Your Ridge Vent Can't Work Without This: Metal Soffit Intake, Explained
Ridge vents get all the attention. They're visible, they're a discrete product, and they're easy to point at.
But a ridge vent is an exhaust. Exhaust without intake is a straw with your thumb over the end — and the intake, on almost every building, is the soffit. Get the soffit wrong and the ventilation system you paid for doesn't function, no matter how good the ridge detail is.
Here's how to spec metal soffit so the whole assembly actually works.
Why Intake Is The Half That Gets Shorted
Attic and roof-cavity ventilation works on air movement: cool, drier air enters low, warms, picks up moisture, rises, and exits high. Continuous flow, driven by buoyancy and wind.
That only works if air can get in. Undersize the intake and the exhaust starts pulling air from the easiest available source — which is often conditioned air out of the building interior through ceiling penetrations. You end up drawing warm, humid indoor air into the roof cavity, which is precisely the opposite of the goal, and it shows up as moisture problems people then blame on the roof.
Intake should meet or exceed exhaust. Not the other way around.
Net Free Area — The Number That Matters
Ventilation isn't measured in how many vents you installed. It's measured in net free area (NFA): the actual open area through which air can pass, after subtracting everything the perforation, screen, and material take away.
A panel that looks open may have far less NFA than one that looks solid but is properly perforated. Marketing photos are not a specification. Use published NFA figures.
SpeedLap 16" Full Vent provides 15 square inches of free area per linear foot. That's the number to calculate with.
Running the Calculation
General practice under the IRC uses one of two ratios. Your local code and building official govern—confirm before you spec.
1/150 — one square foot of ventilation per 150 square feet of ventilated space
1/300 — the reduced ratio, permitted where specific conditions are met, including balanced distribution between upper and lower vents and, in many cases, a vapor retarder
The working method:
Calculate the ventilated area in square feet.
Divide by 150 (or 300 where permitted) to get required NFA in square feet.
Multiply by 144 to convert to square inches.
Split it — typically half intake, half exhaust.
Divide the intake requirement by the NFA per linear foot of your soffit panel to get required vented linear footage.
Example: A 2,400 sq ft ventilated area at 1/300 needs 8 sq ft of NFA, or 1,152 sq inches. Half of that is 576 sq inches of intake. At 15 sq inches per linear foot, that's roughly 39 linear feet of Full Vent soffit — noticeably less than most eaves offer, which is why mixing vented and solid runs is normal rather than a compromise.
Verify the ratio and any conditions with your local building official before ordering.
The Three SpeedLap Configurations
All SpeedLap soffit is 29-gauge Grade 80 steel, cut to order, in smooth and textured colors that match your AG Panel or other roofing profiles.
16" Full Vent
15 square inches of free area per linear foot. Maximum airflow. Use it where you need intake volume.
16" Center Vent
Targeted ventilation. Vented area concentrated in the center of the panel, solid at the edges. Useful when you want a consistent soffit appearance across the building while controlling how much of it is actually open — and where a fully vented run would over-ventilate or where you want visual continuity between vented and unvented areas.
16" Solid
No ventilation. For eaves where you don't want intake at all: over a garage you're keeping sealed, in fire-rated conditions, in areas where wind-driven rain or snow intrusion is a genuine problem, or where the roof cavity above is unvented by design.
The point is that these are mixed on a single building. A well-specified job runs Full Vent where intake is needed, Center Vent for controlled airflow, and Solid where ventilation shouldn't happen — all in the same color, all reading as one continuous soffit.
Where It Goes Wrong on Real Buildings
Blocked intake. Insulation stuffed into the eave is the classic. Perfect soffit, zero airflow. Baffles exist for this reason.
All-solid soffit under a ridge vent. More common than it should be. The exhaust is then pulling from wherever it can.
Counting vents instead of NFA. "We put soffit vents in" isn't a calculation.
Unbalanced systems. Exhaust exceeding intake creates negative pressure in the cavity and pulls conditioned interior air upward.
Mismatched color. Not performance, but it's the one the customer notices. SpeedLap runs in both smooth and textured colors specifically so it can match the roof profile exactly. Order it together.
The Condensation Connection
Ventilation is one of the three levers on moisture in a metal building — alongside controlling the source and putting a barrier between humid air and cold panel.
Ventilation alone won't solve condensation in a post-frame building, because it depends on the outside air being drier than the inside air, which isn't reliably true. Pair it with Zero Drip on the roof panels and you've addressed the problem from both directions.
The Spec Checklist
Calculate required NFA from the actual ventilated area
Confirm the ratio with your local building official
Split intake and exhaust, with intake meeting or exceeding exhaust
Convert intake NFA to linear feet using 15 sq in per foot for Full Vent
Mix Full Vent, Center Vent, and Solid to hit the number
Verify baffles keep insulation clear of the eave
Color-match to the roof panel and order together
Frequently Asked Questions (FAQs)
Why is soffit intake just as important as a ridge vent?
A ridge vent functions as an exhaust and cannot properly release warm, moist air without adequate cool air entering through the soffit. If intake is insufficient, the system creates negative pressure, pulling conditioned interior air and moisture from inside the building into the attic.
How do I calculate the required Net Free Area (NFA) for my roof?
Calculate the total ventilated area in square feet, divide by 150 (or 300 if permitted by code), and multiply by 144 to convert to square inches. Divide this total equally between intake and exhaust, then divide the intake requirement by the NFA per linear foot of your soffit panel (e.g., 15 sq in/ft for SpeedLap 16" Full Vent) to find the required linear footage.
What is the difference between Full Vent, Center Vent, and Solid soffits?
Full Vent: Offers maximum airflow (15 sq in/ft of free area) for high intake needs.
Center Vent: Provides targeted airflow concentrated in the center for a consistent appearance while controlling intake volume.
Solid: Has no ventilation and is used for non-ventilated eaves, fire-rated zones, or areas prone to wind-driven rain/snow intrusion.
Can I mix different soffit panel types on the same building?
Yes. You can combine Full Vent, Center Vent, and Solid panels across eaves to hit your precise NFA calculation. Because they share the same profile and color options, they maintain a continuous, uniform appearance around the entire building.
What are common mistakes that cause soffit ventilation to fail?
Common mistakes include blocking eaves with attic insulation (which can be prevented using baffles), installing all-solid soffits under a ridge vent, estimating ventilation by counting vents instead of calculating published NFA, and under-sizing intake relative to exhaust.
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