Polytunnel build - what sliding door hardware?

[alex robinson]

Spring is underway and I have recently got a new allotment. I have been thinking about what to grow and more than any particular vegetable I have decided I want to grow a large polytunnel.

Looking at new kits they were either incredibly expensive, or incredibly flimsy. Second hand commercial tunnels were good per square metre, but enormous, so I decided to build one out of 63mm mdpe water pipe, slid over scaffold poles. Overall size is going to be about 8 x 5m. (Pictures to follow at some point).

Constructing the main frame seems fairly simple. I have been wondering about the doors however. Ideally I would like a sliding door. Currently this: https://www.fhbrundle.co.uk/sliding-door-gear/max-door-weight-60kg-ibfm looks a good option. Does anyone have any better suggestions or bright ideas please?

Ideally the doors would be 2 part - one layer with polythene for the winter, and a second mesh layer so as to give ventilation in the summer. Again, any elegant suggestions please? I cannot picture a very neat answer either going for 2 layers of sliding doors, or a 2 layer door that folds and slides!

 

[Tris]

Whatever you choose you will need something for them to run on at the bottom otherwise they'll blow about like sails. Simplest method is angle iron set in concrete so you've got a vertical metal strip, then fashion a guide for the door bottom that runs on the strip

Personally I'd keep it simple with a pair of hinged doors either end, poly one goes outwards, mesh one goes inwards

 

[alex robinson]

Whatever you choose you will need something for them to run on at the bottom otherwise they'll blow about like sails. Simplest method is angle iron set in concrete so you've got a vertical metal strip, then fashion a guide for the door bottom that runs on the strip

Personally I'd keep it simple with a pair of hinged doors either end, poly one goes outwards, mesh one goes inwards

I would have expected a bottom rail was needed (hassle and large concrete pours are frowned on at the allotments!) but looking at pictures of some of the professional ones, to my surprise, they appear not to bother.

Doors pivoting inwards aren't ideal as they take up a lot of space. First the space for the door itself, then the space to get a wheelbarrow past it. As you say though, simple is good!

 

[Tris]

Never had a problem with inward pivoting doors, although on our tunnel I made 3ft doors and allowed space for them to fold back a bit. When we put it up here I rehung them to swing outwards, works but more wind prone.

Looking at first tunnels website I'm not sure about the flimsy looking roller pegs they have for the bottom restraint on their sliding door.

Maybe cannibalise a greenhouse frame for the doors? There's often freebies to be had

 

[TheUnicorn]

In my experience, the constant wind, rain, sun, and ground movement means that you always get a lot of movement in doors and frames on tunnels, I would anticipate that and make sure you have the ability for adjustments.

On the subject of a bottom rail, I wonder if a sleeper would be an alternative to a concrete base

 

[glenfield2]

A sliding door! Mustn’t let the missus hear about that. Everything on her allotment is cannibalised - generally by yours truly - from scrap iron, pallet wood, bits of canvas, posts, netting and even trampolines.
Still at least it has been an excuse for me to buy battery tools.
But sliding doors would be a step too far.

 

[Fitzroy]

I looked at poly tunnels a few moons back and came to the same design as you, I didn't go ahead in the end as the wife and I realised we didn't like growing stuff after a season of raised beds. Anyhow my conclusion on doors was to go strictly agricultural as there was so much uncertainty in the shape and rigidity of the tunnel structure. I was planning for simple frame and brace doors wrapped in poly rather than clad in T&G and hung on some strap hinges.

 

[alex robinson]

In my experience, the constant wind, rain, sun, and ground movement means that you always get a lot of movement in doors and frames on tunnels, I would anticipate that and make sure you have the ability for adjustments.

On the subject of a bottom rail, I wonder if a sleeper would be an alternative to a concrete base

I think a bottom rail isn't an option really. It would require too much of a substantial structure to get it stable. Had been hoping there was a crude cheap option for a top rail only door I was missing!

 

[alex robinson]

I looked at poly tunnels a few moons back and came to the same design as you, I didn't go ahead in the end as the wife and I realised we didn't like growing stuff after a season of raised beds. Anyhow my conclusion on doors was to go strictly agricultural as there was so much uncertainty in the shape and rigidity of the tunnel structure. I was planning for simple frame and brace doors wrapped in poly rather than clad in T&G and hung on some strap hinges.

I am not self sufficiency fanatic, but the challenge of growing impractical stuff is fun, along with an element of competition - seeing lots of unsatisfactory, tiny structures on other plots makes (over)building a big one deliciously tempting...

I think you may be right about keeping it simple as speed is of the essence - dozens of aubergines and chilli are germinated already and the melons will be going in soon!

 

[Tris]

Sweet potatoes do well in a poly tunnel, but be prepared for them to take over half of it

 

[Oldman]

I just robbed an old greenhouse of its sliding door and built a wooden frame to hang it on for my cheap and cheerful polytunnel which is now 5yrs old and still ok.

 

[Jester129]

I have an unused greenhouse with just such a door and frame off J22 of the M1 if it is required. You could even have the lean to greenhouse as well if you want. You are welcome to either or both free but you would need to dismantle it yourself?

 

[whereistheceilidh]

personally I would steer away from sliding doors. If you have one then you will need bottom support, especially with the increasing breezes we are getting.
Sliding doors mechanisms also seem to clog....particularly the base track, when wheeling in barrowloads of muck.
We have 2 part doors. Top to open in summer & let pollinators in but closed at the bottom to keep hens & cats out.
Just love having a tunnel....worth the effort, certainly where we are..

 

[Owd Jockey]

Hi Alex, I'm afraid my experience with my polytunnel was not that good. Back in 2023 I bought a cheap 6m x 4m cheap Chinese polytunnel, which I strengthened by building a square wooden frame at either end. Within one of square frame ends I built a door. These Chinese things usually just come with a roll-up flap, which is pretty useless and inconvenient. The door was pretty basic, opening outwards, but functional. The two frames substantially increased the rigidity of the tunnel. I used 12 deep ground anchors that I made myself with some old mild steel stock I had lying around. This tunnel only came with about 10 thin pegs about 6" deep!! I also used about 100m of Para-Cord to hold the plastic canopy in place and reduce wind-flapping.

Got a reasonable crop of of Squash and Courgettes then came came Storm Pia in the December. For about 3 days we had continuous high winds, the ground anchors did their job, but what caused the damage you can see in the photo was the incessant flexing of the cheap Chinese tube steel, which eventually cracked and tore. I could have affected a repair, if I had really wanted to, but I did'nt have a 'swaging' tool and could not find a source for the replacement tubes.

I did not expect great longevity from this pile of $hi*, but not less than a year!