How to fix drainage under replacement deck?

[Daz591]

Hello. I am in the process of repairing/replacing my deck due to rotting joists. Upon removal of some decking boards, I noticed that the original joist construction involves 100 x 50 joists with a sheet of gyprock/villa board??, then a 50 x 50 joist on top. This has resulted over time of debris and water building up around the smaller joists and causing rot. I am guessing the original builder has laid this gyprock in order to slow down rainwater drenching under the house and possibly flooding the garage during heavy rain. I am mindful that a low-lying deck should have ventilation, and it seems to me that this gyprock is preventing this and obviously catching not only water but debris, causing the rotting of the joists. I am of a mind not to replace this gyprock ( if that is what it is??). Any ideas?  Cheers...Darryl

[Daz591]

Hi Dave,

Thanks for the suggestion. I did have a look at that product. I think it's made in the States. Mixed reviews relating to pooling of water. It is also very expensive per square metre. Alot to think about.

Cheers

[Dave-1]

Afternoon @Daz591 

You could potentially use pond liner material that flows down to a wide gutter under your deck instead?

Dave

[Nailbag]

Hi @Daz591 

Your scenario I one that personally I would be treating very seriously. As such, I would be enlisting the services of a decent plumber and get the underground  water ingress sorted. Appreciating your desire to make this a DIY solution, long term this issue needs to be professionally rectified as it will come back to bite you. 

The external wall needs to be dug out and Blue-board sheets fixed to the wall and waterproofed. Suitable drainage needs to be installed with no reliance on sheeting under the deck as that in reality is a short term solution.

Nailbag.