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Flashing Between Siding and Concrete: Explained

Are you tense about the water leakage from your living room wall? Well, you might be thinking about installing flashing as a solution. So, a lot of questions and confusion may arise in your mind. 

You must be thinking about how to use flashing between siding and concrete?

Flashing is arguably the most common solution for water damage. Especially for siding and concrete. However, not all siding need flashing. Moreover, there is a variety of flashing to choose from. Thus, you can’t just install one.

Now, you might still be wondering about flashing. Worry not, we’ve explained everything for you.

So, without a further delay, read on!

The Purpose of Flashing

Water can easily sit on top of the concrete and eventually get absorbed in the siding. This could lead to water damage. In the long term, plywood used under siding can rot

To combat this, some would prefer caulking as a solution. But it mostly cracks over time. Moreover, the mechanism of caulking stores the water inside. As a result, this backfires by causing more damage. 

Flashing is used between the siding and concrete. This helps in directing the water downwards. Thus, it won’t get stuck behind the stucco.

Things to Consider 

Before getting ready to install flashing, you’ll need some basic knowledge of this. Here’s the necessary information that you should know beforehand.

Types of Flashing Available

Let us start with the type. There are basically two types of flashing. Which are- 

Internal Flashing 

This flashing drains out the liquid from the inside of the masonry wall through weep holes. This type is mostly used for windows, doors, or window sills. 

Internal flashing is commonly made from metals like zinc, lead, or copper. 

External Flashing 

This prevents moisture from penetrating the wall where it meets the roof. Sheet metals that are very durable can be a good choice for this type. Other materials like bituminous coated fabrics, plastics, and waterproof membranes are also used. 

Now that we are all clear about the types. Let’s move towards our next part. 

Environmental Consideration

Naturally, humidity, extreme temperature, and other factors are different depending on geography. As using flashing is related to these, the environment should be an important consideration. Seal siding to concrete can also save you from rain and other calamities.

The difference between the average dew points of areas is also contrasting. Hence, consider the weather before choosing your flashing.

Which Siding Needs Flashing 

Siding is basically a shielding mechanism to keep your structures safe. Its purpose is to protect the house’s exterior from harsh weather conditions. Thus sidings are sealed to the concrete wall. 

They’re made of many elements like vinyl, wood, cement, or other composite materials. Some of the popular choices are mentioned below.

Wood Siding

Wood siding should never meet concrete.

It’s actually a pretty bad idea. Firstly, concrete is very porous so it leaks moisture. Thinset can eventually lead to a damp wall. Thus rotting the wood siding, leaving it vulnerable to insect attacks.

Aluminum Siding 

When aluminum siding meets concrete, the effects depend on the ingredients of the cement. Alkaline cement reacts to produce hydrogen gas. 

So in the long run, serious hazards like corrosion or cracking can happen. As mentioned before, concrete can easily leak water. Thus, the wetness can also be detrimental to the siding. 

Which Flashing Should You Use and Why 

So, you need to install the appropriate flashing for these scenarios. Let’s dive into flashing strategies and how to install them.

People usually install vinyl siding over existing aluminum sliding. In that case, installing PVC flashing is ideal. The PVC trim board should be topped with Z-flashing. You need to install it over and into the slab.

Critical spots like vertical surfaces and window trims, using head flashings. J flashings, on the other hand, are best for uneven edges and sealing joints. 

But about metal flashings, we wouldn’t suggest this. Because metals, by nature, are very fragile when in contact with water. Some get easily corroded, some take a while to. 

So installing metal flashings isn’t the best choice. 

Hopefully, you can now determine which kind of flashing you’ll need. Now, spare us some more minutes, we are almost at the end. 

Tips For Installing Your Flashing

Let’s move on to what you should keep in mind while installing flashing. Since the process is very finicky.

  1.  You need to have all the necessary measurements before starting. Especially of the siding and flashing.
  2. For wood siding, trim it into a minimum of ¼ inches (6.4mm). This way, you can insert the flashing in between. 
  3. Be very careful while inserting it. The flashing should be adhesively attached.  

You might be confused about which adhesive to use. But don’t worry my friend. We’ve picked some of the best adhesive recommendations below:

Product 1
Product 2
Product 3

Hopefully, now it’ll be easier for you to pick your adhesive. So, hurry up.

  1. Seal all exposed wood and end grain. Don’t leave the flashing open.

Voila, your flashing will finally be stuck on your concrete.


Question: Can you pour concrete against siding?
Answer: Sidings aren’t usually rated for contact with concrete. As concrete has this nature of absorbing and draining liquid through its pores. So, pouring concrete against siding can cause it to fail. 

Question: Does flashing go under siding?
Answer: This answer is basically situational. Though flashing mostly goes under the siding. But at times, it might be needed to install it on the exterior of the siding. 

Question: What is flashing on a house?
Answer: Flashing is a thin sheet made of water-resistant materials. It’s made to intercept the flow of water or moisture through a masonry wall. It is basically installed between the wall and the siding, intersections, doors, and windows. 

Bottom Line 

That was all that you should know before putting on your handyman cap. Now you can start your project of putting flashing between siding and concrete

Hopefully, you’ll do it without facing any kind of problem. 

Best of luck with your mission!