A vent , comprising: - a support frame having an inner perimeter , - a set of blades arranged in an array, wherein - each blade comprises a first blade element extending from a first end of the blade and a second blade element extending from a second end of the blade, the first and second blade elements being joined to one another at a joint position between the first and the second ends of the blade, the first blade element being joined to the second blade element at an angle, wherein a smallest angle between the blade elements of a blade is between 20 and 160 degrees; - the first end of each blade is attached to a corresponding first part of the frame, and the second end of each blade is attached to a corresponding second part of the frame; - a first substantially flat portion forms an initial part of a cross-section of each blade, and the first substantially flat portion is followed by a ridge or valley portion ; and - at the first end and second end of each blade, the first substantially flat portion is at least partly separated from the inner perimeter by an opening allowing water to drain from the first substantially flat portion onto the inner perimeter . - a support frame having an inner perimeter , - a set of blades arranged in an array, wherein - each blade comprises a first blade element extending from a first end of the blade and a second blade element extending from a second end of the blade, the first and second blade elements being joined to one another at a joint position between the first and the second ends of the blade, the first blade element being joined to the second blade element at an angle, wherein a smallest angle between the blade elements of a blade is between 20 and 160 degrees; - the first end of each blade is attached to a corresponding first part of the frame, and the second end of each blade is attached to a corresponding second part of the frame; - a first substantially flat portion forms an initial part of a cross-section of each blade, and the first substantially flat portion is followed by a ridge or valley portion ; and - at the first end and second end of each blade, the first substantially flat portion is at least partly separated from the inner perimeter by an opening allowing water to drain from the first substantially flat portion onto the inner perimeter . - each blade comprises a first blade element extending from a first end of the blade and a second blade element extending from a second end of the blade, the first and second blade elements being joined to one another at a joint position between the first and the second ends of the blade, the first blade element being joined to the second blade element at an angle, wherein a smallest angle between the blade elements of a blade is between 20 and 160 degrees; - the first end of each blade is attached to a corresponding first part of the frame, and the second end of each blade is attached to a corresponding second part of the frame; - a first substantially flat portion forms an initial part of a cross-section of each blade, and the first substantially flat portion is followed by a ridge or valley portion ; and - at the first end and second end of each blade, the first substantially flat portion is at least partly separated from the inner perimeter by an opening allowing water to drain from the first substantially flat portion onto the inner perimeter . <EOS>