done it ... having stones that drain is better.

 

[PugetDude]

Have the concrete crew pour the slab with a raised rectangle For the shed formed with 2x4’s on edge; they do it all the time here in AZ for garage floors... Slope the adjacent slab for drainage away from the raised section. Strip the form and frame the shed conventionally with 2x4’s use-PT for the bottom plate. It will stay high and dry forever without relying on caulk.

 

[NUTTSGT]

I think people are mixing up if the shed has a floor .... if using the concrete for the floor it's going to leak. If the shed has a floor -- and it's wood without any air under it ... the bottom will eventually rot from the underside.

A plastic one will not care ... and as I have said an elevated on over a pad will work ... but having done it ... having stones that drain is better.

I gotcha and yes.

 

[Handyandy23]

Thanks everyone for all the feedback and opinions. As I kind of expected, a lot of people differ on how they think the best way is to do it.

I'll just clarify or answer a few questions that came up. This is just meant to be a simple little shed to keep my lawn mower and other random yard stuff hidden away. So it doesn't need to necessarily stay bone dry, but at the same time, I don't want it to be so wet that it rots or gets moldy inside.

We decided on having the pool equipment outside of the shed because it can be hidden in front of the back fence and behind the shed to get it out of sight, without taking up the limited storage space in the shed. It also simplifies having to worry about venting in the shed. It's designed to live outside, so I don't really see a major advantage to having it inside.

The small electrical panel is going to power the pool equipment, as well as have enough capacity for a future hot tub install.

The concrete guys are setting up at the start of the week so I'll ask them about giving me a slightly raised pad or stub walls, and see what kind of extra cost there might be for that. I do like the idea of using the concrete as the floor since it's solid and level out the door, as well as just simplifying the build and using less material.