base for lean to shed

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I am planning a lean-to shed that is around 3m x 60cm. It will be sitting on a concrete base that is already there. I am considering this type of frame which then has an OSB Board over it:
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This OSB board will then be the floor of my shed when accessed from inside. I think it's a good idea to raise the floor of the shed as it removes the risk of surface water penetrating the shed. Let me know if you think any different?

I am concerned that these timbers will rot as water will seep through and get into this space when it rains. I could lay it over a section of rood membrane but would appreciate any advice around this. Since everything will be erected on this, it will be a mare to replace the floor at a later date.

Thanks in advance.
 
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rest it on composite base, I bought some from tuin, shed came from elsewhere, but their composite base was the right size keeps the timber dry and off the wet concrete/soil etc. It does need a robust jig saw as it has aluminium bits in it, and it gets hot enough to melt as you cut. current shed has lasted many years with no sign of persistent wet at the base. perhaps for an hour or two after rain.


The lip goes on the inside
 
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I am concerned that these timbers will rot as water will seep through and get into this space when it rains. I could lay it over a section of rood membrane but would appreciate any advice around this. Since everything will be erected on this, it will be a mare to replace the floor at a later date.

Correct, that base will sit in water and rot. It needs to be raised off the ground/concrete, onto something impervious to moisture, like bricks, or tiles.
 
i just screwed lots of pvc door stops to the base of my wooden frame and it's been fine for years. Gets it off the ground and allows air flow underneath
 
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If it were I, I'd rest the shed base on concrete fence posts or railway sleepers. Means the timber isn't sat on wet ground and as mentioned, you get good airflow underneath.

The PVC idea sounds good too.
 
Could the OSB Board (floor) rest on the concrete posts or should I still create a timber frame as show in the original post?
 
Could the OSB Board (floor) rest on the concrete posts or should I still create a timber frame as show in the original post?

I'd build the frame without a doubt. It gives it a lot more rigidity. I have a small 2' x 3' shed used to store timber scraps for the fire, and the OSB floor on that has warped and dipped between the posts its resting on. I'm not fussed as it was free and I can't go in it, but for your shed obviously you'd want the strength.

If the ground is level and you use the two flat sides (where the panels would slide in) they wouldn't move.
 
If the ground is level and you use the two flat sides (where the panels would slide in) they wouldn't move.
The ground is flat. Can you explain the above please. How do you recommend the concrete posts are laid under this base? Also, which panels are you referring to?

I was thinking that the shed sides would be built off this “floating base”. I might put a plinth at the bottom for athletics but structurally, everything would be built off this platform.

Please let me know if I am missing something. Thanks for your help.
 
The ground is flat. Can you explain the above please. How do you recommend the concrete posts are laid under this base? Also, which panels are you referring to?

I was thinking that the shed sides would be built off this “floating base”. I might put a plinth at the bottom for athletics but structurally, everything would be built off this platform.

Please let me know if I am missing something. Thanks for your help.

If you have a concrete base which is flat, then you can just lay the posts on there.

I've attached a picture showing how they should be laid (if you go for this type of post). As the 'faces' of posts are often beveled/rounded, they wouldn't sit right on the ground, but if you lay them as in the picture then the ground and the shed base will both be sat on flat sides

If your base is flat and you lay the posts like this, you'll have no problems building the frame to sit on top of it all. When the posts are down, lay a long spirit level across them all to see if there are any which are sitting too high or too low. You could probably pack them out with a bit of slate or cement.

Hope that makes sense!
 

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You could try using plastic supports under each corner and a couple in the middle to brace the floor. Less labour to install than concrete posts which will crunch on the patio and absorb surface water at the point of contact.
 
I'll post some pics up later of the base we laid for a larger shed, 11' posts all resting on slabs. That was done 5 years ago and all nice and sound still. There is a LOT of weigh in that shed.
 
You could try using plastic supports under each corner and a couple in the middle to brace the floor. Less labour to install than concrete posts which will crunch on the patio and absorb surface water at the point of contact.
What type of plastic braces do you have in mind?
 
These are the ones I used to get it off the floor

Fort such a small space that you wont be walking around in these will be fine and won;t absorb water.

Just get a couple of packs to spread the load

 
These are the ones I used to get it off the floor

Fort such a small space that you wont be walking around in these will be fine and won;t absorb water.

Just get a couple of packs to spread the load

There will be a decent amount of weight in this shed. All of that will be weighing down on these. Will this hold?
Also, will they disintegrate over time?
 
PVC does not disintegrate. It will deform if overloaded. What is overloaded? Who cares, just buy loads, they don't cost much.
I used something similar on the base of a bench I made out of some [enormous, heavy] old 6x12 joists, to keep the ends off the ground. They are unfortunately worn away by moving the bench around but you won't have that problem with a shed, presumably.
 

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