Building Envelopes 101

When it comes to performance, the building envelope—sometimes also called the building enclosure or shell—is possibly the most important part of the house.

What is it?

Quite simply, the building envelope physically separates the outside of your house from the inside—the part you heat and cool. It consists of your:

  • Roof (or upper floor ceiling, if attic isn’t heated)
  • Walls, windows, doors
  • Foundation

Ideally the building envelope includes layers to control air, water, heat, light and noise.

Why is it important?

The building envelope acts as a barrier from the outside elements. It is directly related to the comfort, durability, energy efficiency, health and safety of your house.

If there are gaps, cracks and openings in your building envelope—even small ones—air and water vapor can leak into and leak out of your house.

A poorly performing building envelope can cause:

  • Drafts, condensation
  • Ice damming
  • Wasted energy, expensive bills
  • Poor indoor air quality
  • Higher energy bills

Where and why do houses leak?

Most air leakage occurs at openings and at the joints between materials. Places like doors, windows, attic hatches, floor drains, electrical outlets, etc. All it takes for air to leak through the building envelope is one of these openings and a pressure difference. Pressure differences can be caused by wind, HVAC equipment, and temperature differences.

How can the construction of my home minimize air and moisture leakage?

By making the building envelope airtight. Homebuilders can do this by choosing the right air and vapor control system for your climate.

Doesn't a house have to breathe?

Technically, yes. But just like you, houses breathe in a controlled manner, using high-performance materials, in addition to heating, ventilation and air conditioning equipment to breathe-not its walls, roof, windows and doors.

What are some materials that can improve the performance of the building envelope?

  • Materials with a high R-value and that don't readily absorb water, which include spray foam and rigid foam.
  • Multifunctional, advanced insulation materials that improve thermal and that control air and vapor
  • Caulks and sealants
  • Open-cell foams for noise control