Fitting a polytunnel roof vent

[Philsbees]

I have just erected a new polytunnel (20x12) and purchased a roof vent for it. The instruction is to cut a 30cm hole in the polythene and push the vent in with a twisting motion.
The vent is somewhat larger then 30cm and I am hestating at doing this.
Has anyone done it??
Is it successful?

[Scarlet]

Hi Phil, welcome to the vine. I'm rubbish at DIY so I'm no help but fingers crossed, you will get a response soon.

[Small pumpkin]

Hi Phil welcome to the vine
If you don't mind me asking what make tunnel have you got? I'm with you I wouldn't like to cut a hole in my tunnel either.
I can't help I'm afraid. I had no idea you could get roof vents in a tunnels.

[Jay-ell]

Hi Phil and welcome to the vine.

What does the vent look like? By the sounds of it there's nothing supporting the vent except the polythene - which has just been weakened by having a hole cut in it and as the poly is pulled tight there will be a lot of stress on the edges of the hole. I would be worried about the cover ripping - a bit like what happens to the skin of a balloon when you put a hole in that.

The vents've seen in poly tunnels tend to have the poly battened to timber and the vent set into a frame fixed to that as well.

Is the vent for the actual roof or the ends where there is often wood battens for the door?

Photos or links would be useful.

[Philsbees]

Roof vent

The tunnel is a Northern Polytunnel.
The vent is supported on two steel bars which look well up to doing that. It's just cutting a hole on the polythene and forcing the vent through it. At the end of the day it's made to do just that so should be ok???

[Bigmallly]

Welcome to the vine Phil. I assume it's this one you have bought........https://www.northernpolytunnels.co.uk/commercial-range/fans/polytunnel-extraction-fan-7194.html............ .Did you get the tunnel from this company or make it yourself as it may not fit your bars.

[Jay-ell]

Ah, is it the vent that looks like half an upturned bucket with a string to open it? It says 30-35cm, this is probably smaller than the diameter of the vent so it gives a tight fit that wont leak, the poly has a bit of stretch in it so it will conform to the vent.

I though it sounded like one of those that are really for caravans - my bad.

Did you get the vent from them as well? You could contact their customer services and ask if they have any tips on making the hole (e,g, do it on a hot sunny day do that the poly is supple or try to make the cut in a single sweep so that there's few jagged corners to run).

If it is the model I'm thinking of does the top rotate as one side seems higher than the other. I'd assume that the high side goes on the side where the wind comes from to produce a low pressure zone over the top of the vent to pull the air through,

[Philsbees]

Roof vent

Hi Phil and welcome to the vine.

What does the vent look like? By the sounds of it there's nothing supporting the vent except the polythene - which has just been weakened by having a hole cut in it and as the poly is pulled tight there will be a lot of stress on the edges of the hole. I would be worried about the cover ripping - a bit like what happens to the skin of a balloon when you put a hole in that.

The vents've seen in poly tunnels tend to have the poly battened to timber and the vent set into a frame fixed to that as well.

Is the vent for the actual roof or the ends where there is often wood battens for the door?

Photos or links would be useful.

Thanks for all your help. I've been and gone and done it!
According to my car thermometer at 4.30pm the ambient temperature, here in York, was 28.5 so I decided the polythene should be nice and flexible.
I did as NP suggest and that's use a new Stanley blade and do the cut in one sweep. I went for a hole just under 34cm. When I offered up the vent I thought "that's never going in there" but a steady push and twist and hey presto all done.
It looks ok and should relieve the roof of the tunnel of a lot of heat.

Hopefully it will stand the test of time. We will see.

[Rebel Yogi]

Roof vent



Thanks for all your help. I've been and gone and done it!
According to my car thermometer at 4.30pm the ambient temperature, here in York, was 28.5 so I decided the polythene should be nice and flexible.
I did as NP suggest and that's use a new Stanley blade and do the cut in one sweep. I went for a hole just under 34cm. When I offered up the vent I thought "that's never going in there" but a steady push and twist and hey presto all done.
It looks ok and should relieve the roof of the tunnel of a lot of heat.

Hopefully it will stand the test of time. We will see.

I know this is a really old post but I have been thinking of getting one of these vents for my poly tunnel and I was looking to see if they are effective, is the OP still on this site to give an update on how useful it was?