PIR insulation
What should a thermal and moisture report for a PIR wall include?
A thermal and moisture report helps select the layers of a building element if it describes the actual wall and its conditions of use. A green result in the calculator alone does not explain the behaviour of corners or the effects of leaks. For new construction, it is worth preparing the data so that the calculations can also be used when coordinating windows, installations and the sequence of works. A wall separating a flat from the outside performs differently from a building element between a workshop and a cold store. Record the design temperature on both sides, the heating method and the expected humidity. In a bathroom, laundry and utility room, the sources of vapour behave differently from those in a bedroom. It is also important whether the heating will operate continuously.
First define the boundaries of the analysed zone
The climatic data should correspond to the building’s location. For the moisture analysis, note the façade orientation, the rain shelter and the solar exposure. Choosing a random town just to run the program reduces the report’s usefulness. Describe separately the initial condition of the materials and the planned date for closing the wall.
Enter the complete material build-up
List the layers from inside to outside, including the claddings, adhesive, voids and façade finish. For the insulation, the thickness and the correct lambda are needed. For the diffusion analysis, the vapour flow resistance is added. A PIR board with aluminium foil and a board with fleece under render are not the same entry in the materials database.
Check whether the declared thermal resistance covers only the insulation or also the attached gypsum board. Do not enter the same layer twice. In the masonry, the properties of the finished masonry layer, appropriate to the unit and the mortar, are taken into account. The generic name ‘ceramics’ does not replace the data for a specific solution.
Separate the U-value calculation from the moisture assessment
The resistance of a homogeneous layer can be preliminarily calculated as the thickness in metres divided by the lambda. For the assumed 90 mm and 0.022 W/(m·K), the result is approximately 4.09 m²K/W. This is the resistance of that layer. For the whole wall, the resistances of the remaining materials and surfaces and the appropriate corrections must be added.
The thermal result does not describe the path of rain or the flow of moist air through the gap. The report should show separately the assessment of the surface temperature and the possibility of condensation inside the assembly. When comparing variants, keep the same climate and usage assumptions. Then the differences result from the change of the building envelope.
Check what the method does not cover
The simplified analysis according to PN-EN ISO 13788 does not cover all moisture phenomena. Liquid water transport, moisture capacity and air movement through leaks go beyond its basic scope. It should not be concluded from it that an inadequately sealed assembly will be safe.
For internal insulation, damp masonry or driving rain, a transient analysis may be required. It allows changes over time to be assessed given appropriate input data. The choice of method is made by the designer. Increasing the insulation thickness until a favourable number is obtained does not resolve the model’s shortcomings.
Add the details that change the building’s result
Calculating the flat wall field does not replace checking the ring beam, reveal, ceiling junction and plinth. In these locations the heat flux does not run exclusively perpendicular to the layers. It is worth combining the report for the building element with a list of details requiring analysis of thermal bridges and internal surface temperatures.
Specify the airtightness solution at the window frame, socket boxes and service penetrations. Already during design, services can be relocated to a separate space on the room side. This facilitates maintaining the continuity of the air control layer. Any subsequent change to these locations should be passed to the person responsible for the calculations.
Record the result so that it can be verified
A good printout contains the date, building element variant, material data, boundary conditions, the method applied and clear conclusions. It should also indicate limitations and elements requiring separate verification. Save the input file so that a change in wall or cladding thickness does not require reconstructing the assumptions from memory.
The U-value target and the basis of requirements are established for the specific project. During periods of regulatory change, the designer also checks the transitional rules. The calculator report supports the design but does not approve the solution on its own. It is most useful before purchasing materials, when the layer and junction arrangement can still be improved.
Questions and answers
Can the same report be used for every elevation?
The U-value result for an identical wall field may be shared. The moisture assessment may require distinguishing between solar exposure, rain and elevation orientation.
Does the absence of condensation in the calculation complete the design?
No. Airtightness must still be ensured, thermal bridges checked and details executed in accordance with the adopted assumptions.
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