Proper roof insulation helps reduce heat loss through the roof and improves comfort in your home. When insulating an existing roof, we first assess the complete roof build-up to determine the most suitable technical solution.
For pitched roof insulation, Nu-Isoleren mainly works with URSA glass wool and IKO PIR insulation boards. For certain unheated lofts, we can also insulate the loft floor with EPS beads. The right solution depends on the roof structure, available space, required thermal performance and how the loft is used.
A poorly insulated roof can account for significant heat loss. A good insulation layer helps maintain a more stable indoor temperature.
An insulated roof reduces heat loss through the upper part of the building and helps keep rooms below the roof more comfortable. In renovation projects, the first decision is often whether to insulate the roof slope or the loft floor, depending on how the loft is used and how the roof is built.
If the loft is heated or used as living space, insulating the roof slope is often appropriate. For an unheated loft, the floor may be the better location for the thermal envelope.
An insulated roof reduces heat loss through the upper part of the building and helps keep rooms below the roof more comfortable. In renovation projects, the first decision is often whether to insulate the roof slope or the loft floor, depending on how the loft is used and how the roof is built.
Many existing pitched roofs can be insulated from the inside without replacing the complete roof covering. The insulation is installed on the interior side of the existing roof structure, for example between or below the rafters.
Whether insulating a roof from the inside is technically suitable depends on the existing roof build-up, underlay, available space and the condition of the structure. We therefore inspect the roof before determining the correct insulation build-up.
Depending on the situation, we use URSA glass wool or IKO PIR insulation boards. Airtight connections and an appropriate vapour-control system are also included in the complete roof build-up.
There is no single best insulation material for every roof. The right choice depends on space, structure, thermal target and finishing.
Nu-Isoleren mainly uses URSA glass wool and IKO PIR, plus EPS beads for certain loft floors.
Nu-Isoleren uses several materials because there is no single best option for every roof. We use URSA glass wool where a flexible material is appropriate, IKO PIR where strong thermal performance is needed with limited thickness, and EPS beads for certain loft floor applications.
Glass wool is flexible and can be fitted closely between timber rafters and roof members. This makes it suitable for many pitched roofs, including structures with slight irregularities.
Nu-Isoleren works with URSA glass wool. The material combines thermal insulation with sound-absorbing properties. Careful installation helps minimise gaps and unwanted heat loss.
Find out more about its properties and applications on our glass wool insulation page.
PIR consists of rigid, dimensionally stable insulation boards that offer strong thermal performance with a relatively limited thickness. This can make PIR particularly useful where available build-up height is limited.
Nu-Isoleren works with IKO PIR insulation boards. The required thickness is determined according to the complete roof build-up and the desired thermal performance.
Find out more on our PIR insulation page.
When a loft is unheated and is not used as living space, it can be more efficient to insulate the loft floor rather than include the complete roof slope within the heated envelope.
For certain floor structures, Nu-Isoleren uses EPS beads. Suitability is always assessed for each individual loft floor.
Find out more on our EPS insulation page.
The required roof insulation thickness depends on the insulation material and the desired thermal performance. Glass wool and PIR have different properties, so the same thickness does not automatically provide the same insulation value.
Available space between the rafters, the presence of roof underlay and the intended finish also influence the required thickness. We therefore determine insulation thickness as part of the complete roof build-up rather than using one fixed value.
A good layer of insulation alone is not enough. In many roof build-ups, a correctly installed vapour-control layer and airtight connections are also important to limit unwanted air movement and moisture transport through the structure.
Before work starts, we therefore inspect the existing roof build-up, underlay and any moisture problems. Installing insulation over an existing leak or moisture issue is not a durable solution.
We start with the existing roof structure and determine the appropriate insulation solution from there.
Before installation, we inspect the roof structure and determine where the insulation and airtight layers should be positioned. The insulation is then fitted accurately, joints and connections are carefully finished and, where required, an appropriate vapour-control or airtight system is installed.
We assess structure, underlay, available space and moisture.
We select URSA glass wool, IKO PIR or an EPS loft-floor solution.
The material is installed carefully to minimise gaps.
Vapour control and airtight connections are completed where required.
The cost of roof insulation depends on the roof area, insulation material, required thickness, accessibility, roof structure and any preparation or finishing work required.
Insulating a loft floor has a different cost structure from insulating a complete pitched roof with PIR or glass wool. We therefore assess each property individually and provide a tailored quotation.
Would you like to know the cost for your home? Request a free roof insulation quote without obligation.
Grants for roof insulation or loft floor insulation may be available depending on the region, the property and the applicable conditions.
Amounts and eligibility requirements can change. Before starting the work, check our current information on insulation grants in Belgium, including separate information for Flanders, Brussels and Wallonia.
View roof and loft insulation projects completed by Nu-Isoleren.
Answers about materials, thickness, loft floors and pricing.
This depends on the available space and existing roof construction. Nu-Isoleren works with materials including URSA glass wool and IKO PIR insulation. PIR can be useful where high insulation performance is needed within limited thickness, while glass wool can be a practical solution for other roof structures.
The required thickness depends on the insulation material, available space and desired thermal performance. PIR and glass wool have different thermal properties and therefore do not automatically require the same thickness. We determine the appropriate thickness based on the complete roof build-up.
The price depends on factors such as roof area, insulation material, required thickness, roof structure, accessibility and finishing work. For an exact price, we assess the property and prepare a tailored quotation.
There is no single roof insulation material that is best for every roof. Glass wool is well suited to installation between timber rafters, while PIR is particularly useful where space is limited but high thermal resistance is required. Because PIR generally has a lower thermal conductivity, it can achieve a similar thermal resistance with less thickness than mineral wool. The best choice therefore depends on the roof type, available space, required R-value and whether the roof is insulated internally or externally.
For an existing pitched roof whose covering is still in good condition, insulating from the inside is usually the less invasive option because the roof covering generally does not need to be removed. If the roof is already going to be completely renovated, external insulation can be attractive because a more continuous insulation layer can be installed above the roof structure and thermal bridges can be reduced more effectively.
There is no single minimum Rd value that applies to every roof renovation in Belgium. In Flanders, new roof or attic-floor insulation must achieve an Rd value of at least 4.5 m²K/W to qualify for Mijn VerbouwPremie in 2026, subject to the other eligibility conditions.
In Wallonia, the temporary Primes Habitation 2025–2026 scheme ended on 30 September 2026. New projects are subject to different financing conditions through Rénopack and Rénoprêt.
The insulation thickness needed to achieve a particular Rd value depends on the material's thermal conductivity, known as its lambda value.
When a pitched roof is insulated internally, a properly installed air and vapour control layer on the warm side of the insulation is generally essential. It helps prevent warm, humid indoor air from entering the insulation and condensing inside the roof construction. Joints, wall connections and service penetrations must also be made airtight. The exact type of membrane required depends on the complete roof build-up and the vapour permeability of the roof underlay.
Yes. An old roof does not automatically need to be completely replaced before it can be insulated. If the roof structure is sound, there are no active leaks and the covering is still in good condition, a pitched roof can often be upgraded with insulation from the inside. The timber structure, signs of moisture or mould, the roof underlay and the available space between rafters should first be inspected.
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