Saturday, August 1, 2009

The Tip of the Intake Iceberg

After a winter of reading and plotting, I decided it was likely that I indeed did not have enough ventilation in my attic. The various guidelines (such as this), most of which seem to be rules of thumb, seem to show that I'd need about 6-7 square feet of ventilation, evenly split between inflow to the attic and outflow from the attic for my 2000 square foot house. Some folks debating the topic state that I need double that, which is entirely possible particularly in my hot central Texas climate. What I had existing was approximately 1.5 square feet of ventilation in the roof, and that, not even close to the top where the hottest air would gather.
The villain begins to become unmasked.
My home was marketed to me as fairly energy-efficient, and I do believe that for mid-1990's standard, it was not designed too badly. In fact, the continuous soffit venting around the eaves was a good feature for capturing breeze into the attic from any direction. However, design is only part of the equation: installation is another thing entirely. Looking around in the attic, I noticed a new problem: nearly half of my soffit venting was blocked by improperly installed insulation. This, added to my decidedly under-vented roof, revealed more of my problems.
The reason for the blocked ventilation was soon revealed: roughly half the house has vaulted ceilings (also called cathedral ceilings). These are the areas where the ceiling, when viewed from inside the house, slopes downward to the walls, rather than being flat all the way across. When viewed from above in the attic, the slope starts at the attic floor and goes downwards towards the outside wall. The problem is that the roof is only about a foot above this slope, creating a foot-tall channel that can be easily blocked by insulation batts (the rectangular pre-cut pieces of insulation).
Problem: Seemingly insufficient soffit air intake to the attic
Cause: Nearly half the inflow (soffit) vents are blocked
Air could not flow out the top of my attic if replacement air could not flow in from the bottom. So, in the first real preview of the Efficiency Man spirit, I decided to start crawling around in the attic and opening up blocked channels where I could.
Note: Doing this yourself is not for the faint of heart, short of breath, poor of balance, or lacking of insurance. Working in the awkward spaces, often without proper flooring, while wearing a hat, disposable paper suit, mask and gloves to protect from the insulation fibers, makes just moving around up there difficult. Add to this the poor lighting and the dust you inevitably stir up, and you quickly realize that working in attics is tough on your health, and, as a bonus, hazardous - there are nails poking out in many places, ducting to trip over, and wiring to avoid. Although you should practice the Efficiency Way whenever you can, know your limits and hire a professional for extensive attic work. I personally want to avoid the attic for a good while after this.

No comments:

Post a Comment