Roof vents?

[Tilda]

Hi all,

 

Am trying to spec my DIY install roof vents.

 

I've got a Brink unit, so my external ductings off the unit are 180mm.

Is there a significant gain in using a 180mm external vent like this: https://www.roofinglines.co.uk/product/ubbink-ub48-universal-insulated-roof-vent-terminal-180mm

Compared to a cheaper tile vent like this: https://www.roofingsuppliesuk.co.uk/collections/universal-tile-vents/products/klober-universal-tile-vent-with-cap-terracotta

 

Obviously the cheaper tile vent would need step down adaption to fit the 180 ducting, but the price jump to full size vents is significant. I understand that airflow will be restricted here, but is this a 'big deal' or just an incremental decrease in performance?

The ubbink stuff makes an issue that it's insulated, is this important? or a non-issue if the tile vent is coming straight from insulated ducting?

The roof space is cold and outside envelope, insulated ducting will be used internally.

 

Slightly less relevant second question, is burying ducting under 20cm of roof insulation enough, or do I also need to wrap it in something like this: https://www.mould-stop.co.uk/products/75mm-round-radial-insulated-sleeve-x-10m-roll

 

Thanks for any advice,