Compression Tape on New Windows - Should I Insist?

Home Retrofit
21

Thanks Russell,

sounds like a good foam to use for example for pipe holes that need to be closed. I have multiple holes in the kitchen extension where the builders or plumbers have put the dishwasher washing machine and sink drains through the wall individually. Is it better to use a foam or should I actually close it with brick to restore the envelope and put some sort of insulation in the cavity?

Anyway, seems like a good product and can you recommend some air tightness tape? When would I need a vapour permeable tape? Any suggestions? Thanks

22

The insulation properties of this type of foam, all be it ok, they do not beat the continuity of a proper insulated wall. But i use it around all service penetrations along with tapes, and after removing smaller pipes, cables etc. Its not super cheap so wouldnt wanting to be pumping into open cavities!!!

Theres several brands, each have different models, of thickness, plasterable , non plasterable, water proof etc.

Proclima and Siga do tapes and mebrane, i have used both.

1 Like
23

I used ISO-Blocco One 64/3 (or rather, I persuaded the windows-installation manager to supply the installers with this - it’s a higher-up decision, the actual installers were doing a good job with whatever was supplied to them). Someone on Carbon Coop recommended this, can’t remember who…!
For airtightness tape, on the inside, I used Contega Solido Exo (recommended by John O’Brien, on here.)

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24

Sounds like this ISO-Blocco One is an all in one expansion tape. Wow. Providing air tightness, insulation and waterproofness externally all in one tape.

Do you then still need the Contega Solida Exo on the inside? (Btw, I think the Exo means it is used for the outer seal, isn’t it?)

Anyway, from the discussions above for a good airtightness and insulation people use 1) a tape on the external frame of the window for water proofing, 2) a compression tape between frame and the wall and then another 3) internal airtightness tape. Does that sound correct?

It is quite an effort and cost and I can see that a normal window fitter wouldn’t use all of these.

25

Any one of those layers would exceed normal window fitters’ standards, but unfortunately that isn’t saying much.

I would recommend all three layers but if you are doing a staged retrofit you could postpone at least one tape until you are doing other work on that side of the window. Others might not agree but I feel that it reduces the chances of damaging the tapes after they are fitted.

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26

I received an email from International Passive House Association yesterday that I consider deserves a post in this thread. I’ve tried copying it here and hope it formats in a sensible way.

Passive House Fact Sheet
Number 37

Logo iPHA

Header Fact Sheets
At the International Passive House Association, we bring together leading Passive House experts to share practical knowledge on the topics that matter most in high-performance building design.

Our Fact Sheets offer concise, expert-driven insights into specific technical solutions, helping you stay informed, improve your projects, and apply best practices with confidence.

This issue focuses on multifunctional expanding tape for airtight window installation, highlighting how this innovative solution can simplify detailing while ensuring reliable airtightness.

All iPHA Fact Sheets are available as an exclusive benefit to members, who can access and download the full collection at any time.

Enjoy the read!

Multifunctional expanding tape for airtight window installation

In recent years, the use of multifunctional expanding tapes has increased significantly for the airtight installation of windows in new buildings and renovations. These tapes are applied around the window on three or four sides. They expand after installation, sealing the gaps between the window and the reveal. It is important that the reveals are sufficiently level and connected to the regular airtight layer with a smooth finish or adhesive.

These tapes are available for different gap widths and must be selected and applied accordingly (e.g. 8–12 and 10–15 mm). However, blower door measurements often reveal inadequate airtightness. Frequently, these tapes are incorrectly applied, even to the extent of completely useless double-layer application.

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Studies conducted by the Passive House Institute in 2016 already showed that it often takes a long time (up to four weeks) for the tapes to show full effectiveness. It was also apparent that the gap width decisively influences on the airtightness of the tapes (report in German). Therefore, multifunctional expanding tapes should always be used close to the lower application limit. Even when a correctly applied multifunctional expanding tape has reached its maximum application limit, it often allows significant air flow.

According to its specifications, although the multifunctional expanding tape will be sufficient, it won’t be completely airtight. Specially reinforced multifunctional expanding tape, which is proven to have a high quality sealing effect, can be certified by the Passive House Institute as an airtight product for window connections.

Image: Multifunctional expanding tape under a window frame (cross-section).
© Passive House Institute

Example project

In a large Passive House project, the windows were installed in smooth wooden reveals all around. In many cases, tape specified for gaps of 7 to 15 mm was applied to gaps with a width of 15 to 20 mm. The craftsmen used only this one product specified for a maximum thickness of 15 mm. When four windows were tested using an a-value measurement (airtightness of windows and installation), the average leakage was a considerable 2.2 m³/(hm) at 50 Pa. The target values are between 0.05 and 0.8 m³/(hm) (according to the Passive House Institute’s product certification). This high level of air permeability due to improper application would contribute 0.35 h-1 to the n50 value of the building. That would constitute a worryingly low tolerance for any further potential leaks.

Time-consuming subsequent work involving covering of the installation joints with conventional airtightness tape reduced this value to 0.57 m³/(hm). The share of window joints in the building’s n50 value was thus reduced to just 0.09 h-1, providing security against any unforeseen leaks.

The Passive House Institute and other parties can carry out on site measurements to ensure the quality of installation work.

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Measuring the airtightness of a window including installation joints.
© Passive House Institute

Explore All Fact Sheets

Authors: Wolfgang Hasper and Søren Peper, Passive House Institute
Fact sheet published in 2026
© iPHA / Passive House Institute

More info and sources:
www.passipedia.org

You can find all previously released fact sheets on Passipedia.
Fact-sheets in our knowledge database Passipedia

Contact

International Passive House Association
Passivhaus Institut

Rheinstraße 44 46
D-64283 Darmstadt
Tel: +49 (0)6151 82699-55

info@passivehouse-international.org
www.passivehouse-international.org

27

That’s v informative, thanks for posting,
Mike

28

I have had these fitted to my windows but I went for level of compression rather than gap size to ensure a good seal.

1 Like
29

Anyone who reads the data sheets ought to appreciate this but most probably that doesn’t include the contractor installing the windows.