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BRANZ: mechanically ventilate all new homes

BRANZ proposes new homes be built to an airtightness target and mechanically ventilated.

Recent BRANZ research has prompted a shift in thinking around airtightness and ventilation.

Unlike some other countries where airtightness in new houses is carefully measured and must hit certain targets as part of the building controls process, airtightness is often not a key issue when houses are designed and built in New Zealand.

While new homes have become more airtight over recent decades, there is still a wide variation among individual buildings. Recent testing of apartments found the most airtight measured 1.9 air changes per hour (ach) @ 50 Pascals pressure, and the least airtight unit measured 12.6 ach @ 50 Pa. That is a huge range.

Other research data at BRANZ suggests that a significant proportion of our housing stock is underventilated.

BRANZ recommends a target of 3 ach @ 50 Pa across all types of residential building, an achievable target requiring minimal additional cost.

With regards ventilation, BRANZ is proposing that mechanical ventilation becomes the default option.

You can find out more in the October 2020 issue of Build magazine.



Hot water cylinders fail tests

Six out of 12 electric hot water cylinders failed energy efficiency testing.

EECA commissioned tests of 12 electric hot water cylinders to see how they complied with energy efficiency requirements. Six cylinders failed the test.

Two suppliers have withdrawn four models from sale. One manufacturer is being prosecuted while one investigation has not yet been completed.

You can read more details here.




Research points way to warmer walls

Two newly published research papers look at thermal performance in house walls.

The BRANZ External Research Report ER53 reports the findings of an investigation into the extent of thermal bridging in external timber-framed walls of 47 new build houses.

The average percentage of timber framing compared to total wall area (excluding windows and doors) is above 34%. This is much higher than the 1418% framing content generally assumed by both regulators and the industry. The results strongly indicate that the content of timber framing in external walls in residential new builds is at such high levels that the increased thermal bridging compromises the performance of walls and may mean that designed R-values are not being achieved.

More research is being carried out into what might be contributing to this. A separate research project is looking at potential solutions.

In the second piece of work, BRANZ Study Report SR436 looks at retrofitting loose-fill insulation into walls with the linings on. Of primary concern was that any solutions do not cause damage by insulation carrying water from the back of the cladding to the framing where no underlay is present.

The research found that, without an underlay present, water transfer can occur, irrespective of whether the insulation material itself is hydrophobically treated. It does appear possible, however, to create installed insulation that resists moisture transfer to the inside of the wall.

You can find more information about thermal bridging in timber-framed walls here.

You can find more information about the linings-on retrofit report here.