Responsibility for replacing windows and doors in leasehold property

Maintenance

I own a flat in a leasehold block where the landlord is a community housing association. The association has issued a Notice of Intention to replace all windows and doors in the block to include both communal areas and in the flats themselves and will charge according to the lease. I cannot find any specific reference to the windows in the lease and have, in other similar properties that I own, replaced windows myself at my own discretion and at my own cost. Is it my responsibility or that of the housing association landlord to carry out this work? Who owns the windows? Do I have to allow them to replace windows and doors in my flat?