Insulation: how to save with a better-insulated home
By Laurens Arends · updated 05-10-2026
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Saving by insulating the home
According to Milieu Centraal, a poorly insulated corner house uses on average about 1.900 m³ of gas per year for heating, compared with 800 m³ for a comparable well-insulated home. Economising on insulation therefore mainly means losing more heat and, as far as we are concerned, is not a good idea. The appliance that produces the heat has to work for less time in an insulated home. Often the flow temperature of the heating can also be lowered.
Before you start, check what is already there. A home from 1930 may since have been well insulated retrospectively, and a home from 1995 may still have mediocre glazing. So do not stare blindly at the year the home was built. Check the roof, the cavity, the ground floor and the code in the spacer of the glass yourself. A thermal image can show missing or sagged insulation and thermal bridges, but have the image taken on a cold day and interpreted properly. For air leaks, a blower door test gives more certainty than a thermal photo alone.
The euro amounts below are our own calculations using the fixed calculation price of € 1,52 per m³, 2026 price level. The gas savings and costs come from the Dutch housing models of Milieu Centraal. Do not simply add measures together: after the first insulation measure, less heat loss remains for the next measure.
Small insulation jobs you can do today
| Small job | Starting point | Indicative saving per year |
|---|---|---|
| Sealing gaps and cracks | 50 m³ of gas in a corner house or semi-detached house | € 76 |
| 2 m² of radiator foil behind an uninsulated brick wall | 2 × 11 m³ of gas | € 33 |
| Ordinary curtains in front of all double-glazed windows | 30 m³ of gas | € 46 |
Use draught tape on windows and doors that need to be able to open. Fill gaps between fixed building parts with a suitable material, such as sealant or compriband. Never seal off ventilation grilles. Window film is at most an interim solution: according to Milieu Centraal, professional film on single glazing saves about 3,4 m³ of gas per m², while replacement with HR++ glass saves about 12 m³ per m². If you want to save with insulation, you had better do it properly. If you currently have no budget for it, you can already save considerably today with small insulation jobs.
Major insulation measures: costs and savings
The saving on your energy bill is a gross saving. You first spent money yourself to make that saving possible. Therefore deduct the ISDE from the purchase costs and divide the remaining investment by the annual energy saving. Only after this simple payback period has the lower energy bill fully compensated for the net investment.
The amounts below apply to an average corner house. The subsidy column follows the rounded examples from Milieu Centraal for one insulation measure. In the last column we double the regular subsidy amount, because RVO allows this when you take a second insulation measure within 24 months or combine the insulation with a heat pump, solar water heater or heat network connection.
| Measure | Investment | Subsidy with 1 measure | To pay yourself | To pay yourself with doubled subsidy |
|---|---|---|---|---|
| Cavity wall insulation | € 1.800 | € 450 | € 1.350 | € 900 |
| Floor insulation | € 2.240 | € 280 | € 1.960 | € 1.680 |
| Insulating a pitched roof | € 6.500 | € 900 | € 5.600 | € 4.700 |
| 22 m² of HR++ glass | € 4.700 | € 550 | € 4.150 | € 3.600 |
| External wall insulation | € 23.000 | € 1.750 | € 21.250 | € 19.500 |
The last column only shows what you pay for the measure mentioned. The investment in the required second measure is not included. That second measure of course also delivers its own energy saving.
The next table then shows what you really have left if we spread the net investment over thirty years. This is merely an economic comparison: gross energy saving minus the net investment divided by thirty years.
The net result over thirty years uses the subsidy for one measure: 30 × the annual energy saving minus the investment after subsidy. The calculation keeps the gas price fixed at € 1,52 per m³ and does not include financing interest, maintenance costs, price increases, local subsidies or increase in the value of the home.
| Measure | Gross energy saving | Payback period with 1 measure | Payback period with doubled subsidy | Net result over 30 years | Average economic result per year over 30 years |
|---|---|---|---|---|---|
| Cavity wall insulation | € 608 per year | 2,2 years | 1,5 years | € 16.890 | € 563 |
| Floor insulation | € 198 per year | 9,9 years | 8,5 years | € 3.980 | € 133 |
| Insulating a pitched roof | € 517 per year | 10,8 years | 9,1 year | € 9.910 | € 330 |
| HR++ glass replacing single glazing | € 395 per year | 10,5 years | 9,1 year | € 7.700 | € 257 |
| External wall insulation | € 806 per year | 26,4 years | 24,2 years | € 2.930 | € 98 |
In this model, cavity wall insulation pays for itself quickly. Roof and floor insulation need about nine to eleven years. HR++ glass is mainly financially interesting if it replaces single glazing. Replacing existing double glazing pays for itself much less quickly through the energy saving. Extra comfort, less noise and a possibly higher home value can still justify the choice.
