Thermal insulation: interior or exterior—which should you choose?

In short:

Urgent: A chilly evening highlights the need for insulation to ensure comfort and quiet, and improves sleep.
Solution: Exterior insulation wraps around the wall, reduces thermal bridges, and preserves living space without compromising the building’s exterior appearance.
Budget: Cost estimates, available financial assistance, detailed quotes, and RGE-certified contractors ensure a return on investment and guarantee the quality of the work.

On a winter evening, the street rumbles in the rain. The living room feels chilly despite the heat. You can feel the cold wall behind the sofa. This moment highlights the urgent need forthermal insulation. We’re looking for a solution that combines comfort and quiet, such as installing a custom thermal curtain or a soundproof and thermal curtain that can limit heat loss while dampening outside noise.

Choosing between interior and exterior insulation for your home.

The type of wall and the condition of the building will guide your choice. Exterior wall insulation changes the building’s exterior appearance, while interior wall insulation alters the interior of the room. To determine the best thermal insulation, it’s helpful to follow a few simple tips and compare the available materials. Among the common solutions, rock wool is often used for its performance and versatility in both renovation and new construction.

A detailed description of the aesthetic, thermal, and structural benefits of exterior insulation.

An exterior insulation system wraps around the wall and protects the structure. It significantly reduces thermal bridges and heat loss, which helps lower heating costs and leads to real energy savings. An exterior renovation preserves the living space and refreshes the facade. It also helps improvethe building’sairtightness and can enhance the sound insulation of the walls. A sound and thermal barrier can be added for specific applications. The wall gains a protective layer.

A clear overview of the technical, logistical, and financial drawbacks of interior insulation.

There is a loss of interior space depending on the thickness of the lining. Moisture can sometimes be managed with proper ventilation. Installation errors that create cold surfaces are avoided. This concept incorporates thermal phase shifting. In a comprehensive renovation, these choices are often accompanied by attic insulation to improve the energy efficiency of the entire home. The quality of installation remains crucial to ensuring the insulation’s actual effectiveness and the durability of the materials.

A comparison of thermal, acoustic, and hygrothermal performance based on the selected method.

Measurable criteria guide the decision. An energy performance assessment helps set priorities. In the context of energy-efficiency renovations, these assessments can also determine eligibility for certain grants or assistance programs. Depending on the situation, there may be a tax credit, a specific incentive, or another form of support available.Eligibility generally depends on the nature of the work, the targeted performance levels, and the type of housing. To supplement financing, some households may also take out a zero-interest eco-loan, which allows them to spread the cost of the work over several years.

A numerical breakdown of the expected thermal resistance and average energy savings by method.

The R-value indicates the expected thermal resistance of the wall. External wall insulation (EWI) often achieves a higher R-value for older walls. You can expect energy savings of between 10% and 30%, depending on the situation. These improvements directly contribute to the building’senergy efficiency and can influence its energy rating during an energy audit. The R-value expresses a material’s thermal resistance and serves as a key benchmark in industry regulations. It is particularly relevant to thermal regulations and standards applied to new construction and renovations.

A comparison of insulation materials based on performance, cost, and environmental impact.

The choice of material affects conductivity and thermal and moisture performance. A thorough evaluation balances cost and environmental impact.

Recommendations on the best materials based on the household's budget and environmental priorities.

Bio-based materials promote indoor health and thermal comfort. Mineral wool remains a competitive option in terms of fire resistance. You should choose your insulation based on your budget and environmental priorities. The choice depends on your priorities. In a renovation project, we also ensure thatthe building’sairtightness is improved, as this determines the actual effectiveness of the insulation. Certain materials can also contribute to better sound insulation, which enhances the overall comfort of the home.

The budget and financial assistance needed to undertake cost-effective insulation projects.

The price per square meter varies depending on the method and the insulation material. A quote includes wall preparation and moisture treatment. Depending on the project, materials such as rock wool—known for its controlled thermal conductivity and fire resistance—or eco-friendly materials may be used, depending on environmental priorities. You may be eligible for MaPrimeRénov and Energy Efficiency Certificates (CEE) subject to certain conditions. We verify the presence of an RGE-certified professional for the grant.

Criterion	Exterior insulation (EI)	Interior insulation (ITI)
Thermal performance and thermal bridges	Highly effective, reduces thermal bridges	Less effective on thermal bridges
Impact on living space	No internal loss	A loss of a few centimeters to meters
Project complexity and cost	More expensive and time-consuming	Less expensive, can be done in stages
Compatibility with sound insulation	Compatible and overall better	Possible, but sometimes limited

The step-by-step process and criteria for doing it yourself or hiring a qualified professional.

The project begins with an energy audit and a property inspection. Proper ventilation must be ensured both before and after installation. This step allows us to assess the home’s energy performance and identify areas responsible for excessive energy consumption.

