A vapor barrier is a barrier that reduces the rate that water vapor can move through a material. There is discussion in the industry if a true vapor barrier is even possible. This has led to the use of the term Vapor Retarder. Vapor retarders limits moisture from passing through a materials and have three classes of permeability. Vapor Retarders per the building code have a permeability of less than 10, less than 1, or less than .1 perm.
There are three categories of vapor retarding materials: Impermeable, Semi-Permeable, and Permeable. Impermeable materials include things such as plastic sheets, vinyl wall coverings, plywood, extruded polystyrene, and oil-based paints. Semi-Permiable materials included expanded polystyrene and latex paints. Most other materials are Permeable including fiberglass insulation, open cell spray foam, drywall, and stucco.
In our mixed-humid climate, we want to avoid using impermeable materials in our wall and roof systems. Allowing walls to dry in both directions is critical to the long-term durability of your structure. To further protect your home, you must have a proper ventilation system that is controlling humidity inside your structure.
Natural Ventilation is the process of supplying and removing air by natural means from building spaces by using windows, doors, solar chimneys, and non-powered ventilators.
solar chimney
Most of us spend about 90% of our time inside of a building. As a result, the indoor air quality is critical to our health, productivity, and comfort. Scientific studies clearly show that buildings with proper fresh air ventilation improves productivity and health for occupants. If designed right, proper natural ventilation can be used to increase comfort and reduce energy bills.
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ASHRAE 90.1 is a standard in the US that provides minimum requirements for energy-efficient designs for buildings except for low-rise residential buildings. The standard was first created in 1975. It has since been updated on a regular basis in 2004, 2007, 2010, and 2013.
There are two paths for compliance with ASHRAE 90.1, both the prescriptive path and performance path. The prescriptive path requires all building components to meet a minimum set of standards specified in ASHRAE 90.1. The Prescriptive path includes requirements for building envelope, HVAC, domestic hot water, power, lighting, and other equipment. The performance path shows compliance using a building modeling program to illustrate that the design uses less energy than the baseline building built to ASHRAE 90.1’s specifications.
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A light shelf is a horizontal overhanging element located above the eye-level and typically having a highly reflective upper surface. Sunlight hits the top of the light shelf and bounces inside of the structure hitting the ceiling. This brings light deeper into the structure that reduces energy usage for lighting and glare.
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A Solatube is a tubular daylighting system. The solatube was created in Australia that captures daylight using a dome installed at the roof deck level and reflects it through a cylindrical tube into interior spaces.
When two objects with different temperatures come together, energy will be transferred from the object with a higher temperature to that with the lower temperature. The objects exchange thermal energy until each have reached the same temperature or equilibrium. The basic means to transfer heat include Conduction, Convection, and Radiation.
Conduction – the flow of heat through an object by transferring heat from one molecule to another. Think frying pan on a stove or wood stud that touches the inside drywall and the outside wall sheathing.
Convection – refers to the transfer of heat by a moving fluid. Thing warm air rising and cool air sinking in a room. Convection loops circulate near walls. During the heating season, warm air is cooled by exterior walls and falls towards the floor, creating a convection loop. Convective loops can also happen within framing cavities if the insulation doesn’t completely fill the space.
Radiation – flow of heat from a warm source through space in waves of infrared or visible light energy. Think sunlight through a window.
