Construction Design-Flashing Details and the International Flashing Awareness Day 2022

Late summer, 2021, Aron Jones ( on Instagram) and Gina Hoyt (bigdoglifex3 on Instagram) started the International Flashing Awareness Day to bring awareness to the importance of correct flashing details.  I participated by posting a failed assembly that was lacking correct flashing on my Instagram account.

This year the International Flashing Awareness Day is on Friday, August 26, 2022.  Instead of producing a quick post for Instagram, I decided instead to write a blog covering the subject of flashing in construction.

What is Flashing?

Let’s start with a definition from Wikipedia:

“Flashing refers to thin pieces of impervious material installed to prevent the passage of water into a structure from a joint or as part of a weather resistant barrier system.  In modern building, flashing is intended to decrease water penetrations at objects such as chimneys, bent pipes, walls, windows and door openings to make buildings more durable and to reduce indoor mold problems.”

Flashings prevent water from entering the joints, planned openings and penetrations along with changes in plane in buildings.  Most wood products are moisture sensitive, if they become wet and stay wet, they will over time deteriorate.  How much time will depend on the wood, Red Cedar can take a long time to decay while oriented strand board (OSB) can go quickly.  The key to the longevity of any structure is keeping it dry, and if it gets wet, giving it the ability to dry, or build without using moisture sensitive materials.  Rocks don’t care if they are wet.

Materials Used for Flashing

I’ve heard it said, the best materials are the ones that are installed correctly.  This insight can cure a lot of problems in the building industry, but it is especially important when dealing with flashing products.  The proper management of water is down, out and away.  Gravity will handle the down (as long as a material is sloped in the right direction), the flashings help to get the water out, and proper site design will move it away.

Me installing a sill pan flashing using tape.

Many flashings are made from some sort of metal.  Aluminum, steel, copper and lead are common and have been used, in some cases, for centuries.  Plastics are becoming common.  They are easily mass produced and cheap, but could have durability issues, such as UV radiation which can deteriorate the product or how they may become brittle in very cold temperatures.  Tapes in some instances work great, think window pan flashing.  Again, they need to be protected from UV radiation.  Fluid applied products along with caulks and sealants can be used in conjunction with other flashings to improve performance.  Even wood can be used if correctly protected and the design moves water away.

Effects of Improper Flashing Details

If you’ve been in the construction industry for any length of time, you’ve seen the effects of poorly flashed areas.  Often the first indication of a problem is water staining someplace inside the structure.  A roof leak causing water damage to a wall or ceiling.  Water staining around the interior side of windows and doors may be caused by improperly flashing at the top or head of the window or door.  I’ve seen siding falling off a home, removal of the siding often reveals deterioration of the sheathing or framing due to water damage behind the siding.  I’ve even seen mushrooms growing on wood siding due to water getting somewhere it shouldn’t.  Once the damage occurs, repairs can get expensive.

The Mushroom Incident.

Correctly repairing damage caused by improper flashing details usually means removal of the building component in the area of the problem.  The visible damage is often smaller than what is found behind the cladding, roofing or other finish materials.  If the damage affects the framing, structural repairs may also be required.  It’s much easier and cheaper to properly install flashings when building new than repair the damage caused by water getting into places it shouldn’t be.

Behind the Mushroom.  All caused by not using a roof edge kick0out flashing.  (To be fair, kick-out flashings were not well known when this home was constructed.)

Areas Requiring Flashings

A few of the areas that need flashing details were mentioned earlier, in reality, the list is endless.  Anyplace that water can get behind, through or around needs flashing.  This roof’s valley has what’s called a W-flashing.  When looked at from the end, the flashing looks like a W.  The high center rib is designed to slow fast moving water during heavy rain events from moving into the higher side of the valley as it moves down the roof.  Under this metal flashing is a back-up flashing, usually a self-adhered membrane called water and ice shield.

