Building Ventilation

When creating an energy efficient home, think of your roof as an umbrella. The umbrella or roof provides shade and it’s always cooler in the shade. It’s even more cool in the shade when the air under the umbrella moves. The air around the house and under the umbrella needs to move and the conditioned air inside the house needs to stay inside.

House Wrapping
Most new homes today employ a water/air barrier wrapping material around the house that is tightly sealed at the doors and windows. The places that need the attention are the seams of the material and the protrusions that occur during the remainder of the building process. The warranty information on these materials states that the warranty is void if proper installation procedures are not followed. The manufacturer installation procedures call for taping the seams and protrusions.

There are new building materials that incorporate a radiant barrier into the wrapping paper. You can now install a similar type radiant barrier on your walls as you have in your attic. This would be especially helpful on the South and West facing walls. But remember, to be effective, a radiant barrier requires an air gap.

Skin Venting
The concept of skin venting (passive convective cooling) is to vent the hot, moist attic air out through ridge vents at the top of the roof and replace it with cool, dryer air from under the house. To do this you need an unobstructed path for the air to travel from the crawl space up the exterior wall to the attic and out the ridge vent. This movement of air will occur naturally.

Creation of the air gap in brick installations is easy because the brick doesn’t rest directly onto the wall. There’s a space between the brick and the wall. We just need to ensure the brick gap is exposed to the crawl space usually where the vents are. There are even weep holes at the bottom of the wall to allow a place for water to drain out that collects on the back side of the brick. This installation process has been the same for a very long time.

Once the air gap behind the brick is tied into the open space of the attic eve the air will flow freely from the bottom or underside of the house up the exterior wall and into the attic and out the ridge vent. Creation of the air gap in siding installation requires the use of furring strips to pull the siding away from the wall so there is an air gap. When combined with proper eve and ridge venting this skin venting process can have the same effect of sitting under a fan on a hot summer day.

Fresh Air
With all this focus on keeping the hot air out and the cool air in homes are getting tighter and some are suggesting that we install carbon monoxide detectors in addition to smoke detectors and introduce fresh air intake devices. Fresh air intake devices are fans on timers that come on for a few minutes as frequently or infrequently as desired and pull air through a duct from the outside and inject the air into the HVAC system in from of the media filter and the air conditioner coils.

Media Filters
Another option to consider when replacing your system is high grade pleated media box filters installed next to the air conditioner coils. The concept is that the high density filters cause the air conditioner to work more efficiently, pulling the air through what amounts to an obstructed path. Fiberglass filters don’t stop very many contaminants so the coils become dirty faster and dirty coils are not energy efficient. The media filter is designed for high flow and maximum filtration performance.

Can Lights
Most can lights now come in two versions: sealed and unsealed. The sealed versions are rated to be placed next to combustible material (insulation) and do not allow (much) air flow. The unsealed versions are just the opposite. Installing sealed can lights can almost eliminate the downside of the effect of punching a hole in the ceiling to install the light.

Attic Stairs
Most attic stairs are a giant hole in the ceiling making it the most inefficient space in the house. Now you can buy a cover for your attic stairs that installs in the attic and provides an effective barrier reducing the air transfer that used to occur at the attic stairs.

Attic Fans
In the old days, almost every house had an attic fan. It was a huge metal fan with louvers installed in the ceiling and on those ‘tweener’ days that Houston has so many of you could open the windows and turn on the attic fan and create a fabulous breeze and fill your house with cool fresh air. The attic fan had gone out of favor but is making a comeback with new very small versions that install between standard ceiling joists and can be retrofitted rather easily. The other improvement to these new versions is they are much more quiet.

Powered Roof Fans
There are places where powered roof fans are needed but for the most part residential installations are overkill. Even for the solar variety. The challenge to overcome with powered roof fans is that they are so powerful they can pull the cool, dry air from the inside of your home into the attic through the light plugs and light fixtures. That air has to be replaced with warm, moist air that comes in through doors and windows. This effect causes your air conditioner to work even harder to keep your living area cool and comfortable. If the roof van is powered with AC current, it’s certainly using more electricity than it’s saving.