Water Intrusion in New Central Florida Homes During Hurricane Jeanne

Executive Summary:
In September 2004 Hurricane Jeanne struck Florida. Most of the damage in the Orlando and surrounding central Florida area resulted from severe water intrusion. The local Home Builders Association received over 1,000 complaints from new home owners involving water intrusion. The water intrusion was perplexing for several reasons. First, most complaints were from residents of newer homes. Second, in many cases there were no obvious reasons for the intrusion (e.g., roofing materials were not blown off, windows were not damaged, there was no surrounding flooding). Water, lots of water, seemed to just appear at the base of exterior walls inside newer homes. The objective of this research is to characterize what actually happened, to explain why it happened and to develop recommendations to reduce future water intrusion. To allow better focus, the scope was limited to:

• Recent construction – homes receiving certificates of occupancy in 2001 and afterwards.
• Stucco-clad masonry (1st floor) and frame (2nd floor) walls – the predominant building system in central Florida.

Several approaches were used to collect data:

• An extensive literature search was performed in the areas of masonry walls, stucco finishes, cracks, and water intrusion.
• Experts were interviewed to discuss findings and provide direction. 
• Homeowners were surveyed by telephone to learn more about their home and what they experienced during the storm.
• Home inspections were performed to learn more about affected homes.
• Selected elements of the construction process were observed to better understand workmanship issues.
• Field tests were performed on new and existing homes to measure the extent of water intrusion due to wind driven rain.

Survey results indicate that 20% of all new homes built in central Florida in 2003 experienced water intrusion related to walls during Hurricane Jeanne. A survey of homeowners that reported water intrusion revealed that:

• Although many builders experienced the problem, some builders were affected far more than their market share would suggest.
• Single and two story homes were equally affected.
• The vast majority of intrusion occurred on eastern walls, with some occurring on northeast and northern walls.

A follow-up inspection of these homes found a variety of possible causes including: poorly sealed windows, unsealed wall penetrations (dryer vents, plumbing, electrical, rain gauge, etc.), poorly sealed expansion joints, and numerous cracks of varying shapes and sizes. Findings from an earlier inspection study confirmed the prevalence of these issues throughout the central Florida new home market. This earlier study found that 50% of homes between one and two years old had significant stairstep cracking.

On-site testing was used to assess the relative importance of these factors. Testing of new homes (both under construction and occupied) revealed that stucco clad masonry walls without cracks did not leak, even without paint. Tests of homes that had leaked during Hurricane Jeanne demonstrated that cracks can facilitate water intrusion. Cracks did not need to be wide - cracks less than 0.39mm (1/64 inch) wide allowed water to penetrate the wall, run down and accumulate on the floor in one to two hours of simulated wind driven rain conditions. It is important to note that 57% of the cracks observed were wider than this, but could not be tested because they were not in a testable area of the house. It is also important to note that Hurricane Jeanne brought sustained winds of over 40 miles per hour with rain for a period of over 8 hours.

Given the prevalence of stairstep cracks in new central Florida homes and their propensity to allow water intrusion, the remaining analysis and recommendations focused on the cause, prevention and mitigation of water intrusion through stairstep cracks. The causes of the stairstep cracks observed are not obvious. No significant stairstep cracks were observed immediately after laying the block. However, after the cells were grouted and the roof was installed, numerous stairstep cracks were visible. There were no discernable cracks in the footings related to the stairstep cracks observed in the walls. No problems with soil compaction were found and the required rebar was installed in the footings. No significant stairstep cracks were observed immediately after stucco was applied. However, within one year after the homes were completed, 50% exhibited significant stairstep cracking. The most likely cause of stairstep cracking cited in the literature is differential settlement. However, the absence of discernible cracks in the footings casts some doubt on this explanation as the sole cause. A more likely cause of many stairstep cracks is shrinkage. A common cause of shrinkage cracks in masonry walls is using ‘wet’ or uncured concrete masonry units (blocks). When uncured blocks are used to construct a masonry wall, they continue to cure and experience a significant amount of shrinkage. Typical shrinkage in a 50 foot masonry wall range from 3.1 to 6.9 mm.

Recommendations are provided at two levels. Level I recommendations should be implemented immediately. They are believed to be low cost and high impact. Level II recommendations involve substantive changes to the construction process and should be carefully evaluated by each builder, possibly involving longer term testing.

Level I Recommendations
Level I recommendations should be implemented immediately. These recommendations are believed to be of low cost to the builder and high impact in terms of reducing the potential for water intrusion. Some of these recommendations merely restate existing code requirements and builders are encouraged to ensure that their subcontractors comply. Other recommendations have been suggested by others and have been successfully adopted by some builders. If adopted as a package, they should greatly reduce the potential for water intrusion through masonry walls.

