Over the years, I’ve inspected numerous dwellings in Costa Rica that had no protective flashing installed in conjunction with the roofing system and other buildings where flashing had been installed, but incorrectly, using small metal pieces attached with silicone instead of contiguous sheets of protective flashing inserted into the exterior walls.
In order to effectively waterproof dwellings, contiguous flashing needs to be installed underneath and outside of finished roofing and exterior wall surfaces. Depending on a dwellings structural design, flashing should consist of thin continuous 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 react 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 surfaces. Furthermore, extra care needs to be taken to ensure 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 sufficient overlapping 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.
The most common water infiltration problems in Costa Rica are on the exterior overhangs, (eaves) of buildings, where you can see watermarks running down the fascias and mold discoloration underneath on the soffits. This occurs because the 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 adequate drip edge 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 eaves and causing damage to the exterior soffits (aleros) and fascias (precintas).
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 dwelling, 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 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 (botagua) 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 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 roof and exterior finishes.
The optimum flashing for the edges of your roof is a custom made gutter that overlaps the roof surface and moisture, bugs, bats or rodents cannot enter inside the soffit or under the roof deck.
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 that 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 dry 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 to prevent water infiltration inside dwellings.
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 cementitious 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.
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 Latino 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 issues in your home or are worried about a house 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 since 1993, 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.
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