water drainage under workshop/shed

[Rob Vine]

Hi All
My first post to you.
Last Febuary I pulled down the old rotted workshop in the garden to be replaced by a slightly smaller construction which allows good access to the side and rear. This allows me to apply wood preserve twice a year.
I have fully insulated the inside with a breathable membrane, eps foam lining (1") with a 1" air gap and 5.5mm ply internal wall. The building is heated with an 4' tube and 800watt oil filled radiator (it really held good heat last winter)
However, sitting on a larger concrete base, rainwater flows beneath the building and away, I beleive there to be good airflow as the concrete base does dry quite quickly. My concern is that the floor supports which cannot be treated (I can't get to them) will eventually rot due to being coninually wetted when it rains. Should I therefore, put a means of water deflection around the base to prevent water from flowing beneath the floor/wetting the supports??

Many thanks

Rob

 

[Paul200]

Hi Rob and welcome - a bit late in the day now your shed's up and built but I would have raised it up on lengths of treated timber at 90 degrees to the base timbers - with strips of DPC in between. These timbers will rot eventually but are not integral to the structure so can be replaced. It's as important to get some ventilation underneath as to get it's feet out of the puddles.

For my own storage shed I placed about 15 concrete blocks at even spacings and topped these with the sacrificial timbers sitting on lengths of DPC. Then the shed sits on top. Maybe a bit OTT for your situation but mine's on very rough ground and that setup keeps its feet nice and dry and well-ventilated underneath.

I expect you can lever your shed up sufficient to push a few lengths of timber underneath but getting the DPC in between might be fiddly.

Good luck!

Paul

 

[Roughcut]

Gutters should help also.

 

[Phil Pascoe]

Gutters, and do what you can to avoid windblown rain. Do not stop the ventilation, though. I think you'll have to accept the lifespan of timber is finite.

 

[Terry - Somerset]

A few years ago I replaced a totally rotted shed - at a guess 25+ years old. It was supported on concrete slabs which had moved significantly over time, and 3"x 3" treated softwood.

The treated wood was almost completely undamaged after 25 years. I think any water flow under the shed was fairly limited being close to a hedge/fence which protected it somewhat. So although the area around the shed may get wet, most of the underside should remain dry unless the concrete base allows the water to pool.

 

[Phil Pascoe]

Much depends whether someone had brains enough to soak the ends of the timbers.