Lecture 19 Flashcards
Two things to be considered for exterior envelope (food and walls)
Thermal aspects
Water
Purpose of thermal insulation
To slow the conduction of heat
Thermal resistance
Material effectiveness in resisting the conduction of heat
R-value
Thermal resistance
Higher R-value=
Higher resistance
Thermal performance of a building=
The sum of thermal resistances from all materials
Thermal bridging
Low thermal resistance penetrates the thermal barrier
Thermal bridging is reported by detailing _____
Thermal breaks
Dew point
When air cools bring in grow relative humidity to 100%
Humid rooms have a _____ dew point
Higher
More water vapor in an air mass= ________ vapor pressure
Greater
When air inside is warmer than air outside the vapor pressure moves
Outwards
Vapor retarder
Sheets of water resistant material to diffuse vapor
Vapor retarder is located on the ______ side of the building assembly
Warmer
Is a vapor retarder always necessary?
No
Opposite and cooler side of assembly from the vapor retarder must be “________”
Breathable
Designed so that any moisture that does pass can be turned to vapor
Why should multiple vapor-impermeable layers be avoided
They can trap moisture
Why are roofs more important to thermal performance than walls
Heat rises
Two roof categories
Low-slope roofs
Steep roofs
Pros of steep roofs
Drain quickly
Easy to repair
Minimum slope for drainage of a “flat roof”
1/4” per foot OR 2% slope
Most primary function of enclosure
Keep water out
Pressure equalized wall design
Wind pressures inside and outside neutralize themselves
Rainscreen
Protects the air barrier from exposure to the outdoors
