Why insulate house walls?

Walls can account for significant heat loss. Wall insulation improves comfort in winter and summer, reduces cold-wall effects, lowers heating demand, and helps improve a home’s overall energy performance.

What is the difference between external and internal wall insulation?

External Wall Insulation (EWI) wraps the façade, reduces thermal bridges effectively and does not reduce internal floor area. Internal Wall Insulation (IWI) is often easier to install but can slightly reduce room space and requires careful moisture/vapour control depending on the wall build-up.

Which insulation materials are commonly used for walls?

Common options include mineral wool (glass/rock wool), polystyrene (often used in EWI systems), wood fibre boards and cellulose-based insulation. The best choice depends on wall type, moisture risk, budget and the chosen technique (EWI/IWI).

How do you reduce thermal bridges?

Thermal bridges are reduced by treating junctions (floors, ceilings, corners, window reveals) and selecting an appropriate system. EWI is typically the most effective at reducing thermal bridges, but well-designed IWI can also deliver strong results.

How much does wall insulation cost?

Cost depends on surface area, technique (EWI/IWI), insulation materials, façade condition, access/scaffolding and finishes (render or cladding). A simulation helps estimate a realistic budget for your home.

Are there grants or financial support for wall insulation?

Eligibility and support depend on your situation and the project scope. Gram Energie can guide you through an eligibility check and help you understand available options and the steps to prepare your file.

Do I need a vapour control layer for internal insulation?

It depends on the wall build-up, insulation type and humidity levels. For IWI, vapour control is important to avoid condensation and mould risk. A vapour barrier or smart membrane may be recommended after assessment.

How long do wall insulation works take?

Duration depends on the area and method. IWI can be done room by room, while EWI often requires more preparation (façade prep, scaffolding, render/cladding). A schedule is defined after the initial survey.

Wall insulation: comfort and energy savings

Name: Gram Energie - Renovation Globale BAR TH145
Price range: €€

Well-chosen insulation reduces heat loss, improves thermal comfort and can lower heating consumption. Compare external and internal wall insulation, explore materials and understand the process.

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Wall insulation works and energy renovation

Context and goal

Primary intent: informational. This page helps you understand house wall insulation, compare options and plan your renovation works with confidence.

Explain key insulation materials (standard and eco-friendly options).
Compare External Wall Insulation (EWI) vs Internal Wall Insulation (IWI).
Describe the process, typical cost factors and how to request a quote.
Encourage readers to contact professionals for an assessment and tailored advice.

Insulation materials: standard & eco-friendly

The right material depends on wall type, moisture risk, required performance and the chosen technique (EWI/IWI). Here are the most common options.

Mineral wool insulation (glass wool / rock wool)

Mineral wool (glass/rock)

Widely used and cost-effective. Suitable for IWI and certain EWI systems depending on the build-up.

Cellulose-based insulation

Appreciated for summer comfort. Used depending on the technique and the wall/roof configuration.

Wood fibre (bio-based)

Good thermal lag for summer comfort. Often used with cladding or certain internal systems.

Polystyrene

Common in EWI under render. Efficient and budget-friendly, depending on façade condition and constraints.

External Wall Insulation finishes: render or cladding

EWI finishes: render or cladding

External insulation can be finished with render or cladding. It protects the façade and reduces thermal bridges.

Moisture and vapour control membranes for internal wall insulation

Moisture & vapour control

For IWI, controlling vapour diffusion is essential to avoid condensation. Membranes (vapour barrier or smart membrane) may be used.

EWI or IWI: which technique should you choose?

Two main methods exist: insulating from the outside (EWI) or from the inside (IWI).

EWI – External Wall Insulation

Highly effective against thermal bridges.
No loss of internal floor area.
Finishes: render or cladding.
Often higher cost due to façade prep/scaffolding.

IWI – Internal Wall Insulation

Often quicker and easier to implement.
May slightly reduce usable space.
Moisture/vapour control can be required.
Useful when the façade cannot be modified.

Process: how the works usually happen

Assessment: wall type, home condition, humidity risk, thermal bridges.
Choice: technique (EWI/IWI) + insulation materials.
Quotation: budget, timeline, options (render, cladding, framing).
Installation: correct build-up, junction detailing, vapour control if needed.
Finishing: façade finish or internal finishing, checks and handover.

Cost, support & savings

Cost varies with surface area, technique, materials, façade condition, access/scaffolding and finishing. A simulation helps you estimate your project and plan next steps.

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FAQ – Wall insulation

Clear answers to choose the right option (EWI / IWI), estimate cost and understand the process.

Why insulate walls?

Wall insulation improves comfort, reduces heat loss, and can significantly lower heating consumption.

EWI or IWI: which is best?

EWI is typically best for reducing thermal bridges. IWI can be simpler but needs proper moisture and vapour management.

Which materials are commonly used?

Mineral wool, polystyrene (often for EWI), wood fibre and cellulose-based options—chosen based on walls and constraints.

How to reduce thermal bridges?

Treat junctions (floors/ceilings/windows/corners) and use the right system. EWI usually performs best here.

How much does it cost?

Cost depends on area, method, materials, façade state and finishing. A simulation helps estimate a realistic budget.

Do I need a vapour barrier?

Sometimes—especially with IWI. The correct vapour control layer depends on the wall build-up and humidity risk.

How long will the works take?

It depends on size and method: IWI can be staged room by room; EWI often needs scaffolding and façade prep.

What’s the next step?

Request a simulation to assess your home, compare solutions and plan the most suitable insulation approach.

Start a simulation Request a quote