Building With the Future in Mind Since 1955

(This is the INTRODUCTION from Building Science Corporation’s BUILDER’S GUIDE for Mid-Humid Climates; Written by Joseph Lstiburek, PhD., P.Eng.;

People ask builders all the time, “Why can’t you build homes the way you used to?” Builders can’t help but notice that callbacks and warranty claim costs are rising more rapidly than they did in the past.  Were homes built better than we build today?  Have we forgotten all we learned about quality and durability?

Malheur 4-2007049Many of the homes of yesterday do perform better than homes built today but not for the reasons most people think.

Many builders today are obsessed with quality control.  The quality revolution that has swept through North America has forced builders to focus on producing quality homes.  When faced with the question of quality, a builder typically looks at two things: workmanship and materials.

It is assumed that if good workmanship can be achieved and good materials are used, a high quality home will result.  Let’s examine that assumption.

Countless homes across North America are being built with good workmanship and good materials but are not performing.  We have better paints than we ever had before, but we have more paint problems today. Are today’s painting contractors less skilled than yesterday’s? We have better insulation than we ever had before, but we have more insulation problems today.  Are today’s insulation contractors that much worse than yesterday’s?  We have better windows than we ever had before but we have more window problems today.  Are today’s window installers that much worse than yesterday’s?  The list goes on almost endlessly.

What’s going on here?  How can we have good workmanship and good materials and still have problems?  What if we do the wrong thing with good materials and good workmanship?  Do we still have quality?

The problem is not workmanship or materials; the problem is understanding.  The pieces must be put together correctly.  In order to do so, we must understand how homes work.  Homes today work differently than they did in the past.  The old solutions and old understandings don’t apply.

Homes of yesterday were uncomfortable -too cold in the winter, too hot in the summer -but they usually stood the test of time.  Houses of today are exceptionally comfortable but frequently experience serious problems long before the initial mortgage is fully paid.

Can there be any connection between comfort and durability?  The answer is “Yes”.  In a strange way, what we do to homes to make them more comfortable has in fact made them less durable.

In the last fifty years there have been three important changes to the way we build homes:

      1. The introduction of thermal insulation
      2. The development of tighter building enclosures
      3. The advent of forced air heating and cooling systems

Each of these changes has made homes more comfortable, but also has made the same houses less durable.

Thermal Insulation

Thermal insulation was added to wall cavities and ceilings to keep the heat in the winter, keep the heat out in the summer and make a home more comfortable.  However, by keeping the heat in or the heat out, the insulation kept the heat out of the wall cavities and ceilings themselves.  In doing so, the ability of these assemblies to dry when they get wet from either interior or exterior sources was reduced.  How do you dry something?  You heat it.  No heat flow, no drying.  The addition of thermal insulation increased the “wetting potential” of building enclosures while reducing their “drying potential.”

Tighter Building Enclosures and New Materials

Homes built today are much tighter than the homes of yesterday.  We use plywood and gypsum board in place of board sheathing and plaster.  We platform frame instead of balloon frame.  We use factory-made windows instead of site glazing our windows.  Building papers come in 10 foot wide rolls instead of 3 foot wide rolls.  We put more caulk and glue on our houses than ever before, and we can buy material that actually sticks and holds.  The results are fewer holes and a lower air change.  The lower the air change, the less the dilution of interior pollutants such as moisture (from people, soil and appliances), formaldehyde (from particle board, insulation, furniture and kitchen and bathroom cabinets), volatile organic compounds (from carpets, paints, cleaners and adhesives), radon (from basements, slabs, crawl spaces and water supplies) and carbon dioxide (from people).

IMG_7452 editedThis trend to lower air change occurred simultaneously with the introduction of hundreds of thousands of new chemical compounds, materials and products that were developed to satisfy the growing consumer demand for household goods and furnishings.  Interior pollutant sources increased while the dilution of these pollutants has decreased.  As a result, indoor air pollutant concentrations have increased.

Additionally, chimneys don’t work well in tight homes.  In tight homes, exhaust fans compete with chimneys and flues for available air.  The chimneys and flues typically lose in the competition for available air, resulting in spillage of combustion products, and back drafting of furnaces and fireplaces.  As air change goes down, interior moisture levels rise causing condensation problems on windows, mold on walls, dust mites in carpets and decay in wall cavities and attic spaces.  Yet even though interior moisture levels are rising, builders continue to install central humidifiers rather than installing dilution ventilation or dehumidification.

Traditional chimneys in many new homes have been replaced with power vented, sealed combustion furnaces.  Many new homes have no chimneys or flues and rely on heat pumps or electric heating.  Traditional chimneys (“active chimneys”) acted as exhaust fans.  They extracted great quantities of air from the conditioned space that resulted in frequent air changes and the subsequent dilution of interior pollutants. Eliminating the “chimney fan” has led to an increase in interior pollutant levels such as moisture.

Active chimneys also tended to depressurize conditioned spaces during heating periods.  Depressurization led to a reduced wetting of building assemblies from interior air-transported moisture and therefore a more forgiving building envelope.

Heating and Cooling Systems

Today, forced air systems (heating and air conditioning) move large quantities of air within building enclosures of increasing tightness.  The tighter the building enclosure, the easier it is to pressurize or depressurize. This has led to serious health, safety, durability, and operating cost issues.

Supply duct systems are typically more extensive than return duct systems.  There are usually supply registers in each room, with common returns.  Pressurization of rooms and depressurization of common areas is created by the combination of more extensive supply systems, leaky returns combined with interior door closure.

When typically leaky supply ducts are run outside the building envelope in vented attic roof and crawl spaces, depressurization of the building enclosure occurs.  Depressurization can cause infiltration of radon, moisture, pesticides and soil gas into foundations as well as probable spillage and back drafting of combustion appliances and potential flame roll-out resulting in fire.

Leaky return ducts and chases connected to exterior spaces can lead to pressurization of the building enclosure.  Pressurization can lead to the exfiltration of warm moisture-laden air into wall and roof cavities that are at lower drying potentials because of higher levels of insulation.


The three important changes in the way we build homes today interact with each other.  This is further complicated by the effects of climate and occupant lifestyle.  The interrelationship of all of these factors has led to major warranty problems that include health, safety, durability, comfort and affordability concerns.  Problems are occurring despite the use of good materials and good workmanship.

We cannot return to constructing drafty building enclosures without thermal insulation, without consumer amenities, and with less efficient heating and air conditioning systems.  The marketplace demands sophisticated, high performance buildings operated and maintained intelligently.  As such, buildings must be treated as integrated systems that address health, safety, durability, comfort and affordability. Quality construction consists of more than good materials and more than good workmanship.  If you do the wrong thing with good materials and good workmanship, it is still wrong.  You must do the right thing with good materials and good workmanship.

browncircle browncircle browncircle