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Siding flashing

Not having proper flashing can create a variety of dry rot and deterioration to the plywood beneath your siding materials. Common siding flashing problems can begin with the absence of having kick-out flashing.  Kick out flashing are placed in areas where a roof plane meets a wall surface and it channels water away from the building or siding and into the gutter.   According to the International Association of Certified Home Inspectors  (Inter NACHi), the bottom seam of the kick out flashing must be water tight and the angle of the diverter should  be less than 110 degrees. Additionally, the height of the kick out must be a minimum of 6, though some manufacturer guidelines permit 4 inches, which can reduce effectiveness.

Flashing can be defined as a strip of metal or flexing tape used to stop water from entering any gap or junction between two surfaces or intersections.  Flashing is absolutely essential in any home or building since it prevents major leaks and deteriorations, mold, and structural damage. Flashing is usually layered with other building materials. Flashing is commonly seen on roofs, sidings, windows, gutters, and skylights and there are many types of flashing to choose from. Flashing options include aluminum, copper, lead, rubber, galvanized steel, synthetic tape (flexing tape), and PVC.  These materials all have their own benefits and drawbacks and come in different widths while they can all be cut and bent as necessary. 

Common Issues | Flashing

Another common issue is improper sill flashing.  Sill flashing is plastic flashing that slopes away from the opening so that any water that gets behind the siding won't collect under the window and cause moisture issues.  If the sill flashing is not properly flush with the window opening, it won't perform properly. 

A few common issues in window flashing is the absence of Z flashing. When z flashing is not used above trim pieces, water can “sit” on top of the trim and can damage the wood trim and penetrate the wall cavity. Z - flashing is  tucked in beneath wall cladding and sits above the trim piece. The exposed edge of the z flashing catches the water running down the wall at the top of the window, allowing to flow away from the wall

When it comes to windows, flashing can take the form of a membrane or special wrap. However, it's important to note that not all window flashing wraps are alike,  especially  the installation methods used between commercial or residential complexes and single family homes. If, and in some unavoidable cases no matter how effective siding is at keeping moisture away, when,  water enters and travels behind the siding at the window, it will logically travel down the wall due to the slick house wrap layer and reach the window. Water will go through the smallest of holes and into the wall cavity causing water leaks, mold, and other deterioration. Therefore, it is important to use the correct flashing and wrapping technique.

Note: image displays sill flashing on a new construction window opening

Window flashing 

A common flashing problem is an absence or poor installation of step flashing along walls. Step flashing is L-shaped flashing pieces that attached to roofing shingles along the ridge interfaces between a roof and vertical side wall.  The step flashing works by creating water barrier transition between the wall drainage plane onto the roof drainage plane. If there is no or inadequate step flashing,  interior water leaks, rot and other deterioration can occur to the plywood behind roof and siding.



Another problem is valley flashing.  Valleys are created where two roof slopes meet. There are two types of valleys, opened and closed. You see open valleys when you notice a flashing at the slope, and you see a closed valley when you don’t see any flashing.  These valleys are important in channeling water where there is a change in roof  or slope direction. Moreover there is also "V" flashing and "W" flashing.  In V flashing, problems are more likely to occur when water runs down the slope and reflects off the ridge of the flashing metal, causing it to move up towards the other merging slope and beneath the roofing shingles. This can ultimately create roof leaks. A solution to this problem is to install "W" flashing. W flashing has a raised channel at the center of the flashing to prevent water reflecting to the other side and getting beneath the roofing shingles. 

Pipe collars flashing problems occur where the rubber gasket makes contact with the pipe. Here any cracks will allow water to drip down the pipe into your attic and eventually further below that. Having a properly sealed pipe collar can avoid water leakage issues. Other flashing issues that share common issues is Apron flashing, which is flashing located at the juncture at the top of a sloped roof and a chimney, bay window, or porch. Another flashing issue are Metal pans which are installed below every window and door to collect and direct water that may leak through back out to the exterior.  Flashing issues in these other components can result in water leaks that can cause deterioration.

Roof flashing

Window wrap is another issue if not careful. Improper techniques are usually the culprit when it comes to window wrapping. For example, the window opening through the house wrap has a bottom flap that should be draped into the opening and stapled to the sill. Additionally, any openings in the window wrap should be sealed with flashing or synthetic tape. This window wrap will be the very last line of defense against moisture.  Furthermore,  Flashing tape should go over any nailing, sill, top flashing, and house wrap near the window. This flashing tape will be the first line of defense against moisture. Without this flashing tape, the existing window wrapping is more vulnerable to water intrusion and indoor leaks.


The best way to use window flashing properly is to follow the manufacturer guidelines or use a contractor who is very familiar with the manufacturers specifications. 

Any exterior trim work has horizontal trim at the bottom of each house story line. A typical problem in vinyl siding flashing, when the siding rests on top of the trim above doors or windows, flashing is needed to create a leak-resistant barrier between the piece of vinyl and the horizontal trim. If there is no flashing, water would channel down the vinyl siding and meet the top of the bare trim. Water would then find any small holes or cracks and then flow behind the board. This can cause indoor leaks or begin to rot the trim, sheathing, and other interior components.

Gutter flashing

Yes, gutters can be affected by improper flashing too. Any shingles extending from the roof should extend over a metal drip edge, roof apron or flashing.  This image above has no drip edge. A drip edge protects your shingles and helps protect your fascia boards since water runs around your shingle edge and can penetrate your fascia, OSB boards leaving it to rot. Having a weak fascia due to water exposure can reduce the strength of the fascia board to hold your gutters in place. Adding a simple flashing/drip edge can prevent this problem from happening. 


Quick fact: A house more than 15-20 years  will likely not have a drip edge installed. This component is somewhat new in the building industry.

Note: Image displays window wrap (synthetic tape) on a new construction project after window installation

Window tape wrapping

This image has a drip edge, however it was not properly installed, the fascia board it was meant to protect still ended up deteriorating. Though the image above is an extreme case scenario, it is still possible for it to happen to you in the long run.  Having a metal wrapped fascia board can prevent the fascia board from rotting in case water sliding down from the edge comes in contact with the fascia board. However, in some instances having a metal fascia increase the incentive to not have a drip edge at all.  Additionally, sometimes metal fascia’s are uninstalled incorrectly. Metal fascia’s need to keep in consideration in how the roof plane slopes and how each fascia board overlaps with the other. For example, if a bottom fascia board overlaps a fascia board that is at a higher slope, when water makes contact with the fascia it can travel down the overlapping edge and get trapped behind the metal fascia board and cause significant rot to other wooden components since it will be harder for the water to escape a metal wrapped fascia board. 

Drip Edge: a minor object with critical influence
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