Stucco – The Wrong Installation Leads to Severe Consequences

Your home purchase will most likely be the largest investment you will make in your lifetime. To protect your investment, you need to know that stucco over a wood substrate is prone to water penetration much more that traditional masonry such as brick or stone. Brick & stone have air spaces of 1-2 inches, “drainage planes” that allow moisture to escape through the bottom weep holes, thus keeping the wood substrate mostly free from wood rot. Stucco does not have a defined “drainage plane” thus allows water retention, creating wood decay in a very short time period. The smallest opening can result in a leak that can do severe damage. Typical leaks occur around windows, roof kick outs, vent openings, poor terminations, parapet walls, hidden gutters and on and on. The novice home inspector will not catch most of the installation defects & potential problems. Some problems are not self evident, and those that are can only be detected by a well trained inspector. At Smith Inspection Services, Inc. I can provide you with a full scope of services that include in depth reporting of defects, moisture testing & coring samples to confirm defects & give contractor names to give cost estimates & repair damaged areas. Since receiving my certification from EDI, Exterior Design Institute, I have made a pursuit to inform & educate my clients how to recognize poor construction defects & potential problems before they become the their problem. If you are a home owner call us today so we can find the potential problems to limit your repair cost. If you a prospective buyer call us today to schedule an appointment & discuss the risk & problems involved that are current or potential.

The pictures below are from faulty construction of stucco that led to severe damage:

Listed are necessary items for stucco to perform satisfactorily:

• Substrate which can be wood (plywood or OSB), gypsum board or applied over concrete block. These are typical substrates, but not inclusive. The substrate is designed to provide structural strength to the structure as well as the stucco. Most stucco manufacturers & some building codes (UBC – Uniform Building Code) highly recommend not using OSB which is prone to water absorption & retainage. Pictures above used OSB as the substrate.
• Weather barriers protect the substrate from excessive moisture penetration so that the stucco can drain the moisture before it absorbs into the substrate. Typical weather barriers are felt tar paper or Tyvek which has been proven to be affective. Weather barriers should be double layered to be most effective. Recommend 30# or 60# felt double layered.
• Metal lath should be a galvanized metal membrane that holds the cement plaster fastened every 6 square inches.
• Control joints are metal expansion joints that allow the stucco to shrink & expand from temperature changes. They should be installed at high stress locations & every 144 square feet.
• Weep screeds allow stucco to shed water along the bottom of the wall, “drain the plane”. Weep screeds should extend away from the foundation at least one inch so that the weather barrier can be seen from the bottom. Note: Enclosing the bottom of the bottom allows the water to pond along the bottom of the inside causing wood decay.
• Casing bead, backer rod & approved sealant are recommended around all window & door jambs that work similar to an expansion joint & help prevent water penetration & limit cracking of stucco.
• Flashing is recommended at headers & sills at all window, door, trim exposures & vent openings. Flashing should be 26 gauge sheet metal or non corrosive material. Flashing should be installed at all deck or balcony penetrations into stucco.
• Termination of stucco should be 6” above the ground soil & 2” above the paved areas with weep screeds installed.

**Not adhering strictly to manufacturers specifications & current industry building standards mostly likely will result in stucco failure & costly repairs. ASTM & Uniform Building Code are two of the best current industry building standards.

Stucco is a masonry product consisting of:

• Substrate which can be wood (plywood or OSB), gypsum board or applied over concrete block. These are typical substrates, but not inclusive. The substrate is designed to provide structural strength to the structure as well as the stucco. Most stucco manufacturers & some building codes (UBC – Uniform Building Code) highly recommend not using OSB which is prone to water absorption & retainage.
• Weather barriers protect the substrate from excessive moisture penetration so that the stucco can drain the moisture before it absorbs into the substrate. Typical weather barriers are felt tar paper or Tyvek which has been proven to be affective. Weather barriers should be double layered to be most effective. Weather barrier should never be rolled under at the bottom, but cut to allow draining.
• Metal lath should be a galvanized metal membrane that holds the cement plaster fastened every 6 square inches.
• Control joints are basically metal expansion joints that allow the stucco to shrink & expand. They should be installed at high stress locations (windows & doors) & every 144 square feet.
• Weep screeds allow stucco to shed water along the bottom of the wall, “drain the plane”. Weep screeds should extend away from the foundation at least one inch so that the weather barrier can be seen from the bottom. Note: Enclosing the bottom of the bottom allows the water to pond along the bottom of the inside causing wood decay.
• Casing bead, backer rod & approved sealant are recommended around all window & door jambs that work similar to an expansion joint & help prevent water penetration.
• Flashing is recommended above all window, door, trim exposures & gable vents. Flashing should be 26 gauge sheet metal or non corrosive material. Flashing should be installed at all deck or balcony penetrations into stucco.