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Pricewise Insulation is one of New Zealand’s best known online retailers of Knauf Insulation, Pink Batts, Bradford and Autex Greenstuf. One of the questions our staff are often posed with is as follows:
My house is framed with 70mm studs, leaving a 70mm gap for insulation. Can I still install a 75mm insulation batt, such as a high density Earthwool R2.0/430mm? Or will I risk damaging the plasterboard?
Before we answer that question, let’s take a look at the two most common options available to the home owner who wants an R2.0 insulation in their wall cavity.
Standard R2.0 Wall Batts
A typical R2.0 wall insulation segment is 90mm thick. These thermal wall segments are most commonly installed in the exterior wall cavities, providing an effective thermal barrier around the home. A standard R2.0 insulation segment has no particular acoustic (sound deadening) benefits, though the mere presence of glasswool or other bulk insulation in a wall cavity will always to some extent reduce the amount of noise which finds its way through the wall.
Hi Density Acoustic Wall Segments (R2.0)
From a thermal perspective, these perform identically to the standard R2.0 segments; after all, the “R-value” is the standard way to measure the insulating material’s “resistance” to heat transfer. The difference lies in the density of the material, and the corresponding increase in acoustic or sound blocking benefits. Being only 75mm thick, the R2.0 acoustic wall segment is an excellent option for home owners who want to address both the thermal and acoustic issues, i.e. they want to protect their home from both excessive temperatures and also from the transmission of unwanted sound. As such, acoustic wall segments are commonly installed in the interior walls of the home, between bedrooms, bathrooms, laundries and of course TV rooms and music studios.
… back to the 70mm Cavity Issue
So, you’ve decided you want R2.0 acoustic insulation in the interior walls, and a quick check with the measuring tape confirms what you already suspected – the gap is 70mm, while the insulation you plan to install is 75mm…
While in the bag, insulation segments are typically compressed – either slightly or greatly – to a thickness which is below their officially stated out-of-the-bag thickness. Earthwool, made by Knauf Insulation, for example comes compression packaged which allows a significant number of insulation segments to be squashed into a single bag, reducing storage and transport costs, and of course reducing the number of bags that insulation installers need to lug around the building site. Now the theory is that insulation segments, whatever their squashed dimensions, will expand out of the bag to their full, recommended thickness. But the reality may be somewhat different. In fact, it would be fair to assume that a significant percentage of Knauf Insulation’s R2.0 acoustic segments will never expand beyond 70mm thick, making them perfectly safe to install in a wall cavity the same size. And even if they did expand to the full size – it’s hard to imagine the extra 5mm causing sufficient pressure within the wall cavity to have any impact on the plasterboard or other wall lining.
While the official advice will always be ‘never install bulk insulation which is thicker than the wall cavity’ it’s safe to assume that the likelihood of any issues occurring from installing a 75mm insulation segment inside a 70mm cavity is very low.
Bradford™ Gold Wall Insulation Segments$ 8.84–$ 23.38 p/m2 inc. GST
560mm | Autex GreenStuf® Polyester Wall Insulation Pads$ 13.91–$ 22.09 p/m2 inc. GST
Pink® Batts® Thermal Wall Insulation$ 9.48–$ 13.85 p/m2 inc. GST
430mm | Knauf Earthwool® Glasswool External Wall Insulation$ 12.02–$ 18.38 p/m2 inc. GST