Designing Spaces That Reflect You
joist caps for decks

How to Install Joist Caps for Decks [A Step-By-Step Guide]

Creating an outdoor area for your family to spend more time together can be one of the most fulfilling feelings in the world. With all of the preparation, planning, and physical development involved, it’s no surprise that homeowners are looking for helpful hints to make their decks last as they can. Today we will discuss joist caps for decks.

Unfortunately, many homeowners believe that materials like composite decking boards can permanently prolong the life of their deck. One reason this is misleading is that, while the deck planks themselves may not decay because of the elements, the wooden frame underneath them will.

Just as you’ll need to preserve the deck slats you’ll be walking on, you’ll also need to keep the joist caps for decks that support it all together. This guide will show you everything you need to know about joist caps so that your deck will last for many years to come.

What Is a Joist Cap for Decks?

joist caps for decks

Joist caps are metal caps designed to cover the post. Do you want metallic-protected joists without the stress of carving and cutting? Then you may want to consider joist caps. Depending on your preferred size and design, there are caps to fit single or double-width joists. 

Similar to the strength and durability of an aluminum coil stock, they supply an unbreachable barrier to moisture penetration. However, they are pricier than the other alternatives and have some disadvantages. Water can seep into the space between the cap and the joist, creating a moisture problem because of poor ventilation. 

If you want the best out of this option, install the caps correctly and tape the joints. Also, note that it works best when coupled with a hidden fastening system. The best part? The installation process is relatively easy. It is the perfect project for a DIY enthusiast.

Now that we know why waterproofing decks is crucial, how exactly do you do it? While there are various options, from the well-known tar paper to the relatively new flashing tape and the DIY method of old motor oil, for this article, we will focus on the conventional metal joist caps. 

Let’s dive in!

The Right Ways to Install Joist Caps

Using joint caps is one of the most cost-effective and efficient ways to keep rot and water damage from shortening the life of your deck. To effectively install them on your joists, follow the steps below.

1. Inspect Your Deck for an Overall Assessment

joist caps for decks

Like any other installation process, it begins with an inspection to get a lay of the land- what works, what doesn’t, and what needs replacement. There are a couple of boxes to tick in your inspection, such as: 

  • The Wood
    This is probably the most vital check as it lays the framework for the deck. You should check that it is still sturdy.

    Examine the ledger boards, beams, and joists beneath and above the deck, and check for holes or breaks in the wood. Inspect the surrounding area for sawdust and areas regularly in contact with water, especially the edges where joists connect.

    Feel for soft or spongy areas to detect decay or rot. If you find any defects, you may need to replace the affected wood before installing the caps. You can use a nail or screwdriver to check for decayed wood.
  • The Fasteners
    Check for loose nails and hit them back into place, or change them and tighten all loose screws. Inspect for rust or corrosion because they can affect the surrounding wood.
  • The Railing
    Everybody knows railings serve two functions; aesthetics and safety, with the latter being more important. Before you take on the assignment of waterproofing your joists, ensure your deck is safe and habitable.

    Unsurprisingly, according to the International Association of Certified Home Inspectors, there are more rail-related accidents than deck collapses. Apply pressure on the railing to check strength and stability. Check that the distance between the balusters is less than four inches apart to discourage children or pets from wiggling through.
  • The Lighting and Electricity
    While this is not as vital to the installation process, you might as well do a complete check. Inspect the electrical outlets to ensure no loose wires, keep all cords properly hidden to prevent tripping accidents, and install adequate lighting.

    Once the inspection is complete and you are sure the deck is in great shape, you can move on to the next step.

2. Purchase the Materials Needed

joist caps for decks

It is advisable to purchase everything you will need before the start of the project to prevent last-minute runarounds once the installation begins. The tools for this project include;

  • A long measuring tape
    This tool is important to measure the desired length of joist caps before installation. You may need varying measurements depending on the deck design, especially for awkward corners. 
  • A Chalk Liner
    An essential for any craft project, it will help make markings wherever necessary to ensure the caps are well-measured and laid.
  • A Tin Snip
    If you need to reduce the length of the cap to fit on a joist, tin snips are perfect. Once you measure and make a mark with the chalk liner, you can go in with the snips to get your desired length. They are handy and relatively easy to use.
  • A Hammer and Power Drill
    While most joist caps have adhesives, you will need a hammer and power drill if you plan to use Shadoe Track in the deck construction. For this project, you may want to consider a cordless power drill because it can drill holes, fasten as well as install screws and nails. Also, ensure to get fasteners compatible with the decking materials.
  • A Sander
    It is vital that the caps fit perfectly to eliminate the risk of trapping moisture underneath, and that is where a sander comes in. You can even out any rough joist surfaces and smoothen the edges. A cheaper alternative is sandpaper- it does the same thing but costs much less.

3. Clear Out the Area

It is always better to clean out the area before starting the installation. Clean the deck thoroughly to remove debris that may be stuck between the boards or above the joists. 

If you plan to fix the caps before the construction begins, ensure to smoothen the surface of the joist. You can also coat the wood with a liquid sealant before installing the caps for double protection- this will ensure that any moisture that seeps underneath the cap will not affect the wood.

