Caulking: What Should and Should Not Be Caulked on my Siding?

Tradition might have you thinking: “Caulk everything!” While caulking is indeed an overall important protective measure for your siding and home, “more” isn’t always better. What’s more important is focusing on “the where.” 

In fact, many newer siding systems, such as James Hardie fiber cement siding, don’t require caulking where you’d traditionally expect to see it. In this post we’ll outline some key locations and why and when they matter — and even introduce a few alternatives to caulking. 

Behind Your Siding 

During freezing and thawing, frost or condensation can gather on top of your sheathing (behind your siding, but on top of studs). Air circulation and a drainage plane is crucial here to keep things dry. 

Above Header Flashing

Anywhere there is metal flashing above a horizontal trim board you’ll want to leave 1/4″ clearance. However, you’ll want to apply a “caulking dam” in the corners. For example, with window trim, flashing will be at top, the caulking dam in the corners, and the sides and bottom of the window trim will be caulked to meet the siding.

Where Two Siding Boards Meet

Rather than caulking where two horizontal boards meet, siding manufacturer James Hardie recommends flashing behind the joint. For example, you can cut a prefinished aluminum trim coil into a square and place it behind the siding joint, where the siding meets with “nominal contact.” If water makes its way into the seam, the metal directs the water back out on top of the lap below it.

Bottom of the Wall/Wall Gaps

Sometimes homeowners want to use caulking to fill the gap at the bottom of a wall, where the siding overlaps the foundation. The most important thing when setting siding above grade is to maintain a 6″ clearance below the first row of siding. If your foundation line is less than the recommended six inches, metal flashing can help solve the issue. 

Remember, any water that gets behind the siding needs to be able to drain out the bottom. This is why it’s filling the gap with spray foam or caulking isn’t always the best choice. Instead, use aluminum trim coil, which allows for proper flashing — and also proper drainage and air circulation.  

What if Every Joint on My Home is Caulked?

There’s a chance everything is fine, but there are many variables, too. Keep your eye on siding that might be retaining water. Indicators of this could include siding that is swelling, cracking, or peeling underneath the laps. Any of these issues could be worth a close look. 

Another area to look for in wood siding is nails that appear oversunk. A common misconception is that the builder may have done this intentionally to ensure nails are embedded into the siding. Although this could be the case, more often than not it’s an indicator that the nail was fastened into a stud, and the wood siding is now swelling, beyond the nail head. If you are concerned with the condition of old siding, call a local expert. 

Keeping moisture out and air circulating properly are key to protecting your home from damage. Sometimes caulking is the answer, while other times flashing is a better alternative. Before you run for your caulking gun, always refer to your manufacturer’s installation manual, guidelines and specifications and, when in doubt, contact a siding expert.