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Insulating the concrete slab in the attic, with walkable boarding
Thermal insulation for the concrete slab in the attic: Multistrat directly on the concrete slab, Wolle boards between spacers and walkable boarding to move about on.
Technical content: Bogdan Ivănescu, graduate engineer, PhD candidate at the Technical University of Cluj-Napoca · updated on 16.10.2026
Three zones, each with its own role
Reflectiva Multistrat is laid over the concrete slab, with the aluminium facing up. Above it comes the Wolle thermal insulation fibre. So that the attic can be walked on, Wolle is installed between spacers and covered with walkable boarding.
Multistrat occupies 5 mm
The Reflectiva Multistrat layer is only 5 mm thick. The emissivity is 0.05, and the reflectivity is 95–97%.
Emissivity: an emissivity of 0.05 means that the aluminium face radiates only 5% of the heat that an ordinary surface would radiate, and therefore does not give off heat by radiation. The lower it is, the better. What this means →Reflectivity: the proportion of the radiant heat reaching the membrane that is sent back. What this means →60 cm between spacers
The usable width between the spacers is 60 cm, and the Wolle P800 board is 61 cm wide. It fits tightly, without gaps, and holds itself in place. The spacers are the same height as the insulation.
50 or 100 mm
The starting point is 50 mm of Wolle. For 100 mm, choose 10 cm boards (P1500 or P2100) or P800 in two layers.
Distance from the chimney
Around the chimney and any strong heat source above 120 °C, leave a clear zone of 50 cm all around.
Without walkable boarding
If walkable boarding is not required, Wolle P800 is rolled out directly over Multistrat.
See the application →
Installation steps
Click on the central image to enlarge it.
Products for this application
Warranty
- ✓Reflectiva Multistrat: 50-year warranty, service life of at least 50 years
Frequently asked questions
Which side of Multistrat should the aluminium face?
The aluminium faces up, and the grey side faces down, towards the concrete slab.
What spacing should I leave between the spacers?
60 cm clear. The Wolle board is 61 cm wide, so it fits tightly and holds itself in place.
How tall are the spacers?
They are the same height as the insulation: 5 or 10 cm.
What should I do around the chimney?
Around the chimney and any strong heat source above 120 °C, leave a clear zone of 50 cm all around.
Configure the application
Choose the option and the insulation thickness, enter the attic surface area and view the quantity required for each product.
Your selection
Option Wolle insulation thicknessMaterial requirements
The quantities include 3% for wastage and are rounded up to whole rolls and packs.
Enter the surface area in order to request the quote.