Warm roof insulation: Efficient thermal insulation for flat roofs

Avoid heat loss and moisture damage with the right insulation for your warm roof – perfectly prepared for PV, greenery & co.

Warm roof insulation: Functionality and structure

A warm roof is a single-skin, non-ventilated roof construction in which all layers lie directly on top of each other. The structure typically consists of:

Supporting structure (e.g. reinforced concrete or wooden ceiling)
Vapor barrier to block moisture from the inside (not required for compact roofs)
Thermal insulation (e.g. cellular glass)
Waterproofing (bitumen or plastic, we recommend EPDM)
Useful or protective layer (e.g. gravel, greening or PV mounting)

This construction minimizes thermal bridges and offers effective protection against moisture. However, it requires careful planning, particularly with regard to the vapor barrier, in order to avoid condensation problems.

With GLAPOR cellular glass sheets, this structure can be produced both in a compact bonded design (absolutely leak-proof) and in a loose-laid design as a UMS Roof (100% reusable).

Warm roof insulation materials in comparison

Criterion	GLAPOR cellular glass boards	EPS / XPS / PUR	Mineral fiber insulation
Raw material	✓ 100 % recycled glass	Petroleum-based	Sand & lime (mined)
Water absorption	✓ None (vapor-tight)	Possible through diffusion	Possible
Compressive strength	✓ Up to 1,600 kPa - also suitable for parking decks	Max. 700 kPa	Rather low
Fire protection class	✓ A1 (non-combustible)	B1-B2 (combustible)	A1
Emissions / leaching	✓ None - emission-free	Waste is dispersed during processing	Fiber dust possible during installation
Waste disposal	✓ Reusable, urban mining ready	Construction waste or hazardous waste	Cumbersome, partly landfillable (for bitumen lamination)
Lifespan	✓ Lifelong - across generations	Characteristics fluctuate when exposed to moisture	Properties change with moisture

Warm roof insulation with cellular glass: processing options

Classic: Flat roof insulation with cellular glass laid in hot bitumen

Absolutely backflow-proof and resilient gradient insulation with cellular glass boards laid in hot bitumen.

Innovative: GLAPOR Urban Mining Smart Roof

Circular, highly pressure-resistant gradient insulation made of 100 % cellular glass. Quick and easy installation without adhesives, easily removable.

Not sure which product

is the right one for you?

GLAPOR Technology Team

+49 (0) 9633-400769-0
technik@glapor.de

Guaranteed free of charge & non-binding

Warm roof insulation: The advantages of cellular glass

For a safe and durable warm roof, you need an insulating material that works reliably under all conditions. GLAPOR cellular glass offers just that:

Technically stable – for a lifetime: no moisture absorption, no deformation – permanently reliable insulation performance.
Compression-free and extremely pressure-resistant: Ideal for green roofs, terraces, technical or PV surfaces (up to 1,600 kPa).
Best fire and heat protection: non-combustible (A1) and thermally insulating – without compromise.
Fast, clean processing: easy to cut, no processing waste – no microplastics, just clean glass powder (Z0).

GLAPOR cellular glass is therefore the well thought-out solution for anyone who wants to insulate a warm roof in a permanently efficient, resilient and sustainable way.

Why GLAPOR cellular glass boards are superior to PUR insulation for green roofs with PV systems

On flat roofs in use – especially in combination with photovoltaics – the insulation is permanently exposed to high loads, UV radiation and strong temperature changes.
Conventional polyurethane insulation materials (PUR/PIR) reach their physical limits here:

Moisture sensitivity:
PUR absorbs moisture in the event of damage or leaks. This increases the thermal conductivity and reduces the insulating effect. cellular glass, on the other hand, is completely watertight and vapor-tight – without any risk of softening or loss of insulation value.
Risk of subsidence under load:
PV frames generate permanent dynamic loads. PUR can compress or deform over the years. cellular glass remains dimensionally stable and compression-free – even under permanent load.
Fire behavior:
PUR/PIR is an organic, combustible insulation material. PV systems increase the risk of fire and insurance companies demand highly safe insulation materials. GLAPOR is non-combustible (A1 according to Euroclass) – a decisive safety advantage.
Service life and heating of the PV system:
PUR/PIR is more sensitive to ageing and chemicals, particularly in the event of UV exposure or leaks. The heating of PV systems due to the aluminum lamination on PIR insulation materials must also be viewed critically (UV reflection). cellular glass is fully mineral, rot-proof and retains its properties for the life of the building.

Circularity:
PUR can neither be deconstructed by type nor recycled to a high standard. cellular glass in the UMS Roof is completely deconstructable and reusable – true circularity through direct reuse.

Conclusion for planners and building owners:

If you want to create a green roof with a PV system that is permanently safe, fire protection-compliant and can be dismantled, you need insulation that can withstand loads and moisture for decades without damage.

GLAPOR cellular glass boards – compactly bonded or loosely laid in the UMS Roof System – offer just that:
If you want to build a green roof with a PV system that is permanently safe, fire-resistant and can be dismantled, you need insulation that can withstand loads and moisture for decades without damage. GLAPOR cellular glass boards – compactly bonded or loosely laid in the UMS Roof System – offer exactly that: non-combustible, waterproof, pressure-resistant, compression-free, durable and recyclable.

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✔ Customized project consulting

cellular glass 100% made in Germany

✔ 1 00+ million m³ of cellular glass installed

✔ Customized project consulting

cellular glass 100% made in Germany

✔ 100,000,000+ m³ of cellular glass installed

Frequently asked questions (FAQ) about warm roof insulation

FAQ

How many cm of insulation does a warm roof need?

The required thickness depends on the desired U-value and the insulation material used. According to the German Building Energy Act (GEG), the U-value should not exceed 0.20 W/(m²K). With cellular glass, this value can already be achieved with a lower insulation thickness.

Which insulation is best suited for a flat roof?

cellular glass is particularly suitable for flat roofs as it is pressure-resistant, water-resistant and non-combustible. It is also ecologically beneficial as it is made from recycled glass and is free from harmful substances.

What is the difference between an inverted roof and a warm roof?

With a warm roof, the insulation lies under the waterproofing, whereas with an inverted roof it lies on top. The warm roof requires a careful vapor barrier, whereas the inverted roof requires special insulation materials that are water-resistant.

What are the disadvantages of a warm roof?

A warm roof can lead to moisture problems if not installed properly, especially if the vapor barrier is not installed correctly. Precise planning and execution is therefore crucial.

What are the disadvantages of an inverted roof?

One disadvantage of the inverted roof is the limited choice of insulating materials – only water-resistant materials may be used. In addition, moisture penetrating between the boards can lead to thermal bridges and noticeably reduce the insulating effect. This reduces energy efficiency, especially if the water drainage does not function reliably or the installation was not carried out properly.