I have a raised ‘decking’ area which was built out of reclaimed old fencing so some of the posts/decks are already 20+ years old (it was originally just used for staging a big wendy house contraption I built a few years ago). My girls have outgrown it so we have taken the wendy houses down and we are going to replace with a small greenhouse. My concern is that the wood will rot/give way at a point in the future and I would have to dismantle the greenhouse, fix and rebuild. Would it make more sense to rip the whole lot out and build a proper concrete pad? I assume using concrete would also have an additional heat sink benefit to aid growing in the summer?

I reckon you’ve done well to get 20+ years out of old fencing, and probably won’t get too much more. A greenhouse when laden with glass is not an insubstantial weight and may cause some movement in the timbers, which if substantial may crack the glass. Aluminium greenhouses are fairly easy to reglaze/move etc, but if it’s a timber one then you’ll be looking at a major undertaking once the decking base becomes unviable.
If it were me I’d be looking at resetting it on a proper base rather than the decking, and also leave space inside for a bed to grow tomatoes etc in, although diseases can build up in the soil if it’s not replaced frequently. It’ll also enable you to get some power in there for heaters, lighting etc.
And get the biggest greenhouse you can afford/fit into the space. They’re never big enough!

Was going to start a similar thread myself! We moved into a new place last year, there’s a substantial decking area (about 7m x 7m) but it’s right at the bottom of the garden so we’re never going to use it for dining, etc. Seems really solidly constructed and it would be a shame to rip it all up, but also we’d like a greenhouse and the space is ideal.

Were told by a gardener mate that it’ll just rot where it gets soaked from watering. What if we were REALLY careful tho lol or set up some kind of dripper system to avoid splashing? It seems really strong, but I don’t know how much extra weight it could hold, would a big poly-tunnel be as useful as a proper greenhouse? Could bolt that down to the decking easily enough.

Basically just want to be told, yes it’ll be fine, crack on with the decking as a base but happy to listen to sanity!! 🤣

Were told by a gardener mate that it’ll just rot where it gets soaked from watering.

That is a very good point.

And get the biggest greenhouse you can afford/fit into the space.

Ahhh… Unfortunately it is only a small thing (we have the space for much bigger) but we were given it by the in-laws and I’d rather not spend too much.

Our garden is on a steep slope, there were 2 levels of decking, the top one about 7mx7m the lower one 7m x 2m maybe..

The bottom one has now gone. I”m amazed we hadn’t fallen through it. I knew there were some rotten bits but so much of the structure had rotted from the inside out and wasn’t visible
I think both decks went in at the same time so the upper one may be in the same condition but I’m ignoring that fact as its just to big a job to comprehend at the moment..

I would be inclined to remove a deck you’re not going to use or look after as it’ll just look horrid very quickly.
If its in good nick it someone may be able to reuse the planks, I’m giving the salvaged bits of mine to an allotment group to build planters out of..

don’t put a green house on it…..

I’m sort of going to do that with our greenhouse. Over the years the land has subsided where the green house is (new build, garden 15 feet higher than field behind) and the greenhouse isn’t level.. I have decking to the side of it which is nice and level. Plan is to remove the glass (breaking a fair few in the process, no doubt) move frame, then put down some large joists to re-position the greenhouse on.

Inside I’ll probably put raised boarders with a path of well spaced deck boards, but use the smoother sides. Liberally apply decking oil.

That’s new wood, so I don’t know what the OP’s original wood is like.

Don’t forget decking gets really wet from the rain, so watering shouldn’t be too big an issue unless water sits on the wood for a long time – i.e. under grow bags.

Don’t forget decking gets really wet from the rain, so watering shouldn’t be too big an issue unless water sits on the wood for a long time – i.e. under grow bags.

well yeah, I think that’s the main issue, plus it’s not like you’re going to dismantle the greenhouse regularly to give the decking it’s annual coat of Ronseal or whatever!

Were told by a gardener mate that it’ll just rot where it gets soaked from watering.

I would have thought that using a wooden base for growing stuff in a greenhouse would provide almost perfect conditions to rot the wood – damp and very warm.
probably best to put it on a stone base of some sort.

I have this problem.

I want to build a base for a metal shed (there was a previous thread) but the location would be on the third parking space we have at our house. We will want to move in a couple of years so I want to be able to say we have three parking spaces since it’s a possible significant benefit to the house. If I dig up the tarmac, we’d only have two. So I’m considering a timber support that could be removable.