Application of thick XPS thermal insulation, construction rules I.

As the thickness of the insulation increases, feasibility issues have arisen that were not apparent with previous sizes. The usual sizes are much larger than those used today and in the future; 20-36 centimeters compared to 5-6 centimeters 20 years ago, but 10-12 centimeters used a few years ago. Thoroughness in terms of the entire building (from the basement, through the walls to the roof) and the perfection of the designs are also realistic expectations. Impeccable behavior, high level of technical performance, and long-term and safe resistance to the stresses that arise are the strengths of XPS.

How thick should the insulation be?

The simple answer: with the chosen insulation thickness, the given insulated structure – with attention to the building as a whole (!) – should meet all current regulations and requirements. In addition to the current energy requirements, there is always a structural protection and thermal sensation aspect. No harmful condensation should occur anywhere, nor should any space divider (wall, ceiling, floor) be such that the “draw” temperature is uncomfortably low (which is closely related to the possibility of avoiding the risk of condensation).

It should be noted that the thermal conductivity of XPS varies depending on the manufactured thickness. As the manufactured thickness increases, the λ (W/mK) value decreases slightly for RAVATHERM products, and significantly for other manufacturers. In the case of RAVATHERM XPS 300 SL (smooth surface) and RAVATHERM XPS 300 WB (patterned surface), it is 0.033 W/mK between 30-60 mm, and 0.035 between 80-280 mm. For larger material thickness requirements, a welded product is made, when the sheets are multiplied in the factory with their own material and welded, in the required total thickness. In such cases, welding several thinner sheets results in a better total λ value – in the case of RAVATHERM XPS products, between 120-280 mm.

Thick thermal insulation

The increase in thickness does not affect the basic installation/design principles, such as

• when combining with plasticizer-containing materials, a separating layer (e.g. PP felt) must be installed between XPS and plasticizer-containing (e.g. plasticized/PVC) boards both
• when gluing and in the case of permanent stress, the XPS temperature must be observed for short-term max. + 80 oC, permanently max. + 70 oC heat resistance and solvent sensitivity
• In the case of THRs, the surface reinforcing glass fabric mesh embedded in the system adhesive, starting from a reliably load-bearing base (!) continuously covers (protects) the XPS thermal insulation material (bottom, top, at openings, wall ends, etc.) with a surface-continuous (with a min. 10 cm overlap) layer (at the bottom, top, at openings, at wall ends, etc.

When installing thick XPS thermal insulation, it is essential to use an electric (scissor) melt-cutter suitable for on-site cutting, or a suitable (dust-extracting) saw.

What is the consequence of increasing the thickness of XPS?

It is clear from the above that XPS remaining within a reasonable thickness range (20-30 cm) does not require any special measures beyond compliance with general principles and rules.
Due to the flexible material structure of XPS, the increased volume fluctuation does not have a detrimental effect on the thermal insulation, however, thermal expansion (~0.07 mm/mK) must be taken into account during design.

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