Roofing 101: Know Before You Go
Why not estimating enough material can cause trouble.
Measure twice, cut once. We’ve all heard this axiom and likely suffered from the consequences of not heeding it. Planning ahead is always helpful to avoid unexpected and unnecessary expense in the long run. The most important function when contracting work is getting the bid right. If you do not get this takeoff right, your poor aim will likely miss the profit goal. Such was the case for one roofing contractor whose inferior material ordering led to damaging mold growth in a condo complex. Unfortunately, mistakes like this can potentially cause more damage than the project is worth. Yet, with the emergence of data enabled solutions for the roofing industry, such as aerial roof measurement and weather verification, contractors are now able to use technology to make bidding construction projects easier and more accurate.
It all began when the contractor was hired to remove and replace a roofing system on a large multi-family complex built in the 1970’s. With the intent of replacing the deteriorated facia and gutters, the original gutters were removed in preparation for upcoming work. Unfortunately, the contractor didn’t order enough material to complete the project, so by the time the additional material arrived, rain had occurred which caused mold growth in several apartment units. Moisture readings were taken from the concrete slab at the perimeter and center of all the rooms resulting in high perimeter readings, yet normal central readings. In addition, drywall moisture readings were taken at various locations to compare against a baseline reading. Although the drywall moisture levels registered higher closer to the concrete floor, the levels were not considered high enough to promote mold growth. Wall studs, base plate and plaster were also tested with no abnormal readings.
Moisture was migrating into the building envelope through capillary action, and it was subsequently evaporating into ambient air. As the relative humidity rose, the drywall began absorbing some of the surface moisture to create a damp environment ideal for mold production. However, those areas of expressive mold growth on the drywall occurred not because of core drywall moisture but because of areas of lower surface temperatures. This allowed moisture to condense and hydrate mold spores.
The relationship between mold and surface temperatures means that the colder the surface, the higher the relative humidity. Solar radiation warms the exterior wall surfaces, creating temperature gradients from the exterior to the interior. Depending on temperature, air can hold varying amounts of moisture in the vapor state. Warming the interior wall surface, as it occurred in the second bedroom due to an increase of direct sunlight, allowed ambient air to hold more moisture. This prevented condensation on the lower part of the wall yielding no proliferation of mold in the second bedroom.
We then must consider the moisture’s point of origination. Where did it come from? The topography around the perimeter of this property is such that rainwater inevitably flows toward or bounces onto the building foundation. Rainwater can be deposited on the lower exterior portion of the building envelope because of splashback—rainwater bouncing off the ground adjacent to the building. Thus, it is imperative that rainwater from the roof be captured and diverted away from the building. Diagram A visualizes how rainwater can splashback against plaster and the foundation. The splashback is further exacerbated by capillary suction.
One of the single largest sources of moisture in conditioned spaces is the migration of moisture from the surrounding soil into foundations and subsequently into conditioned spaces within a structure.
Capillary suction refers to a major moisture transport mechanism which moves moisture into porous materials. Capillarity is a function of, among other things, pore size and available moisture. If the pore size in a material is small, such as in concrete, then capillarity is possible. Capillary water is drawn into the footing and then into the perimeter concrete slab. Once in the slab, the capillary water can evaporate into the interior of the building enclosure. Source control will best mitigate mold proliferation by minimizing the infiltration of water through corrective repairs. The following repair recommendations were provided to minimize moisture intrusion for the property.
- Replace gutters around the perimeter of the building
- Attach downspouts and properly divert away from the building
- Keep landscaping trimmed back from a plaster wall at the weep screen
- Keep sprinkler systems from directly contacting a plaster wall
- Construct a proper grade slope to divert water away from the building
SkyMeasure by CoreLogic reduces the mistakes. A property measurement service created by roofing experts that provides a new level of accuracy, simplicity and affordability. With SkyMeasure aerial roof measurement reports, contractors can be confident their numbers are right and that the correct amount of materials can be ordered every time.
Learn more about CoreLogic Roof Intelligence Solutions.
Guy Kopperud is an industry solutions principal in the Insurance and Spatial Solutions group of CoreLogic. Guy has worked in the construction industry since 1987 as a general and sub-contractor specializing in construction, building forensics and product development. Guy is responsible for providing industry technical and business-lens guidance for all insurance and spatial products at CoreLogic.
Guy has extensive knowledge with exterior cladding, roofing and fenestration systems. He has performed architectural testing and inspections on a vast array of buildings throughout the United States to determine the cause and effect of construction related defects. This experience has lead Guy to develop nanotechnology coatings designed to increase the energy efficiency of HVAC/R equipment as well as biological remediation of structures. Guy has since returned to the CoreLogic team in 2017, tasked with the growth and development of knowledge based thought leadership available to our insurance and spatial clients.