What Is Stack Effect?
The “Stack Effect” occurs when warm air rises through air leaks between a home’s upper floor and attic, and draws outside air into the home through leaks between the floor and crawlspace or basement. This happens in summer and winter and is similar to the way a chimney operates. Warm air rises because it is lighter than cold air and, since it has no place to go, it escapes out of the upper levels of our homes. But when air escapes, new air has to come in to replace the air that escaped. This “new air” typically comes from the crawl space vents and up from the ground, which is typically filled with moisture. As you may imagine, the quality of this replacement air is not good. In addition to mold spores, mildew, insects, and rodent droppings, the stack effect can also increase radon levels inside your home in areas prone to increased radon levels.
If your home is not properly sealed, these particulates will enter your home and can lead to a variety of respiratory problems including Asthma and allergies. Up to 40% of the air we breathe on the first floor of our home comes from the crawl space. Precept Construction is committed to improving the Indoor Air Quality of new homes by reducing the stack effect.
Common Places of Air Leakage
- Air leaks are common where plumbing and electrical penetrations exist along exterior walls, ceilings, and floors.
- Most homes have indoor walls and chimney chases that are open to the attic and/or basement, leaking indoor air out and letting outdoor air in.
- Basements are usually very leaky, letting outside air in and creating drafts.
- Even newer homes frequently have leaks around baseboards, stairways, and through recessed can lights. Discolored carpet around baseboards is an indication of air movement.
- Well insulated homes can be very leaky, since insulation does not stop air leaks – air passes right through it like a filter.
Steps to Reduce Stack Effect
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- Foaming or caulking accessible plumbing and electrical penetrations between conditioned and unconditioned spaces such as under sinks, in laundry rooms, ceiling fixtures, and through framing lumber and floors.
- Closed crawl spaces are excellent for improving the air quality in crawl spaces and reducing susceptibility to insect damage, wood rot, and mold issues by reducing moisture. For more information on closed crawlspaces visit www.crawlspacecare.com.
- Weather-stripping and caulking doors and access hatches.
- Replacing recessed lights with new, insulation contact airtight (ICAT) lights.
- Installing gaskets on electrical outlets and switches.
- Installing an “attic tent” or other insulated cover over an attic access hatch.
- A Blower Door test can measure exactly how leaky a home is and pinpoint areas in need of air sealing. Attack the areas of greatest loss first to achieve the most impact.
If you believe that stack effect is leading to energy loss or health related issues, there are many Home Energy Rating Services (HERS) that can perform the tests and determine a course of action, including recommending contractors to perform the modifications.
Scott Allred is the owner of Precept Construction LLC. He can be reached at scott@preceptconstruction.com or 286- 6811. Please visit our website at www.preceptconstruction.com.