Dew point is the least useful and most confusing tool for understanding vapor control in architectural design, yet the
term is inescapable. Proposing alterations to a wall or roof assembly turns into a Where’s Waldo? game of locating the
dew point and figuring out where our changes might be moving it. But our real concern isn’t the location of the dew
point—it’s controlling condensation so our walls and roofs don’t rot.
Condensation occurs only where there is a relatively cool surface (think: cold beer, warm day) and, for that reason, there
are three – and only three – ways to control condensation: warm the condensing surface, prevent moisture (especially
moisture-laden air) from reaching the cold surface, or remove moisture from the environment.
In this presentation, Christine Williamson provides architects and architects in training with a more useful framework
for evaluating condensation risk in walls and roofs, giving them the tools to understand the risk level of a proposed wall
or roof assembly without ever having to run a dew-point calculation or hygrothermal model.
Learning Objectives:
- Describe the two primary concerns in building-enclosure design
- Describe the three approaches to condensation control in wall and roof design
- Articulate the connection between condensation control and the vapor permeance of building
materials
- Identify specific commonly proposed design changes to a standard cavity-insulated residential
wall that would make it more risky or less risky from a condensation-control perspective
Speaker:
Christine Williamson
@BuildingScienceFightClub
Christine Williamson has spent her career in building science forensics, discovering why buildings fail, and
working with owners, architects, and builders to remedy the problems. Her new construction consulting
helps architects use building science not only to mitigate risk of failure, but also to help them make their
projects as energy efficient as they are beautiful. She is the founder of the Instagram account
@BuildingScienceFightClub, an educational project that teaches architects about building science and
construction. She graduated from Princeton University and studied at Boston Architectural College before
completing her Master's of Architecture at New School of Architecture + Design. She is a member and past
chair of ASHRAE Technical Committee 1.12, Moisture Management in Buildings.
Moderator:
Agata Mancini
M.Arch., OAA Principal, Assembled Light