Batts vs Blow-in vs Spray Foam Insulation

Batts

Batts are pre-cut blankets of insulation laid between the ceiling joists. They are the usual choice for a roof space with enough height to move around in, and they come in the widest range of R-values. We install Knauf Earthwool® glasswool batts.

• Best for: open ceilings with good access, and walls and floors during renovations.
• Watch for: gaps and squashing, which cut performance, and clearances around downlights and flues.

Blow-in glasswool

Modern blow-in insulation is loose glasswool blown through a hose into the roof space. It forms a seamless, even layer and reaches tight and awkward spots where batts are hard to lay. It is not the same as old cellulose loose-fill, often called "the fluff", which was made from shredded paper and is one of the most common things we remove.

• Best for: low-pitched, cramped or broken-up roof spaces.
• In walls: Knauf SUPAFIL® Carbon Plus glasswool is injected into the empty gap in double-brick cavity walls, without renovation.

Spray foam

Spray foam is sprayed on as a liquid, then expands and hardens into a dense, airtight layer that bonds to the structure. Because it air-seals as well as insulates, it suits places with little or no roof space and parts of the house that let in draughts.

• Closed-cell foam: about 20mm thick for R1.0. It has very low water vapour permeability, so it suits underfloors, external walls and anywhere moisture is a concern.
• Open-cell foam: about 45 to 50mm thick for R1.0. It is softer and is used more in ceilings and internal walls.
• Best for: skillion and flat roofs, suspended timber floors, renovations with open wall frames.

How the prices compare

Our typical price for new batts is $15–$30 per m² installed. Blow-in and spray foam are quoted after the assessment, because the price depends on the area, the access and the thickness needed to reach your R-value.