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Best way to lay a large base for greenhouse and summerhouse

My back garden garden is 59' x 23' and I am thinking of locating a greenhouse and summerhouse on the East facing side. The greenhouse will be 14' x 8' and the summerhouse about 20' x 10'. The problem I have is that the garden on that side is quite uneven. The soil is quite clayish too so no intention of keeping the soil surface inside the greenhouse. What's the best way for me to create a base? Buld a low frame around the perimeter and fill the inside with rubble and sand and flag it or fill it withh rubble and concrete it? Or is there another way? Any advice would be very much appreciated.

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  • LoanaLoana Posts: 427

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    Hi Greenlove, we have clay soil and uneven ground too. My greenhouse is set on a row of level bricks with soil interior. I don't plant into the soil, i use grow bags and pots. Sometimes get odd weed grow up and odd ants nest but soon get rid of those.

    Last summer i finally achieved my dream of a summer house, only waited 10 years but i tell you it is the best thing ever, we absolutlely love it, perfect for relaxing out of the cool wind which comes across our back garden. I love to read in there and listen to the birds, our dogs come and lay with us, best money i ever spent on the garden.

    So, here are my tips for you..we laid a level patio base on the uneven ground, after removing the turf with a turf cutter. It took a day with 3 chaps, my son, my brother and my dad?

    My summer house came from lithuania, flat packed on a trailer....completely untreated. We spent 3 days coating each piece with two coats of wood preserver and then a dear friend came and helped with the assembly. This took 2 days with 4 of us, including the roof. 

    Then my hubby and i painted it, another couple of days and two coats of sadolins.

    Worth every penny and every minute of the time and effort, i'm sure you will love it. 

    Ps. I did go for the self build option as able to buy a better quality summer house for the money. I ran a small electric radiator in it over winter (after having an electric cable fitted) and it kept the damp out of it.

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  • hogweedhogweed Central ScotlandPosts: 4,045

    My greenhouse is built on a concrete slab Only a couple of inches bigger than the greenhouse base.  I dug it out myself, put up wooden shuttering and then got a builder in to mix the concrete for it. I think it was about 4-6 inches thick. I don't think we bothered to put hardcore down But did put builders plastic between ground and concrete. And remembering to put a pipe in vertically for the electrics. The weight of a greenhouse is evenly distributed so no fear of it sinking in any bit. The excavated soil I just spread around the garden. Much prefer concrete slab as it makes it easy to sweep, keep clean and water the slab to increase humidity. A day to dig, a day to lay concrete, a week for it to set and then two days to build the greenhouse. Job done. I did have to get a bloke in to help build it as it is def a two person job. Frame up first day, glass in second day. 

    The only tricky bit for me was making sure it was level as my ground slopes away on two sides of it. I did get the builder to check it all out before laying the concrete. He mixed the concrete in a concrete mixer with a labourer. 

    Last edited: 07 May 2017 10:20:04

    'Optimism is the faith that leads to achievement' - Helen Keller
  • raisingirlraisingirl East Devon, on the Edge of Exmoor.Posts: 5,891

    If you pour a concrete slab it will need to be a minimum of 100mm thick and you need good sturdy shuttering - a timber box around the outside, to hold it in place while it goes hard. If you lay the shuttering so it's a level surface, you can take out the uneveness of the ground but the 100mm has to be the minimum depth. So if your ground is very uneven in some places the slab could be very deep. That's not a problem for the concrete, but it adds to the cost. Or you could level up the under-base using hard core and then sand, so your concrete is a very even thickness. In which case you need to have a permanent edge to that hardcore layer so it doesn't wash out over time. If you need roughly 30m2 of slab, 100mm thick, that's 3m3 of concrete. A standard cement mixer holds about a quarter of a cube so if you mix it yourself (or a builder) by hand that's at least 12 mixer loads of concrete. That is a lot to do in a day. (OH managed 9 one day but couldn't really stand up the next day). And if it takes two days you get a joint so you'd probably need to do the two slabs separately. Or you can get 'readymix' who'll turn up with one of those big wagons and pour all of it in one go. You need a few people around to rake it out flat if you go that route and you have to calculate the amounts exactly right because they'll bring what you order and you have to have it all - they won't take it away again if it's too much (it goes hard in the mixer truck and that costs them a fortune to get out again).

    Slabs are a much easier DIY proposition - you can do a bit at a time.

    Concrete is faster but you need to get the preparation right and know exactly what you're doing when you start because you can't really change your mind half way through. And you can't easily move it later if you decide you don't like it. Slabs can always be lifted and shifted.

    “Light thinks it travels faster than anything but it is wrong. No matter how fast light travels, it finds the darkness has always got there first” 
  • greenlovegreenlove Posts: 164

    @Loana: your summerhouse is absolutely stunning. May I ask where you got it from?

    @hogweed: the way the ground is in my garden I dont think I need to escavate at all. The garden at the moment has a 6' wide patch which is soil and then a 2' wide concrete path and then the remaining 15' are lawn. The greenhouse and summerhouse will go over the 6'+2' side. The first picture shows that area. In the 6' area the soil is about 3-4" below the concrete footpath (you can see that in the second picture. The concete path is where the orange bucket is). The reason why I mentioned hardcore was to do with the fact that I am conscious I have to concrete a rather large area which will need a lot of concrete so I was thinking that filling with hardcore will mean less concrete needed.

