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What is the Building Envelope & How Does it Affect Insulation?

What is the Building Envelope & How Does it Affect Insulation?

There is nothing quite as uncomfortable as a cold and drafty house in the middle of winter.  Does your floor feel cold or damp when the weather outside is rainy? If so, your house might have a faulty envelope. 

The building envelope is the outer shell of the house. It includes the roof, walls, and floor. The envelope protects the interior of the home by keeping it dry and at a comfortable temperature.  Bad envelope quality allows drafts and water in and permits heat or air conditioning escape, creating a poor insulation barrier.

Everybody wants to live or work in a home that is dry, temperate, and comfortable, but what if your home or office is currently drafty and damp.  Is there anything you can do to improve the situation?  Absolutely!  The addition of envelope insulation to an existing structure can correct problems such as

  • Poor air quality
  • Fluctuating interior temperature 
  • heating or cooling loss

By incorporating the ideas outlined in this article you can have a home that is comfortable, cost efficient, and safe.

Pro Tip: You can use a infrared thermal imaging camera (link to Amazon) to identify air infiltration issues in your home.

What is Envelope Insulation?

Envelope insulation, also commonly referred to as the thermal envelope, is a layer of protective material applied to the exterior and/or interior sub walls, subfloor, and roof of a building to create a living space protected from the outside elements (source).

This barrier keeps moisture and drafts from entering the living spaces of the home through cracks, joints, and access points. The final exterior finish of the building, such as vinyl siding, will create an additional layer of protection against the elements.

This YouTube video outlines the building code requirements for ensuring a reliable thermal envelope:

Mandatory Requirements: Building Thermal Envelope


Why do you need Building Envelope Insulation?

Without envelope insulation, your home is susceptible to whatever elements are outside. Extremes of heat and cold, strong winds and rain, and hours of direct sunlight can lessen the air quality and affect the temperature inside your home. To correct these problems, a tight envelope must be created. 

Envelope insulation has three main purposes. 

  • Moisture control– insulation of the roof, basement, crawlspace, and walls will prevent moisture from seeping into the building
  • Air control-insulating around door and window openings, exhaust vents, and utility access points prevents outside air from entering the occupied space of the building
  • Thermal control– insulation of the roof and walls prevents temperature shifts caused by extreme sun exposure
What is a Building Envelope? | Foam University

Moisture Control through the Building Envelope

Moisture control is one of the primary reasons to use building envelope insulation.  

Moisture can enter a building in places you would not expect.  Rainwater can seep under shingles and ridge flashing, allowing water to soak into plywood or composite board sheathing.  

Problems caused by water seepage on building roofs include:

  • Mold
  • Mildew
  • Wood rot
  • Water on insulation and wiring

Another common place moisture can enter building is through joints in the exterior wallboard.  Wind driven rain can collect behind siding and soak the exterior wallboard.

Extensive damage to the interior of the building can occur through moisture damage as water leeches into

  • Stud walls
  • Roof joists
  • Flooring materials
  • Electrical boxes
  • Drywall

Applying rigid foamboard to the exterior of the building and sealing it with seaming tape will prevent moisture from entering through the wallboard.

Moisture can also penetrate the interior through the foundation. Concrete slabs and basement walls can absorb excess water.  A wet environment or improperly designed drain field can allow standing water under the home’s foundation. This creates condensation and seepage through the concrete, allowing moisture into the living area of the home. 

To protect your home from moisture, follow these steps.

  • Use home wrap or rigid foamboard insulation between exterior walls and siding.
  • Apply foamboard insulation to exterior of basement walls 
  • Coat interior basement walls with water sealer.
  • Use spray foam insulation in the space between walls and door or window frames.
  • Use rigid foamboard and a plastic peel and stick barrier between shingles and roof sheathing
Understanding Air and Vapor Barriers INSIDE your House

Air Control through the Building Envelope

Regulated air flow and temperature control is another reason a tight building envelope is important. 

A drafty house will not only be uncomfortable, but it can also provide health hazards you might not know about.  Exterior air quality can be greatly diminished in cities and industrial areas due to pollution and smog.  Agricultural products that float on the air can also cause health problems.  Without proper insulation, your house is open to penetration from many airborne hazards. 

The biggest exchange of air comes from door and window openings, around vents, and through access points for electrical, telecommunications, and entertainment services.  While it is necessary to have these openings, several things can be done to help stop these air leaks that occur through these orifices:

  • Be sure doors and windows fit snugly inside frame openings.
  • Use double pane glass.
  • Use storm doors. 
  • Use spray foam insulation around door and window frames.
  • Use insulation between stud walls where access points are necessary
  • Access points should be appropriately sized and placed to prevent excess air flow
  • Use spray foam around access points
  • Regularly clean vents and vent screens

Thermal Control through a Tight Building Envelope

The third major reason a tight building envelope is necessary is to maintain regulated temperatures inside the building.

Lack of thermal control occurs due to the abundance or absence of sunlight shining on the house at any time throughout the day.  Too much sun on the windows or roof creates a warmer environment.

Too little sunlight creates a cooler environment.  The location of doors and windows can greatly affect the internal temperature of a building due to light exposure.

If you are planning a new build you should maximize heat and cooling by placing windows and doors in areas to either attract or avoid direct sunlight, depending on your climate.

Existing homes can use the following energy-saving techniques to help with thermal energy controls. 

  • Be aware that southernmost windows will receive the most sunlight
  • Be aware that northernmost windows will receive the least sunlight
  • Use double paned windows
  • Use solid core doors, rather than hollow
  • Use shades or insulated drapes on windows and door glass
  • Use rigid foamboard insulation between shingles and roof sheathing
  • Use reflective rolled insulation between interior roof joists
  • Skylights should be made from tinted material
  • Doors and windows should fit snugly into openings
  • Use sealer and pan flashing in window and door frames

Other areas that might create problems

Chimneys, window air conditioning units, and passageways between a garage and house are all openings that can cause a loss of energy efficiency.  Each area needs to be evaluated for heat loss, air flow, and moisture buildup.

If any issues are found, they should be corrected immediately.

  • Chimney caps should be used to stop drafts from blowing down
  • Chimney flue should be kept closed when fire is not burning
  • Doors or a fireplace insert will keep interior air from escaping through chimney
  • Use sealer around window air conditioning units
  • Use a hose to remove dripping water so it will not run down the walls 
  • Regularly clean vent filter on air conditioner
  • Enclose passageways between garage and house if possible
  • Be sure garage door and home door are both insulated and fit well
Infrared Thermal Imaging Reveals Air Infiltration and Insulation Deficiencies


A well-designed building envelope can not only improve the comfort of your home or office but could also improve your health and quality of living.

By stopping unwanted air leaks, protecting against temperature extremes, and prohibiting invasive moisture from permeating your home you can save yourself money and prolong the life of your building.

Wrapping the exterior of your home in rigid fiberboard, insulating the interior walls and crawlspaces with blown or rolled fiberglass, and sealing around doors and windows will provide a tighter building envelope.

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