Deck Joist Waterproof Protection

If you're building a deck, which you want to last a long long time you've probably heard in some shape or form about protecting it from the forces of nature, especially water and moisture. There are several things that you can use such as stains and sealer, which can with very little money, extend the life of your decking but that is just the surface. What about the underlying structure that is holding it up? It doesn't make any sense that the decking would be in top condition a decade from when it was installed but the joists are rotting away underneath, making the deck a very unstable and unusable structure to be on if anything at all.

Just as you take care of the deck tiles that you walk on, you need to treat the substructure that is holding the deck there in the first place. Here are a few ways you can waterproof and treat your structure to stand much longer.

Why Waterproof Deck Joists

One of the first questions that arise is the fact that deck joists are already water treated so why do the same thing again? There are quite a few reasons why you should consider water treating your deck. First of all, The way that Joists are attached to decking, there are quite a lot of ways that there can be cracks, crevices, and other stress marks in joints between these pieces of lumber. Since these are on the underside of your deck, therefore they are very poorly ventilated meaning it can trap moisture and cause rot. 

Although the pressure treatment will protect the wood for some time, it will eventually give in to the moisture and water if it is not able to dry quickly enough. Trapped moisture, even if it is in treated lumber, will eventually give way to rot and cracking in the wood. 

It is also imperative to understand that treated lumber isn't actually just treated to the core, The pressure treatment only penetrates the wood to only a few inches. With larger joists and beams, that means the center is probably just plain old wood. But again, it's on the inside of the wood so why does it matter? It most definitely does. 

Your average long nails and screws that go into each joist provide many entrance holes that would take the water to the middle. Once the water reaches inside, it will cause the wood to rot quite literally from its core. This can even cause damage to the overall structure as one joist that expands or contracts due to heat will cause the entire structure to lose balance. 

How to Waterproof Deck Joists

There are many ways you can go on with waterproofing your deck joists. From the tried and tested good old method of using tar paper to the more modern flashing tape. You can even home remedy it by using some motor oil. There are just many methods that you can use depending entirely on what your budget is.

1- Tar Paper

Before there was that fancy joist tape, companies used to manufacture and sell Tar Paper. This is the tried and true method when it comes to protecting those deck joists and beams for many many years to come. 

This also happens to be one of the cheapest methods as a roll of 15lb felt tar paper is generally very inexpensive. The installation process is also relatively easy. With a staple gun, you attach the tar paper strips to the deck-facing edge of each joist. 

This basically serves as a waterproof barrier for the top of your deck joists meaning no moisture would remain or stay trapped in them.  

2- Deck Joist Flashing Tape 

Deck Joist tape was conceived and further manufactured for one purpose and one purpose only, that being sealing your deck joists.

These rolls of tape are very easy to apply with just a peel and stick process in these. They come in a variety of widths to cover your deck in single-width or even double-width applications. This tape covers not only the top surface but also the top inch or two of each side. As is with felt strips, the tape works as a moisture barrier, preventing water that collects on the tops of the beams or joists from penetrating into the wood. 

Read more: Extending Your Current Deck

3- Joist Caps

These are literal pieces of metal that protect your joists from water and rot. These metal caps are modeled around the edge caps that are used on roofs but are shaped to fit around the top of the joist. These come in many sizes and shapes to cover single joists or double-width joists. These caps provide a very strong barrier against water. Use a chop saw to cut them to length and to pop these on. Joints that come between joists and beams are protected with tape.

4- Seal Deck Joists

 In case you do not want to use tape or felt, then you should consider using a sealant on your deck joists.

For this, you would need to purchase a water-resistant sealant designed for decks. Before installing the joists you should coat each joist and apply an extra coat to the ends. 

Be aware that the sealant will not protect the screws or nail holes that are created when you install the decking and also, and this will also take significantly longer to treat each joist. 

While these are some of the methods you can use to water treat your deck joists, this is not an end-all and there are many more ways you can use to protect your decking. You can even have decking such as stone deck tiles which protects your decking from the top as stone tiles such as tanzanite stone tiles do not absorb any water.

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