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    @raisingirl: unfortunately the mixer truck is not an option because there is no access to the back garden and using a wheelbarrow would be a nightmare due to the layout of the house/garden, etc. So in my case one of those small cement mixers would be the only option if I went down the concrete route.

    Slabs is another option but it would mean that I would have to break down the 2' wide concrete path which would be a nightmare.

  • LoanaLoana Posts: 427

    Hi greenlove, ours came from eurowood.lt via a local intermediary. Ours is 3m x 3m and cost about £2500 complete with fixings and then there was the cost of wood preserver and sadolin. I had the colour made up at a trade paint place, hope that helps. You have quite a project ahead of you but it will be worth it ? Keep us posted of your progress

  • raisingirlraisingirl East Devon, on the Edge of Exmoor.Posts: 5,891
    greenlove says:

    @raisingirl: unfortunately the mixer truck is not an option because there is no access to the back garden and using a wheelbarrow would be a nightmare due to the layout of the house/garden, etc. So in my case one of those small cement mixers would be the only option if I went down the concrete route.

    Slabs is another option but it would mean that I would have to break down the 2' wide concrete path which would be a nightmare.

    See original post

    It's do-able with a small mixer (and at least two people) but I'd do it as two separate slabs, one for each structure, not one big slab. 

    Could you not use the concrete path to set the level of the base and slab over it rather than break it up? Too high or too uneven?

    “Light thinks it travels faster than anything but it is wrong. No matter how fast light travels, it finds the darkness has always got there first” 
  • greenlovegreenlove Posts: 164

    Loana, thank you very much. I will have a look at that one. image It is indeed a big task but it needs to be done. I do tend to have a skill for landing myself in big projects. My original idea was to actually design and build the summerhouse myself. Instead of using the type of wood that yours is made with I thought about building a frame like the ones they build for drywalls and then using featheredge or some type of wooden planks that overlap, fill the middle with insulating material and then use plasterboard or plywood sheets on the inside. In terms of doors and windows I am currently about to fit new windows and doors in my house so I thought to use the back door for the outhouse and the glass from my old double galzed windows to make simple windows for the summerhouse. It would be probably about 1/3 of the price.

    Raisingirl, the current concrete path is the right height but it follows the dips and peaks of the ground and as such is very uneven. I could leave it as it is and just pour concrete over it but that means that there's only going to be about an inch of concrete on the highes part of it.

    Another option might be to lay a concrete border about 10" wide all around the perimeter of the area and then fill the middle bit with sand and paving slabs on top? That may be slightly more cost effective but also makes it easir to dismantle in the future if plans change in the garden?

  • hogweedhogweed Central ScotlandPosts: 4,045

    If you intend to put the greenhouse longways along the fence, you will need to be about 2 ft from the fence to give you access both to the fence and to replace any damaged glass on that side. That means that your found will cross over the concrete path by about two foot. So the height of your found will be the highest point of the concrete path. Unless you intend to dig up the path where it runs through the greenhouse?

    If I were to just do a found all the way round I would do it properly - dig down, hardcore in the bottom, concrete poured on top. If you don't intend to remove that bit of path, you will need shuttering all round as it is higher than the ground.

    'Optimism is the faith that leads to achievement' - Helen Keller
  • Loana, absolutely love your summer house and totally agree with you about it being the best purchase for your garden. We have a victorian detached house with big stained glass windows at the front but tiny wee things at the back so we cannot really ever see the garden. My shed , looks straight down the main drag of my garden ( it's sort of a U shape around the house with a 8 ft strip, north facing onto a road at the front which is this years project ) and if you sit on the veranda you can see the newly done bit of garden we did last year with raised bed on top of tarmac. It's wonderful to be sat in there on a cold breezy spring day watching the life in the garden, and in summer when the sun goes down and the fire isn't quite enough to keep warm. 

    My partner put the whole thing up on his puff, minus the roofing felt in a day - he is a cabinet maker so is quite quick with wood stuff. I couldn't believe how quick the kits go up. Well worth the money. He added a couple of days later, extra posts to the over hanging roof ( decking posts from Wickes) built two huge planters around them using old scaffolding boards and finally decked them. 

    My shed was build on the old garage concrete base, then a waterproof membrane put on top of that, then a treated wood frame bolted down. It also came in planks , flat packec. Once he got the structure up he landed insulation sheets in between the joists of the frame to help keep the heat in. 

    My greenhouse was, if I remember rightly, bolted down to the concrete that covers my entire garden , no disguised by raised beds etc. It's only one of those cheap plastic windowed things but it does the job - well until the greenhouse envy I get when I see others gets the better of me and I convince him to buy me a pretty one ?. if you get half as much enjoyment out of your summer house and greenhouse as I do you will very content in your lot. Sorry abo all the pics just wanted to show how easy it was to go up. ( easier for me as I just made tea and bacon butties ) took him 8 hours from start to water tight. 

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  • Sorry not sure why some of the photos have gone upside down and I don't know how to amend. Apologies 

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