Do I need a shed base?

[transatlantic]

I'm going to be purchasing a log cabin soon, which will be errected on an existing concrete slab (the slab is far larger than the shed). The old shed that was in the same place, was just placed directly on the concrete, and suffered from rot through out the base.

From all the information I have read, you can place new sheds directly onto concrete, so I am wondering why the old shed had so much rot?

Could it be that the concrete slab is not level? and so water was able to pool? If so, what should I be doing?

I'm wondering if I could use something like the following, such that if the concreate is not level, the pooling water won't rise up into the base of the shed (as it won't absorb into the plastic)?


http://www.plasticshedbase.co.uk/shed-b ... x-8ft.html

 

[PlacidCasual]

If the pad is larger than the shed water will spalsh back wetting the shed. Also it can wick under the base and allow rot. Ideally you want your concrete base to be the same or less than the foot print of you shed, even then you want you shed on bearers to allow air flow to prevent rot. Ideally the surface surrounding your base should be free draining.

My advice if you are using an existing over size base is use bearers and probably even lift these off the ground using bricks that way your bearers won't rot and you'll get an air flow to ensure the base stays dry.

 

[Rorschach]

Concrete blocks with DPM between them and the base of the shed since concrete will wick moisture.

 

[Steve Maskery]

My mate Stuart has just taken delivery of a new 20'x10' shed. We erected it last week.
He had an existing slab, slightly dished with a drain hole in the middle. He laid an array of blocks (like for block paving) over the slab, at, I'm not sure, say 400mm, on a dollop of mortar, all levelled up nicely. The base (bases, actually, there we 3 or 4 of them) were laid directly on the blocks. So there is air underneath and surface water drainage.
The DPC might have been a good idea, I guess, but it's too late now.

 

[Rorschach]

DPC is cheap and will make a big difference. I like pond liner for these kinds of jobs, it's thick, durable and UV resistant.

 

[RobinBHM]

I would pack up all the joists so they dont sit on the concrete slab.

You could use some plastic wood in short lengths like these

http://www.kedel.co.uk/recycled-plastic ... astic.html

And maybe glazing shims for fine levelling if needed.

The old ones rotted because the slab is bigger than the shed, so when it rained the water flow under the shed soaking the joists.

Idealky a shedd base is smaller than the shed so the cladding sits down over the concrete base keeping it dry

 

[transatlantic]

Thanks for the replies. Interesting to see people saying the shed base should be smaller than the footprint of the shed. E everything I have read says it should be slightly larger, around 50mm. So would the plastic base I mentioned above be no good?

Sent from my SM-J510FN using Tapatalk

 

[RobinBHM]

A shed base is normally the size of the framework, so the cladding sits outside the base and water can drip off down the side of the slab, keeping the top dry.

If you build on a bigger slab, then just space the joists off the ground with a rot proof material, concrete blocks for example, or plastic spacers.

I dont think you need a plastic base like your link, although it would work well as they are hollow crates so water will run through them

 

[YorkshireMartin]

We had a couple of very friendly installers for our shed. One of them had obviously done a fair bit of woodwork as he pinged the fact the bench I was putting in the shed was properly jointed with M&T and they both did a really good accurate job. We discussed how best to rot proof the shed, the base being slightly larger than the shed itself as my original plan had been a custom build.

In the end, what he suggested was to put DPC underneath the floor joists and be done with it. Air gets under the shed and I cant see how the moisture can breach the DPC in this situation really, unless it's splashed. The area of ground the shed is in gets waterlogged a lot, so I had to dig down really deep for the concrete pour and put about 2 tonnes of hardcore in there, then a thick layer of pebbles and finally sand.

Only time will truly tell if it worked but so far so good.