Sealing Electrical Penetrations
Through the Airtight Layer
Preserving the airtight layer is one of the most challenging aspects of high performance buildings such as Passivhaus. Passive house certification requires that a building achieve an airtightness rating of less than 0.6 air changes per hour at 50Pa. Given that in the passive house space builders are accountable to that air exchange rate, it is imperative that any penetration point that could compromise this value be remedied in a manner that is not only effective, but durable and cost effective.
In this blog we will explore different types of electrical penetrations and how they can be effective managed.
Cable Grommets
Figure 1 (Blog Header): Cable grommet installation. Image credit: Isocell. Figure 2: Cable grommet allowing penetration through membrane without compromising airtightness. Image credit: Isocell
Ideally electrical penetrations should only enter a building at a single location such as a services cavity or shaft where airtightness principles can be thoroughly applied. However this is not always possible due to the number of cables or the layout of the building. This is especially true of retrofits where it is not always possible to relocate cable penetration points.
Where a cable must penetrate though a membrane a cable grommet can be used to maintain the airtight layer.
Advantages:
- Easy and quick to install.
- Easy to understand for novice trades.
- Durable and effective sealing around the cable.
Points to consider:
- Each grommet must be sized correctly to the cable. For example the 3AIRDD3K (pictured below) can only accept cable diameters from 8-12mm. If the cable is larger then the next size up grommet must be selected
- The rubber sealing piece must not be cut to allow larger cables.
Tapes
Sealing tapes can be used as an alternative to grommets in some circumstances. Tapes are effectively a DIY grommet, however careful application methods must be used to ensure a durable and effective airtight seal.
Figure 3: Butyl Stretch tape being used for penetration sealing. Image credit: Isocell
Advantages:
- No requirement around the size of the penetration. One tape does all sizes.
- Multiple different tapes such as Butyle Stretch, Airstop Elasto, Airstop Plasto tapes can be used with similar effect.
- Smaller stockholding requirement for builders
Points to consider:
- Practice makes perfect – some training and experience is required to make a perfect seal.
- Butyl type tapes can get soft and sticky in hot environments. This can make installation a little tricky. Recommend keeping tapes cool until ready to use.
- Joint sealing tapes such as Airstop Elasto are not as stretchy which can make installation more time consuming.
Figure 4: Sealing around flexible conduit using Airstop Elasto. Photo credit: Isocell
Sealing Compounds
Situations where lots of cables must penetrate the airtight layer in one location can be challenging to keep airtight. Thick sealing compounds like Omega PoBit can be used in a similar manner to potting compound.
Advantages:
- Paintable sealing solution to seal many cables in one area.
- The thick paste like consistency of PoBit Sealing Compound allows for sealing service shaft plates.
- Sealing compounds like PoBit Sealing Compound are UV durable and suitable for external use.
Points to consider:
- Drying times apply to paintable solutions.
- Several coats may be required to develop a durable seal.
Figure 5: Omega PoBit sealing compound used in multiple sealing situations. Note electrical sealing on bottom right. Image credit: Isocell
No matter the sealing type you encounter, Siegware has a solution.
For more information about airtightness products please visit:
https://siegware.com.au/isocell-airtightness-systems/
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