Roof and wall insulation in Poland: which rules apply after September 2026?

Poland’s official register records the repeal of the 2002 building regulations on 21 September 2026. A separate Act dated 31 July 2026 sets out the circumstances in which the earlier provisions can still be applied. A design that relies on them should identify the relevant transitional provision.

For an energy retrofit, give the designer a precise description of the proposed works. The designer can then identify the applicable procedure, record the performance requirements and show in the calculations how the roof or wall meets them. The change in the register alone tells you little about an individual building.

Article 102a of the Polish Building Act provides an 18-month period from 20 September 2026. For a building permit application, a separate application for design approval or a construction notification covered by the article, the developer may elect to use the provisions applicable up to 19 September 2026 by filing a declaration with the authority handling the case.

That election also determines the basis for the technical design. Articles 102b and 102c separately address certain works exempt from the listed formalities and the maintenance and use of residential buildings. Check which provision covers the project before placing a material order.

Under the former provisions, the maximum corrected thermal transmittance, Uc, for an external wall adjoining a room with a design temperature of at least 16°C was 0.20 W/(m²·K). The corresponding maximum for roofs, flat roofs and ceilings below unheated attics was 0.15 W/(m²·K). Check both the room temperature and the legal basis before using these values.

Other design temperatures and other types of building element have their own requirements. An unheated garage therefore needs a separate assessment. In an existing building, replacing a roof covering and reconstructing the entire roof may also require different design documents.

The U-value describes heat transfer through the complete assembly. Thermal conductivity, λ, is a property of an individual material. For a uniform layer, dividing its thickness in metres by λ gives its thermal resistance, R. Two layers of equal thickness can therefore contribute different amounts of resistance.

A 100 mm PIR layer with λ = 0.022 W/(m·K) gives R ≈ 4.55 m²·K/W. At λ = 0.036 W/(m·K), the same thickness gives approximately 2.78 m²·K/W. The final roof or wall calculation also includes the remaining layers, the framing and any necessary corrections for fixings.

A lower thermal conductivity reduces the thickness needed for a given resistance. That can help at parapets and thresholds where extra depth would affect an adjoining detail. On a pitched roof, a continuous layer above the rafters also limits the heat flow through the timber if the joints and supports are designed accordingly.

Check moisture control, fire performance and load capacity for the proposed PIR assembly. A thin-faced insulation board needs a separate weatherproof covering. Specify the fixings, sealing layers and finish together. Depending on the application, mineral wool, EPS or XPS may better satisfy other design requirements.

The building assessment includes its ventilation, airtightness, energy supply and services. Air leakage at a window junction or a poorly operating ventilation system can still cause significant losses after roof insulation is upgraded. A whole-building energy indicator describes a different quantity from the U-value of one wall.

Plan the sequence of a retrofit around the junction of the roof and wall. A thicker insulation layer at the eaves can move the line of the gutter. Insulating a façade can require deeper sills and new flashings. Include those alterations in the scope and budget so that adjoining layers can be connected without gaps.

Ask the designer to record the applicable provisions, target values and calculated layers. Confirm whether the developer must file a declaration under the transitional arrangements. Keep the dated design revision and check the legal position again if construction is postponed.

Specify the product, declared λ, thickness and any additional properties in the order. Have the designer check a proposed substitution before installation. During the work, inspect the insulation at junctions and the seals around penetrations while they are still accessible. Those checks connect the calculation to the roof or wall actually built.