All growing environments need the right ventilation because too much warmth and humidity can be just as damaging as too little.
Aluminium or Treated Timber is clamped around the outside of the polytunnel framework at approximately 3ft from ground level. Ventilation net of 50% shade is then placed from this rail to the ground and either trenched or attached to base rails (if ordered).
A polythene blind can also be added which screens off the Side Ventilation net when required. This gives you the option of full or partial ventilation. A simple gear mechanism lowers the screen from the side timber rail allowing ventilation of plant foliage whilst still protecting root systems from wind chill.
Please note, the vent screen blind cannot be used in conjunction with aluminium side vent and aluminium base rails
Do I need to treat the timber doors/frames? 
First Tunnels Fantastic Festive Offer 
Do you want to use and store rainwater for Polytunnel irrigation? 
Potting On
I deliberated over this decision. Should I or should I not add side ventilation/screen on my 14ft x 20ft Polytunnel? After weighing up the pro’s and con’s I decided YES. (Just down 1 side) I have to say, it has been a brilliant asset, I certainly made the right choice and a great retirement gift. (Although it has been firmly closed for the past couple of days)
A polytunnel should always be given maximum ventilation by day during the summer. It is best to close up in the evening to keep the night temperature as high as possible. A large difference between day and night temperatures can cause problems – especially with tomatoes.
On sunny days which are followed by frosty nights the tunnel should be ventilated by day but closed up an hour or so before the sun goes down.
http://www.firsttunnels.co.uk/productdetail.asp?prodid=1&catid=2
Any reason the vents are not available with aluminium base rails..?
The reason I ask is that your construction video (6hrs in 6mins) seems to show vents with aluminum rails.
Still trying to decide if we are after the vents on our planned tunnel.