We have just had a kitchen extension built, with adjoining wc.
Throughout the project, there has been much discussion with our builder around ensuring adequate insulation, as one wall is basically glass doors and there are also roof windows.
As the weather has turned colder over the last few weeks I've realised that there is a back draft coming through both the oven extractor and the extractor in the wc. Without an outside wind it is blowing through, but when the wind blows they really are like wind tunnels.
I contacted my builder, who said "the extractors are standard for building control requirements but you can buy back draft ones and change them if you want to".
I am astounded. There has been so much detail required in the planning permission application and building plans - yet it seems it is okay to have what are virtually 2 holes in the roof letting the wind blow through. The builder has told me untruths before, so I'm not sure whether to believe this or not.
Both of the extractors' ducting leads up to the roof, with cowls (as attached photo). I am wondering if it would be possible to either replace these cowls for models that include some sort of backdraft shutter - or to install a separate backdraft shutter below the cowl ? This would seem like an easier/cheaper option than replacing both extractors. Online, I can see chimney cowls that include anti-downdraught, but am unsure if these can be used for extractor ventilation.
Any thoughts would be appreciated. Thank you.