Base Flashing: Essential Roofing Component

You know how hard it is to design and build buildings because you are an engineering student or an engineer.

The roof, and especially the base flashing, is an important part of building design that is often overlooked.

Base flashing is an important part of any roofing system because it prevents water from getting in where the roof meets vertical surfaces like walls or parapets.

Without the right base flashing, buildings are more likely to get water damage, which can cause major structural problems, lower property values, and expensive repairs.

In this article, I'll talk about how important base flashing is and how it fits into the field of engineering.

I'll talk about the different kinds of base flashing materials, how to install them, and how to keep them in good shape so that you can design and build buildings that are as water-resistant as possible.

Let's get started!

Understanding Base Flashing in Roofing Systems

Formal definition:

1. The flashing provided by the upturned edges of a watertight membrane on a roof 2. Any metal or composition flashing at the joint between a roofing surface and a vertical surface, such as a wall or parapet.

Base flashing is an important part of a roof system that is designed and put together correctly.

It is a type of roof flashing that is used to seal the joint between the roof deck and a vertical surface like a wall, chimney, or skylight.

Base flashing keeps water from getting in and causing other kinds of damage.

It also keeps water from getting through to the roof deck.

It helps keep water damage from happening where a roof meets a vertical wall and the roof goes from vertical to horizontal.

Base Flashing and Counter Flashing

Base flashing and counter flashing are both types of roof flashing that work together to keep water out of joints or as part of a weather-resistant barrier system.

Base flashing is put up along walls, skylights, pipes, chimneys, and other roof features that stick out.

It gets rid of water that is running down the roof's surface.

Counter flashing is put on top of base flashing and covers the top of other flashings, like step flashing.

It keeps water from getting into places on the roof like where the chimney meets the roof surface.

Counter flashing is usually made of galvanized steel, which is stronger and lasts longer than flashings made of aluminum.

During construction, it is important to put the counter flashing in the right place so that rainwater doesn't leak into the house along the base of the chimney.

In the first step of the installation process, a circular saw is used to remove about 1 inch of mortar from the joints to make room for a custom-made piece of flashing.

Counter flashing is cut by hand on the job site to make sure it fits perfectly.

You can put step flashing behind siding, but you can't put counter flashing there.

A lot of the time, step flashing is used with counter flashing.

Base and counter flashings aren't the only types of roof flashings.

Headwall, valley, and gutter apron flashings may also be used, depending on the project.

Importance of Proper Installation

Base flashing must be put in place correctly if the roof system is to last and work well for a long time.

The flashing must fit well with other parts of the roof, like the counter flashing, which goes above or next to the base flashing.

The purpose of counter flashing is to direct water away from flat surfaces and onto the base flashing.

Why Base Flashing is the Unsung Hero of Building Construction

Still hard to understand? Let me change the point of view a bit:

Are you sick of having to deal with annoying things like drywall, insulation, and electrical wiring when you build something? Well, we've got an answer for you! Don't worry about making your building watertight.

Just let water in and watch it slowly ruin all your hard work.

Trust us, you'll save time, money, and energy by doing this.

Who really needs base flashing?

Okay, that was just a joke made to look like a TV ad.

Now let's go back to the explanation.

Types of Base Flashing Materials

Base flashing is an important part of a roof system that is designed and put together correctly.

It keeps water from getting into the space where a roof meets a vertical surface, like a wall or chimney.

There are a few common materials used for base flashing, and each has its own pros and cons.

Metal Base Flashing Materials

Most base flashing is made of metal.

They are strong and last a long time, and they keep water out very well.

Some of the most common types of metal flashing used for base flashing are:

  • Lead: Lead is one of the oldest and most durable materials used for flashing.

It keeps water out for a long time and is easy to shape and put in place.

  • Copper: Copper is also a great material for flashing because it can be shaped, is strong, can be soldered, and is easy to work with.

It is highly resistant to the caustic effects of weathering and corrosion.

  • Aluminum: Aluminum flashing is light and easy to shape, which makes it great for roof flashing situations that aren't as simple.

But it doesn't last as long as steel flashing.

  • Stainless Steel: Stainless steel is a strong, long-lasting material that doesn't rust or get damaged easily in other ways.

It costs more than other types of metal flashing, but it does a great job of keeping water and other types of damage out.

  • Zinc Alloy: Zinc alloy is a versatile material that doesn't rust and is often used for base flashing.

It's easy to put up and does a great job of protecting against water and other types of damage.

Other Base Flashing Materials

For base flashing, you don't have to use metal.

You can also use other materials.

