Damp clay soil under house – should I take action?

Hi,

You mention clay underfloor, on a slope. Clay will normally have an underlying sandstone shelf at some depth, and I think water is seeping downhill on this stone, to you.

The first thing I would have said would be to put in bigger or more wall vents, but you have those. So that's step 1. An ag drain on the uphill side should help, if you can run it to a good spot. I had to do that at a previous house.

Permanent damp underfloor is never desirable in the long term, so I would say monitor it now, and if it persists, you could also put in some forced ventilation. You can get a wind driven extractor

Wind driven turbine system cost nothing to run and that is good for your pocket and for the environment

which I think is ugly, but you might have an out-of-the-way spot for it

Cheers

Thanks for the reply Geoff.

In terms of monitoring how frequently should I check on it - weekly, fortnightly, monthly..?

How quickly can timber start to suffer the ill effects from excessive moisture? - I don't want to obsess over it - nor do I want to be too relaxed about it either...

Hi,

Well, you want to be able to see a change for the better. If you put in an ag drain on the high side, it should have an effect pretty quickly, say after a month.

If you have not done that, and it is the same in a month or two, then you would probably be considering forced ventilation.

So have a look each month or so. Dry rot is a fungus which actually needs wet conditions. It would take longer than a month or two to develop from nothing.

Cheers

Originally Posted by DIYwannabe

Like many places in Australia we have had heaps of rain over the past year – the most since we have had the house – but none for about week. Should the soil have dried in that time?

Sorry I can't offer much advice re the underfloor ventilation, but I can say that when we removed our old garage slab from atop the clay soil, it hadn't rained for several weeks, yet by the time the bobcat had run over it a few times it became like a mire, so much so that we had to delay work for a week or so to let it dry out.

I guess the point I'm trying to make is don't underestimate the water retention of clay soil, so anything you can do to assist drying has to be helpful. Unfortunately *too* dry is probably not desireable either!

Thanks Geoff and Bloss.

Bloss you make a valid point about the ACT weather conditions.

I will take your advice and keep an eye on things but not stress too much about it.

Thanks again to all for advice - this forum is fantastic for such discussion.

Cheers