Do I Need Listed Building Consent for Secondary Glazing?

What the law actually says

Under the Planning (Listed Buildings and Conservation Areas) Act 1990, listed building consent is required for any work that would "affect the character of the building as a building of special architectural or historic interest."

The legal test is whether the work:

• Alters the external appearance of the building
• Changes the special interest features
• Is irreversible without damaging original fabric

Secondary glazing fails all three tests. It's fitted internally behind the original window, it doesn't touch the listed fabric, and it can be removed without trace by unscrewing the subframe.

What Historic England says

Historic England's official guidance Energy Efficiency in Historic Buildings: Secondary Glazing for Windows (revised 2024) states:

"Secondary glazing is often the most acceptable means of upgrading the thermal performance of historic windows. It can significantly reduce heat loss and noise transmission without altering the external appearance or compromising the significance of the building."

This is the document conservation officers refer to when assessing applications. Reference it in any correspondence.

When you DO need consent

These specific scenarios may trigger a consent requirement:

Conservation areas vs listed buildings

There's an important distinction many homeowners miss:

• Listed buildings:Listed building consent protects the building itself. Internal alterations may need consent if they affect "special interest" features.
• Conservation areas (not listed): Planning permission protects the external appearance of the area. Since secondary glazing is internal and invisible from outside, conservation area status alone does not trigger any consent requirement.
• Article 4 Direction:Some boroughs (Camden, Hackney, Islington, Kensington & Chelsea) have removed permitted development rights for window replacements. This affects replacement glazing — not secondary glazing.

How to talk to your conservation officer

If you want to do a courtesy check (we recommend it for Grade I and Grade II* buildings), here's the script that works:

1. Email your local planning department asking for a pre-application opinion (usually free, takes 10–14 days).
2. Include: photos of the existing window, a description of the secondary glazing system (slim aluminium subframe, hinged or vertical sliding to match), and confirmation that no original fabric will be altered.
3. Reference Historic England guidance: "As supported by Historic England's Energy Efficiency in Historic Buildings series."
4. Confirm the installation is reversible.

Most authorities respond confirming "no consent required." Save that email — it's worth its weight in gold when you sell the property.

If you're refused

Refusals are unusual but recoverable. Most refusals happen when:

• The officer mistakes secondary glazing for replacement glazing.
• The proposed frame profile is too thick (the original Victorian sightlines need to be visible).
• The colour clashes (matching the existing window colour almost always resolves this).

Solutions: switch to a thinner subframe (we use 25mm slimline profiles for sensitive applications), match the powder coat to the original window colour, and supply manufacturer data sheets confirming reversibility.

The Presswarm conservation track record

We've installed secondary glazing in hundreds of listed and conservation properties across Hertfordshire and London since 1973. The Presswarm name has been associated with successful listed building installations in areas including:

• Hampstead Conservation Area, Camden
• Bedford Park, Chiswick
• Hertford Old Town Conservation Area
• St Albans City Centre Conservation Area
• Highgate Village Conservation Area

Related reading

• Secondary glazing for listed buildings
• How much does secondary glazing cost?
• Secondary glazing overview