Flashing; Tangible Protection for Your Home

Over the years, I’ve inspected numerous dwellings in Costa Rica that had no protective flashing installed in conjunction with the roofing system and others where flashing had been installed, but incorrectly, using standard overlapping metal pieces instead of contiguous sheets of protective flashing.

In order to effectively waterproof dwellings, contiguous flashing needs to be installed underneath and outside of finished roofing and exterior wall covering materials. Depending on a dwellings structural design, flashing should consist of thin contiguous sheet metal, galvanized steel, aluminum, copper, zinc or membrane materials.

Some architects specify flashing materials such as copper, aluminum and stainless steel to compliment specific architectural designs. However, various metals eact chemically with cement and others such as aluminum react when in contact with steel nails. The appropriate materials need to be specified by a professional who understands how galvanic action between dissimilar materials causes premature deterioration of building products.

Once the appropriate flashing and fastening materials have been selected and fabricated, they should be installed by a tradesman, experienced with watertight joints and overlaps on roof openings, edges, ridges and valleys as well as exterior wall openings, angles and joints of building structures.

Wind-driven rain is common in Costa Rica, and to prevent water infiltration, flashings need to be tightly fastened with galvanized or aluminum screws or nails to exterior finishes and roofing surfaces. Furthermore, extra care needs to be taken to insure that the fasteners are not over torqued into the flashings, permitting water to enter where the fasteners penetrate the flashing material.

Additionally, we are less than twelve degrees from the equator here in Costa Rica and the ultraviolet radiation is intense. This ultraviolet radiation causes excessive contraction, expansion and deterioration of exterior building materials, including metal products. Successful flashing installations require extensive experience with watertight joints and overlaps of contiguous sheet metal as well as with the application of high performance adhesives, in order to adequately waterproof dwellings.

Metal flashing should be amply installed with expansion joints to compensate for thermal expansion and contraction from ultraviolet exposure. Moreover, some dwellings, with specific structural requirements need flashing made from waterproofing membranes such as rubber or plastic sheet material.

In order to achieve the most reliable installation, flashing should be custom made to fit each dwellings structural configuration and should be installed in the following areas to prevent water infiltration into the dwellings.

  • Openings – around protruding skylights, ventilation pipes and chimneys, before roofing is installed.
  • Roofs – in valleys, before the finished roofing materials are installed and on ridges and at edges after the finished roofing materials are installed.
  • Overhangs – behind gutters and under finished roofing materials to prevent wind-driven rain and accumulated water in gutters from entering under the roof and into the overhanging soffits.
  • Windows & Doors – under sills, thresholds and above jambs, before exterior siding and trim are installed.
  • Walls – at ground level and where upper walls meet roof structures, behind exterior siding and embedded into plaster, with drainage holes to permit any infiltrated water to flow out and away from the dwelling .

The most common water infiltration problems in Costa Rica are on the exterior overhangs, (soffits) of buildings,  where you can see watermarks running down the fascias and mold discoloration underneath on the soffits. This occurs because traditional local construction methods consisting of the exterior soffits (aleros), fascias (presentas), soffit ceilings (cielos), gutters (canoas), and downspouts (bajantes) do not properly drain rainwater from the roofs. When inexpensive traditional construction methods are used, the rainwater accumulates inside the gutters because they are too small or additional downspouts are needed to help drain rainwater off the roof. Without proper flashing installed where the back of the gutter meets the roof covering materials, there is nothing to prevent the excess water from entering inside the exterior roof overhangs and causing damage to the building materials as well as unsightly stains on the exterior surfaces.

Watermarks and mold occur from the lack of protective flashing materials in the following areas:

  • Behind gutters, under the edge of roof covering materials where no drip edge (borde de goteo) was installed. Rainwater rapidly fills the gutters and backs behind the gutters and into the soffits.
  • On the soffits between the finished roof materials and the top of the fascias when drip edge flashing has not been installed. Wind driven rain enters the soffits in the gap on top of the fascias, under the finished roofing materials.
  • On the ridges (cumbreras), under ridge cap materials that are too small, not fastened tightly or do not cover the ridge edges. Driving rainwater infiltrates under the ridge caps into the attic or interior ceilings below.
  • In the valleys, (limahoyas) under the roofing materials sitting on top of the valley gutter flashing. Water flowing down the roof enters the valleys with great force and if it does not drain away quickly, the water enters under the roofing materials and into the attic or interior ceilings.
  • Under decorative roofing materials such as clay tiles, when no protective sheathing or underlayment was installed. When the roof leaks without sheathing or underlayment layers below the finished roof surface, the water infiltrates directly into the attic or interior ceilings.

In many dwellings, the exterior overhanging eaves (aleros) are either open rafters that permit water to flow from the roof directly to the ground or they can be enclosed with soffits made of tongue and grooved wood strips (tablia), drywall products, cementious laminates, such as fibrolit or new plastic components that are now available. Traditional building materials like tablias, may not show signs of water infiltration for sometime because they are more durable, but eventually they become saturated with moisture and then the average homeowner will notice the deterioration.

Replacement of the fascias and soffits is inevitable without flashing installed or when flashing has been installed incorrectly. If caught in time, before serious deterioration occurs, repairs can usually be made.

On the upper eaves of a roof, where the roof surface meets the vertical walls that do not have soffits, flashing needs to cover the finished roofing materials and the edge of the wall to prevent rainwater from entering the gap where the roofing materials meet the exterior wall. If this area is not properly flashed, rainwater will pass underneath the roofing material, inside the walls.

