Attic ventilation rules for Florida homes sit in Section R806 of the Florida Building Code, Residential. The current edition is the 8th Edition (2023). Here is what each part asks for.
| Section | Requirement |
|---|---|
| R806.1 | Enclosed attics and enclosed rafter spaces need cross ventilation for each separate space, with openings protected against rain |
| R806.2 | Net free vent area of at least 1/150 of the vented space |
| R806.2 exception | 1/300 is allowed when 40 to 50 percent of the required vent area is high and the rest is low |
| R806.3 | At least a 1-inch gap between insulation and roof sheathing at the vent, and nothing blocking airflow from eave vents |
| R806.5 | Unvented attics are permitted when all of its listed conditions are met |
What ratio does the code require?
Section R806.2 of the Florida Building Code, Residential sets the minimum net free ventilating area at 1/150 of the area of the vented space. Net free area is the open area air can actually pass through after screens and louvers. It is smaller than the outside size of the vent, so use the rated net free area printed on the vent's label or data sheet.
When can the ratio drop to 1/300?
The exception allows 1/300 when the vents are split between high and low. At least 40 percent and no more than 50 percent of the required area must come from vents in the upper part of the attic, within 3 feet of the ridge or highest point measured vertically. The rest must sit in the bottom third of the attic, which in practice means soffit vents.
The split matters because hot air leaves at the top and has to be replaced by air coming in low. A roof with lots of ridge vent and painted-over soffits does not meet the exception, even if the total vent area looks generous.
How do I size vents for my attic?
Work from the attic's square footage, which on a single-story house is close to the ceiling area below it.
| Vented attic area | Net free area at 1/150 | Net free area at 1/300 | High vents at 1/300 (40 to 50%) |
|---|---|---|---|
| 1,500 sq ft | 10 sq ft (1,440 sq in) | 5 sq ft (720 sq in) | 2 to 2.5 sq ft |
| 2,000 sq ft | 13.3 sq ft (1,920 sq in) | 6.7 sq ft (960 sq in) | 2.7 to 3.3 sq ft |
| 2,500 sq ft | 16.7 sq ft (2,400 sq in) | 8.3 sq ft (1,200 sq in) | 3.3 to 4.2 sq ft |
These figures are our arithmetic from the code ratios. Your permit drawings or inspector may measure the vented space differently on complex roofs.
What does R806.3 say about insulation?
Where eave or cornice vents are installed, the code says insulation, blocking and bridging must not block the free flow of air. It also requires at least a 1-inch space between the insulation and the roof sheathing at the vent. Blown-in insulation pushed tight to the soffits is a common way to lose intake air, so baffles at each rafter bay keep that channel open.
Are unvented attics allowed in Florida?
Yes. Section R806.5 permits unvented attics when all of its conditions are met, such as keeping the attic inside the building thermal envelope. A typical example is air-impermeable spray foam applied to the underside of the roof deck.
In a 2026 ruling on a new Orange County home with a spray-foamed unvented attic, Florida Building Commission staff said the attic is governed by section R806.5, per declaratory statement DS-2026-030. Staff also said R806.5 does not require dedicated supply and return vents in that attic.
There is a warranty side to this decision. The Owens Corning standard shingle warranty lists damage caused by improper or inadequate roof ventilation, unvented attics, or enclosed roof rafter assemblies among the things it does not cover. Check your shingle maker's terms before you seal an attic under a shingle roof.
Do solar attic fans help?
They lower attic temperature more than they lower your bill. The Florida Solar Energy Center tested two photovoltaic attic fans on an occupied 1,045 square foot home in Cocoa. The results from FSEC's photovoltaic attic fan study:
- Peak attic air temperature dropped by an average of 22 degrees F.
- Air conditioning use fell by about 6 percent, or 2.8 kWh a day.
- Estimated annual savings were about 460 kWh, worth roughly $37 at the energy prices of the time.
- The authors put the payback at over twenty years.
The test home already had a radiant barrier. The authors said savings may be larger in homes without one, with less ceiling insulation, or with the air handler in the attic. The same paper notes that line-powered attic fans often draw 250 to 300 watts, and earlier research found that draw can exceed the cooling savings. Solar fans avoid that because they run on their own panel.
We install solar attic vents. Treat them as a comfort upgrade for a hot attic, not a fix for missing intake vents.
Should ventilation be fixed during a reroof?
A reroof is the easiest time to add soffit intake, cut in ridge vent, or remove mismatched vent types, because the deck is open. Your permit office decides which code provisions apply to your job. Even where nothing forces a change, poor ventilation is a warranty exclusion on shingles, so it is worth correcting while the roof is off.
Read our Florida Building Code roof requirements guide for the deck nailing and secondary water barrier rules on a reroof, and how long a roof lasts in Florida for what heat does to shingles. For a reflective option, see cool roofs and reflective shingles in Florida.
Hot upstairs rooms or a sweating attic? During a free roof inspection we count the soffit and ridge vent area and compare it with the code ratio.
Sources
- 2023 Florida Building Code, Residential, 8th Edition, Chapter 8, Section R806 roof ventilation
- Florida Building Commission declaratory statement DS-2026-030 staff analysis, unvented attic under R806.5
- Florida Solar Energy Center, Performance Assessment of Photovoltaic Attic Ventilator Fans (FSEC-GP-171-00)
- Owens Corning Standard Product Limited Lifetime Warranty, Pub. No. 10023873-I (August 2026)
