[tjunction]

Hello

We've recently got a new plot which is in good condition, but lacking any kind of shed, greenhouse etc. There is however a small area of grass behind the plot (which actually makes our half plot a bit bigger than it should be). Apparently a few years ago the fence was rebuilt and this created the extra space. Our neighbours have sheds/greenhouses on their equivalent space but apparently it's no good for growing as there is some rubble etc in the soil.

Anyway the plan is to build a structure here. Partly for a bit of shelter if there is a sudden downpour or we need to store a few old tools (nothing worth nicking, apparently there have been a few thefts) and partly as somewhere to start off seedlings etc. So we are leaning towards a polytunnel/greenhouse rather than a shed.

We can spend a bit of money on this but I'd rather not go overboard. But I don't want one of the bargain polytunnels you can buy which look like they'd fall apart if you sneezed near them! There's a fair chance we'll be moving house in a few years time (and would most likely have to give up the plot then) so I'm not thinking anything built to last for decades!

Also, one other consideration is that I'm 6'4" tall, and it would be nice to be able to stand up inside the structure!

The current design I have in mind is a simple 1.8x2.4m (6x8') structure composing a timber frame a bit like a shed but covered in polytunnel type UV resistant polythene. It seems like using a timber frame rather than hoops would give more standing room and would make it easier to fit shelves within the structure. While the design seems simple enough I did a bit of searching round online and I was a bit surprised to not really find any similar designs already. So I'm wondering if there is going to be some major drawback I've not considered?

Anyway attached is my current sketch design, let me know what you think. I have priced up the materials at around £100 which seems pretty good. But will it work? Is it overkill?

[Kevin67]

Just a couple of thoughts, if I may:

Go as cheap as you can without compromising on performance.
High sided structures are wonderful! I do hate the low arches of many "polysheds". (p/s)
You might benefit from double-insulating the lower two-feet of the p/s.
Think of security and what level of damage you are willing to tolerate with a break-in (inc. not fitting a lock).
Snow-loading weight on the roof.
Rain-water collection - not least to prevent puddles of water immediately outside the p/s.
Auto-ventilation. Auto-irrigation.
Rodent-traps.
An enclosed space is never big enough - can you go bigger until some maximum is achieved?
Think of a dry working area inside the p/s for when it's raining (usually unexpectedly!).
Is it worth putting a small wall barrier outside to keep the rodents from (burrowing) in?

Even if you move, try to keep it modular. That way, you can either move it later easier or sell it and so removing it for the buyer will be easier also.


It looks a great project!

[pigguns]

I did look at this and was put off by my trial I set up- the polythene tears as the wood frame is not as smooth as a polytunnel tube- hot spots etc.  I ended up with corragated uPvc sheets from Wicks instead.  Don't underestimate windage!

[cadalot]

Take a look at what rickvanman on youtube built off from his shed 7GnCFS8awI8list=UU5ee0c5sX4I_I4r3FSIFbcQ

[sunshineband]

I did look at this and was put off by my trial I set up- the polythene tears as the wood frame is not as smooth as a polytunnel tube- hot spots etc.  I ended up with corragated uPvc sheets from Wicks instead.  Don't underestimate windage!

I was going to ask how windy your site is. Ours has 80mph gales regularly and poly-sheeting does split the moment a tiny tear appears. The stuff with the woven thread through it wears where it rubs on the frame too, and we have made our main construction using uPVC low profile sheets I bought on the internet.

[tjunction]

I did look at this and was put off by my trial I set up- the polythene tears as the wood frame is not as smooth as a polytunnel tube- hot spots etc.  I ended up with corragated uPvc sheets from Wicks instead.  Don't underestimate windage!

Thanks for this comment. I guess you're right, wind will move the polythene a bit and that will wear it out. I'll look at using PVC sheets instead, I guess it will be more expensive but should be more durable too!

[Kevin67]

I had generic builders polythene stapled over a wooden frame which lasted 2 years and was still going strong until 2yo grandson poked his fingers through it.

