How to seal attic and basement air and heat leaks (C) Daniel Friedman Steven Bliss Energy Savings Retrofit Details: Sealing Attic, Basement, & Floor Air & Heat Leaks

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This article describes a real world approach to finding and sealing elusive air leaks in older buildings in order to gain the most heating or cooling energy savings.

Sketch at page top and accompanying text are reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

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Energy Saving Building Retrofit Details: Theory vs. Reality

Window open stack effect (C) Daniel Friedman

The text below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss - with permission. Links to the original article follow this text. In original form this material was a sidebar to Down East Retrofit.

Heating cost energy saving retrofit realities rarely match textbook diagrams. Pipes and wires get in your way, spaces are inaccessible, and the building details you discover often boggle the mind. And because textbook buildings rarely match real ones, real energy savings often fall short of predictions.

Researches have found that airflows around, behind, and through insulation account for many of the missing BTUs.

To combat these heating and air leaks, sophisticated energy savings retrofitters often concentrate on basement and attic work - trying to block the main heat loss and air leak pathways up through the building.

Once the exterior walls have been insulated and sealed, as in the Turner retrofit (discussed in this article), infiltration and heat loss through leaks and convective loops in the interior wall partitions rival losses through the building exterior walls.

Attic leaks (called "bypasses" or "thermal bypasses" -
see THERMAL TRACKING & HEAT LOSS) rob the building of heat in two ways:

Stack effects increase building air infiltration and blow heat out of the structure

First they increase the overall rate of air infiltration driven by the stack effect.

The taller the building height between low and high leaks, the stronger will be the stack pressure. In a tall New York City building where top floor tenants kept the windows open in winter - they were too hot - the stack effect was a virtual gale of out-blowing hot air. Notice that tissue we taped to the under-side of the window sash? Any desktop papers near an open window would simply blow outside! -- DJF.

These same stack effects and thus building heat losses occur in one and two story residential homes as well.

Not only do stack effects draw heat out of a building, any indoor air contaminants such as airborne crawl space mold are drawn upwards through the rest of the building.

How to seal attic and basement air and heat leaks (C) Daniel Friedman Steven Bliss

Illustrated in the sketch at left, air and heat loss leaks in old building floors can be tricky to seal - particularly with board-type subflooring. If the building is built over a vented crawlspace or an unheated basement, the floor should be sealed as well as possible from the prime living space.

This limits air infiltration and keeps moisture (and possibly airborne mold or radon gas if present) out of the living space. If the basement is finished and heated, it is usually sealed at its walls, not at the floor above.

Stack effects and convective loops chill the building's interior walls

Second, as we detail at CONVECTIVE LOOPS & Thermal Bypass Leaks, stack effects in buildings chill the interior walls - increasing conduction (heat) losses through them.

Sealing in the home's interior will reduce infiltration, but it won't stop partitions and plumbing or electrical chases that are open to the attic from filling with cold air. Only sealing in the attic will help.

In addition to increasing fuel bills, drafts and cold walls make it hard for the building occupants to feel comfortable no matter how many BTU's the heating system is churning out.

Basement thermal bypasses increase the stack effect in buildings

Basement air leaks and thermal bypasses increase the stack effect and carry moist air (or mold, gases, or other airborne contaminants) into the building occupied spaces above where they cause problems.

The collection of sketches (above left) show typical attic and floor air leaks and thermal bypasses and how to seal them.

While the principles apply to all buildings, each structure will demand creative solutions.

Energy Savings Retrofit Case Study - Down East Retrofit

Superinsulating a sprawling fuel-gobbling building was not enough: finding and sealing elusive air leaks was a vital second step in gaining major energy savings.

See  ENERGY SAVINGS RETROFIT CASE STUDY for an updated online version of the original articles (below)

Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Building Air Leakage Articles


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