The extension of a three-storey home in Wahroonga, Sydney, has included extensive insulation to deal with poor acoustic and thermal performance. Stephanie McDonald reports.

The project had to overcome site difficulties, with the home backing onto the Ku- ring-gai Chase National Park in Sydney. The client’s requirement was for the large three-storey home to be extended to four-storeys, taking advantage of a large gap at the bottom of the building caused by the sloping site. The new addition was to fit in a family room, study, toilet and laundry.

Large sandstone boulders were scattered across the property, which presented problems for construction. “Boulders like this affect the capacity of the building to retain heat, amplifies the sound of a room as noise bounces off the rock and necessitates the structure to work around the rock due to the impracticality of excavating the boulders from the site,” says Neil Harvey, architect of the project, from NF Harvey and Associates.

To overcome the problem of bad thermal and acoustic performance, Harvey and the client agreed that insulation should be an important part of the project. Three Bradford products were used to achieve the insulation requirements — around 70sq m of Optimo sub-floor insulation; 25 sqm of SoundScreen for the walls, which has a R2.5 rating; and 30 sqm of Bradford Gold for the ceiling, with an R3 rating.

“I specified Bradford Optimo insulation as it is specifically designed for timber floors like the Wahroonga property and could be fitted to the new floor as well as the existing floor on the other sections of the building,” Harvey says.

The Optimo batts, which are made using rockwool, were installed on the floor from the bottom up between joists, with straps fixed to joists every 500 mm to ensure the insulation was secure and didn’t fall out. “The 1,500 mm by 410 mmm sized batts make things easier as their size replicates the common distance between regular joist spacing used for floors,” says Michael Lehman of Michael Lehamann Builder and Project Manager, who installed the insulation.

During the installation of the Optimo batts, Lehman says the building team encountered challenges with the older sections of the underfloor and areas where the building sat flush against the rock and earth. He also found it difficult to get underneath the floor in older parts of the house.

“The floor was set at numerous heights to accommodate the site’s slope and the team needed to slide on their backs into tricky corners to install the Optimo. The spaces between the joists were also irregular, which is sometimes the case in older properties of this sort,” Lehman says.

“This meant some batts were too small and others too large to fit in between, requiring effort to cut the batts to the appropriate size.”

Bradford SoundScreen batts were installed between the internal and external walls between the individual studs for acoustic properties, which were placed at standard widths. “The batts are rigid enough to stand up for a time prior to nailing the inside Gyprock wall on,” Lehman says. “For most internal walls, it’s hard to get anything more than thermal rating R2 into the walls, but Bradford Soundscreen has a R2.5 rating and are 90 mm thick.”

Lehman says the product is similar to other wall insulation products he has used before, taking two people two- and-a-half hours to install it in this project.

The new family room sat below a kitchen, so to prevent noise traveling between the two levels, Harvey specified Bradford Gold R3 insulation batts with a thickness of 165 mm and a width of 430 mm. “They only need to be temporarily supported before the ceiling went in, which is similar to most batt insulation products,” Lehman says.

“For ceiling areas with little space it is easier to install the ceiling batts before the ceiling is installed. When there is ample space in the ceiling, it is quick to install the Bradford Gold batts after the ceiling has been fixed. For larger jobs I would usually hire a specialist insulation contractor to do the installation.”

Stephanie McDonald

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