[tinyallotment]

Hi

Here is a picture of out shed/polytunnel. The shed was free from a local network. Try freecycle or streetbank and you will always find sheds for free if you are willing to dismantle and take away.

The polytunnel cost us £12 to build. We wombled the blue plastic tubing from a skip. and the plastic cost a £10 donation to charity. A local market garden was replacing the plastic on their massive tunnels and this was an off cut.

I would imagine the whole thing (shed/tunnel) cost close to £50 once you include fixings, paint, felt for the roof etcetera.



paul

[tjunction]

Thanks for the comments.

I have been thinking more about the construction and the possibility of wanting to dismantle and move it at a later date. I'm leaning towards the idea of making side and end panels that can be screwed/bolted together on site (much like a commercial prefab shed). These would be timber frame and probably covered with mini profile corrugated PVC (though I guess I could use plywood for some parts).  I can still anchor them to the ground by inserting smaller posts inside and fastening the panels to these posts.

Another advantage of this approach would be that I could construct the panels at home where I have power tools etc to hand and simply assemble down at the allotment.

Also being more modular gives the scope for extending it later if necessary!

I'll see if I can come up with some more plans!

[pigguns]

I had generic builders polythene stapled over a wooden frame which lasted 2 years and was still going strong until 2yo grandson poked his fingers through it.

wow I have some of this, but don't use it outside as I'm worried it's not uPvc it'll go brittle.   You mean blue membrane stuff?

[Kevin67]

No. Mine is not blue, it is clear and on a very large roll.

Some years ago I did have some plastic from a garden shop and that did go brittle inside 2 years and was useless (and expensive).

[beesrus]

I think I can help you here TJ.
A few years back I built something almost akin to your plan due to wanting it to be moveable , and it's survived the gales very well indeed when other plot neighbour'shop bought badly designed greenhouses and polytunnels have been wrecked. It was originally 8x6 but I have now extended it to 12x6ft.
I used 50x50 tannilised timber for walls and roof (19x38 roofing batten is a bit small in my mind), drilled and screwed with appropriate 3" screws.
Being a builder/carpenter, I added a small 6mm ply triangular gusset to each roof span apex, and anchored the whole greenhouse by screwing the structure to 4 no. 3x3 old posts concreted into the soil as you would fence posts.  I made up the roof frames at home where I could cut them to length and the appropriate mitres and gussets required. Woodwork was spaced at roughly 620mm centres to fit 1200 high x 600mm wide 4mm uv treated greenhouse polycarbonate sheets..... very strong. A good price at nick-gray plastics at his website or his ebay shop.... 2 x 10 sheets of 1200 x 600 will be enough for 8x6ft structure apart from one end wall, for which you could use something else. Those packs of 10 are £37.50 each... a good price. I've bought several things off him for other building projects and he's a good efficient business.
The polycarbonate sheets help strengthen the building as they act as screwed braces. I also attached one diagonal 50x50 brace to opposite corners to add further strength. Also, the pitch of the roof was determined by the 1200mm length of the sheets with a slight overhang for guttering purposes. All four original "roof frames" were tied together with one internal 50x50 ridge beam attatched to the uniform sized gussets.
It stood me in at £130 all in.... made the door out of 50x50 as well and just hinged and hooked it.

The polycarbonate acts very well as an insulator, far better than glass, lets in 90odd% light, is treated and lasts for donkey's ears..It also doesn't get tooooo hot in the Summer, like a polytunnel can. I taped the ridge joint with aluminium tape, but any strong tape will do. Sheets were just screwed to timber using 30mm dry wall screws, mostly with little washers to spread the load of the screw, although not really necessary.Every 200mm screws on roof sheets have created a waterproof seal to the timbers.... I haven't needed to silicone it at all, and of course, I had in mind for it to be moveable.
Being reasonably tall myself, I wanted a bit of height too, so the actual side walls floor to eaves height is 1700, so I screwed a 5o0mm base dwarf wall around the bottom of the posts with slats acquired around our allotment site. The pitched roof gives a good 7 to 8ft height at the ridge.

Here's a picture from yesterday with early peas waiting to spring forth