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Calculators for the building envelope
Pick an element on the house section: the roof, a wall, the window or the floor. Each calculator shows how heat, or sunlight, passes through that element, with climate data for your location.
Tap the roof, a wall, the window or the floor to open its calculator.
The four calculators
Four calculators, one for each element: roof, wall, window and floor. They use manufacturer-declared λ values, climate data for the chosen location and the methods of the European standards. Results appear instantly, without an account.
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U′ and R′ for attic rooms, unheated lofts and flat roofs, including the timber, month-by-month condensation and summer behaviour.
Worked exampleOpen the calculatorAttic with 18 cm of wool between the rafters and 5 cm under them: U′ 0.175 W/(m²K). With 10 cm under the rafters: 0.143.
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U′ and R′ for Porotherm or AAC masonry with external insulation, with the temperature through the layers, condensation and a year of heat loss.
Worked exampleOpen the calculatorPorotherm 25 N+F with 10 cm of white EPS: U′ 0.304 W/(m²K), i.e. R′ 3.29 m²K/W.
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How much sun reaches the window in each season and how much an overhang shades it, hour by hour, from PVGIS data.
Worked exampleOpen the calculatorAn unshaded vertical south facade receives on average between 1,018 kWh/m² a year (Brașov) and 1,101 kWh/m² (Craiova).
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A slab on ground for a house without a basement, to EN ISO 13370, with the soil type, plinth insulation and insulation above or below the slab.
Worked exampleOpen the calculatorA 120 m² house in Bucharest with 10 cm of polystyrene on the slab loses about 1,422 kWh through the floor in a winter, against 3,644 kWh without it.
What the calculators don’t tell you
The calculators describe the physics of a single element in a typical situation. They don’t give ratings or say whether a solution suits your house; that takes a PHPP model of the whole building.
Methods
Standards and data sources
The calculations use public standards and data you can check yourself.
| Source | Used for |
|---|---|
| Passive House Institute · PHPP | Passive House criteria and the energy model of the whole building |
| Mc 001-2022 | Romania’s nZEB requirements: the minimum thermal resistance R′ for each element |
| SR EN ISO 6946 | Thermal resistance and U-value, including timber and fixings in the element |
| SR EN ISO 13370 | Heat transfer through the ground, for the slab on ground |
| SR EN ISO 13788 | Condensation inside elements, month by month |
| SR EN ISO 13786 | Time lag and damping of the summer heat wave |
| PVGIS · JRC | Solar radiation and temperatures 2005–2023 for each location (European Commission Joint Research Centre) |
| Declarations of performance | Material conductivity λ, taken from manufacturers’ declarations (DoP), not from distributor catalogues |