How to waterproof under deck?

[Bubbles8712]

 

 

 

We have a 5.0L X 3.0W X 1.7H deck which has an enclosed area underneath - except for the rain that comes from above!

I want to waterproof underneath the deck so I can have an additional storage space.

My thinking is to get 17mm polycarbonate sheeting and use 42 X 19mm H3 DAR Pine to help create a 1:10 fall across the length.

The deck has 13 joists. I’ll screw the 19mm pine underneath 3 of these joists, using spacers to help create a 60mm fall across the whole length. Photo below.

I’ll then attach the polysheets to the joists that have the 19mm pine screwed in. Then a gutter at the end to catch the water.

Questions

1. Is the 42 x 19mm H3 pine suitable to be used as described? It is quite cheaper than other H3 pine and want to ensure it’ll be okay to be damp for the most part of winter. The deck won’t dry much during winter.
2. Is a fall of 10mm every 1m sufficient? I’ve got about 60mm across 5m.
3. Any other recommendations?

cheers

[Nailbag]

Hi @Bubbles8712 the trays were custom bent on site by a roofing plumber running into again a custom gutter tray. The trays themselves are not fixed to or by the decking boards. Instead they are sitting on recessed yellow tongue flooring as per the photo. The trays are screwed into the side of deck joists, Then custom flashing sat over the joists/tray sides

The rubber strips on top of the joists are as @EricL rightly picked up is Protectadeck. 

This provided a waterproof seal from there decking screws as well as under-deck protection

This section of the deck extension was over what was too be a single carport. The more complicated one, was a pointed section. on the front of the house separating the deck on each side. I wanted to make a room underneath waterproof while removing the pointed one above. These photos will give you a better understanding how this task was achieved.


Divided deckPointed section demolishedNew wall installedTrays installedExternal custom guttering installedTray caps installedWIP

[MikeyDIY]

Hi @Nailbag sorry to hijack this older thread but this solution is genius (!) and I was wondering if you have more photos of the system? Or have you written it up online somewhere? I’d love to see how the guttering worked. Is the colourbond work limited to the trays, side flashing and guttering? sorry again and thanks in advance!

[Nailbag]

Sorry @MikeyDIY these are all the photos I have. I utilised the expertise of a roofing plumber along with a my draft-person to achieve the end result in providing my end goal, in what I needed to build myself in preparation for the plumber and be within building regulations as an owner builder. This was a very complex project and was fortunate enough to have a young but very experiences roofing plumber to work with. I had the vision, and they gave the experience I needed to pull it off. My recommendations would be to do the same mate.

regards, Nailbag