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The System 10 calculator
Estimate the energy saved, the space gained in the habitable attic, the risk of condensation and the materials required for the selected package.
Technical content: Bogdan Ivănescu, graduate engineer, PhD candidate at the Technical University of Cluj-Napoca · updated on 16.10.2026
All results are calculated estimates, based on the package values in the Isoflect document “System 10 thermal insulation packages” and on the assumptions displayed under each calculator. For a calculation on your project, upload your project →
How much you save in the habitable attic
Compare the System 10 package with a conventional insulation of the same thickness and with the current state of the roof.
The package
Wolle thickness between the rafters
Indicative value, which you may modify; it converts the centimetres gained into money.
- Thermal resistance R of the package—
- Thermal transmittance U of the package—
- Energy through the roof with System 10—
- Energy with conventional insulation λ 0.038 of the same thickness—
- Energy with the roof in its current state—
- Annual saving compared with the current state—
Composition of the annual saving
| Compared with conventional insulation | Compared with the current state | |
|---|---|---|
| Energy consumed (price per kWh) | — | — |
| Consumption-related taxes and charges on the energy bill | — | — |
| Total | — | — |
The consumption-related taxes and charges are distribution, transmission, green certificates, levies, excise duty and VAT, which are paid for each kWh. Their share is according to Eurostat, household consumers, 2025.
The space gained
- Conventional insulation λ 0.038 for the same R—
- System 10 thickness (Wolle and the interior membranes)—
- Thickness saved—
- Usable floor area recovered—
- Habitable volume recovered—
- Value of the recovered space—
—
All packages
| The package | R, m²·K/W | U, W/m²·K | kWh/m² per year | Saving compared with conventional, kWh/m² per year | Conventional insulation λ 0.038 for the same R |
|---|
How we calculate (calculated estimate): the energy through the roof, per m², is Q = degree-days × 24 × U × regime ÷ 1,000 ÷ efficiency (or COP), separately for heating (heating degree-days, base 18 °C) and for cooling (cooling degree-days). The R and U values of the packages are those calculated for the entire build-up, from the Isoflect document “System 10 thermal insulation packages”; for Basic, Basic+, Medium and Medium+, the values are without the optional external membrane. Conventional insulation is calculated with λ 0.038 and the same thickness as Wolle (R = thickness ÷ 0.038); the thickness of conventional insulation for the same R is R × 0.038. The System 10 thickness adds the interior membranes: approximately 1.5 cm for Basic and Basic+, approximately 2.4 cm for Medium, Medium+, Premium and Premium+. The usable floor area recovered is a strip with a width equal to the thickness saved ÷ sin(pitch), along the length of the eaves walls. The value of the recovered volume is the m² value related to a reference height of 2.5 m (estimate). The degree-days are indicative long-term average values; energy prices are indicative and may change. The calculation does not replace an energy audit.
Limits of the calculation
The results are calculation estimates and have a margin of error of approximately ±15%. Actual values depend on the quality of installation, the airtightness of the building, thermal bridges, orientation and shading, the temperature maintained in the house, the actual efficiency of the heating system and the weather in each year. The calculation refers only to the roof; walls, windows, the floor and ventilation are not included. Energy prices are average values, according to Eurostat, average prices for household consumers, including all taxes, and are subject to change. The calculator does not replace an energy audit or a specialist design.
Where condensation may form
See the temperature through each layer of the roof in winter, and the point at which the room air would reach the dew point.
Insulation thickness between rafters
A humidity of 60% is usual in a dwelling; in a bathroom or kitchen it may exceed 70%.
- Dew point of the room air—
- Temperature at the surface of the finish—
- Temperature in the plane of the vapour barrier—
- Temperature at the inner face of the rafter—
—
How we calculate (calculation estimate): steady-state winter conditions, with surface resistances Rsi = 0.13 and Rse = 0.04 m²·K/W (SR EN ISO 6946) and the dew point according to the Magnus formula. The total resistance of each package is the documented value from “System 10 thermal insulation packages”; the part not belonging to the Wolle insulation is placed on the warm side, where the interior membranes are located, and for Premium and Premium+ the difference relative to Medium is placed on the exterior side, where Roof Pro is located. Through the rafter, timber with λ 0.13 W/(m·K) replaces the insulation, while the interior membranes remain continuous. The System 10 vapour barriers are the membranes on the warm side (Multistrat and Gold). The calculation shows where the vapour would reach the dew point; it does not replace a complete hygrothermal assessment of the design.
Which materials you need
The material requirements for the selected package, in whole rolls and packs.
The package
Wolle thickness between the rafters
Exterior membrane
Material requirements
The quantities include 3% for overlaps and waste and are rounded up to whole rolls and packs. For Wolle, the configuration of slabs and rolls is determined at the quotation stage, according to the clear spacing between rafters.
You receive the quotation for the selected package, with the final price; you send the request from the packages page, where you select the package and thickness again.