This is the fourth post in our series on Passive House Design. If you missed either of the previous, click on the links below to get up to speed! LEAP’s intelligent design process consists of four main steps. Today we explore the importance of air sealing, and pink slime—that’s a technical term.
Passive House Design Process
“Your Love is Lifting Me Higher”
We want you to have a love affair with your house or office building (or why not both?). It should be an uplifting space that makes you want to sing and dance. And hopefully it’s just you dancing—because your building is (or should be)—coated with pink slime. Not the psychomagnotheric slime that had lady liberty strolling around, cracking domes like soft boiled eggs, but the air sealing kind.
Air sealing is critical to temperature and moisture control, and reduces draftiness, noise and pollutants. It also plays an important role in energy efficiency. Proper sealing of joints and penetrations in the building envelope can reduce energy consumption for heating and cooling by 30%.
The Ghosts of Air Sealing
The wind whistling past your building at night can do more than just make eerie noises. It can actually create a negative pressure zone, which tries to suck air out from the inside. Here is a list of critical locations where air tries to get out (or in—refer to image at the top):
- Around doors and windows
- Around electrical fixtures
- Basement band joist and exterior penetrations
- Wiring/plumbing/duct penetrations
- Vertical meets horizontal planes: (roof to wall, floor to wall, wall to wall)
Air Barriers are materials that stop moisture-laden air from entering building assemblies, reduce air leakage and, wind-driven air from entering into and through insulation. Examples of air barriers:
- Interior drywall, fully sealed for continuity and air tightness.
- Exterior sheathing: plywood, OSB*, fully sealed for continuity and air tightness. (*needs coating)
How do you ensure that these sheathings are fully sealed? Pink slime to the rescue! Certain spray foams and caulks are applied to the framing members to effectively seal the locations mentioned above. One of the products we like is by Owens Corning. They make a spray foam with flexible seal technology (and yes, it is pink). Not all spray foams can be used for air sealing. Some do not adhere well to the frame, and some are too rigid, which means they can crack and create gaps as the structure settles.
So, with yet another set of important design considerations to manage…
Who Ya Gonna Call? LEAP ARCHITECTURE!
We ain’t afraid of no gaps!
LEAP works with energy star certified framers and contractors, who know how to seal and frame correctly, saving you from any number of scary scenarios down the road. Proper air sealing is that much harder if the framing member aren’t in correct place, which is why LEAP specifies a detailed instructions for framing and construction. One of our the most notable directives: ROCK the CEILING FIRST!
LEAP specifies that the ceiling be sheet-rocked before the wall framing goes up. This allows the space behind the walls to basically be capped by the ceiling, instead of creating an ‘air corridor’ directly up to the attic and below to the basement. The energy benefits gained using this method totally outweigh any inconvenience for builders.
So how do you know that you have achieve effective containment? Well, blower door testing is a diagnostic tool designed to measure the air tightness of buildings. It uses a calibrated fan capable of measuring airflow, mounted in a flexible panel positioned in an external door. A pressure-sensing device measures the air pressure created by the fan. The fan both pressurizes and depressurizes the home. By recording both flow and pressure in each direction, the system is able to provide highly detailed information about building air tightness.
There are two main ways that blower-door tests are reported: airflow at a pressure difference of 50 Pascals (cfm50) or air changes per hour at a pressure difference of 50 Pascals (ACH50). The first number — cfm50 — can be read directly off the airflow manometer at the time of the test. The second number — ACH50 — can only be calculated once the building’s volume has been determined. To calculate ACH50, multiply cfm50 by 60 minutes per hour and divide the product by the building volume, including the basement, measured in cubic feet.(1)
Passive House Design requires an ACH50 of 0.6, which is pretty rigorous to achieve. Aside from Passive House, standard New York State requirements for building tightness are likely to be upgraded by October 2016, where all constructions must meet and ACH50 of 3. This means 3 air changes or less per hour, which will require installation of a whole house ventilation system per ASHRAE standards.
[box type=”bio”] Contact LEAP to design an air-tight building worthy of an ecto containment unit and watch as we fire up our foam insulation spray guns (we won’t cross the streams!).[/box]