Cavity wall insulation
In the model, cavity wall insulation delivers the shortest payback period and is therefore the best way to save with insulation. The energy bill drops by € 608 per year. After € 450 subsidy for insulation, you first still pay € 1.350 yourself. That investment is paid back after about 2,2 years. Over thirty years, with prices remaining the same, according to our calculation € 16.890 remains, on average € 563 per year after the net investment has been spread over that period.
The measure is only possible if the home has a suitable cavity that is not yet properly filled. Have the width, contamination, moisture load and existing insulation investigated beforehand. Also check for the presence of protected bats and birds: the Omgevingswet prohibits damaging their roosts or nests or disturbing the animals. Consider insulating your home in a nature-friendly way if appropriate. In addition, check the conditions for the subsidy for insulation.
Floor insulation and ground insulation
In the model, floor insulation saves € 198 per year. After the indicative subsidy for insulation, € 1.960 of the investment remains. The simple payback period is therefore 9,9 years. Over thirty years, after deducting the investment, according to our calculation you are left with € 3.980, on average € 133 per year. The warmer floor surface also provides comfort that has not been valued in euros.
With an accessible crawl space, insulation directly against the underside of the ground floor is usually preferable. If the crawl space is too low, ground insulation can be an alternative. According to Milieu Centraal, ground insulation in a corner house saves about 100 m³ of gas per year, compared with 130 m³ for floor insulation. Shells are a form of ground insulation. Different subsidy amounts and conditions apply to ground insulation. Check them beforehand.
Roof insulation
Roof insulation is a good way to save with insulation. It lowers the energy bill in the corner house model by € 517 per year. After the subsidy, you pay € 5.600 yourself. The simple payback period is 10,8 years. With a calculation period of thirty years, € 9.910 remains after deducting that investment, on average € 330 per year. A pitched roof can be insulated on the inside or outside.
An unheated attic that can be closed off can also be kept outside the heated envelope by insulating the attic floor. According to Milieu Centraal, that saves about the same and requires less material. Preferably have a flat roof insulated from the outside, with the insulation on top of the roof boarding and under the roof covering. Verbeterjehuis.nl warns that insulating a flat roof from the inside gives a high risk of condensation and wood rot. For the roof too, check the requirements for the subsidy for insulation.
HR++ glass and triple glazing
When replacing 22 m² of single glazing, HR++ glass saves € 395 per year in the model. After € 550 subsidy, you pay € 4.150 yourself and the payback period is 10,5 years. Over thirty years, € 7.700 remains after deducting the investment, on average € 257 per year. If you replace existing double glazing, the gross saving drops to € 106 per year.
The investment is then only paid back after more than thirty years and, with the energy saving alone, does not yet produce a positive result over thirty years. If the double glazing and the frames are still in good condition, immediate replacement based on the energy saving alone is not financially attractive.
The choice can still be logical when the frames or panes are due for replacement. In that case, only attribute the extra costs of HR++ or triple glazing compared with the necessary standard replacement to the energy saving. With glass, look at the U-value: the lower, the better. Milieu Centraal gives about 5,8 W/m²K for single glazing, a maximum of 1,2 for HR++ glass and 0,4 to 0,9 W/m²K for triple glazing. For the higher ISDE amount, triple glazing must, according to RVO, achieve a maximum of 0,7 W/m²K and be fitted in new frames.
Wall insulation if the cavity is not suitable
For an average corner house, Milieu Centraal gives about € 23.000 in costs, € 1.750 subsidy and 530 m³ of gas saving. At € 1,52 per m³, our calculation comes to € 806 gross saving per year. After subsidy, you still pay € 21.250 yourself. The simple payback period is therefore 26,4 years. Over thirty years, with prices remaining the same, € 2.930 remains, on average € 98 per year after spreading the investment.