The assessment specifies moisture levels, cracks, wall type, and solutions. Professionals can also calculate expected performance based on the R-value, which indicates the thermal resistance of the materials used. A simple checklist helps avoid unpleasant surprises on the job site. You should choose an RGE-certified contractor with a ten-year warranty and references. The estimate must provide a detailed breakdown of costs.

This checklist is helpful for the construction site.

Moisture and structural inspection.
An estimate of the cost per square meter.
Check the warranties and deadlines.
The access plan for the scaffolding.
Proper ventilation and humidity and temperature controls.

Practical examples and case studies showing actual savings before and after insulation, backed by hard numbers.

The figure brings the project to life. A house from the 1970s illustrates a common scenario.

The standard case shows a 20% reduction in energy consumption. A 100-square-meter single-family home often achieves energy savings of 15 to 30%. The payback period typically ranges from 5 to 15 years. Hybrid solutions are often recommended when exterior wall insulation is not feasible.

The Nokomis service Nokomis improve the thermal and acoustic comfort of your home.

Acoustic comfort complements thermal comfort. A fabric solution is sometimes used to supplement wall insulation.

The typical customer wants peace and quiet and a comfortable indoor climate. They are usually between 30 and 50 years old and often work from home. They prefer eco-friendly products made in France for aesthetic reasons. They are looking for a quick improvement without major construction work. A quiet environment improves sleep and concentration.

The catalog features soundproof curtains and acoustic sheers. Easy installation provides immediate thermal insulation and soundproofing. Nokomis offers a quick assessment and a personalized quote. We often recommend these products as a complement to wall insulation.

Insulation	Thermal conductivity λ (W/mK)	Asset	Estimated price (€/sq. ft.)
Cellulose wadding	≈ 0,040	Highly moisture- and temperature-regulating and eco-friendly	€ to €€
Glass wool	≈ 0,035	Good value for money	€
Expanded polystyrene	≈ 0,032	Thin yet high-performance	€
Wood wool	≈ 0,038	High-performance natural acoustic insulation	€€

The choice depends on the condition of the building and your budget. An informed decision balances thermal performance with acoustic comfort. You can request a free simulation or a quote to get started.

Frequently Asked Questions About Thermal Insulation

What is the most effective thermal insulation?

The neighbor who loves DIY replies, “Sure, sometimes we get carried away with performance claims, but when it comes to the most effective thermal insulation, blown-in materials like cellulose wadding often come out on top. They distribute evenly, fill in the nooks and crannies, and look clean when installed properly.” Plant-based fibers—like wood wool or cotton-based products like Métisse—are a good choice if you’re looking for natural materials and temperature regulation. Recycled cotton wool, on the other hand, adds acoustic benefits, which is great for bedrooms. Bottom line: choose based on the project, humidity levels, and your budget—and be prepared for a few construction hassles. And hey, a coffee break never hurts.

What does "thermal insulation" mean?

To put it simply, thermal insulation refers to all the techniques used to limit heat transfer between a warm environment and a cold one. We usually think of it in terms of homes, but it also applies to industry, the automotive sector, the cold chain, the food industry, and textiles. It’s all about the details, the materials, the thicknesses, and sometimes patience—and it makes a real difference in our daily comfort. Tested and approved for walls and attics. Here’s a tip: start with visible cold spots, then think about ventilation—otherwise, moisture will take its toll. And yes, it saves on wasted heating every winter.

How do you insulate a cold wall from the inside?

Ah, the infamous cold wall—the bane of north-facing rooms. We’ve tested this here: installing a thin sheet of extruded polystyrene (Depron, 3, 6, or 9 mm thick) doesn’t provide a ton of insulation, but it does counteract the cold-wall effect and prevents condensation on interior walls. It’s a quick, clean fix—perfect when you want to avoid major renovations. Be careful, though—it doesn’t stop overall heat loss, so it’s best to combine it with exterior insulation or lining if possible. A tip from experience: pay close attention to airtightness and ventilation, and keep a towel handy to wipe up the first few attempts, because yes, it takes practice. And celebrate the small victory.

How can you raise the temperature by 2 degrees in a house?

A simple DIY hack that might make you smile, yet it really works. Slip a sheet of aluminum foil between the radiator and the wall—just like kitchen paper—to reflect heat back into the room instead of letting it escape into the wall. I tested this during a chilly weekend, and the results were surprising: improved comfort without breaking the bank. Be careful not to stick it on haphazardly; leave a small gap for air circulation, and choose a sheet that’s slightly stiff rather than crumpled. And of course, combine this with wall or radiator insulation for real, long-lasting savings. A simple trick that puts a smile back on your face. And a hot cup of tea.