Leaking sash windows

Sculler

In May 2019 my wife and I moved into a new 3-bedroom flat in a converted 1904 former post office sorting office building.  High standards were promised and reasonably successfully achieved generally.

However, we have a total of 21 windows, all timber vertical sliding sash, double glazed, and all of which leak air, very noisily, in high winds.  The consequent air leakage must be well above that permitted by building regulations.  This was reported to the developer and freeholder during the defects liability period, but brushed off.  Unfortunately, the design is, in my opinion, defective as it relies entirely on brush seals, not rebates or staff and parting beads.  High winds (such as Storm Henk) mean that there is constant whistling and draughts.

Is there any chance of claiming for remedial work under our lease or under the NHBC guarantee?

Albermarle

Presume these are new windows, not the originals ?