This is where we are hoping to tap into the collective brain power of all deck builders out there. Through trial and error and sharing ideas we can all up the quality of our builds, so if you have tips of your own to add please drop them on the comments section below.
You can lay a thin sheet of metal on top first, or an elastomeric or WRB membrane, so water that falls through the decking gaps is not left standing on the top of the joists. Reminder that when choosing that material and colour, be aware that it will probably be slightly visible between the gaps in boards

1) Cover your joists: As long as wood can dry, it’s okay for it to get a bit wet on occasion. The important thing to avoid is standing water. We are big fans of putting a drip edge on top of the joists before laying the decking so they may never even get wet, and if they do it is a matter of water running down the sides.

2) Gaps are necessary between boards for drainage, but also so they don’t build up debris. Too small a gap will let water flow until it clogs up with dirt, then it will hold moisture. Make sure the gaps are big enough that you can sweep it and the debris falls through. The thickness of the head of a deck screw should about do it.

Some builders install boards tight together for the aesthetic of tighter joints, running with the assumption that they will shrink, but that isn’t always the case. If the wood you are working with is quite wet it may stay the same size or shrink a bit, but if the wood is dry it may actually expand when exposed to regular rainfalls.

3) Don’t sink the screws too far into the decking or you will create tiny reservoirs where water will sit and soak in. Don’t count on the screw to pull your board tight, put some weight on it if need be and leave screws flush with the top surface so the wood can better shed water.
It’s a great look, but it can be more time consuming. And the downside is that you don’t have a lot of meat for the screws to hold unless you are using 2×4 or 2×6 decking. Take care not to drive screws too hard and strip the wood.4) Under-mounted deck fasteners: this one requires a bit more effort – a lot of people who choose this method seem to do so for the clean look of boards with no screws, in doing so it alleviates the problem of water damage at screw holes. To do this, a metal bracket is screwed to the side of the joist so you actually screw up into the bottom of the board and pull it down.

5) Double joists at the joints: there will always be a slight gap where two deck boards meet, allowing water to run down between them and sit on the top of the joist. A way to avoid this is to build your base with doubled joists with a gap between them. This takes more planning in design because you need to decide ahead of time where your joints will be and it takes a few more joists, but it can extend the life of your decking.
If you plan this well and order the right lengths of decking, you can reduce waste from cutting, and using longer lengths of decking can reduce the amount of double joists you’d need. The cut ends of wood are at a lot more risk of absorbing water, and if you look at an older deck you can see that it is the joints in the decking that are pretty much always the first parts to go.

7) When staining decks:
 if you are doing this in the autumn or the spring, first check the weather and the drying time of the stain. Written on the can should be the functional temperature range for application as well as how long it will take to dry. Make sure the weather isn’t predicted to go below the recommended temperature within the listed drying time.6) Diamond lath to keep out visitors: less than being about durability and more about quality of life, having raccoons or skunks set up a homestead under your deck is no fun; screwing diamond lath to the back of the deck joists and burying it should dissuade most animals.

8) Wood grain: if you work with the growth rings of the wood facing up in a convex (rather than concave) direction, the grain will in theory repel water from the surface rather than create a cup that will withhold water. Shedding water is the key to extending deck life.

9) Deck-to wall connections: this is where most jobs go sour. Either build a deck that is completely independent of the building (with Sonotubes near the wall connection), or go through the proper steps to not create a gaping hole in your building envelope that welcomes water, air, and carpenter ants, just to name a few of the unwanted invasions.

Once the exterior cladding has been trimmed away at the joint with the deck, there should be metal drip cap tucked under the original weather barrier that carries water clean over the edge of the rim joist that is bolted into the wall. Squares of self-sealing elastomeric membrane can be placed behind the joist in contact with the wall in order to avoid wicking of water through the hole created by the bolt.

10) Last but not least:  Don’t forget to factor a 2% slope away from other structures in order to drain water in the right direction. The base structure should set the slope, and the decking will simply follow the same angle.

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