INSPECTION II – LESSON 4: Introduction

Introduction to Home Insulation and Moisture Management


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266 – 269 78 – 79 NHIE Volume 2 Structural Systems and Business
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In today’s modern homes, different types of insulation can be used to help create a comfortable and energy efficient home. There are also several ways to prevent moisture intrusion and buildup within a home.

Inspectors are required to note the approximate depth of insulation, and any evidence of water penetration in the attic. Additionally, deficiencies should also be noted in the following:

  • Attic space ventilation that is not performing.
  • Missing insulation.
  • Attic ventilators.

Items like heat and energy recovery ventilation systems (HRV and ERV) are beyond the scope of the inspection. Although it is helpful to note when these systems are present, and if there is a need to have the system evaluated by a qualified specialist.

Some methods of insulating are thick walls. These are often expensive, but can provide an energy efficient and comfortable environment. Another option is a cavity wall or two walls with empty space between. Stationary air is actually a good insulator and is how most insulation achieves its R-value. The problem becomes evident if air is moving within a space, that is why a way to seal off the walls is what is recommended.

Most modern homes use either blown-in or batted fiberglass insulation. Older homes often used cellulose (shredded paper) which is not recommended today as it can retain moisture which can lead to mold and fungal growth. Spray foam insulation is also commonly used today within walls and attics.

There are other ways to help with efficiency and comfort within a home; several passive examples include:

  • Shade trees over certain sections of the home.
  • Orienting a house where the sunlight is facing towards an area (such as a solar panel) or away from a certain area (such as a bedroom).
  • Having a wider eave to create shade in areas that are warmer.
  • Painting a home a certain color to reflect heat.
  • The use of solar screens over windows with direct sunlight can reduce the temperature of a room.



Some key factors of home ventilation are to dilute and remove pollutants that can build up in a home.

Common pollutants in a home can include water vapor, carbon dioxide (from breathing), carbon monoxide (from combustion of gas-fired appliances), and volatile organic compounds (VOC).

VOC can often come from plywood or OSB, paint or stain, and other building adhesives.
These can cause health problems for occupants with asthma or other sensitive allergies. Moisture can also lead to condensation and mold problems.

Most openings in building materials are small, but when added up, they can total up to several square feet of openings. In older homes, this was common and allowed the house to be “drafty.” Today’s home builders create homes that are sealed very well.
This is great from an energy-saving perspective, but it also reduces ventilation and can create moisture problems. Air sealing can have a greater impact on energy use than adding insulation.

Codes require that new homes be air-sealed and have outside air mechanically added to the home to exchange the air at a rate of 5 times per hour or less.

Another issue with newer homes is the improper installation of building materials.
For instance, if a home has spray foam insulation, but there are either static exhaust vents installed, or a low-efficiency rated gas-fired furnace installed with a type b vent passing through the roof, the encapsulation is not encapsulated. These issues create openings in the spray foam and can allow entrapment and a buildup of moisture in the attic space. This can lead to damaged building materials in the home, and allow for mold and fungal growth.

Remember the following:

  • Stationary air is actually a good insulator. That is how most insulation achieves its R-value.
  • Dilute and remove pollutants.
  • Most openings in building materials are small, but when added up, they can total up to several square feet of openings.
  • Air sealing can have a greater impact on energy use than adding insulation.
  • Codes require that new homes be air sealed.
  • New building materials are more complicated.


Ventilation and Insulation Terminology


  • Air Barrier: Building material that prevents unconditioned air from passing through it and into the thermal envelope; or conditioned space in the home.
  • Basement Wall: A wall that has 50% or more of the wall below grade with an enclosed conditioned space.
  • Building Thermal Envelope: Conditioned space within a home (heated or cooled). The envelope within walls, ceilings, floors, basement walls, and slab-on-ground foundations creates a separation between unconditioned (outside these items) and conditioned space (within these items). The thermal envelope may be within an attic or crawlspace if built as such. (Foam encapsulated attic, for example).
  • Dew Point (Temperature): The point where air vapor becomes liquid water at a certain temperature. The higher the dew point temperature the more liquid within the vapor.
  • Fenestration: Openings within a home, such as windows, doors, and skylights.
  • Humidity, relative humidity: The true amount of water vapor in the air, compared to the amount of water that may exist. This is represented as a percentage. Raising air temperature while keeping the water vapor constant reduces relative humidity, and the opposite increases the relative humidity.
  • Mass Wall: Above-grade walls consisting of concrete, insulated concrete, masonry, structural brick, rammed earth, and timber logs.
  • Permeability: The amount of resistance in a material to prevent or allow moisture and vapor to pass through it. Perms or permeability is expressed as a number greater than zero. For instance, glass has a low permeability, whereas a vapor barrier has a high permeability.
  • R-Value: The ability of a material to reduce heat transfer expressed as a number greater than zero. A higher number indicates a better ability to slow heat transfer. Often used in measuring insulation in an attic, for example.
  • Solar Heat Gain Coefficient (SHGC): The amount of solar radiation that passes through a window. The lower the measurement, the less solar radiation that can pass through.
  • U-Value (factor): The ability of a material to allow the transfer of heat. Expressed in a number more than zero. The larger the number, the more heat can transfer through and the lower the R-value.
  • Vapor Barrier: Usually a material used to prevent vapor from passing through it. Often used interchangeably with vapor retarder.
  • Vapor Diffusion: The process of water vapor passing through a permeable material from an area of higher vapor pressure to that of less vapor pressure.
  • Vapor Drive: A situation where vapor diffusion is increased through increased heat and pressure. An example of this would be when dew settles on a roof in the morning. Once the heat rises in the day, it pushes water vapor from the dew into the roofing material.
  • Vapor Retarder: A material that helps slow the water vapor from passing through it. These are rated in Perms and are measured as follows:
    • Class I is rated at 0.1 perms or less.
    • Class II is rated between 0.1 and 1.0 perms.
    • Class III is rated between 1.0 and 10.0 perms.
  • Ventilation (building): When outside air is supplied to the inside of a house or removing inside air from a home. This can be from natural, unexpected means, or mechanically controlled means.