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Calculate the thermal performance of your building components. Layer custom masonry, insulation, and finishes to check compliance with Nearly Zero Energy Building (nZEB) regulations in Ireland.
Thickness: 102mmλ: 0.77 W/mKR: 0.132 m²K/W
Thickness: 150mmλ: 0.031 W/mKR: 4.839 m²K/W
Thickness: 100mmλ: 1.33 W/mKR: 0.075 m²K/W
Thickness: 12.5mmλ: 0.19 W/mKR: 0.066 m²K/W
Excellent performance. This configuration is below the maximum permitted U-value target of 0.21 W/m²K.
Whether you are planning a new self-build project, an extension, or applying for an SEAI home energy upgrade grant, achieving the correct U-values is crucial.
In construction and thermodynamics, a **U-value** (thermal transmittance) measures the rate of heat transfer through a structured element, such as a wall, roof, floor, or window assembly. The unit of measurement is **Watts per square meter degree Kelvin (W/m²K)**.
The fundamental rule is: **the lower the U-value, the better insulated the structure, and the less heat escapes from the home.**
Thermal conductivity (often represented as lambda, λ, or k-value) represents how easily heat passes through a specific material. It is measured in W/mK. Materials like silver EPS (0.031 W/mK) have very low conductivity and serve as good insulation, while concrete blocks (1.33 W/mK) conduct heat rapidly.
Thermal resistance (R-value) measures how much a material resists heat flow. It depends on thickness ($t$) and conductivity (λ) through the formula: $R = t / \lambda$ (where thickness is in meters). To calculate a building element's total resistance, you sum the individual resistances of all layers, including internal and external air film constants.
All new dwellings built in Ireland must satisfy Nearly Zero Energy Building (nZEB) standards, which are regulated by Part L of the Irish Building Regulations. These guidelines mandate maximum backstop U-values for various structural components:
| Building Element | nZEB Maximum Reference U-value | Typical Material Strategy to Achieve Target |
|---|---|---|
| External Walls | 0.21 W/m²K | 150mm cavity insulation, 100mm external insulation, or ICF systems. |
| Pitched Roofs (At ceiling level) | 0.16 W/m²K | 300mm mineral wool quilt rolled between and over joists. |
| Ground Floors | 0.21 W/m²K | 100mm high-density PIR insulation boards under the concrete screed. |
| Windows & External Doors | 1.40 W/m²K | Double-glazed low-E argon-filled glazing or triple glazing. |
Generally, external wall insulation (EWI) is considered exempted development under planning guidelines since it maintains the external texture and color of the house. However, if the house is a Protected Structure, or if you live in an Architectural Conservation Area (ACA), planning permission will be required. Always consult a qualified BER assessor or architect before starting EWI.
Standard U-value calculations assume flat, uniform layers. However, real buildings contain thermal bridges—areas where structural elements interrupt the insulation (such as timber studs, concrete lintels, block corners, or steel beams). These bridges conduct heat rapidly. nZEB regulations require a separate Psi (ψ) value calculation to adjust for linear thermal bridging, or the use of accredited construction details.
No. This interactive tool is designed for preliminary planning, estimation, and educational purposes. Official building control sign-offs in Ireland require compliance calculations to be conducted using standard DEAP (Dwelling Energy Assessment Procedure) software by an officially accredited BER assessor or chartered engineer.