▽ +09.00Thermal insulation
Inverted roof system
A roof build-up with the insulation above the waterproofing membrane, shielding it from heat and impact.
What it is and how it works
In an inverted roof the thermal insulation sits above the waterproofing membrane rather than below it, shielding the membrane from sun, temperature swings, traffic and damage.
Its usual build-up from the bottom: the slab, a screed to falls, primer and membrane, XPS boards, a geotextile separation layer, then the protection or finish (tiles on bedding mortar, or gravel). The membrane is flood-tested before the insulation goes down.
- Family
- Thermal insulation
- Used in
- Roof waterproofing
- Build-up
- 8 layers
Where it fits — and where it does not
A good fit for
- Flat concrete roofs of villas and buildings
- Trafficked roofs and terraces
- Roofs that will be tiled or paved
Not a fit, or needs a check
- Roofs without enough height for the build-up at doors and parapets
- Membranes incompatible with polystyrene, without separation
- EPS instead of XPS above the membrane
Application pages
Advantages and limitations
Every system has strengths and limits; the right choice starts from the site conditions.
Advantages
- The membrane is protected from UV, heat and damage
- Insulation and waterproofing in one designed system
- A usable roof surface
Limitations
- A heavier build-up that needs more height
- Leaks are harder to trace once covered
- Correct falls and drains are essential
System build-up
Top to bottom. Final thicknesses and materials follow the approved specification and the product TDS.
System build-up8 layers
Inverted roof system
Select a layer to see what it does.
Tiles or final finish
Mechanical protection and the walking surface.
Bedding mortar
Levels and fixes the tiles.
Geotextile separation layer
Prevents abrasion and keeps the mortar off the boards.
XPS insulation boards
Above the membrane: they insulate and shield it from heat and impact.
Waterproofing membraneCore layer
The core of the protection: bituminous, PVC or liquid PU, as specified.
Primer
Full bond between membrane and substrate.
Foam-concrete screed to falls
Directs water to the drains.
Concrete slab
The structural element.
Preparation and application
Surface preparation
- Screed to falls checked towards the drains
- Upstand heights and door thresholds coordinated
- Drains suited to inverted roofs, taking water at membrane and surface level
Application sequence
Screed to falls
Foam concrete or a screed laid to falls.
Waterproofing
Primer and membrane with all details.
Flood test
The membrane tested and recorded before covering.
Insulation
XPS boards, tight and staggered.
Separation
Geotextile over the boards.
Protection and finish
Bedding mortar and tiles, or gravel ballast.
General educational content; final values and requirements follow the manufacturer’s TDS and the approved project specification.
Checks and common mistakes
Quality checks
- Falls survey before waterproofing
- Flood-test record
- Board joints and coverage
- Drains clear after finishing
Common mistakes
- Skipping the flood test
- No separation layer under the mortar
- Drains blocked with mortar
- Upstands lower than the finished build-up
Common questions
Why put the insulation above the membrane?
It keeps the membrane at a stable temperature and protects it from UV and damage.
Which membrane goes under an inverted roof?
Bituminous, liquid PU and other membranes are used; compatibility with XPS and the details decide.
Next step
Considering this system for your project?
Send drawings or site photos; our engineers review the case and propose the right specification.