What it is
Recycled paper, milled to a fibre and treated with borate for fire and pest
resistance. It is blown from a machine outside through a hose. Around 80% recycled content, and the
lowest embodied carbon of any insulation we install by a wide margin.
The case for
- Density. Cellulose is around three times denser than blown fibreglass, and
that density resists air movement within the layer. In a windy attic, a dense layer keeps
performing where a light one is being scoured.
- It fills irregular spaces. Around truss webs, over uneven joists, into the
awkward corners of an older attic, it settles into the shape rather than bridging over it.
- Fire performance. The borate treatment means it chars rather than flames, and
it is tested to the same standards as everything else on the truck.
- Embodied carbon. If that matters to you, it is not close.
The case against, honestly
- It absorbs water. A roof leak into cellulose means removal. Blown fibreglass
in the same situation often sheds the water and dries out. If your roof has a leak history and you
are not fixing it this year, that matters.
- It is heavy. On an old ceiling with lath and plaster, or undersized joists,
the load is worth thinking about. We look at the ceiling before choosing.
- It settles. Predictably, which is why it is installed above the target depth
to a specified coverage — but a contractor who blows it to sixteen inches and leaves has
given you less than R–50 in two years.
How we choose
Standard truss attic with a sound ceiling and no leak history: cellulose. Lightweight or historic
ceiling, or a known roof problem: blown fibreglass. Nobody should be selling you either on
ideology, and if a contractor only ever installs one material, that is a stocking decision rather
than an engineering one.
What the rebate thinks
Nothing. The programme pays on R-value achieved, not on material.
More on the two materials here.
