Key numbers
19% of homeowners said improving energy efficiency was their primary reason for remodeling, per NAR's 2025 Remodeling Impact Report (National Association of Realtors / NARI, 2025).
| 10% | DOE says ducts in vented, unconditioned attics increase heating and cooling energy use by 10%. Source: U.S. Department of Energy, Building America, 2014 |
|---|---|
| $139 billion | U.S. homeowners spent $139 billion on improvements affecting home energy use in 2023, nearly four times the 2003 amount. Source: Harvard Joint Center for Housing Studies, 2023 |
| 40% | DOE says insulating window attachments can decrease winter heat loss by 40% or more and summer solar heat gain by up to 60%. Source: U.S. Department of Energy, 2024 |
Roof ventilation for most homes needs 1 square foot of net free vent area for every 150 square feet of attic floor, split evenly between intake low at the eaves and exhaust near the ridge. That is Owens Corning’s recommended ratio; the building code allows 1 square foot per 300 when the ventilation is balanced between low and high. For a typical 1,500 square foot attic, that is 1,440 square inches of vent at 1/150 (720 intake and 720 exhaust), or 720 square inches at 1/300 (360 and 360). The most common mistake we find in Colorado Springs is not too little exhaust; it is too little intake.
The math, step by step
- Measure the attic floor. Length times width of the space under the roof, not the roof surface. A 30 by 50 foot attic is 1,500 square feet.
- Pick the ratio. Divide by 150 for the recommended amount, or by 300 for the code minimum with balanced ventilation. 1,500 divided by 150 is 10 square feet.
- Convert to square inches. Vents are rated in square inches: multiply by 144. 10 square feet is 1,440 square inches.
- Split it. Half intake, half exhaust: 720 square inches each. Keep exhaust at or below half.
- Turn it into vents. Divide each half by the vent’s net free area rating.
| Attic floor area | Total at 1/150 | Intake / exhaust at 1/150 | Total at 1/300 | Intake / exhaust at 1/300 |
|---|---|---|---|---|
| 1,000 sq ft | 960 sq in | 480 / 480 | 480 sq in | 240 / 240 |
| 1,500 sq ft | 1,440 sq in | 720 / 720 | 720 sq in | 360 / 360 |
| 2,200 sq ft | 2,112 sq in | 1,056 / 1,056 | 1,056 sq in | 528 / 528 |
The 2,200 square foot row matches Owens Corning’s own ventilation calculator, which returns 528 square inches each of intake and exhaust for that attic at the 1/300 ratio.
Intake: the half people forget
Intake vents let cool, dry air in low on the roof. Options:
- Continuous soffit vents under the overhang, the most common choice.
- Individual soffit vents, which often fall short of the needed area.
- Roof-deck intake vents near the eave, for homes without soffits. Owens Corning rates its VentSure InFlow at 10 square inches of net free area per linear foot.
Use one intake type per attic, keep insulation off the vents with baffles, and check that old soffits were not painted or blocked shut.
Exhaust: pick one type and size it
Exhaust vents let warm, moist air out high on the roof: ridge vent, box vents, turbines or powered fans. A ridge vent gives the most even airflow on a gable roof. Whatever you choose, use one type per attic; two types on one attic can pull air from each other instead of from the soffits. Hip roofs with short ridges may need a mix of ridge and box vents to reach the number, sized together.
What we see on Colorado Springs roofs
- Box vents on the roof and no soffit intake at all, so the attic pulls house air.
- Soffits blocked by insulation, paint or new siding.
- A ridge vent added on top of old turbines.
- Bath fans venting into the attic instead of outside, which feeds winter frost.
On a reroof we fix these as part of the job, because the ridge and eaves are already open. For the symptoms that tell you something is wrong, see signs your attic ventilation is failing. Switching from wood shakes? Read ventilation changes when replacing cedar. For the rest of the roof, see what a roofing system includes and energy-efficient shingle options.
Integrity Roofing and Painting is veteran-owned and family-run since 1990, an Owens Corning Platinum Preferred contractor with 650+ Google reviews. Call (719) 488-2800, book a free Colorado Springs roof inspection, or see roof replacement in Colorado Springs.
Sources: Owens Corning, Proper Attic Insulation (1/150 recommendation, balanced 1/300), Roof Ventilation Calculator, VentSure InFlow intake vent and VentSure Rigid Roll instructions (no more than 50 percent at the ridge); confirmed through Owens Corning's search index because the pages render with JavaScript.
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