Shed bases, damp, and condensation

[Pete Verdon]

Hi,

I'm shortly going to be ripping down two crappy old rotten sheds, and replacing them with a 10' x 13' metal one. The base is patio-type slabs in concrete; I don't know what's underneath but it's build up 8 or ten inches above the grass so it's fairly substantial. The surveyor when I bought the house described it as "sound", while also picking holes in lots of other things, so I think it's ok. The shed has no floor, and will fastened directly to the base.

This all seemed fine, but having read some other posts here I'm wondering if there's likely to be a problem of damp and condensation. It seems unlikely that the base would include a damp course. I don't need the shed to feel like my front room, but I do intend to store quite a lot of stuff down there (I don't have a garage, and the loft hatch is very small) and I wouldn't want it to be damaged by damp.

Do you think I'm likely to have problems? If so, what can I do about it, either when building the shed or if I find I have a problem later. I don't want to spend more than I have to - I wasn't planning to replace the sheds at all for a while, but I've just discovered quite how rotten they are and it won't really wait.

Pete

[Adrian]

If it's one of those Yardmaster sheds then (in my experience or erecting one of their garages) damp coming up from the floor will be only a small part of your troubles - the roof on mine leaked like a sieve !

Metal sheds are prone to condensation problems - and an 'unsealed' concrete slab floor will cause you problems.

I'd suggest some kind of damp-proof membrane (anything from thick plastic - slippery to walk on - up to a 'proper' chipboard floor sitting on timber joists above a membrane).

You'll also want to apply insulation (expanded polystyrene slabs are probably cheapest) to the inside of the roof, walls and doors - as otherwise they'll be running wet in no time.

Sorry to be pessimistic - but I wouldn't go the metal shed route again... ever !

If you insist - do make sure that you have enough self-tapping screws to finish the job _before_ you start - my Yardmaster kit was short by about 100 of the little perishers - which meant searching around the shops for extra screws in little (expensive) plastic blister packs....

My recommendation would be for a timber shed - or even a timber / steel-frame hybrid like the one I'm currently using for a studio. Skeleton framework in steel box section, wooden panels screwed to it with great big self-tapping bolts. Timber roof with two layers of torched-on felt..... luvverly !

Adrian West Cork

[Bob Mannix]

"Pete Verdon" wrote in message news: [e-mail]...

There is only one answer - ventilation. Drill or cut holes top and bottom both ends and cover with louvred grilles. Circulating air is the only cure for condensation. I would leave the floor as it's concrete and significantly above ground level but I would try and allow ventilation of the floor where possible (use of shelving systems or even duckboards to keep stuff from lying flat on the concrete).

[Stuart Noble]

I'd forget ventilation and line it with polystyrene. The key difference between a shed and a garden studio is insulation. Sounds like the OP needs something in between.

[Pete Verdon]

Well, it started off as a simple shed just to store stuff in, and been upgraded in my mind a few times :-) .

I am already planning to line the walls with chipboard or similar to avoid damaging them when moving stuff around inside (I assume that a cheap tin shed is going to be pretty thin sheet). The walls are 5'6" or thereabouts (pitched roof higher in the middle) so I was going to line it with 8x4 sheets on their sides, leaving 18" at the top where the wall's less likely to be damaged. Maybe I should be fitting polystyrene to the walls above that, and to the roof?

I have also seen (and can't remember if I dropped in the "basket" when buying the shed) solar-powered ventilation cowls, which seem like a reasonable idea.

I would also aim to keep most things off the floor, on general principles.

Pete

[Stuart Noble]

I reckon without at least 25mm polystyrene or Celotex on walls and ceiling it won't be a suitable storage area for anything other than the lawn mower :-). You could probably just glue it to the metal but it will damage easily without some sort of covering, and I don't know how easy that would be to fix. I'd use a moisture resistant flooring grade chipboard

[Peter Lynch]

I put a solar power ventilation fan (not sure if it's the same as your cowl) in my conservatory roof to try and reduce the heat build up. Even though you could see the fan spining rapidly when the sun came out, it failed utterly to make any measurable difference.