Air Infiltration and Acoustics
This domain pairs two performance topics that share a root cause: leaks and sound paths both follow gaps. Questions ask you to interpret air leakage results, choose the right acoustic rating for a noise source, and explain why field performance differs from the laboratory.
Air infiltration
- ASTM E283 is the laboratory air leakage test, run at 75 Pa (about 1.57 psf) differential pressure. Results are expressed per unit of frame area or crack length and are compared against the NAFS limit for the performance class.
- Leakage paths: weatherstrip compression, sash locks and multi-point hardware, corner joints, weep and drainage paths, and the gap between frame and rough opening.
- Real buildings add stack effect, wind and mechanical imbalance, so the installed air barrier continuity at the frame perimeter matters as much as the product rating.
- Air leakage carries moisture; exfiltration in cold weather wets the wall cavity.
Acoustics
- ASTM E90 measures laboratory transmission loss; ASTM E413 converts it to STC; ASTM E1332 converts it to OITC, which weights low frequencies more heavily and suits traffic and aircraft noise.
- Field ratings (ASTM E336, expressed as NIC or ASTC) always fall below laboratory STC because of flanking and workmanship.
- Improvement levers: mass (thicker or laminated glass), a wide sealed airspace, dissimilar pane thicknesses to avoid coincidence dips, laminated interlayers for damping, and airtight frames.
- Gas fill contributes little acoustically; gaps and flanking paths can negate an expensive glazing upgrade.
Worked example
A hotel near a highway complains about traffic noise with an STC 32 unit. Reasoning: traffic noise is low-frequency dominated, so OITC is the better selection metric and the STC number was misleading. The fix combines a laminated inboard lite, asymmetric thickness, and a careful check of perimeter sealing and flanking through the wall. Expect a modest improvement of a few decibels per change, not a dramatic jump, and verify with a field measurement rather than relying on the laboratory label.
Traps that cost marks
- Selecting glazing on STC for aircraft or traffic noise instead of OITC.
- Assuming air leakage ratings predict field airtightness without a continuous air barrier.
- Believing argon fill improves acoustics appreciably.
- Ignoring that a slightly open sash or missing gasket destroys acoustic performance.