Foundations: Ensure that site work for foundations meet code requirements as well as recommendations from the National Concrete Masonry Association (TEK 10-1A 2001).
“Footings should be placed on undisturbed native soil, unless this soil is unsuitable , weak, or soft. Unsuitable soil should be removed and replaced with compacted soil, gravel, or concrete. Similarly, tree roots and construction debris should be removed prior to placing footings.”

Step Down Ledge: Provide a step down ledge or seat for the concrete block approximately one inch below the slab to provide holding capacity for water that penetrates the exterior surface of the wall (Lstiburek 2005). 

Concrete Block: Age concrete block 21 days before use to permit early shrinkage before walls are constructed (TEK 19-2A 2004). Note that block will continue to shrink, but not as much – for example, 30% of block shrinkage will still occur after 9 months (Gulde 2006). Ensure that mortar ingredients are mixed in proper proportions.

Stucco: Ensure that stucco is installed to ASTM standard C926 for 2 coat stucco. The minimum two coat process starts with a 3/8 inch first (scratch & brown) coat followed by a 1/8 inch second (finish) coat. The first coat process includes densification with a hard float. This densification is critical, since the consolidation that occurs influences the shrinkage-cracking and water penetration characteristics of the plaster. The first coat does not require scoring. The first coat should be allowed to fully cure before applying the second coat (some experts have suggested seven days). This allows the first coat to provide the best possible substrate for the second coat, and allows the first coat to crack (if it is going to crack) before the second coat is applied. The second coat should cure for 28 days before painting. The stucco mix should be reinforced with suitable fibers to increase cohesiveness, tensile strength, impact resistance and to reduce shrinkage; ultimately reducing cracking (Melander 2003).

To reduce the risk of construction stress-induced cracking, roof tiles should be loaded five days prior to lathing installations and interior furring strips and drywall should be nailed prior to stucco installation.

Paint: Use a premium, high build, acrylic coating with the following characteristics:

• Meets Federal Specifications for resistance to wind driven rain (TT-C-555B).
• Allows water vapor transmission (high perm rating) permitting water to evaporate from the wall to the exterior.
• High flexibility/elongation to cover existing and new cracks.

Service: Near the end of the warranty period, repair all visible cracks and apply a second coat of paint. Cracks should be repaired with an elastomeric waterproof sealant patching compound. The method will depend on crack width and the sealant product, but might typically include:

• Less than 0.4 mm (1/64 inch) – apply a brush grade compound with a small brush.
• Between 0.4 mm (1/64 inch) and 0.8 mm (1/32 inch) – apply a knife grade compound.
• Between 0.8 mm (1/32 inch) and 6.4 mm (1/4 inch) – route out crack ¼ inch wide by ¼ inch deep; apply two coats of knife grade compound. 

Note that commercially available caulking compounds are not suitable materials for patching hairline cracks. Because their consistency and texture is unlike that of stucco, they tend to weather differently, and attract more dirt; as a result, repairs made with caulking compounds may be highly visible, and unsightly (National Association of Certified Home Inspectors 2006). http://www.nachi.org/stucco.htm

Encourage the homeowner to observe the repair process. Reassure them that most shrinkage cracking occurs over the first few weeks and most settlement cracking happens over the first year. Remind them that cracks are continuously moving with temperature changes, moisture content and shrinkage. Remind them that they must provide regular maintenance - identifying and repairing cracks - if they wish to minimize the risk of water intrusion into their home. Provide instructions for future maintenance of cracks.

Level II Recommendations
Level II recommendations involve substantive changes to the construction process and should be carefully evaluated by each builder for impacts on market acceptance, cost, building system, and the construction process. The evaluation may also involve longer term testing of viable concepts.

Foundations: Adding reinforcement to footings can lessen the effects of differential settlement on footings and thus reduce the incidence and severity of wall cracks (TEK 10-1A 2001).

Wall/Floor Joint Details: Investigate and consider alternatives for floor/wall joint details that promote water entry into home. For example, for architectural designs with block kneewalls and raised floor slabs, pouring the floor slab directly inside the wall into “h” blocks virtually guarantees that water entering the wall will flow down the wall, onto the floor slab and inside the home.

Crack Control Strategies for Walls: Crack control strategies seek to address the combined effects of movement due to drying shrinkage, carbonation shrinkage and contraction due to temperature change (TEK 10-1A 2001). Strategies use two related techniques: control joints and reinforcement to limit crack width. Control joints are vertical separations built into the wall to reduce restraint and permit longitudinal movement. Empirical rules have been developed to guide the location of control joints in masonry structures (TEK 10-2B). Normally, however, single family homes are not large enough to warrant the use of control joints (Graber 2006) and for low-rise buildings in most regions of the United States there are no provisions in the model building codes prescribing the use of steel reinforcement or control joints (NAHB Research Center 1998). If walls are longer than 40 feet, control joints should be considered no further than 25 feet on center (Graber 2006). Where lateral or out-of-plane shear loads need to be transferred across the control joint, a shear key spanning the control joint and composed of smooth dowel bars mounted in plastic sleeves will allow the walls to move longitudinally.

