Raised deck for shed base - Should I deck or not?

[beatts]

I am building a raised deck, .....well its not really raised as such but the ground is uneven so its going to be secured to 100 x 100 pressure treated posts, concreted in, at various points over the frame.

I am using 47 x 150mm joists throughout with noggins etc and its all pressure treated timber etc.

I have no problem in building the frame (it is 5.2m long x 3.1m) but was wondering should I top the frame with something before putting the log cabin on top.

The log cabin has a 22mm pine tongue and groove floor and is slightly smaller than the frame I am building (its a shade under 5x3).

I am happy to use deck boards to top the frame and then build the cabin on top but it means ultimately there will be two floors and decking isn't cheap.

Could I use WBP exterior ply or any other suggestions?

thanks


P.S I made the frame that big because that is the exact space I have between a wall and a fence so the frame fills the gap nicely.

 

[theprinceofdarkness]

I would consult the cabin manufacturer. As far as I know most "sheds" are designed to sit on a concrete plinth, because the floor will come with "joists" (holding the floor boards together) but these are too thin to be load supporting as they are mean't to rest on something solid. Now it sounds like you are trying to support them on your joists, which is OK, if you know the exact spacing of the original. Its actually better for your frame to be slightly undersized, so that when water drips of the walls of the cabin, it does not drip onto your timber and splash back and rot the bottom of the walls. In my last place I built a 12' X 8' shed on sloping ground, so one end was about 3 " the other about 2 ' above ground level, so I dug a trench, laid footings built a wall, then infilled with the trench soil, bit of concrete on top the a layer of roofing felt then my joists were laid on this. Worked very well and has lasted over 30 years.
Frank

 

[beatts]

Thanks

The frame is already built now so it cant be modified, I am just in two minds whether to deck it £250 ish or Ply it £120

Most of the decking wont be seen as its sitting under the shed.

 

[Belboz]

Why are you keen on creating a second floor from ply/decking??

Can you not merely wait until the cabin arrives and then check the layout of the cabin base. That would then enable you to add in any strengthening to the 'gap' for the cabin to the decking frame. This would support the cabin floor properly and give it extra strength.

The other issue is whether you are better to have any airflow under the cabin which you wouldn't get with a second ply subfloor (you would get a little with spaced deckboards)

One of the numerous experts on here will advise you better about the need for airflow under the cabin. It may well not be an issue but it would impact on whether you decide to have a second subfloor and what you construct it from.

Just my tuppence worth though.

 

[big-all]

also keep in mind

the shed may be close to the limits and placing it on a raised decking may take it over the limit and require planning permission

http://www.planningportal.gov.uk/permission/house

http://www.planningportal.gov.uk/permission/commonprojects/outbuildings