NZ 1950s weatherboard house – what would you do with this wall retrofit? Looking for practical advice
I’m renovating a 1950s timber-framed weatherboard house in Auckland and I’m trying to work out the best way to retrofit insulation to the existing external walls.
The house appears to have been built without wall underlay. The existing weatherboards are direct-fixed timber weatherboards, and I’m not planning to remove or replace the external cladding.
I’ve opened up one bedroom internally so I can see the wall construction. The wall is approximately 95 mm timber framing.
My original idea was:
- Remove the existing internal wall lining.
- Inspect the framing and bottom plates for moisture damage, rot and borer.
- Repair any localised timber issues.
- Install insulation into the existing 95 mm framing.
- Create some form of drainage/separation layer on the internal side of the framing.
- Install a suitable wall underlay/membrane on the inside of that separation layer.
- Reinstate the internal lining.
I’ve been looking at the BRANZ research around retrofitting insulation to older walls, particularly SR484, and the concept of creating a small drainage/separation space rather than simply filling the entire cavity with insulation.
The complication is that I have diagonal timber bracing in some of the wall cavities and the bottom plate also makes some areas difficult to detail. I may not be able to use exactly the same method throughout the entire wall.
What I’m trying to decide
Would you:
A. Continue with an internal retrofit using a drainage/separation mesh + internal wall underlay + insulation where physically possible?
B. Use a different method around the diagonal bracing/bottom plate and transition between the two methods?
C. Forget the internal cavity/drainage approach and use another insulation method?
I’m also trying to understand the consent/exemption implications in NZ, because I want to do this properly rather than assume something is exempt when it isn't.
particularly interested in hearing builders, building surveyors, or people who have actually dealt with older unlined/direct-fixed weatherboard walls.