If your home has no usable cavity, an interior insulated wall lining or external wall insulation can still offer a solution. An interior wall lining takes up indoor space and requires good moisture-proof detailing. In addition, other modifications to the interior may be needed that drive up the cost.
External insulation avoids that loss of space and can deal with thermal bridges better, but it changes the façade and may require a permit. External wall insulation becomes financially more interesting when you have to renovate the façade anyway. In that case, only attribute the extra costs of the insulation to the energy saving.
Subsidy for insulation in 2026
The subsidies in the tables are indicative examples, not a fixed percentage of your quote. The ISDE is calculated per square metre and depends on the area actually insulated, the insulation value, the material and the number of measures. According to Milieu Centraal, one measure covers on average about 12% of the costs. With two or more eligible measures this is on average about double, but with an expensive quote the actual percentage can be lower.
For owner-occupiers, home insulation in 2026 runs via the ISDE. According to RVO, the basic subsidy for one measure is, among other things, € 5,25 per m² for cavity wall insulation, € 5,50 for floor insulation, € 16,25 for roof insulation, € 20,25 for wall insulation and € 25 for HR++ glass. For triple glazing or vacuum glazing with new frames, it is € 111 per m².
If you have a second insulation measure carried out within 24 months, or combine insulation with a heat pump, solar water heater or heat network connection, then according to RVO the regular insulation amount doubles. The biobased bonus does not double. Insulation you install yourself does not receive ISDE. You apply for the subsidy after the work has been carried out and need, among other things, an invoice, proof of payment, a photo and a registration code.
From 2026, a one-off subsidy of € 400 is also possible for a suitable energy-efficient ventilation system that you combine with insulation. Ventilation alone does not double the insulation subsidy. View all current conditions on our page Insulation subsidy.
Insulation and ventilation go together
Sealing unintended draughts is sensible, but closing off ventilation openings is not. Moisture from showering, cooking and breathing must be able to get out and fresh air must be able to get in. Leave grilles open, keep mechanical ventilation on and clean grilles and vents. Briefly airing with a window does not replace continuous ventilation. In summary: sealing gaps reduces the uncontrolled air supply. Without sufficient ventilation, this can cause moisture and air quality problems.
And so you must always combine insulation and ventilation. After thorough sealing of gaps, demand control with CO₂ and humidity sensors can better match ventilation to use. Balanced ventilation with heat recovery also limits heat loss via ventilation air, but requires suitable ducts and good maintenance. It is because insulation and ventilation in fact belong together that since 2026 you can also get € 400 subsidy for ventilation in combination with insulation.
Frequently asked questions about saving with insulation
How much can you save with insulation?
That mainly depends on the starting situation. According to Milieu Centraal, a poorly insulated corner house uses about 1.100 m³ more heating gas than a comparable well-insulated home. At € 1,52 per m³, that is, according to our calculation, about € 1.672 per year, but in a partly insulated house the remaining saving is lower. Bear in mind that you first pay the investment yourself, reduced by any subsidy. That is why it is better to also look at the net result over a fixed calculation period, such as thirty years.
What is the lifespan of insulation?
Properly installed roof, wall and floor insulation can last for decades. The actual lifespan depends on moisture, sagging, fixing and deterioration.
What is the difference between wall insulation and cavity wall insulation?
Cavity wall insulation fills the space between the inner and outer wall. Wall insulation applies a thicker layer to the inside or outside. Cavity insulation is usually cheaper and has the shortest payback period in the corner house model used. External wall insulation can achieve a higher insulation value and is also possible if there is no usable cavity.
Does insulating with shells in the crawl space help?
Shells on the ground can limit moisture from the crawl space and provide some ground insulation. However, they do not insulate the floor directly. Milieu Centraal therefore calculates a lower gas saving for ground insulation than for insulation against the underside of the floor.
What does the lambda value of insulation material mean?
The lambda value in W/(m·K) indicates how well a material conducts heat. The lower the lambda, the better the material insulates per centimetre. For the whole layer you look at the Rd value and for the complete building construction at the Rc value. For both the Rd and the Rc value: the higher, the better.