DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (http://www.diychatroom.com/)
-   Building & Construction (http://www.diychatroom.com/f19/)
-   -   building an outbuilding on a floating pad (http://www.diychatroom.com/f19/building-outbuilding-floating-pad-97062/)

Zman1 03-02-2011 06:31 PM

building an outbuilding on a floating pad
 
I am building a workshop on a 5" concrete slab that I poured for a basketball court. I am in Ohio. I plan on placing a wooden floor of treated lumber over the concrete. Two questions:
Will I need a vapor barrier?
Does Ohio code allow me to attach the floor joists to the concrete slab as a permanent structure?

Ron6519 03-02-2011 06:50 PM

Quote:

Originally Posted by Zman1 (Post 601252)
I am building a workshop on a 5" concrete slab that I poured for a basketball court. I am in Ohio. I plan on placing a wooden floor of treated lumber over the concrete. Two questions:
Will I need a vapor barrier?
Does Ohio code allow me to attach the floor joists to the concrete slab as a permanent structure?

They might not allow you to convert a basketball slab into a building base.
You usually need a footing below the frost line and foundation adequate for the building load.
How big was this going to be?
I'd call or meet with the local building dept and see what you need to build this before you start investing in materials.
Ron

Zman1 03-02-2011 07:31 PM

Building is to be 16x24 and the slab is 17x21 and 5" deep. I plan on starting on the edge of the slab. I was told the problem would be attempting to attach the building to the slab.

Ron6519 03-02-2011 10:39 PM

Quote:

Originally Posted by Zman1 (Post 601301)
Building is to be 16x24 and the slab is 17x21 and 5" deep. I plan on starting on the edge of the slab. I was told the problem would be attempting to attach the building to the slab.

I see a problem with the building being 3 feet longer then the slab to start off with. But that aside, buildings aren't generally just put on slabs for a reason.
Your shop, do what you think will work.
Ron

Zman1 03-02-2011 11:07 PM

I am positioning the building so it is entirely on the slab - with the building on the edge of the concrete on the east and north side. Building is 12x16 not 16x24 (I wish) Thanks

iamrfixit 03-03-2011 04:37 AM

Around here you can build on a floating slab as long as the building is under 1000 sq ft. My shop is 24 x 36, 720 sq foot and sits on a floating slab. It is merely a 4 inch thick slab with an 6 inch wide trench about 12 inches deep all around the perimeter. That is well short of frost depth for this area. We have pretty extreme weather, two weeks ago it was -20 and five days later it was almost 70. I built the shop in 1990 and it has only a few hairline cracks, the small footprint allows the slab to move as a unit with frost heave and not cause any damage.

The problem with building a shed that is smaller than the slab is water infiltration. No matter how you try to seal the bottom plate rain will hit the slab, pool and get into the building. This isn't a problem when a building fits the slab, as the siding carries the water down over the edge of the concrete and onto the ground, there is no place for water to pool and run in.

If I were going to put a shed on an over-sized slab, I would start with a couple treated 4x4 or 4x6 runners and assemble floor joists and floor sheathing on top of those. The slab will keep the shed level and the runners will keep the floor elevated so it is not sitting in water puddles for extended periods. This will allow for plenty of air circulation so everything can dry up after the rain stops. If you just frame the floor right on the slab it will likely remain wet for days or even weeks after a rain, if it remains wet constantly you are up for mold, rot and all that goes with it. You could also use several concrete blocks, the solid half blocks or even deck pier blocks instead of runners, anything to keep the floor structure elevated so it isn't sitting in water.

Zman1 03-03-2011 08:31 AM

Thanks for the input. I am planning on putting a treated floor over the top of the concrete with treated joists (2x4) and placing a heavy bead of caulk along the sides that the concrete extends past the building. The pad does have two small places where water pools after a rain. It has been in place for 15 years so I had to get approval from the grandkids to use the pad for a workshop. I don't know if I should insulate the floor and use a vapor barrier . I was thinking of laying heavy plastic down and then attaching the plates, insulation and then the 3/4 inch sub floor treated - I know plastic will eventually break down so maybe tarpaper would work better. Trying to keep all the heat I can get in the building. Thanks again for the response.

Zman1 03-03-2011 08:34 AM

If I don't attach the building to the pad - what about wind as we get pretty strong winds here - all open fields to the west for several miles.

bob22 03-03-2011 08:40 AM

Quote:

Originally Posted by Zman1 (Post 601585)
If I don't attach the building to the pad - what about wind as we get pretty strong winds here - all open fields to the west for several miles.

Look at:
http://www.itw-redhead.com/redselec01.asp
These or similar are available at big box stores or building suppliers.

DexterII 03-03-2011 08:50 AM

Before you get too far along, your best tack would be to contact your local building authority, as Ron mentioned, so that you know what is permissable, and what is not. Depending on your municipality, you may even be able to garner some iinitial information regarding construction of sheds, outbuildings, etc. from their website, in order to be better prepared to discuss details with them. Like others, you have probably heard horror stories about building inspectors, but except for a a few incidents, I have found the majority of them to be from planet earth. Regardless, they are the only persons who can tell you whether you can even use your existing slab, so that is where I would start.

iamrfixit 03-03-2011 06:44 PM

I would use 2" foam between the joists, no vapor barrier required. Go with the pink closed cell foam not white bead-board. The pink will stand up much better over time and will not absorb water. It is also considered impermeable so it actually acts as a vapor barrier. It comes scored so it will snap it off at 16 or 24 inch centers and it can be easily cut with a table saw or circular saw.

Depends how you are building it if you should attach.

If you are framing the building up to sit on the slab, then installing a raised floor inside by laying the joists and insulation inside the building on the slab, and then covering that with plywood then I would definitely anchor the building. The floor is not really a structural part of the building if it is built this way.

If you are only using the slab as a base, building a floor structure with joists on top of that then insulating and sheeting the floor structure with plywood and framing the building on top of that; then the floor is a structural part of the building. The weight of the shed and the contents will hold it down. There are millions of portable sheds built that way that are not tied down. It would not take much to anchor it if you wanted and certainly would not hurt anything.

If you are required to comply with a city code, some areas with particularly violent weather may require sheds to be anchored. How the shed it built will also decide whether it is considered a permanent structure. If it IS considered permanent then it would require permits, code compliance and inspections. Also you would most likely be taxed on it as part of your property taxes. Most portable buildings are exempted from that. A portable shed that is anchored to a slab still does not make it a permanent structure.

I would do it the second way, and I would raise it enough to get some type of circulation under it, even if it were only sitting on a treated 2x4 runner under the floor structure. No amount of caulking will keep water from getting under walls anchored to an oversized slab. The structure will move and break the seal, the concrete around the shed is like a highway for water to travel in. A floating floor may provide protection against that water but the water would still be under there rotting away.


All times are GMT -5. The time now is 12:26 PM.