✅ No More Thermal Bridges
It wraps beams and columns, cutting every "bridge" of cold communication with the interior.
External vs Internal Insulation: Comparative Selection Guide for Every Building
The decision to energy-proof your building is the most important step. The next one is choosing the right method. While the goal is the same - keeping heat inside in winter and outside in summer - applying insulation externally or internally completely changes the building's behaviour.
Although external insulation (ETICS) is now considered the "golden rule", there are many cases where internal insulation is the only option. Let us examine the pros, cons, and when to choose each.
1. External Insulation: The Building's Shield
As we saw in the previous article, the thermal facade "dresses" the building from its external side.
✅ Shell Protection
It saves the structural frame (concrete/brick) from cracking due to contraction and expansion.
✅ Thermal Comfort (Capacity)
The walls stay warm. When you turn off the radiator, the home takes a very long time to cool down.
✅ No Interior Disruption
You don't lose a single centimetre of your floor area and the crew works outside.
❌ Higher Cost
Requires scaffolding, specialised renders and more labour.
❌ Changed Appearance
It changes the building's external look. Not permitted on listed buildings or traditional settlements.
❌ Weather Dependent
Work cannot proceed during rain, heat waves or frost.
2. Internal Insulation: The Flexible Solution
Here the insulation material (e.g. rock wool, EPS or XPS) is placed on the internal side of the external walls and usually covered with plasterboard.
✅ Instant Room Heating
Because you no longer heat the cold bricks of the wall, the room air heats up in half the time. Ideal for holiday homes or rooms used a few hours a day.
✅ Lower Cost & Speed
No scaffolding needed. It can be applied room by room, any season of the year.
✅ Ideal for Apartments
If you live in a block and the other owners won't agree to ETICS, you can insulate just your own apartment internally.
❌ Space Loss
Depending on system thickness, you may lose 5-10cm from each external wall of the room.
❌ Moisture Risk
If not installed correctly (e.g. no vapour barrier), moisture can be trapped between the insulation and the cold external wall, causing mould.
❌ Thermal Bridges Remain
At points where internal walls and floors meet the external wall, cold continues to pass through.
3. The Verdict: What Should I Choose?
The final decision depends entirely on your needs, constraints and budget.
🟢 Choose External if…
…you are renovating the entire house, building new, or want the ultimate and longest-lasting energy shield without compromise.
🔴 Choose Internal if…
…you live in a listed building (or stone house where you want the stone visible), have a limited budget, want to renovate gradually just one room (e.g. a cold north bedroom), or have a holiday home that needs to heat up fast on weekends.
💡 The Experiment in Our Model (100sq.m. House): Let's take the "10x10 Model" and assume we only use it on weekends. With External Insulation, the radiator would run for hours until it "charges" the frozen walls before you feel warm. With Internal Insulation, heat is trapped immediately in the room air. The space would reach 20°C much faster, consuming fewer kWh for that weekend. Conversely, for a permanent residence, external clearly wins in total annual consumption.
4. The 10x10 Model Experiment: Permanent vs Holiday Home
In the 10x10 Model with external insulation, the radiator runs non-stop for 2-3 hours to "charge" the frozen walls, but afterwards retains warmth for a very long time after switching off.
With internal insulation, the room reaches 20°C in just 30 minutes, but cools equally fast after switching off. For a weekend holiday home, that's an advantage. For a permanent residence, external insulation clearly wins on total annual energy consumption.
Related Articles
What Is the ETICS System (External Insulation) & What Are Its Advantages When Do We Choose Internal Over External Insulation? Insulation Thickness: How It Affects Performance (5cm vs 10cm) External Insulation Cost per sq.m.: Detailed Pricing Guide
Insulation Systems: Complete Solutions for Every Building
Return to category.
Go to categoryCentral Guide
Return to the central guide.
Go to guide