· by Michael Blair, Nashville's Roofers
Shingles age from both sides. The sun works on the top and a hot attic works on the underside, and in Middle Tennessee the underside is the one that gets ignored. A roof over a poorly ventilated attic can lose years off its life without any visible cause.
What balanced means
Ventilation works as a system: cool air in at the soffits, hot air out at the ridge. The usual guidance is roughly equal intake and exhaust area, and the common failure is plenty of exhaust with almost no intake.
Without intake, a ridge vent pulls air from wherever it can — often from the conditioned house through ceiling penetrations, which is worse than no ventilation at all.
How intake gets blocked here
Blown insulation pushed into the eaves during an energy upgrade is the most common cause, and it is invisible from inside the house. Baffles at each rafter bay prevent it and are frequently omitted.
Painted-over soffit vents are second. Several coats of exterior paint across perforated vinyl or aluminum soffit closes most of the free area without changing how it looks.
- Insulation pushed into the eaves with no baffles
- Soffit vents painted over
- Mixed exhaust types short-circuiting each other
- Bathroom fans discharging into the attic instead of outside
Do not mix exhaust types
A ridge vent plus powered gable fans, or a ridge vent plus box vents, can short-circuit. The fan or the lower vent draws air from the nearest opening rather than from the soffits, so the far end of the attic gets no flow at all.
Pick one exhaust strategy for a given attic space. Continuous ridge with continuous soffit is the most reliable on a typical Nashville roof.
How to check without a ladder
On a hot afternoon, put a hand near the ceiling of an upstairs room. A ceiling that is noticeably warm to the touch indicates an attic running far above outside temperature.
In winter, look for frost or damp on the underside of the sheathing, and for rusted nail points. Both mean moist house air is reaching the attic and not leaving, which rots decking and destroys insulation performance.