Home · Choosing insulation
Choosing insulationEvery facade insulation quote names a material and a thickness. Almost none explains why. Below you will find what those two choices mean for your comfort, your heating bill, your subsidy and your price — so that you can read any quote, including someone else's.
In the conversations we have, "I want to insulate" is almost never the opening line. It starts with a cold living room, a bill, or a facade that has had its day. These five reasons come up most often — usually two or three at once.
In winter an uninsulated wall is 8 to 12 degrees colder than the room air. You experience that as a draught, even when there is none. Once insulated, that cold-radiation effect disappears — you notice the difference in comfort immediately, before the first bill arrives.
According to the Flemish government's Woningpas, insufficiently insulated external walls are the second largest cause of heat loss in a home, after the roof. External wall insulation typically delivers 30 to 35% savings on heating costs, indicatively €350 to €600 per year for an average house.
Anyone who has bought a home with EPC label E or F since 2023 must reach at least label D within six years of the notarial deed. Wall insulation is one of the most heavily weighted measures. Miss the deadline and a fine of €500 to €5,000 follows, plus a new deadline.
Cracks in the render, weathered joints, a dated colour. At that point you are paying for the scaffolding and the finish regardless. The insulation board in between is then the cheapest part of the whole exercise — and the only one that keeps paying back for thirty years.
Insulation keeps heat in during winter and out during summer. A south- or west-facing facade that heats up all afternoon releases that warmth into the bedrooms in the evening. With an externally insulated shell, that heat stays on the outside of the wall.
The EPC label appears on every property listing and is the first thing buyers look at. A facade that has just been insulated and finished also sells with a very different story than one where the buyer still sees work ahead.
Before you start on materials and centimetres, one thing has to be settled: which side of the wall the insulation goes on. That determines everything that follows, and it is not a matter of taste.
| Method | When | Insulation value | Points to watch |
|---|---|---|---|
| External wall insulationETICS — what we do | The facade is due for renovation, or you want the maximum result | Highest: any thickness is possible and thermal bridges are dealt with | Your facade becomes 11 to 21 cm thicker; its appearance changes; you carry on living there throughout |
| Cavity wall insulationfilling the existing cavity | Your home has a clean, wide enough cavity (usually built from around 1960) | Limited: you are bound by the cavity width, typically 5 to 6 cm | Quick and cheap, but the facade stays as it is and the result never matches external insulation |
| Internal insulationon the inside face | The facade may not or cannot change from the outside (protected appearance, building line) | Reasonable, but thermal bridges at floors and internal walls remain | Costs living space, requires a correct vapour barrier and means emptying the rooms |
If your facade sits on the building line or right on the plot boundary with no centimetre to spare. If its appearance is protected or fixed by a planning condition. And if you have only just had your facade renewed — the gain is then rarely worth the demolition, and we would rather tell you that now than after the quote.
In those cases cavity or internal insulation is the better route. We do not fit those, but we will tell you honestly that is how it stands.
The lambda value (λ) tells you how well a material holds back heat: the lower, the better per centimetre. The rest of the table is about what a board asks of you — thickness, weight, fire behaviour and price.
| Material | λ (W/mK) | Thickness for Rd 4.5 | Fire behaviour | Strengths | Price |
|---|---|---|---|---|---|
| Graphite EPSgrey expanded polystyreneOur standard | ± 0.032 | ± 14 cm | Combustible — within a certified system | Best insulation value per centimetre, light, quick to install | €€ |
| White EPSclassic expanded polystyreneAlso possible | ± 0.036 | ± 16 cm | Combustible — within a certified system | Cheapest board, but ± 12% thicker for the same result | € |
| Mineral woolrock or glass woolOn request | ± 0.036 | ± 16 cm | Non-combustible (A1) | Vapour-open and sound-absorbing, but heavier and more demanding to fit | €€€ |
| Wood fibrebio-based boardNiche choice | ± 0.043 | ± 19 cm | Combustible | Best summer comfort and ecological, but the thickest and the most expensive | €€€€ |
Lambda values according to the technical ETICS Handbook; the exact figure is given per system in the manufacturer's technical approval (ATG) and varies slightly by brand. The thicknesses in the third column follow from Rd = thickness ÷ λ, rounded up to the next common board thickness. PIR insulates better still per centimetre (λ ± 0.022), but does not feature in the common ETICS systems for a rendered facade and is not used here.
