Inversion Roof

Judge for yourself.

On the Advantages of Inversion Roofing

Under external factors, the top layer of flexible roofing, which ensures waterproofing, may deteriorate over time. This leads to penetration of moisture vapors and condensation formation in the lower thermal insulation layer. Once accumulated in sufficient quantity, moisture begins to seep into the room, causing leaks on the ceiling.

At negative temperatures, frozen condensation can detach the waterproofing membrane from the base, leading to cracks and ruptures in the waterproofing. An unprotected roof can quickly deteriorate, causing major problems for its owners.

Modern designers have found an alternative and made a visually ordinary flat roof the most reliable and multifunctional. This is the inversion roof. According to Ozhegov's dictionary, inversion means components arranged in reverse order. This is the core difference: in an inversion roof, the insulation layer is placed above the waterproofing, not beneath it as traditionally done.

The thermal insulation layer, located on top, protects the waterproofing from inevitable mechanical damage, solar radiation, aggressive weather, and sharp temperature fluctuations, thus extending the service life of the entire roof structure.

Moreover, you can freely walk on an inversion roof, install pathways, place furniture, create flower beds or vegetable gardens. Some kindergartens even feature play areas on rooftops, of course, following safety rules. The idea of using the roof as additional space has gained widespread popularity in major cities.

Structure of Inversion Roofing

• The deck must be strong enough. Ideally, it should be a reinforced concrete slab with a 2–5 degree slope toward drains. This slope prevents water accumulation and ensures proper drainage to downspouts.
• The waterproofing layer may consist of self-adhesive materials, PVC, or TPO membranes. Self-adhesive and rolled materials with glass fiber base are the simplest and most cost-effective option. Commonly, glass-based waterproofing (Stekloizol) is used.
• The insulation layer for inversion roofing must retain its thermal performance even in wet conditions. The best choice is extruded polystyrene (or expanded polystyrene). It is fire-resistant, hydrophobic, non-toxic, has low thermal conductivity, and is highly durable. It is available in boards ranging from 30 to 120 mm in thickness, various sizes, with flat or stepped edges. Easy to cut with a knife. Fixing methods include:

• melting Stekloizol with a gas heater at several points and firmly pressing it against the polystyrene board;
• adhering boards using bitumen-based adhesive without solvent.

• The filtering layer is essential to prevent excess moisture and soil erosion, enhancing structural strength. Use glass fiber cloth or geotextile. They come in rolls of various sizes and are easily cut. Lay them overlapping. The fabric must lie flat, without folds or misalignment. Use special adhesive for glass fiber cloth, typically sold with the material.
• The drainage layer consists of gravel. Its optimal thickness for inversion roofing is 70–80 mm.

Types of Inversion Roofing

An inversion roof can be used for recreation, work, vehicle parking, or children’s play areas. Currently, the most popular types include:

• Gravel roof — the simplest and most budget-friendly option. It consists of several layers:

• Concrete slab.
• Cement-sand screed with a slight slope.
• Waterproofing layer.
• Thermal insulation layer. To prevent heat loss through joints, polystyrene boards should be laid overlapping by up to 40 cm.
• Gravel layer, 5 cm thick.
• Geotextile fabric.

• Green roof is similar in composition to the gravel roof. The difference lies in using a root-resistant layer instead of standard geotextile, on which a soil layer is placed. The depth of the soil layer depends on plant type. For grasses, 15 cm is sufficient; for perennial flowers, 20 cm; for small shrubs, 30 cm; for large shrubs and trees, up to 60 cm. To prevent rapid soil compaction, walkways made of paving slabs can be installed. These are made from the same material as in regular gardens. Plant selection depends not only on personal preference but also on structural load capacity, as wet soil has significant weight. For example, a 25 cm layer of wet soil creates a load of 300 kg per square meter. Alternatives include special substrates for growing plants, which are lighter. The waterproofing, insulation, and filtration layers must extend 15–20 cm up the walls above the lawn level at junctions with vertical structures.
• Car park roof — another type designed for heavy loads, thus requiring a more robust structure:

• Slabs with increased load capacity.
• Waterproofing layer. In addition to external weather, it protects the insulation from cement milk from inside.
• Thermal insulation boards.
• Sand layer, 5 cm thick.
• As a separator, building cardboard can be used.
• Surface layer. For example, asphalt-bitumen mixture.

Installation of inversion roofing requires specialized knowledge and high skill. It is best to entrust the work to professionals. This will significantly extend the roof’s lifespan and reduce future maintenance costs.