4. Prepare the Materials

Prepare the Materials

Measure, mark, and cut the cap to your desired length. Measurements must be precise, especially at corners where the joist connects to the beam. Achieve this by snipping the cap using tin snips at the junctions. Next, set out the joist caps for the edges.

5. Start the Process

Remove the sticker on the adhesive and place the cap directly above the joists to cover the top surface and a bit of the edge. You can apply a bit of pressure to ensure it sticks. 

Protect the joints between the joists and beams with tape, eliminating the risk of water getting underneath the cap and causing problems. 

It’s advisable to install the caps first when using Shadoe Track. After installing the joist caps for decks, hand nail Track with galvanized nails. A hand-nailing system is preferred to a nail gun because it is more precise. 

When angling the decking, fix Shadoe Track sections between the joists above the ledger board to reinforce it. For double joists, fix a Shadoe Track on each side to fortify it. 

Once you have installed your joist caps, you can rest assured that your deck’s longevity and durability are ensured. Nevertheless, carry out regular inspections on your deck to make sure that there is no moisture or debris collection, rots, or defects.

Should I Use Joist Caps when Building A Deck?

Should I Use Joist Caps when Building A Deck

You may wonder, “deck joists are pre-treated, so why do they need extra protection? There are multiple reasons, and I am happy to share them with you. 

Firstly, there are numerous gaps and cracks in the connections between the deck and the joist, and they tend to collect moisture and rot because of poor ventilation. While the lumber is typically pressure-treated, with repeated exposure to moisture, it will eventually give way to decay. 

Another point to note is that the treatment does not reach the core of the lumber. And since nails and bolts penetrate the center, allowing the entrance of moisture, the wood can rot from within and affect the entire framework.

Deck Joist Cap for Deck Framing

Other Ways to Protect Your Deck Joists

Other Ways to Protect Your Deck Joists

There are numerous options for protecting your deck joists. You can protect the joists and beams on your deck by using joist caps for decks or one of the techniques listed below. Nevertheless, they are made to ensure that your joist caps for decks will be strong and rot-free for upcoming years.

  • G Tape
    G Tape tears quickly by hand, eliminating the need to fumble with cutters or multipurpose knives while wrapping a joist. It is weather-resistant and compatible with metals, timber, polymers, and glass when applied properly. Furthermore, after 24 hours, it creates a watertight bond.

    Another great advantage of G-Tape is that, despite being highly adhesive, it will not adhere to itself and can be relocated without losing grip. This enables you to keep job expenses down while avoiding the waste of entire pieces of flashing. Lift the tape, level out any creases, and re-flatten for a clear application.
  • Self-Adhering Flashing Tape
    This flashing tape is perfect for sealing joints, crevices, openings, and other unsightly gaps in exterior insulation systems. It is typically 25 millimeters thick and attaches completely to the substrate to avoid moisture from passing through and into the material.

    It is primarily made of long-lasting, cross-laminated, high-density polyethylene pieces. Furthermore, it is supported by a robust, pressure-sensitive rubberized asphalt binder.

    Overall, it is appropriate for use with timber, plywood, oriented strand panel, cement, and masonry. Lastly, it is available in rolls up to 75 feet long and widths of 4 to 9 inches to fit your project’s needs.
  • Non-Skid Butyl Tape
Non-Skid Butyl Tape joist caps for decks

So, in short

This membrane can be applied to both horizontal and vertical plank surfaces to protect against moisture and water leaks while also providing a stronger link for fasteners and screws.

It is extremely tacky but does not curdle like asphalt at high temps. It is also more adherent than bitumen membranes and sets more quicker than acrylic adhesives.

Tack-stapling may be needed to keep it in place in cooler temperatures, but the material will self-seal around certain penetration levels. Overall, this flashing tape was designed to protect ledgers and is suitable with all decking materials.

Many workers today will opt for a less expensive bitumen flashing. It will, however, dry out with time, lowering the efficacy of flashing.

Furthermore, the temperature is an important factor in selecting the correct flashing tape. Modified bitumen materials, on average, do not perform well in cold conditions. Most become less adhesive around 50°F and do not adhere well below 40°F.

High temps can also cause issues. Typically modified bitumen can spread at high temperatures, particularly when installed beneath metal that is directly in contact with sunlight.

The points raised above explain why traditional metal joint caps continue to be a viable option for deck builders. However, it is best to consult with a professional to determine which method is best suited to your requirements.

Final Thoughts but before you go …

While homeowners frequently focus on the appearance and prevention of rot on the surface of their decks, equal care ought to be given to the substructure.

Rain and snow settling between the gaps in your deck boards will eventually create a moist substructure. Any moisture that remains on the wood can cause harm over time.

The solution to this problem with deck boards is simple: seal the wood on a regular basis. This method, however, is not suitable for the supporting joists because the woods must be able to breathe and release moisture.

This is where the joist cap comes in handy. A properly fitted joist caps for decks creates a barrier between the joists and the deck boards, protecting your deck from moisture damage.


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