We work with EPS as standard, white or graphite. Not because it is always the best material, but because for a house facade it gives the best balance between insulation value, price, weight and workability. Graphite EPS is our first choice: the same performance in fewer centimetres, which matters for sills, roof overhangs and the plot boundary.
Where fire safety comes into play — an apartment building over 10 metres, for instance — a non-combustible build-up is the right choice, and we say so. In Belgium, requirements apply to the fire behaviour of facades from 10 metres upwards; above 25 metres all facade components must be non-combustible. A detached single-family house is not subject to those rules.
The Rd value is the insulation value of the board itself: thickness divided by lambda. The higher it is, the more heat stays inside. Here is what every centimetre of graphite EPS delivers.
Calculated for graphite EPS with λ = 0.032 W/mK. With white EPS (λ ± 0.036) every value is roughly 12% lower: 10 cm then reaches only Rd 2.8 and therefore no subsidy, 12 cm reaches 3.3 and 16 cm reaches 4.4.
Rd 3.0 m²K/W is the minimum value at which external wall insulation qualifies for a subsidy, and the work must be carried out by a contractor. With white EPS you only reach it from 11 cm.
14 cm of EPS or mineral wool is what the Flemish government assumes for external walls in its 2050 energy target. That is where we start, not below it — you do a facade once every thirty years.
The scaffolding, the sheeting, the substrate preparation, the bonding and fixing, the reinforcement layer, the detailing around windows and sills, the render and the labour: all of it is identical whether you fit 12 or 16 cm. Only the board gets thicker.
Saving on centimetres therefore means saving on the cheapest item in the quote — and on the only one that keeps paying back for thirty years. In our quote we set two thicknesses side by side with the price difference, so you can choose for yourself rather than having to take our word for it.
A reinforcement layer goes over the insulation, and over that the finish that gives your facade its face. This is the choice you will look at for thirty years — and the one where the price difference is largest.
| Finish | Appearance | Indicative price excl. VAT | Worth knowing |
|---|---|---|---|
| Render & decorative plasterover insulation | Smooth or textured, hundreds of colours and structures | €110 – 150/m² insulation included |
The standard finish. You choose structure and colour; finer grains look crisper, coarser ones hide more. |
| Brick slipsover insulation | Keeps the classic brick appearance | €200 – 280/m² insulation included |
The premium choice for those who insulate but do not want a rendered facade. More labour, so a clearly higher price. |
| Render without insulationfacade renovation | New look, same insulation value | €40 – 80/m² | If the facade only needs renewing cosmetically. You still pay for scaffolding and finish — the insulation board is then the cheap addition. |
| Facade paintingmineral or siloxane paint | Refreshing a sound facade | €25 – 45/m² | The entry-level option, together with Vedipaint from our group. No insulation gain, but protection and a fresh facade. |
All amounts are indicative prices per m² excl. VAT, materials and installation included. On colour: dark shades absorb more solar heat and warm an insulated facade more strongly than a solid wall, which creates stress in the finishing layer. System suppliers therefore set a minimum lightness value per render — which shades are possible is stated in the technical data sheet of the chosen system. We take that into account in the colour advice.
A quote of €110/m² and one of €150/m² can both be correct. This is what makes the difference — in order of weight, and board thickness deliberately does not come first.
Scaffolding, traffic management and protection of the surroundings · substrate preparation and repairs where needed · insulation boards, reinforcement layer and final finish · detailing at sills, plinths, corners, window and door junctions · a clean handover and a photo record of every phase.
On VAT and subsidies we keep it short: 6% VAT applies to homes older than ten years where materials and installation are supplied by the same contractor and invoiced to the end user — we always supply both together. As for subsidies, we promise nothing up front; our grants and VAT page sets out honestly what you are and are not still entitled to in 2026.
Photos of your facade, a few clicks, and you see an indicative price range straight away — with the thickness and finish you choose yourself.
VediWorks is one of Vedi Group's four companies. Interior painting, a post-construction clean or maintaining shared areas: one contact, the same crews, the same standard.
