Is external or internal wall insulation better?

External keeps the thermal mass inside and avoids losing floor area, but it changes the appearance, which is often unacceptable in a Conservation Area or on a stone frontage. Internal preserves the exterior but consumes space and needs careful detailing at floor and window junctions to avoid cold bridging.

Will insulating cause damp?

It can, if a vapour-closed material is applied to a wall that needs to dry inwards, or if ventilation is not upgraded alongside. Done as a designed system rather than a product purchase, it does not.

Do these works need building regulations approval?

Renovation of a thermal element engages Part L, and installing insulation, replacing windows or changing a heating system are all notifiable — usually through a competent person scheme or a building regulations application.

Can retrofit be combined with an extension?

It is the most cost-effective time to do it. Scaffolding is up, floors are open and the disruption is already happening, so the marginal cost of upgrading the existing fabric is far lower than doing it as a separate project.

Retrofit · Cornwall

Retrofitting an older Cornish house — get the sequence wrong and you create damp

Much of Cornwall's housing stock is solid-walled: granite, killas rubble, cob, or early cavity construction that behaves like neither. These buildings historically stayed dry by being permeable and draughty. Sealing them up in the wrong order is the most reliable way to produce mould in a house that never had it.

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The right order of operations

Fabric first, ventilation with it, heating last — and never insulation without a moisture strategy.

Fix the water first: roof, gutters, ground levels, failed cement pointing and render
Insulate the loft and floors, where the cost-to-benefit ratio is strongest
Only then consider wall insulation, and choose a breathable build-up on solid walls
Design ventilation deliberately as the building tightens — extract, background or mechanical
Size the heat source once the fabric is fixed, not before

Why breathability is not a fashion

A solid stone wall gets wet and dries out again. Wrap it internally in an impermeable insulation with no vapour control strategy and the drying path closes; moisture then accumulates at the interface. Wood-fibre and lime-based systems, correctly specified, allow the wall to keep working as it was built to.

Heat pumps in older houses

They work well in Cornish houses once the fabric is improved and emitter sizes are right, and poorly when installed into a leaky house with undersized radiators. The design work — heat loss calculation room by room — is what determines whether the running costs are what was promised.

Frequently asked

Straight answers.

Is external or internal wall insulation better?: External keeps the thermal mass inside and avoids losing floor area, but it changes the appearance, which is often unacceptable in a Conservation Area or on a stone frontage. Internal preserves the exterior but consumes space and needs careful detailing at floor and window junctions to avoid cold bridging.
Will insulating cause damp?: It can, if a vapour-closed material is applied to a wall that needs to dry inwards, or if ventilation is not upgraded alongside. Done as a designed system rather than a product purchase, it does not.
Do these works need building regulations approval?: Renovation of a thermal element engages Part L, and installing insulation, replacing windows or changing a heating system are all notifiable — usually through a competent person scheme or a building regulations application.
Can retrofit be combined with an extension?: It is the most cost-effective time to do it. Scaffolding is up, floors are open and the disruption is already happening, so the marginal cost of upgrading the existing fabric is far lower than doing it as a separate project.

Upgrading an older Cornish home?

Tell us the construction and what you have already done — sequence matters more than product choice.

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