The standard horizontal joint reinforcement is 9-gauge wire in either a “ladder” or “truss”
configuration, available in standard lengths of 10 and 12 feet (NAHB Research Center 1998). Bond beams which serve both as structural elements and as a means of crack control are a horizontal course or courses of U-shaped masonry block into which the reinforcing steel and grout is placed. As the wall shrinks, the steel undergoes shortening, resulting in compressive stress (TEK 10-1A 2001). The surrounding masonry offsets this compression by tension. At the point where the masonry cracks and tries to open, the stress in the reinforcement turns to tension and acts to limit the width of the crack by holding it closed. The net effect is that reinforcement controls crack width by causing a greater number of smaller cracks. As horizontal reinforcement increases, crack width decreases. Smaller size reinforcement at closer spacings is more effective than larger reinforcement at wider spacings. Bond beams are typically presumed to offer tensile resistance to an area 24 inches above and below its location in the wall and horizontal joint reinforcement is usually placed in joints at a vertical spacing ranging from 8 inches to 24 inches (NAHB Research Center 1998). Graber (2006) recommends adding 9 gauge joint reinforcement every other course to help hold cracks tightly together.

Weep Holes:
Provide weep holes in the first course of block to allow water that does penetrate the exterior surface of the wall to escape (NAHB Research Center 1998, TEK 19-4A 2001, Bomberg 2006). Note that although the CABO, UBC, and ACI 530 building codes do not prescribe the use of weepholes or flashing, both BOCA and SBC require that weepholes be provided (NAHB Research Center 1998). BOCA requires a maximum spacing of 33 inches on center, and that they shall not be less than 3/16 inch in diameter. SBC prescribes maximum spacing of 48 inches on center, and that they shall be located in the first course above the foundation wall or slab, and other points of support, including structural floors, shelf angles, and lintels. Cotton sash cords (removed before putting the wall into service) and partially open head joints are the most common types of weep holes (TEK 19-4A 2001).

Several related provisions are useful to support the weepholes. First, mortar must be prevented from blocking the weepholes. This should be accomplished by ensuring that the masons minimize the mortar dropped into cavities and providing mortar collection devices (e.g., screens) at regular intervals as the wall is laid-up to disperse minor mortar droppings enough to prevent blockage (TEK 19-4A 2001). Secondly, pests must be prevented from entering the wall. This can be accomplished by inserting stainless steel wool into the openings or using proprietary plastic or metal vents (TEK 19-4A 2001). These concepts are summarized in Figure 66.

 

Flashings:
To better contain the water that does penetrate the exterior surface of the wall and direct it to the weepholes discussed previously, flashings should be considered (TEK 19-4A 2003). Perhaps the most critical unflashed location in current masonry construction is at the base of the walls. Flashing materials include sheet metals (stainless steel, cold-rolled copper and galvanized steel), composites and plastic/rubber compounds). Flashing should be longitudinally continuous or terminated with end dams. To attain longitudinal continuity, joints must be overlapped and bonded/joined to prevent water movement through the lap joint. Flashings should always be paired with weep holes, as described in the Level I recommendations. Typical flashing details for masonry walls are shown in Figure 67. Several proprietary systems are described in Appendix C. Challenges that must be overcome to design and install an effective flashing system include the handling of vertical grouted cells and assurance of consistent installation (Gulde 2006).

Alternative Building Systems: Alternative building systems such as cast-in-place concrete (Zoeller and Crosbie 2005) or pre-cast concrete panels may greatly reduce the risk of cracks and water intrusion associated with concrete masonry construction.

Recommendation for Homeowners
Homeowners should understand that stucco is likely to crack and that the homeowner isresponsible for ongoing maintenance of the home. Cracks should be repaired with an elastomeric waterproof sealant patching compound. The method will depend on crack width and sealant product, but might typically include:

• Less than 0.4 mm (1/64 inch) – apply a brush grade compound with a small brush
• Between 0.4 mm (1/64 inch) and 0.8 mm (1/32 inch) – apply a knife grade compound

Between 0.8 mm (1/32 inch) and 6.4 mm (1/4 inch) – route out crack ¼ inch wide by ¼ inch deep; apply two coats of knife grade compound.

Technical Reports & Papers:
Mullens, M., B. Hoekstra, I. Nahmens, and F. Martinez, Water Intrusion in Central Florida Homes During Hurricane Jeanne in September 2004, Report to U.S. DOE, University of Central Florida Housing Constructability Lab, August 2006. [Download Report]

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