TEP ROOF OY · MATERIAL AND INSTALLATION GUIDE
Expanded clay roofs with additional insulation
Expanded clay can provide thermal insulation and form roof falls. It generally forms a ventilated layer. The load-bearing structure, vapour control layer and actual waterproofing substrate are specified separately.
Traditional or additionally insulated build-up?
- In a traditional solution, expanded clay provides insulation and forms the falls. In an additionally insulated or hybrid roof, insulation boards such as EPS or mineral wool are also installed below it. Additional insulation can reduce the overall thickness required.
- The required height is also affected by drainage falls and any building services within the roof build-up. Compare the total weight, build-up height and thermal target. Selecting expanded clay does not yet specify the additional insulation material, product or thickness.
What supports the waterproofing?
- Waterproofing is not installed directly on loose expanded clay. The design specifies an even substrate, such as roof support slabs or a concrete topping slab, together with suitable waterproofing and fixing. Check junction heights from the finished roof surface.
- The structural deck is usually concrete. Check its load-bearing capacity and joints together with the weight of the expanded clay, additional insulation and waterproofing substrate. Coordinate outlet locations, levels and water routes with the layers before installation.
Ventilation and vapour control work together
- Leca recommends a vapour control layer for expanded clay roofs, particularly on precast decks. A bituminous membrane is a typical option, but the product and sealing are specified according to moisture conditions. Ventilation does not compensate for air leakage at joints and penetrations.
- Design ventilation routes, eaves openings and any additional ventilators for interrupted areas too. Account for building services, fire stops and other obstructions. Additional insulation changes how the build-up dries; check its effect for the selected combination.
Check the work sequence and acceptance
- Before placing the expanded clay, check continuity of the vapour control layer, penetration seals, ventilation connections, and building services installations and protection. Agree the expanded clay grading, quantity and unloading location according to the design and site lifting arrangements.
- Inspect falls and the waterproofing substrate before waterproofing. Agree weather protection, particularly where additional insulation slows drying of moisture beneath it. Record inspections of concealed layers; resolve any temporary construction drainage before work begins.
Use and design responsibility
TEP Roof Oy guide cards support project preparation and the definition of contract scope. They are not project-specific construction designs. The project structural designer is always responsible for checking the suitability of the solutions presented and adapting them to the project's structures, loads and requirements. Construction requires project-specific design and approval, together with the current manufacturer's instructions for the selected products.
Sources
An editorial compilation by TEP Roof Oy. The product- and system-specific source instructions must be checked for the selected solution.
- Leca Finland Oy: Leca expanded clay roof with additional insulation: options and build-up height Checked 19.10.2026
- Leca Finland Oy: Designing a Leca expanded clay roof: structure, ventilation and vapour control layer Checked 19.10.2026
- Leca Finland Oy: Installing a Leca expanded clay roof: work sequence and moisture management Checked 19.10.2026