Among these things are:

Terne-Coated Copper is a type of copper that is covered with a mixture of lead and tin.

It keeps water out very well and is easy to shape and put in place.

Anodized aluminum is a type of aluminum that has been treated with an electrochemical process to make it more resistant to corrosion and wear.

It protects well against damage from water and other things.

Galvalume is a steel sheet coated with an aluminum-zinc alloy.

It is very resistant to water and other types of damage.

It is very strong and will last for a long time.

  • Rubberized asphalt: Rubberized asphalt is a flexible and durable material that can be used for base flashing in areas where movement is likely.

It protects well against damage from water and other things.

  • Butyl Rubber: Butyl rubber is a type of synthetic rubber that is very resistant to damage from weather and other causes.

It keeps water out very well and is easy to shape and put in place.

  • Polyvinylidene Fluoride: Polyvinylidene fluoride, also called kylar or hylar, is a type of plastic that is very resistant to damage from weather and other causes.

It keeps water out very well and is easy to shape and put in place.

Installing and Maintaining Base Flashing

Base flashing is an important part of a building's system for keeping water out.

If the installation isn't done right, water can get in and damage the structure.

To make sure the installation goes well, follow the steps below:

  • Clean and prepare the roof surface.

Remove any trash and cover the underlayment with a waterproof layer of felt or tar.

  • Cut and Install Flashing: Cut pieces of building paper and self-adhesive flashing to fit and install them in the right order (bottom, sides, always overlap any lower pieces).

It is important to fill any gaps with sealant and make sure the flashing is secure.

Flashing should be attached to the roof with roofing nails so that they are under the protection of the shingles.

  • Choose High-Quality Materials: Use high-quality materials that meet local codes and are right for the installation, such as vinyl or metal-flanged windows with drip-cap flashing or skylight kits that include flashing.
  • Regular Inspections: Roofs should be checked by a professional on a regular basis to make sure they don't start leaking.

Flashing leaks can cause a lot of water damage and mold growth because water gets into the building.

Maintaining Base Flashing:

Roof flashing needs to be kept in good shape to prevent water damage and leaks.

Keep your flashing in good shape by doing the following:

  • Regular Checks: Every spring, look at the flashing for thin spots or gaps along the joints.

Use a trowel to put a thick layer of roof cement on any thin spots or gaps along a joint.

  • Fixing Flashing: Use roofing cement or a patch made of the same material as the flashing to fix small holes or corroded spots.

If the flashing is badly corroded, take off a few rows of shingles and the old flashing and put on new flashing.

  • Get help from a professional.

Some repairs might seem easy enough to do yourself, but you need to know how roofing works to fix roof flashing correctly.

If you fix the flashing on your roof wrong, you leave your roof open to more damage.

Flashing before Brick or Stone

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Use cases

Used in:Description:
Buildings for living in:One of the most common places where base flashing is used is on homes. When the base flashing is put in correctly, the area where the roof meets the outside walls is watertight. This keeps water damage from happening inside the building. Base flashing is especially important in places where it rains or snows a lot, because that makes it more likely that water will get into the building.
Business Buildings:Office buildings, stores, and hospitals are all commercial buildings that need base flashing installed to protect them from water damage. Most of these buildings have flat roofs, and base flashing is needed to keep water from pooling on the roof and leaking into the building through the seam between the roof and the outside walls.
Buildings for Industry:Warehouses and factories, which are types of industrial buildings, often have big roofs that can be damaged by water. Water can damage the things inside a building if it gets in through the roof. This can be avoided by installing the base flashing correctly.
Government Buildings:Base flashing protects public buildings like schools, libraries, and government buildings from water damage. Also, installing the base flashing correctly helps keep the building's structure strong, making sure that it is safe for the public to use.
Multi-unit Residential Buildings:Apartments and condos, which have more than one unit, need base flashing installed to protect the building from water damage. Base flashing keeps water from getting into a building through the seam between the roof and the outside walls, where it can do a lot of damage to the inside.


In conclusion, base flashing might seem like a small part of building design and construction, but it is very important and can't be stressed enough.

Base flashing can protect a building from water damage and expensive repairs if it is put in place and kept in good condition.

But aside from the technical parts of base flashing, it's important to think about how it affects sustainability and the environment.

Engineers and builders can help make the world a better place by choosing base flashing materials and methods that are good for the environment.

Also, installing base flashing well requires a level of attention to detail and commitment to quality that should be used in all parts of engineering and construction.

Remember that it's the little things that matter the most.

Links and references

EPA's Moisture Control Guidance for Building Design, Construction and Maintenance:

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