Thermal and acoustic insulation for windows: from self-expanding tapes to soundproofing for windows

Timber, PVC or steel window frames: seals alone aren’t enough to stop draughts

When it comes to ensuring wind and air tightness, seals are not the only element to consider when designing or installing the doors and windows of a building.
Regardless of the material – whether timber windows, PVC windows or steel windows – every frame, including those for doors and French windows, must always be installed with a clear focus on ensuring continuous airtightness and windtightness, as well as effective soundproofing.

An improperly installed high-performance window or door frame will compromise the overall effectiveness of the system and fail to meet the needs of the end user.

What must a door or window frame guarantee to be considered high-performance?

The three-level method for window insulation.

Insulating a door or window frame doesn’t simply mean choosing the right thermal insulating tape for windows or the best seals. It means addressing each of these elements from the initial design phase through to the specification of the materials. And to do so without overlooking anything, there’s a method.

The three-level method, normally used in most European countries, identifies the airtightness, windtightness and thermal-acoustic insulation levels for proper placement of doors and windows.
Implementing this approach means investing in window soundproofing while also improving the overall energy efficiency of the building, selecting a window insulation system that prevents draughts and heat loss.

To achieve optimal performance, it is important that each level be carefully considered at the design stage. Rothoblaas offers specific solutions for each of the three levels.

The three levels of door and window insulation: windtightness, soundproofing and airtightness.

Selecting the right window insulation involves choosing dedicated solutions for both the interior and exterior of the frame.

1. Windtightness level: exterior

The outermost level must ensure protection against weather conditions. If not properly treated, it can lead to problems of infiltration and accumulation of stagnant water at the bottom of the window opening. A window sealing tape is the first product to consider – PLASTER BAND OUT, for example, is breathable, prevents the build-up of condensate at the window junction and provides excellent wind protection even at low temperatures.

2. Thermal-acoustic insulation level: intermediate protection

The intermediate level must guarantee the thermal insulation, soundproofing and mechanical fastening of the windows. When selecting products, it is important to remember that effective noise reduction does not always equate to good thermal insulation.

At this level, two types of product should be effectively incorporated: a self-expanding tape for frames, or a sealing foam that combines thermal and acoustic performance – essentially a twofold window insulation layer.

EXPAND BAND self-expanding tape by Rothoblaas ensures long-lasting, permanent elastic expansion, providing protection against water, dust and wind.  WINDOW BAND offers a triple function: it seals door and window joints against air and heavy rain while maintaining thermal-acoustic performance across the full depth. It is the self-expanding tape for door and window frames: a single product capable of sealing all three levels.

For timber windows, the self-expanding tape par excellence is FRAME BAND. Airtight and watertight, it interrupts noise transmission at the junction between the structure and window frame. Thanks to the adhesive band, its application is easy and precise without the need for further glue.

Lastly, for perfect window soundproofing, true professionals choose HERMETIC FOAM, the high-performance elastic sealing foam with certified soundproofing up to 63 dB, tested by the IFT Rosenheim institute (in accordance with UNI EN ISO 10140-1:2021). It stays waterproof and airtight, even if trimmed after hardening, thanks to the closed-cell structure.

3. Airtightness level: interior

The most internal level must be airtight. Its function is to prevent the passage of vapour laden air, which could cause condensation in the installation joints and mould on the surface. SEAL BAND is Rothoblaas’ single-sided tape for simple sealing of corners, edges and other complex junctions. The double liner facilitates placement, while the impregnated paper backing ensures excellent workability and fast application. It seals so well that it is certified to Passive House Standards.

SMART BAND, on the other hand, is versatile and effective across multiple levels. It features a special separation film that can be split at any point without the need for pre-cuts. It meets all the requirements to be classified as a tape for sealing external doors or windows, ensuring maximum safety even in case of stagnating water.

The window installation plane: effects on the junction and performance

The position of the door or window frame within the wall thickness is a strategic technical choice: It directly affects insulation continuity and the formation of thermal bridges.

Correctly assessing the installation plane helps improve the energy efficiency of the junction, while also extending the system’s durability. The thermal-acoustic behaviour and durability of the junction vary significantly depending on the selected installation position. Let’s look at the main application scenarios:

• Internal flush installation
  A simple solution allowing the window to open fully, but carries a high risk of heat loss. The window is positioned further inwards, with a greater risk of low internal surface temperatures. In order to avoid thermal bridges in buildings with external insulation, it is recommended that the side reveals of the window opening be insulated, too.

• Central flush installation
  The most common method in traditional buildings, where the frame is mechanically fastened directly to the load-bearing structure of the building. It helps reduce thermal bridges, especially when combined with effective insulation of the side reveals. It is ideal for timber frame structures with an insulated cavity.

• External flush installation
  The external insulation covers the fixed door or window frame and the subframe, if present, ensuring excellent internal surface temperatures. The door or window is mechanically fastened directly to the load-bearing structure of the building.

• Installation in the insulation layer

  This solution is adopted in the most high-performance constructions. It allows for a reduction in linear thermal bridging values but requires greater care during placement and thicker insulation layers.

Door and window frames and various load-bearing structures: example installations.

To better understand the importance of integrating window insulation solutions directly into the design, it is useful to compare various door and window frame insulation methods with a focus on the junctions between the window, wall and subframe across different construction systems.

The diagram helps identify the most suitable installation method based on the material and position of the door or window frame: choosing the right combination of sealants and tapes is crucial in guaranteeing:

• Thermal insulation and soundproofing

• Water and air tightness

• Fire resistance and durability of the joint

Attention to detail at the joints is essential: CLT and external flush installations in particular, require the highest level of precision.

Properly insulating door and window frames: there’s a video guide, too

For a clear understanding of how to install the products in real-world conditions, a written guide may not always be enough.

Installation instructions, practical tips and examples of watertight, airtight and soundproof doors and windows are all included in this video:

And to have all Rothoblaas products for door and window fitters, designers and builders at your fingertips – from fastenings and tapes to tools – download the dedicated Brochure now