Another vulnerable location of water infiltration is at the ridge caps (cumbreras), which are at the very top of the roof, (cumbrera) where the roofing materials meet at the peak. If the ridge cap flashings are not contiguous sheets, tightly fastened to compress against the roofing materials, rainwater flows underneath and passes into the attic or interior ceilings.

Furthermore, in the valleys, (limatons) where the intersection of two sloping roof planes  connect, a sufficient width of valley gutter flashing (limajolla) needs to be installed to prevent wind driven rain and water flowing down into the valley from entering under the roofing materials and into the dwellings interior ceilings.

Many times, fastening of the flashings is complicated by corrugated roofing products, manufactured to look like traditional clay tile (tejas). Before you purchase decorative roofing, you should consult with an experienced builder who can explain all that is involved with fabricating and installing custom-made flashings compatible with this type of roofing.

One solution is to install new drip edge flashing behind all gutters between the top of the fascia and the bottom of the roofing material. Another configuration of flashing should be installed on the upper edges of the roof as well as install wider and longer, (contiguous without seems), ridge cap on all ridges.

The average construction worker cannot properly complete flashing installations. Here in Costa Rica, the common flashing materials available from the local building suppliers are small and cut into standard sizes. These standard materials need to be overlapped and sealed with high performance adhesives, in order to create waterproof barriers that prevent rainwater from entering dwellings.

When installed correctly, custom fabricated contiguous sheet metal flashings will provide the homeowner with many more years of reliability. Proper flashing is made from rolled aluminum in variable lengths by custom fabricators who understand how to cut and bend metal to form waterproof barriers. It’s advisable to utilize the services of a metal flashing fabricator who also installs the finished product. This way, there is less room for error since the installer cannot blame the fabricator for flashings that do not fit tightly to the roofing and exterior finishes.

Only experienced tradesmen, who understand the characteristics of roofing systems and how to fabricate sheet metal flashing components, should be trusted to install flashings on your home.

Anyone who tells you they recommend applying silicone or other sealants to prevent water infiltration, does not understand moisture related problems and solutions. Silicone sealants can be used in conjunction with flashing to extend adhesion life, but not as a moisture barrier to prevent water infiltration. Exterior sealants applied to roofing materials and flashings dry out and crack prematurely, from the intense ultraviolet radiation here in Costa Rica. The cracks in the dried out sealants allow water infiltration in the gaps where they were applied.

Silicone type exterior sealants are a temporary bandage for a terminal problem. Properly installed sheet metal flashing is a long-term solution for water infiltration problems.

In Costa Rica, various building systems are utilized to construct dwellings. Concrete block construction has been a favored system for centuries. Modern frame construction, finished with synthetic siding or cementious laminates and plaster to seal the exterior walls has been widely used over the past few years. However, the modern frame method is extremely dependant on specific flashing materials with proprietary installation techniques that most local construction workers do not understand.

When constructing masonry walls, corrosion-resistant flashing should be installed:

  • Beneath the first course of masonry above finished ground level
  • Above the foundation wall or slab
  • At all points of structural support
  • On sills, angles, lintels and copings
  • When building with the modern frame method, flashing needs to be installed as above and in the following areas:
  • At the top, sides and bottom of exterior window and door openings
  • Where roof and wall structures connect
  • Behind wood or synthetic siding
  • Continuously above all protruding trim
  • Embedded in plastered walls

Furthermore, flashing should be installed on exterior installations such as porches, decks or stairs where they attach to wall and floor structures.

Dwellings constructed with masonry or plastered exterior walls, when traditional concrete stucco or synthetic products have been specified, require the installation of 3/16″ diameter weep holes, 48″ on center, in the following locations.

  • At the top of the foundation wall
  • On the bottom of window and door openings
  • At supporting points, angles and copings
  • Under protruding trim
  • Where roof and wall structures connect

If adequate flashing and weep holes are not harmoniously installed, the dwelling will retain moisture and eventually mold will accumulate on the exterior surfaces as well as inside the dwelling.

In order to maintain the exterior of homes here in Costa Rica, many homeowners are accustomed to cleaning and then painting over watermarks and mold. This has been an acceptable method of concealing water infiltration problems.

However, during the past decade, mold related illnesses have increased and some folks simply cannot tolerate the health related problems caused by excessive moisture in their homes.

If you find that the exterior of your dwelling or one that you are considering to purchase has watermarks on walls, facias or soffits, don’t hesitate to hire an experienced construction inspector to identify the cause and provide you with permanent solutions.

Some folks, in trying to save money, ignore these symptoms until they discover water infiltration inside the dwelling. By then it’s usually too late to avoid having to spend a lot of money to correct the problems. If you’re noticing moisture related problems on your home or are worried about new housing you’re considering to purchase, do yourself a favor; make Costa Rica Construction Inspector your first call, not your last resort.

The writer, Tom Rosenberger has lived and worked in Costa Rica for 23 years, inspecting land, homes, condominiums and commercial buildings for people who want to purchase existing property or build new construction.   With Tom’s detailed inspection reports, the homeowner can be confident that their dream home will be everything they imagined. Various Inspection Reports are available for your review at: www.costaricahomebuilder.com. If you would like to contact Tom you can send him an email at; tom@CostaRicaHomeBuilder.com.



Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s