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A practical guide for leaseholders wanting to install secondary glazing, including freeholder permissions, lease terms, and mansion block considerations.
Living in a leasehold flat means navigating layers of permissions that freehold homeowners don't face. If traffic noise, aircraft noise, or draughty windows are making your flat uncomfortable, secondary glazing is often the perfect solution—but you need to understand the process first.
Here's everything leaseholders need to know about installing secondary glazing in mansion blocks, purpose-built flats, and converted properties across London.
Secondary glazing has a crucial advantage over window replacement: it's an internal modification. This distinction matters enormously for leaseholders because:
For most mansion blocks and purpose-built flats, these characteristics mean secondary glazing requires minimal—if any—formal permissions.
Lease terms vary widely, but most contain provisions about alterations. Key clauses to check:
Look for wording about "internal alterations," "improvements," or "additions." Common formulations include:
Some leases specifically address windows. Look for:
Secondary glazing typically doesn't trigger window clauses because you're adding an internal element, not modifying the external windows.
Some leases require you to restore the flat to original condition when you sell. Secondary glazing is easily removed if needed, so this usually isn't problematic—but worth noting.
For expert secondary glazing advice and free consultations for listed buildings in London, contact Secondary Glazing Specialist on 020 7060 1572.
Penny Hargreaves
Heritage Acoustics Writer
Living in a leasehold flat means navigating layers of permissions that freehold homeowners don't face. If traffic noise, aircraft noise, or draughty windows are making your flat uncomfortable, secondary glazing is often the perfect solution—but you need to understand the process first.
Here's everything leaseholders need to know about installing secondary glazing in mansion blocks, purpose-built flats, and converted properties across London.
Secondary glazing has a crucial advantage over window replacement: it's an internal modification. This distinction matters enormously for leaseholders because:
For most mansion blocks and purpose-built flats, these characteristics mean secondary glazing requires minimal—if any—formal permissions.
Lease terms vary widely, but most contain provisions about alterations. Key clauses to check:
Look for wording about "internal alterations," "improvements," or "additions." Common formulations include:
Some leases specifically address windows. Look for:
Secondary glazing typically doesn't trigger window clauses because you're adding an internal element, not modifying the external windows.
Some leases require you to restore the flat to original condition when you sell. Secondary glazing is easily removed if needed, so this usually isn't problematic—but worth noting.
If permission is needed, the process typically involves:
Response times vary from 2 weeks to 3 months depending on the freeholder. Factor this into your planning.
London's mansion blocks—those grand late-Victorian and Edwardian apartment buildings—present specific considerations:
Mansion blocks typically have restrictive covenants maintaining external uniformity. The key question: is secondary glazing visible from outside?
With quality secondary glazing in slim aluminium frames, the answer is usually "barely" or "not at all." From the street, you see the original windows unchanged. The secondary units, set back in the reveal, are virtually invisible—especially if specified in a dark colour.
Many mansion blocks are listed buildings. Secondary glazing is generally acceptable because:
However, in Grade I or II* listed buildings, you may need Listed Building Consent even for internal works. Check with your managing agent or local conservation officer.
Installation is from inside only—no scaffolding, no access to communal areas, no disruption to neighbours. This simplifies the process considerably.
Post-war purpose-built blocks usually have simpler lease arrangements. Common scenarios:
Victorian houses converted into flats often have complex arrangements:
If you own a share of freehold with other leaseholders, you may need to agree alterations through your management company. In practice, secondary glazing rarely raises objections.
More likely to need formal consent. Approach the freeholder with clear documentation showing the internal, reversible nature of the works.
Some converted properties have a head leaseholder between you and the freeholder. Check your lease to understand who grants consent.
To support your application, we can supply:
Many leaseholders find that presenting professional documentation results in swift approval.
If you're a leaseholder looking to improve comfort in your flat, don't let permission concerns delay you unnecessarily. In most cases, secondary glazing is straightforward to approve because it doesn't affect the building's external appearance or structure.
Request a survey for your flat, and we'll provide the documentation you need for any consent applications.
Call 020 7060 1572 to discuss your leasehold situation.
London's leading secondary glazing specialists for Grade I, Grade II, and Conservation Area properties. Every project begins with a complimentary heritage survey.
