Cavity Brick Walls - best way to insulate

State: All

TPA Question:

I am working on a project which is in Leura NSW 2780 (Blue Mountains – NatHERS climate zone 24, NCC Climate zone 6).

The client wants cavity brick walls exposed both internally and externally.

The architect does not want to add a stud wall between the two leaves but is happy to have a 150mm air gap between the 2 leaves with 85mm air gap in some locations due to detailing.

The client is hoping for 7-7.5 star.

Whilst I have worked on plenty of projects with BV or cladding that have a stud for glass wool insulation, I have not had much experience with new cavity brick walls.

I am nervous to suggest blow in insulation without understanding the detailing required to avoid water wicking across the wall structure.

The architect was thinking to simply attach some rigid board insulation to the external side of the internal brick leaf but he wants advice from me about whether this is the right way to go.

I understand that foilboard is an option but can be fiddly to install.

Can you please advise about detailing insulation for this type of wall.

e.g. can the builders simply attach XPS or EPS rigid board, how do the wall ties fit in with this, how large does the air gap between the insulation and the external brick leaf need to be, reflective wrap or XPS/EPS with reflective side? are there any condensation issues to be aware due to the rigid board not being vapour permeable and the project being in Climate zone 6 etc etc.

TechLink Response:

• There are many ways to include added insulation into the cavity between inner and outer leaves of masonry.
• There needs to be an understanding of brickwork codes and standards with relation to the width of cavity.
• When cavities become larger than the 50mm nominal width there is a trigger to use special cavity ties.
• Any insulation in a standard cavity with standard ties must not compromise the possibility of water penetration to the inner skin.
• EPS and XPS board products may be used or hydrophobic bulk products like Knauf Superfil.
• Board products like Kingspan Kooltherm K8 Cavity Board and Foilboard come with a propriety masonry ties for the specific installation and specific manufacturers installation procedures. These may introduce slightly different block laying approaches that the block/brick layers will have to follow, involving staggered lifts rather than progressing both leaves of blockwork simultaneously.
• Options not limited to the following links provided as examples.
• https://www.foilboard.com.au/installation-guide/double-brick-cavity-insulation/
• https://www.kingspan.com/au/en/products/insulation/wall-insulation/kooltherm-k8-cavity-board/