Another area on a roof that requires flashing details is any penetration through the roof material.  These penetrations include plumbing vents, vents for heating or ventilation equipment, attic ventilation boots, electrical masts, skylights and fireplace and woodstove chimneys.  Chimney flashings can become quite detailed.  This simple box chimney (below) has five different flashings.  There is a solid end wall flashing at the bottom and top edge of the chimney where chimney box meets the roof, step flashing along both sides of the chimney, one piece of step flashing covers each individual shingle where the roof meets the side of the chimney.  There is a counter flashing that covers both the end wall and step flashing, this counter flashing goes behind the stone veneer.  There is a cap flashing that protects the top of the chimney, this continuous square piece of metal covers the entire top and bends down over the top edge of the stone veneer with a slight bend to move water further away from the stone.  And then a pipe flashing where the chimney pipe exits the top of the cap flashing is installed to keep water from moving down alongside the chimney pipe.  (Neither the cap flashing nor pipe flashing were installed at the time this photo was taken).  That’s a lot of very important water management detailing.  If not properly installed, it could be years before an issue is detected, which may require some expensive removal of finished building materials to repair.

Another important flashing on a roof is the kickout flashing.  I mentioned it earlier, this is what it looks like.  It diverts water from where a wall meets a pitched roof.  A simple detail that is often overlooked.

Walls are other areas that require different flashing strategies.  Walls have planned or punched openings.  These planned openings are windows or doors, they may be a vent for a heating system or other piece of exhaust equipment, like a dryer or kitchen/bathroom vent.  There could be pipes that penetrate the wall, such as an electrical conduit, gas line or line set for air conditioning or heat pump equipment.  It’s important to keep water out of these holes in the wall.  This simple pipe (photo on left) seal is the inner most line of defense in keeping water (and air) out of the wall cavity.  The house wrap is then sealed to the pipe.  Depending on how the cladding is installed, there may be a wood, metal or plastic box that fits around the pipe, that box should be integrated into the house wrap to keep water from moving behind the box.  This can result in up to three different flashing to seal the penetration.

Window and door flashings are quite involved.  Most will have some sort of pan flashing in place, (photo of one being installed is above), before the window or door is installed.  The installation then requires integration into the water resistive barrier (WRB) or house wrap.  After the window is installed, a drip cap is placed over the head or cap of the window to prevent water from moving behind the window and into the window rough opening.  I often see this flashing omitted.  I believe the reason is many builders think the window flange is providing this protection.  Depending on the window manufacturer, there may be some protection, but their instructions will indicate the need for the head or cap flashing.  Once the head flashing is in place, the WRB then covers the upper leg of the flashing.  Lots of steps to protect one of the most vulnerable areas of a home.  The photo to the left shows how I managed windows in my home using a fully adhered WRB, basically the house wrap is a three-foot-wide piece of tape.  The home also features a rainscreen which further helps keep water moving down.

So, we’ve covered some of the flashing details for roofs and walls, how about wall to foundation.  The photo below shows an insulated concrete form (ICF) that meets a wood framed wall.  This home has a continuous layer of exterior insulation that planes out with the foundation insulation, but we still want any moisture that should find its way behind the continuous insulation a way to move out.  This metal flashing also protects the foundation insulation from UV degradation and damage from lawn care and weed whipping.  The top leg of the flashing, which is bent in a “Z”, is taped to the wall sheathing.


I’ve covered just the tip of the iceberg when it comes to flashing details.  It’s often difficult to think like water, but it’s what is needed when implementing an effective and long-lasting flashing strategy.  Caulks and sealants can work as a flashing, but someone has to maintain those products.  Often, it’s better to have a more durable product that requires less maintenance when deciding what products to use.

I have to commend Aron and Gina for their dedication and effort in educating both homeowners and contractors on the importance of this topic.  Also, a big thanks to Siga North America for their contributions to this year’s International Flashing Awareness Day.  Watch for Instagram posts from some of the industry’s best and brightest on August 26, 2022.  You can do this by following the hashtag, #internationalflashingawarenessday.

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