Call us now ! Send us an email Saint Andrews RD Columbia United States

Back to Top

Call Us Today!
(803) 256-3022

3 Reasons for Mold Under Your Roof


Whether it's on the underside of your roof, eating away at the rafters, or nestled in the attic insulation, mold in your attic or roof space can give you a nasty shock. But before you make a plan for remediating the mold, you need to figure out how the moisture got through the roof and how you can keep it from happening again. Here are three reasons for finding mold on the underside of your roof or elsewhere in the attic.

1. Condensation

The warmer and wetter the air in the attic is, the more condensation can build up on the underside of the roof deck. Although condensation seems fairly harmless in most situations - such as on windows or milk jugs - it can be quite a destructive force in this situation. Once enough condensation has built up, it begins to saturate the roof deck until it's a great home for mold.

In addition to encouraging mold, this situation causes water damage to the roof deck itself. It can cause splitting and warping of the wood, rusting of the roof nails, and rot in addition to helping mold and even encouraging termites.

Some situations that factor into increased condensation can include:

  • Poor attic insulation (allows warmth to enter the attic from the home's living space)

  • Wet basement or crawl space (allows water vapor to work its way up to the attic)

  • Insufficient attic ventilation

  • Extremely warm, humid climate

  • Badly installed vent fans (such as the bathroom and kitchen fans; all fans should vent to outside, not into the attic)

If you suspect that your attic has too much condensation, you may need to increase the amount of ventilation, improve the insulation, or change the venting patterns to prevent a recurrence of mold.

2. Leaks and Flooding

A leak is probably your first thought when considering roof mold problems. And it's true that a leak can saturate the underside of the roof, as well as other nearby attic areas, with water until it's an ideal environment for mold. However, these leaks aren't usually just random failures of shingle integrity. If you haven't had a storm recently, the failure is likely to be due to:

  • Flashing failure around roof penetrations such as the chimney

  • Water trapped in place by an ice dam or a wet pile of leaves on the roof

  • Damaged flashing at edges, valleys, or other transition points

Clogged and flooding gutters can also allow water to infiltrate the roof in some instances. When a gutter is so full of debris that it backs up all the way to the fascia, water damage can ensue.

3. Pests

Animals and birds that make their home in your attic can do more than you'd think to encourage mold growth. For one thing, if they've made any holes to let themselves into the attic, you could have rain and snow blowing through the hole. And like humans, animals can raise humidity in their surroundings, encouraging condensation and reducing the effectiveness of vents.

However, it's their waste that's likely to be the largest problem. Common pests such as mice, rats, squirrels, opossums, and raccoons can excrete large amounts of urine and feces, which both have water content and can make the area a haven for mold growth. Bat guano and bird droppings can have a similar effect, increasing the ambient humidity and soaking insulation.

These three factors can all have a lot to do with why your roof and attic became moldy in the first place. Whether you need help increasing attic ventilation and insulation, replacing a moldy roof, or even just diagnosing how your roof deck came to have a mold problem, get in touch with Residential Roofing Services right away for your free estimate.

Residential Roofing Services
Columbia, Irmo & St. Andrews, South Carolina

Phone: 803-256-3022

Business Hours:
Monday-Friday 7 a.m.-5 p.m.