Reply To: Dampness in a brick house, ventilation systems

[Ian McChesney]

Hi Alex
Very interesting…and challenging. Re the house location – you mention an ‘uphill side’ – is the house on a hill, or largely on the flat butting against a hill? You mention there is no underfloor access, but is there space to get underfloor if there was access?

I ask this because it might be that the dampness is also caused by evaporation from the damp underfloor area – if polythene groundsheet and underfloor insulation were able to be installed this could resolve some of the issue. Regardless, getting a hole cut in the floor to access the underfloor area (e.g. through the bottom of a wardrobe), even if it is just for inspection, in the overall scheme of things is a relatively low cost action to give a better understanding of the situation.

Re the solid brick wall, rising damp and DPC. One sign to look out for re rising damp is whether there are any watermark lines around 600-900mm from the ground, which is around the limit of capillary rise. It’s probably fair to say that even if DPC was installed it has deteriorated, or other building practices may have compromised the damp course (e.g. internal plaster walls that bridge the DPC). I’ve reverted to my UK Energy Advice Handbook, since this is a more common situation over there – they suggest injected damp proof courses. The UK practice appears to be drilling a series of holes through the mortar and injecting a silicon based material that laterally spreads, thus providing a damp-proof layer. There is a useful video on YouTube showing how it works:

Whether this is available in NZ/Dunedin I don’t know.

Anyway, I think your systematic approach around drainage, and extract ventilation is good. These things should be done first – although coming into summer it might be hard to judge how effective they are. Regarding a log burner and/or ventilation system. It might come down to how the place is currently heated. But a log burner has the ability to provide great heat output, and a drying effect, so this could be good.

In the UK positive pressure ventilation systems are being recommended for dampness situations (but not as a substitute for good heating, and not necessarily in preference to balanced pressure systems….the source I have is a few years old which is when PP systems were prevalent). They will blow some pretty cold air in the winter and evenings though (i.e. a negative heater!). Re whether PP ventilation or balanced pressure would be best – I suspect that it is the air change effect of the ventilation per se, not anything to do with the positive pressure, that provides the benefit. Balanced pressure systems provide the extra benefit of heat exchange.

good luck
Ian

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