DPC for framing around a bathroom?

Question

I’m repairing rotted out sections of framing around our bathroom and there’s a strip of metal flashing underneath the bottom plate that’s significantly deteriorated and will be removed. I can’t find anything in the NCC about needing a DPC for interior walls or walls surrounding a wet area so I’m not sure if I should replace it with something like Plascourse or install the new bottom plate directly on the slab.

Note: mould remediation is in progress. Mould remover has been liberally applied multiple times, I’m being very heavy handed with it as I have a sensitivity to mould and want the active spore count as close to 0 as possible. The slab is stained and the cement board is going to be replaced.

JacobZ · Answer

Hi @ChaosDomain,

It's difficult to say with any certainty why a metal flashing was used in that particular location, especially without knowing exactly how the bathroom was originally constructed.

My best guess would be that it was simply the builder's preferred method at the time. Building practices and product preferences can vary considerably between builders and across different eras.

Aluminium dampcourse, such as this

https://www.bunnings.com.au/cagroup-230-x-0-45mm-x-10m-super-grade-aldamp-dampcourse_p1060332

is still available if you would prefer to use it instead, although the effect would be more or less the same as that of the plascourse.

With modern waterproofing membranes, your bottom plate should be well protected regardless of what material you use to create a barrier beneath the bottom plate.

Let me know if you have any further questions.

Jacob

ChaosDomain · Answer

Hi Jacob,

thanks for the confirmation that I was on the right track. Is there a reason why a different material would be used for the DPC around a wet area? The other side of the hallway is bedrooms and the DPC under that wall is Plascourse or similar.

JacobZ · Answer

Hi @ChaosDomain,

It's generally a good idea to have some form of barrier between the bottom plate and the concrete slab, even for internal walls. While the NCC may not specifically require a DPC in this situation, it can help prevent any moisture in the slab from wicking into the timber and causing problems down the track.

A product such as

https://www.bunnings.com.au/cagroup-150mm-x-30m-x-500um-plascourse_p1090521

is inexpensive, easy to install, and provides some additional peace of mind while you have everything opened up. Given you're already replacing the affected framing and carrying out mould remediation, I'd certainly be inclined to include a barrier rather than installing the new bottom plate directly onto the slab.

It can be adhered to the bottom of your bottom plate using some

https://www.bunnings.com.au/selleys-320g-liquid-nails-construction-adhesive_p1233751

before the bottom plate is fixed in place.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob