We reduced air leakage and thermal bridges by replacing our through-roof plumbing waste piping vent system with a combination of air admittance valves (AAV) and a two-way, filtered outdoor valve. Oregon’s plumbing code recognized AAVs, but restricted their use to 3 per house and required one through-roof vent. On appeal, the City of Portland allowed us to install AAVs according to manufacturer’s guidelines so we could eliminate all through-roof vents, using the “alternate materials and methods” provision through its Alternative Technology Advisory Committee (ATAC) process.