Information
Attic ventilation in a hot-humid climate.
Southwest Florida is not a Midwest attic. Heat and humidity sit on both sides of the roof. Vents only help when intake and exhaust are a system — and when they are not pulling rain into the house.
Information
Companion notes to the spray-foam page.
1. Climate Zone 1A / 2A, not the Midwest
Lee County and most of coastal Southwest Florida sit in IECC Climate Zone 1A or 2A: hot-humid. Attics here run extremely hot. Outdoor air is wet. Advice written for a cold, dry winter — “just add vents so the roof can dry” — misses that the incoming air is already humid and that wind-driven rain uses those same holes.
2. Vented vs unvented vs hybrid
| Approach | What it needs | Usual fit here |
|---|---|---|
| Vented attic | Clear soffit intake, ridge or high exhaust, insulation on the floor, ducts that can live in hot air or be sealed hard. | Most existing houses. Cheap if the soffits are actually open. |
| Unvented / conditioned | Air-impermeable insulation at the deck, soffits closed, mechanical ventilation of the house. See the foam page. | When the air handler already lives in the attic. |
| Hybrid | Thin foam at the deck plus other insulation. Vents usually close. | A designed mix — not “foam and leave the ridge open.” |
3. Soffit and ridge that actually work
Intake at the eave, exhaust at the ridge. Paint, insulation baffles that got crushed, and bird-blocked soffit strip kill the intake. A ridge vent with no intake just pulls from the house. Balanced net-free area matters more than adding a third turtle vent on the back slope.
4. Bathroom fans and powered attic fans
Bath and kitchen fans that dump into the attic are adding moisture to the hottest room in the house. Route them outdoors. A powered attic fan on a vented attic can pull rain and AC air through the ceiling plane. On a foamed, sealed attic it fights the assembly. Do not add one to “help” foam.
5. When “more vents” make a leak worse
Extra exhaust with blocked soffits pulls from the living space. Gable vents on a house that already has a ridge can short-circuit the path and leave the far slope dead. In a tropical storm, low vents on the windward wall are openings. More holes are not a moisture plan.
6. Read this next to the foam page
If the attic is going to be foamed, the vents close and the house needs a ventilation plan of its own. If the attic stays vented, foam at the deck is the wrong product. Do not mix the two from a sales pitch.
CGC1540882 · CBC059473 · CCC1330892 · CPC1458687
More notes