Identifying Roof Condensation Damage: 4 Signs to Watch For
Roof condensation is one of several structural issues that can lead to severe damage if not addressed. Left untreated, it can compromise the entire roof structure. The primary cause? Moisture buildup. Condensation occurs when warmer air cools rapidly, creating moisture that collects in the roof’s internal layers.
During the day, the building’s roofing material—particularly dark roofing—absorbs heat from the sun, raising the temperature in the air cavity between the insulation and the roof. This area can reach temperatures 50 to 70 degrees higher than the rest of the building, increasing evaporation and drawing moisture into the cavity.
However, due to the insulation, individual roof cells (the space between the foil and plywood roof, often constructed of 2×4 sub-purlins) cannot properly vent and dry out. When the building cools at night, this trapped moisture condenses and seeps into the wooden roof members. This cycle repeats daily, worsening damage over time.
Roof Leaks – Water from roof leaks can easily enter the building, exacerbating moisture buildup and accelerating condensation.
Building Materials – Lumber used in construction often contains a moisture content of 19% or higher. If this moisture is not allowed to dissipate before insulation is installed, it can lead to excessive condensation within the roof structure.
Occupant Operations – Certain tenant activities, such as operating boilers, foam production, or bakeries, can introduce additional moisture into the roof cells. Additionally, tenants can unintentionally contribute to condensation issues by:
- Sealing vented skylights can trap moisture, causing condensation damage.
- Closing HVAC economizers reduces ventilation, contributing to condensation.
- Preventing ventilation at the roof line hinders moisture escape.
- Keeping the building closed up allows moisture to build up inside.
- Building full-height walls inside the structure can block airflow and increase moisture.
- Tenant-installed foil insulation or roof overloading can heighten condensation damage.
- Extended vacancies leave the building un-vented, leading to additional moisture buildup.
What to Look for When Roof Condensation Occurs
#1 Black streaks caused by iron in the purlin hangers.
#2 Gang nail plate stamped for trusses rusting above the old foil line. These plates are very thin and stamped when made, so they cannot withstand rust.
#3 Sub-purlin hangers. These are made from an aluminum alloy and do not rust like metal hangers.
#4 Black streaks caused by iron in the GLB (Glue-Lam-Beam) hinge connection.
Protect Your Roof from Condensation Damage with Saunders Seismic
If your commercial property shows signs of roof condensation damage, don’t wait to take action. Saunders Seismic specializes in diagnosing and repairing condensation issues to prevent costly repairs.
Contact us to discuss solutions that will help protect your building’s roof structure.