Thermo-modernisation fastening techniques 04 January 2024

Despite a tightening of standards for greenhouse gas emissions worldwide, there remain both public and private buildings that are inadequately heated and consume a lot of energy – often due to piecemeal thermo-modernisation renovation work having been undertaken. The main challenge facing the stakeholders on such renovation projects is defining the purpose, nature and scope of the work to be carried out, which is where the right components for the job, including fixing techniques, will play an important role in ensuring the efficient and effective implementation of any renovation.

At a time of ever increasing gas, electricity and fuel prices, more and more people are considering investing in thermo-modernisation for their homes, which is the best way to reduce heat loss and positively impact household budgets. In addition to replacing heating sources, an important approach is the replacement of joinery, especially of windows, as well as insulation of the roof and external walls. 

Due to the introduction of the common European Green Deal Strategy, which aims to reduce CO2 emissions, thermo-modernisation is a necessity, but also a very costly investment. That’s why homeowners should take advantage of the different kinds of programmes under the thermo-modernisation allowance scheme, which provides funding for materials and work related to home insulation.  

To receive a grant, it’s necessary to meet conditions set out in the programme, with the scope of work defined by an energy audit, carried out before the thermo-modernisation begins. This will show the energy condition of the building and indicate how to improve it, the costs, effects of implementation, as well as the expected energy consumption and costs after the work is done. Windows are usually the first items to be replaced. The programme specifies the conditions to be met by the various components used during renovation and refurbishment, not only windows, polystyrene, or wool, but also construction chemicals and fixing techniques.

Window replacement in thermo-modernisation and the role of frame mountings

Window joinery plays an important role in the energy balance of a building. It has an impact, not only on heat loss, but also on passive solar energy gain. On average, windows’ share of heat loss amounts to 15% – 25%, especially in houses built before 1990 – when it was standard for windows to be installed without taking energy savings into account. This is one of the reasons why the replacement of windows with new, improved-performance windows, should be a prelude to further thermo-modernisation work; indeed, it’s advisable to install, fix and seal windows correctly before the insulation layer is applied to the walls. 

Windows are constantly exposed to the elements along with the forces imparted when closing and, opening them. In addition, the joinery-to-wall connection must be a tight one and, regardless of their size and the material from which the windows are made, they should form a uniform system with the building wall. 

This is where various Klimas Wkręt-met fastening techniques offer versatile solutions for these types of assembly.

For installations where a window protrudes beyond the face of a wall and is mounted using special consoles, or guides, for example, Klimas Wkręt-met’s KPS-FAST-S/KPR-FAST-K screws work well, and it’s recommended that two, or multi-point mountings onto the window recess using frame dowels be used, e.g the KPS-FAST-S. On the other hand, when extending into the thermal insulation zone using a dedicated fixing system, KPR-FAST-K frame dowels from the Klimas Wkręt-met range are suitable. Worth noting that the length, diameter, number and placement of fasteners must be adjusted to the dimensions of the frame and any recommendations by the window frame manufacturer. 

When it comes to installation in a window opening, without protrusion, the use of screws is recommended, e.g flat head WHO/pan head WHOW. As a rule, in single layer walls, windows are set at half the thickness of the wall, while in two layer walls with a thermal insulation layer of 15cm – 20cm, they are set as close to the outer edge of the wall as possible. In two layer walls with insulation of more than 20cm, the joinery can be installed outside the wall, in the thermal insulation zone. In three layer walls, windows must be installed directly in the insulation layer, between the supporting wall and the façade wall.

When installing in the centre of the window opening through suitable mounting holes in the frame to the solid substrate surround, the use of hardened, self-tapping screws for WHO frames is recommended. These screws are equipped with a notched thread, which guarantees a secure and durable fixing in both masonry (concrete, ceramic, and silicate bricks) and wooden substrates, while the tapered head ensures a secured fixing into PVC. On the other hand, for the installation of wooden profiles it is recommended to use a WHOW screw with a cylindrical head, which guarantees the lowest possible head exposure – while also ensuring secure seating.

If the window is located on the outer edge of the wall and is flush with it, the use of LO frame connectors is recommended; this is a high-quality expander connector made of galvanised steel. 

Roof thermo-modernisation and rafter insulation screws 

Insulating the eaves of a building is the ideal solution if insulating the roof without renovating the attic is the intention. Covered from the outside, the roof truss is protected from changes in ambient temperature, improving the energy balance of the building. With this method, not only can all work be carried out from the outside, but it also has many advantages over traditional roof thermal insulation technologies, such as a reduction in heat loss of the building and protecting the roof structure. In addition, it offers more design options for the attic and does not reduce its height. 

For structural reasons, roof insulation is possible on sloping roof structures where the angle of inclination is greater than 20 degrees; PIR panels are often used in this method of insulation, although both rock wool and wood wool have varying technical parameters, which determine their thermal insulation effectiveness in such applications.

In addition, the correct installation of this type of insulation depends on the right choice of screws and how they’re used. Klimas Wkręt-met offers WKPC carpentry screws in such scenarios, which meet the right ETA confirmed technical parameters. With their additional thread under the head, stable fixing of the counter battens is ensured and loads are transferred from the insulation directly to the rafters, thus protecting the insulation installation from damage. As well as its WKPC carpentry screws, Klimas Wkręt-met offers a wide range of screws and carpentry fasteners for various applications.

External wall thermo-modernisation and the ThermoDrive V2 fastener

Due to surface areas involved, thermo-modernisation of external walls is one of the biggest challenges in the whole process, which is where mechanical fasteners play an important role. They perform several functions such as load transfer, including the protection of the ETICS system against wind suction forces and detachment from the substrate. Mechanical fasteners also have the task of stiffening the entire insulation system, eliminating movement and deformation of individual insulation boards; limiting the formation of point thermal bridges; and protecting against failure due to any loss of adhesion and load bearing capacity of the adhesive layer with the substrate. 

A new generation of thermal insulation fixing, suited to such scenarios, is Klimas Wkręt-met’s ThermoDrive V2 fastener, which can be used for fixing polystyrene and mineral wool to substrates made of concrete, solid ceramic brick, ceramic hollow brick, lightweight aggregate elements and cellular concrete. In addition, the V2 fastener is suited for use with uneven substrates, including those contaminated with old layers, e.g involving plaster and/or adhesive. The ThermoDrive V2 fastener can also support ETICS-on-ETICS scenarios during the renovation of external walls constructed with large slab technology, and can be used in a concrete ‘texture’ layer with a minimum thickness as low as 40mm, whilst achieving high strengths. 

Of note for contractors and ETICS system providers is the rigidity of the V2’s sleeve, which increases the durability and safety of insulation systems. The sleeve has been designed in such a way that the screwed steel pin, which allows the insulation layer to be fixed, is sufficiently isolated – so the fastener displays a minimum point thermal conductivity coefficient. In addition, and particularly noteworthy for a metal stud fastener with such a wide range of applications, is the fact that the point thermal conductivity value of only 0.001 W/mK is apparent – irrespective of the thickness of insulation to be attached to the substrate.



Will Lowry Content Director t: +44 (0) 1727 743 888

Will joined Fastener + Fixing Magazine in 2007 and over the last 12 years has experienced every facet of the fastener sector – interviewing key figures within the industry and visiting leading companies and exhibitions around the globe. Will manages the content strategy across all platforms and is the guardian for the high editorial standards that the brand is renowned.