Vents in Polytunnel roofs.

[Mole]

I've noticed various folk stating that it's not possible to have vents in the roofs of tunnels. Not so! I've had one for years. Just make a wooden frame, one dimension the distance between two hoops, the other, how wide you like (mine is about 18"). Fix to hoops with builders band, cover builders band with hotspot tape. Cut polythene in centre of frame and batten to frame. If you want a lid for it, make another frame, clad with polythene and hinge to outside of the first frame.

For the first 18 months, we actually just had a split which I made with a stanley knife - it vented hot air when necessary...

[fen not fen]

For anyone considering buying a new tunnel I would strongly recommend one with side vents. We inherited a 'normal' tunnel and it gets unbearably hot and we had all sorts of problems with fungal diseases later in the summer. We bought new ones with side vents and it's a lot easier to control the temperature. Also more air moves around, so even with last years blight friendly August (and loads of spuds growing around and about) we had no blight in the tomatoes at all.

Fen

[bigpepperplant]

I can agree with this. I have always regretted not buying a tunnel with side vents - I got a ventilated ridge instead and frankly it didn't seem to do anything. I had to resort in the end to cutting 'windows' in the plastic at intervals to stop plants literally frazzling in the high summer (recommended by Joy Larckom in Grow Your Own Vegetables but not a good idea I don't think since it looks horrible, the plastic loses tension and you can't seal the windows up easily again).
so, all in all, yes get side vents!!

[cevenol jardin]

In the polytunnels i've seen around here people vent the tops by pushing the plastic apart where the seams are and holding it open with a short plank of wood (i've even seen one prised open with an old wooden veg crate )- platic remains tense but the vents are where they are needed as the hot air rises upward and out. I personally haven't tried this yet I've only seen others do it, but wondered if anyone has tried this method?