PAS 2035 retrofit and the planning consents it needs

PAS 2035 is a technical framework, not a planning consent, so a whole house retrofit can be fully compliant with it and still be unlawful. Whether PAS 2035 retrofit planning permission is needed depends on the measures, the building type and the designations on the property. External wall insulation on an ordinary house outside a designated area is often permitted development. The same insulation on a house in a conservation area, on a flat, or on a listed building needs an application, and in the last case a separate listed building consent as well.

The retrofit assessment will not tell you this. It is not what it is for.

What PAS 2035 is and what it does not do

PAS 2035 sets out how domestic retrofit should be assessed, designed, installed and evaluated, with defined roles for the retrofit assessor, coordinator, designer, installer and evaluator, and installation governed by PAS 2030. It sorts dwellings into risk pathways, with traditional construction, protected buildings and more complex buildings routed into the higher risk paths where more assessment and design input is required.

What it does is manage technical risk, principally moisture, ventilation and performance. What it does not do is address planning, listed building consent, advertisement consent or building regulations approval. Those sit outside the framework entirely, and a coordinator is not required to identify them.

So on any funded or TrustMark registered retrofit, someone has to ask the planning question separately. On a privately funded job, that someone is usually the homeowner, and the point at which it surfaces is often when a neighbour objects to render appearing on a Victorian terrace.

External wall insulation and the planning line

Insulating a solid wall externally adds typically 90mm to 150mm of insulation plus a render finish, which changes the appearance, the depth of the window reveals and the roof overhang relationship. Three positions cover most houses.

The similar appearance condition is the one that catches brick houses. Rendering a brick terrace is not a similar appearance to brick, whatever the colour, so even outside a designated area the permitted development route can fail. Where the original finish is already render or pebbledash, a render finish over insulation is far easier to justify.

Detailing matters to the planning judgement as much as to the physics. Window reveals that end up 150mm deeper read as a different building, and eaves that have been extended with a rough closing detail are what officers point at in refusal reasons.

Conservation areas, article 4 directions and listed buildings

In a conservation area, the cladding exclusion means external wall insulation on the front and visible elevations will need permission, and will often be refused where the building has architectural detail that the insulation would bury. But rear elevations are a different conversation, and a scheme that insulates the rear and the side externally while treating the front internally is frequently the one that gets consent.

Article 4 directions take away more. Many authorities have made directions removing householder rights in conservation areas, covering windows, doors, roofs and front boundary treatments, so the starting assumption in a conservation area should be that permission is needed for anything visible.

For a listed building, both planning permission and listed building consent are required, and consent is governed by the statutory duty to have special regard to preserving the building and its features of special interest. External insulation on a listed building is rarely acceptable on principal elevations. Internal insulation is possible but engages the same consent regime, because it affects historic plaster, joinery and the moisture behaviour of the wall. A Heritage Statement assessing significance and explaining each measure is what carries that application.

Window replacement and the design tests

Replacing windows in a house is usually an alteration within Part 1 Class A, subject to the similar appearance condition. In a conservation area with an article 4 direction, and on any listed building, it needs consent.

The design tests officers apply are consistent and worth designing to from the start.

• The opening pattern, so a two over two sash is not replaced by a single casement.
• The sightline width of the frame and glazing bars, since slim profiles read far better than standard units.
• The setback of the window in the reveal, which is where most replacements fail, with new units sitting flush instead of recessed.
• The material, and whether a timber or a slim profile aluminium alternative is available.
• Trickle vents and their position, which are a Building Regulations requirement and a visual intrusion on a traditional window.
• Glazing bar arrangement, with applied bars treated as inferior to true divided lights on a sensitive building.

Building Regulations apply in parallel. Replacement windows have to meet the Part L standard for the element, and on a listed building or in a conservation area there is scope for a relaxation where compliance would unacceptably alter the character, which has to be agreed rather than assumed.

Illustrative example: a solid wall 1890s mid terrace in a conservation area with an article 4 direction. The approved scheme externally insulates the rear elevation with render, internally insulates the front with a breathable woodfibre system, replaces rear windows with slim double glazed timber units set in the original reveals, and retains the front sashes with secondary glazing. Both planning permission and, because the building is in a conservation area rather than listed, only planning permission is needed for the external work.

Heat pumps, solar and other measures

Each measure has its own route. Air source heat pumps for a dwelling sit in Part 14 of the GPDO, with conditions on siting, size and noise, and those conditions were amended in 2024, so check the current text rather than older guidance. Domestic rooftop solar also sits in Part 14, with limits on projection and position and an exclusion for listed buildings.

Insulation measures inside the building envelope, loft insulation, floor insulation and internal wall insulation on an unlisted building, are not development at all and need no permission. Ventilation is the measure most often forgotten: a mechanical extract or a continuous ventilation system needs an external terminal, and on a front elevation in a conservation area that is a visible intervention.

Where the retrofit drives overheating risk, particularly in a top floor flat or a converted roof, the mitigation can itself need permission, since external shutters and brise soleil change the appearance. Our note on overheating in roof level and mansard flats covers that interaction.

Moisture risk and breathable build-ups

Planning officers do not assess condensation risk, and heritage officers very much do. On a solid wall building, an impermeable external render or an internal insulation system with a vapour barrier can trap moisture in a wall that was designed to dry outwards, and the result is decay in embedded timbers and failed plaster.

PAS 2035 requires a moisture risk assessment for the relevant risk pathways, and the right technical answer on a traditional building is usually a breathable build-up: woodfibre or mineral insulation, lime based plasters and renders, and ventilation that removes moisture at source. That answer also tends to satisfy a conservation officer, which makes it the approach to propose rather than a lower cost closed system that will be queried on two fronts.

Thermal bridging is the connected issue, since insulation stopped short at a reveal, a party wall or a floor junction creates a cold spot where condensation forms. Our note on thermal bridging detail at planning stage explains how to show those junctions.

Sequencing consents with the retrofit plan

1. Commission the retrofit assessment and get the measures and risk pathway identified.
2. Establish the designations: conservation area, listed status, article 4 direction, and any condition on an earlier permission.
3. Split the measures into those needing no consent, those within permitted development and those needing an application.
4. Discuss the sensitive measures with the conservation or planning officer before the design is fixed.
5. Apply for permission and listed building consent together where both are needed.
6. Confirm the Building Regulations route and any relaxation for historic fabric.
7. Only then fix the installation programme, because a refused front elevation changes the whole specification.

Where a wider scheme needs an energy case, an Energy Statement sets out the measures against the building's performance. You can see which documents a particular property is likely to need by entering the postcode on PlanScope.

This is general guidance, not legal advice. Permitted development limits and the PAS framework are both revised from time to time, so check the current position with your local planning authority before relying on it.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.