In recent years, discussions on the widely understood problems of modern construction were undeniably dominated by issues related to construction power engineering and the increasingly stringent requirements regarding real energy efficiency in the construction industry.
The saving programmes adopted throughout Europe forced a new approach to solving those problems. The reasonable voice of serious environmentalism that estimates the impact of manufacturing and using specific materials on the earthly biosphere, in all of its most complex relationship, is increasingly heard.
In Poland, in less than 40 years, the normative transfer coefficient for walls was reduced fivefold and in 2021 it will be six times lower than in the 1960 s. This is a completely new reality that requires completely new architectural solutions, new and far more effective sources of heat, modern heating systems, doors and windows with thermal performance considered “extraterrestrial” until recently and above all modern, highly effective thermal insulation materials for our buildings.
Such new material, widely introduced to modern construction industry, is the rigid polyurethane foam, PUR, or its polyisocyanure variety, PIR.
Their properties can be considered in a wide variety of contexts. However, to remember even the most basic of them, it is inevitable to compare them with the elementary properties of the most popular thermal insulators of today’s construction sites, namely boards of foamed polystyrene, EPS, and the defibred rock material that forms boards of mineral wool, MW.
1. CONTEXT OF THERMAL INSULATION (ENERGY)
Splendid thermal insulation performance is the most important distinctive feature of the PUR/PIR foam. It can be assumed that the parameter that best describes the thermal performance of materials is lambda (λ), i.e. the heat transfer coefficient [W/mK]. Considering the average of the materials available on the market, it can be assumed as approx. 0.040 for mineral wool, 0.034 for EPS and 0.023 for PUR/PIR-type foam Thermano boards.
THERMAL INSULATOR LAYER THICKNESS
A natural consequence of the differences described is the necessity of using a different material thickness for each thermal insulation material. As soon as in 2021, for a typical roof slope, we will be required to install a thermal insulation ensuring the building an insulating power estimated by the heat transfer coefficient of Uc(max) at not more than 0.15 W/m2K.
This can be achieved with mineral wool of approx. 26 cm or THERMANO boards of
approx. 14 cm thickness.
This significant reduction of the thickness of the thermal insulation, and, consequently, of the roof structure, translates to considerable profits. The over-rafter roof thermal insulation system can significantly increase the loft cubic volume and reduce to minimum the impact of roof thermal bridges, which is very onerous in other systems. Wooden elements of the roof framework enable an unconventional arrangement of this part of the house, a material reduction of spending on this part of flashing and a considerable reduction of the load on the structure itself.
LOAD ON THE STRUCTURE
At this point, it is worthwhile to refer to a simple example. Imagine a situation, in which we need to thermally insulate a 200 m2 roof up to the Uc(max) of 0.15. For this purpose, we need to use the mineral wool with approx. 150 kg/m3 density and approx. 26 cm thickness. The same insulation effect can be achieved by thermally insulating the roof with Thermano boards of approx. 14 cm thickness and 32 kg/m3 density.
With simple multiplication, we receive a surprising result – the weight to encumber the roof with is approx. 7800 kg for mineral wool and only 896 kg for Thermano. It should be remembered that the additional “tonnes” must be purchased, paid for, transported and installed on the roof. In this context the balance of profits and losses clearly indicates the advantage of the modern polyurethane board thermal insulation.
2. CONTEXT OF STRENGTH AND DURABILITY
Rigid polyurethane foam boards are very durable. Due to its mechanical properties, it is difficult to deform (CS(10)150); due to low absorption, it is non-absorbent and resistant to periodical and permanent exposure to water < 2% – (WL(T)2). Furthermore, it is resistant to most biodegradation effects and an unusually wide of aggressive chemicals.
The most known, specialised in durability testing, Forschungsinstitut für Wärmeschutz e.V. (Thermal Insulation Testing Institute) (FIW, Monachium) performed a very compelling evaluation regarding:
thermal conductivity,
compressive strength,
moisture content,
dimensional changes of PUR specimens extracted from actual existing buildings after 28 and 33 years of use.
In the general final evaluation, FIW confirmed that the PU foam shows no material (worth mentioning) damage and no defects. Furthermore, after 33 years of use the PUR insulation boards remain fully functional and still show all declared specifications and performance.
3. CONTEXT OF INSTALLATION
The roofers that attended the training sessions regarding over-rafter Installation of Thermano boards held by Balex Metal evaluate working with rigid PIR foam boards very clearly.
Masters or beginners in that trade, they all emphasise that from their point of view, the work is easy, quick, free from harmful dusts and fibres, with no danger of damaging the boards and above all without the risk of a mechanical failure of the films and membranes used.
The wide range of thickness of Thermano (40 to 120 mm), the small weight of boards at large covering area (1.2 x 2.4 m) and the safety of moving on the stable, wooden elements of the framework are important arguments point to the clear benefits that Thermano boards offer to the contractor, regardless of whether thermal insulation is applied to the roof, wall or floor.
4. CONTEXT OF ENVIRONMENTAL PROTECTION
At present the environmental point of view can still seem rather abstract and futuristic, but nothing could be more misleading. Sooner than we think, also in Poland, designing methods including the widely understood “sustainable development”, “green certificates”, “multiple criteria-based methods of building assessment, e.g. BREAM, LEED” etc., will become common. Then, already at the initial LCO assessment it will be evident that the proposed “polyurethane” solutions are more beneficial.
Considering the multi criteria-based analyses, we also need to realise that worse ratings
(i.e. increasing costs) will apply to the materials, of which the environmental costs of production, application and use will be high, while the winning materials will feature e.g. a relatively low content of natural fossil materials.
This is the area, in which polyurethanes prove their advantage once more, because the manufacture of the basic ingredient (polyols) can be sustained by vegetable oils, as opposed to fossil raw materials. The practice shows that already the present technologies allow up to 17% (by weight) of bio-renewable content (corn, sunflower, linseed, soybean, palm, castor and fish oil, and even agricultural waste) and up to 7% recycled material. Thus, in near future, at least to a large extent, the manufacture of polyurethanes will not be associated with infernal rectification fumes of refinery columns, but with the heady scent of rapeseed, linseed or exotic, green palm forests.
