Thread: How achieve slope on a deck

Seems you have two issues here - the slope of the decking and preventing water running through to the enclosed area underneath.

1. To determine the slope simply transfer the level line at the wall (high) bearer/ joist/ ledger that the decking is to sit on to the outer bearer/ joist/ ledger position on the the posts then measure down the appropriate amount all the way around the outside (this will depend on the distance eg: over 3m span 20-30mm would be common). If there are no gaps between boards then you will need a greater fall, if there are gaps you can get away with less fall.

2. Even though the deck is covered you will get water ingress from rain pushed by wind. Depending how water resistant you want it to be you could use a complete layer of compressed fibre sheet screwed to joists and silicon sealed at edges with the boards laid on top. Or if the water only manages to get in part way from the edge you could use the sheet only to protect those areas.

Not a kosher way to do it, but for a cheap fix that would last maybe ten years or so you could afix a double layer of black builders plastic across the joists with staples and then place the decking over it. Without direct sun and UV exposure this will work quiet well, but of course if the membrane is damaged then water will go through.

I have used a layer of gal or zincalume sheeting screwed up under joists that were sloping to the outside so that any water that gets through the decking runs to the outer edge and off.

Bit hard without seeing your exact situation, but maybe these ideas will get you started.

Originally Posted by Bloss

Not a kosher way to do it, but for a cheap fix that would last maybe ten years or so you could afix a double layer of black builders plastic across the joists with staples and then place the decking over it. Without direct sun and UV exposure this will work quiet well, but of course if the membrane is damaged then water will go through.

I have used a layer of gal or zincalume sheeting screwed up under joists that were sloping to the outside so that any water that gets through the decking runs to the outer edge and off.

Thanks Bloss. They're good ideas as my original decking was laid flat and instead of planing all the joists or adding blocks to achieve the slope, I'm considering either of your 2 ideas. cheers mate
Larry

Half a carton of Brass Monkey Stout or a bottle or two of Margret River Red should put a good sort of a tilt on it for you.

Originally Posted by Cliff Rogers

Half a carton of Brass Monkey Stout or a bottle or two of Margret River Red should put a good sort of a tilt on it for you.

s'aright Cliff - use the empties to gauge the angle of the slope ...

Larry

Originally Posted by oseagram

s'aright Cliff - use the empties to gauge the angle of the slope ...

Larry

Compound angles on decking slopes can be troublesome - beero'clock best to celebrate completion not to work out what the angles are )

Two degrees sounds somewhat steep for a timber deck. The usual cross-slope on a roadway or bridge deck is 2 percent (not 2 degrees) for satisfactory drainage. Since timber is smoother than pavement, a flatter slope should work just as well, perhaps as low as 1.5 percent; this works out to 0deg 50min. Such surfaces are usually measured as percent instead of angles, because that's how they're best laid out anyway. With such a flat slope, the compound-angle effect will be almost negligible, and a touch with a belt sander should be sufficient for butted joints, and not needed at all for mitred joints.

Joe