Why does intake matter more than the ridge vent itself?

Because a vent cannot exhaust air it cannot replace. With inadequate soffit intake, the ridge vent draws its make-up air through the ceiling below — from the conditioned house — which pushes warm moist air into the roof space. That is the opposite of what it was installed to do, and it is a common finding when a new ridge vent makes a condensation problem worse.

Should intake and exhaust be equal?

Intake should be at least equal to exhaust, and slightly greater is preferred. The convention is a 50/50 split of the required net free area between low and high, with any imbalance biased toward intake. An excess of exhaust is the failure mode; an excess of intake simply means the roof breathes at the eaves.

Can I have a ridge vent and gable vents?

It is usually a mistake. Two high-level exhausts on the same space short-circuit: the ridge vent draws from the gable vent rather than from the eaves, and the lower half of the roof stops ventilating entirely. If a ridge vent is installed, gable vents are normally blocked off.

What is net free area and why is it less than the opening?

It is the effective open area after the baffles, filters and insect mesh inside the vent are accounted for. A product with a 50 mm slot might deliver a fraction of that as usable airflow. Manufacturers publish net free area per linear metre for this reason, and sizing against the physical slot overstates the ventilation by a wide margin.

Ridge Vent Linear Footage Calculator

Calculate the ridge vent material needed for a roof's ridge line, with waste allowance.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market

Imperial · sales tax

Schematic, drawn to the proportions you entered — not to scale on screen.

Who is doing the work?

Waste is set to 5% by hand. Pick a tier above to replace it, or keep your own figure.

Total Ridge Length (ft)

Waste Allowance (%)

Ridge vent needed

51.67 ft

High confidence

With the figures above, the ridge vent needed comes to 15.8 m. This is calculated for United States and cites IRC 2024. Building in another market? Change the selector above so the units and code reference follow.

Estimated cost — your price

Price per ft ($)

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

Total ridge vent = ridge length × (1 + waste allowance), the standard method for estimating continuous ridge vent material

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

Why does intake matter more than the ridge vent itself?: Because a vent cannot exhaust air it cannot replace. With inadequate soffit intake, the ridge vent draws its make-up air through the ceiling below — from the conditioned house — which pushes warm moist air into the roof space. That is the opposite of what it was installed to do, and it is a common finding when a new ridge vent makes a condensation problem worse.
Should intake and exhaust be equal?: Intake should be at least equal to exhaust, and slightly greater is preferred. The convention is a 50/50 split of the required net free area between low and high, with any imbalance biased toward intake. An excess of exhaust is the failure mode; an excess of intake simply means the roof breathes at the eaves.
Can I have a ridge vent and gable vents?: It is usually a mistake. Two high-level exhausts on the same space short-circuit: the ridge vent draws from the gable vent rather than from the eaves, and the lower half of the roof stops ventilating entirely. If a ridge vent is installed, gable vents are normally blocked off.
What is net free area and why is it less than the opening?: It is the effective open area after the baffles, filters and insect mesh inside the vent are accounted for. A product with a 50 mm slot might deliver a fraction of that as usable airflow. Manufacturers publish net free area per linear metre for this reason, and sizing against the physical slot overstates the ventilation by a wide margin.