Sustainable Architecture Pillar 6: Sealed Building Envelope

What could Sustainable Architecture possibly have in common with Submarine Design + Build?

Perhaps not a lot – except for one critical component!

Sustainable Architecture Pillar 6: Sealed Building Envelope

Imagine if you were in a submarine at the bottom of the ocean and you noticed that a crack had formed on the window/portal seal allowing:

  • Valuable oxygen from inside the submarine to escape, and
  • Freezing water from outside to flood in

Would you continue, business as usual?

Or would you drop everything, resurface and get it fixed?

The heat loss equivalent of this example happens in virtually every Australian home, every day.

The Sealed Building Envelope

A breach anywhere in the shell of a submarine compromises the entire vessel.

For a submarine to function, the entire shell must be completely sealed.

The same is true for a Passive Solar House.

A breach anywhere in the ‘shell’ – or Building Envelope – of a Passive Solar House compromises the energy performance of the entire building.

For a Passive Solar House to be truly sustainable, the entire Building Envelope must be completely sealed.

What constitutes a breach?

A breach in the Building Envelope of a house occurs through:

  1. Air Leakages, and
  2. Thermal Bridges

1. Air Leakages

An Air Leak in the Building Envelope is the Sustainable Architecture equivalent of a crack in the shell of a submarine.

In winter, it allows valuable heat inside to escape while allowing unwanted external cold air inside, with the reverse being true in Summer.

Examples of Air Leakages include:

  • Unsealed doors/windows,
  • Unsealed vents, skylights and exhaust fans
  • Gaps within or around wall insulation, between floorboards, around wall penetrations (eg. air conditioners, heaters)
  • Gaps within or around ceiling insulation and around ceiling penetrations (eg. downlights, pipes, cables etc).

2. Thermal Bridges

A Thermal Bridge is an element of a building that allows heat to travel through it more quickly than through other elements of the building.

A Thermal Bridge can be as disastrous as a flyscreen window on a submarine – allowing unwanted heat transfer en masse.

Examples of Thermal Bridges include:

  • Inappropriately specified windows, doors and skylights
  • Poorly designed/constructed junctions between floor to wall, wall to roof, balconies to window and door frames.

Locating Breaches

Unlike in Europe, the significance of Air Leakages and Thermal Bridges is virtually unknown and not a regulatory requirement in Australia.

In Europe, infrared cameras are used to locate Air Leakages and Thermal Bridges caused by inadequate detailing on plans, incorrectly specified materials or poor workmanship.

Acceptable Thermal Bridges

Infrared Camera used to detect Thermal Bridges

The image above is an example of how infrared cameras are used to detect Air Leakages and Thermal Bridges in a typical German home. The lighter the colour the warmer the materials.

Although double glazed, thermally improved windows and doors are used in the house above, they have a higher U-value than the walls. As expected, they are lighter in colour compared to the walls (since they allow more heat to escape through them). In this case, they represent a Thermal Bridge – however, the amount of heat transfer in this case is within pre-determined, acceptable limits.

Unacceptable Thermal Bridges

The images below show a photo and an infrared scan of an upper storey bedroom.

Photo and Infrared Scan of Upper Storey Bedroom

As can be seen in the infrared scan on the right, there is an obvious thermal bridge at the junction where the wall meets the ceiling. The dark colour indicates that there are gaps in the insulation as that corner is significantly darker and therefore colder than the rest of the room.

This will require further investigation and rectification, otherwise the builder may be liable for any structural damage that might result.

Sealing the Building Envelope

In order to achieve a Passive Solar House, it is the Architect’s/Designer’s responsibility to design a sealed Building Envelope. This will require:

  • Windows and doors to be specified that allow heat transfer within acceptable limits.
  • Connections and junctions of different building materials to be extensively detailing during the Working Drawing stage so that the Builder can appreciate the level of precision required.

Once the architect/designer has faithfully sealed the Building Envelope on plan, it then becomes the Builder’s responsibility to build the dwelling accordingly. The finished product should have no Air Leakages and Thermal Bridges should be within acceptable values.

Sustainable Architecture: Sealed Building Envelope Conclusion

For a house to be truly Passive, the Building Envelope must be completely sealed.

Breaches in the Building Envelope of a house occur via:

  1. Air Leakages, and
  2. Thermal Bridges

In order to achieve a Passive Solar House, it is the Architect’s/Designer’s responsibility to design a sealed Building Envelope.

Once the Architect/Designer has faithfully sealed the Building Envelope on plan, it then becomes the Builder’s responsibility to build the dwelling accordingly.

The next article in this series will focus on Sustainable Architecture Pillar 7: Material Selection.

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