Many homeowners know that preventing water intrusion and insulating well are key ingredients for a comfortable, quality and energy efficient home. What most homeowners aren’t aware of, though, is how important it is to also control vapor and air; and those who are aware often don’t know the order of importance for all four factors.
So here’s the order, and we’ll take a moment to review why the order is what it is: 1) Water 2) Air 3) Vapor 4) Insulation.
Now, most people would naturally place water control as number one. Water is, without a doubt, the number one enemy of a home. It can rot out wood (structure), destroy contents, lead to mold growth, invite pests, cause poor indoor air quality, and a whole slew of other problems very quickly. Water is such a threat to structure that the National Flood Insurance Program was created to help aid in flood damage repairs beyond basic homeowners insurance policies.
What isn’t so obvious is the order of the next three items on the list. Most people would place insulation as number two when, in fact, it falls in last place. That’s not to say insulation isn’t important (it’s very important), but it’s not quite as important as controlling air and vapor.
Most good insulation contractors and experts in building science push the importance of air sealing to a greater degree than insulation – especially in modern times after a lot of research has proven its importance. If the home is well insulated but not adequately air sealed, air can freely enter and leave the home through multiple points and much of the insulation becomes almost a waste.
Likewise, if a house controls water and air well but doesn’t control vapor, moisture related problems will develop over time, as well as poor indoor air quality. Vapor control is climate dependent (as is insulation), making it especially difficult to deal with properly. Vapor tends to migrate from the warm side of a wall to the cold side, and some regions are predominantly hot while others are predominantly cold. To complicate things further, the goal of vapor control is to prevent vapor intrusion, but that same prevention measure can also prevent vapor that does get in from escaping or quickly drying. When it comes to vapor control, be sure to discuss options with your contractor and his or her specific reasons for using a certain method in your climate.
Insulation is crucial, but the other three items on the list should be in place and done well in order for the insulation to perform optimally. A house that is fully air sealed but lacks in insulation will typically outperform a home that has plenty of insulation but no air sealing. And a house that controls air, vapor and thermal issues well but doesn’t protect well against water will deteriorate fairly quickly.
If you’re planning to invest in improving the quality, comfort and efficiency of your home, be sure to remember this order. Always control water first (even small leaks), then ensure the house is air sealed well, then make sure vapor is controlled, and finally ensure your insulation levels are sufficient. Do all four and you’ll have a sound, safe and comfortable home that is capable of withstanding natural forces for a very long time.
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