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The Building Envelope

From "Best Built Home"
episode DBBH-104F

To understand how it's possible to make a home efficient you need to understand what the building envelope is. This segment will explore what the building envelope is and how it works -- and how homebuyers can be sure they are getting a "better" home. Host Lynda Lyday explores the components of the envelope and discusses why they are important. You will then see how builders can control the building envelopes in their homes to ensure their buyers get an efficient, durable and more comfortable home.

If you've ever stood next to a window or door and felt a draft, then you've experienced "leaky" construction. In a leaky home the heating and cooling literally goes right out the window, but today's builders are using science and technology to build more energy-efficient, air-tight homes.

What Is the Building Envelope?

The key components of the building envelope include the:

foundation,
floor systems (figure A),
walls (interior and exterior) (figure B) and
roof system (figure C).

Figure A

Figure B

Figure C

Tom and Ann Lopez and two of their children in the kitchen of their new home.

Homeowners Tom and Ann Lopez, who you met in Episode DBBH-101 of the Best Built Home workshop, may not know if they have a "best-built" envelope, but they can feel its improvement.

"If you were to ask us, compared to our old house, is this house as drafty as the old house, I'd say it's night-and-day difference," Tom said. "There are no drafts in this house. In fact, this house is almost soundproof in a sense."

The Lopez family has already started to experience how having a good envelope gives them a more comfortable and energy-efficient home. "As far as heating and cooling and utility bills are concerned," Tom said, "I think it's a lot more efficient in the time that we've been here. We haven't had any sort of radical heating or cooling bills."

Figure D

Figure E

Figure F

Figure G

To better understand your home you have to comprehend the importance of the building envelope (figure D), which helps define the structural integrity of the house. You should ask yourself the following three questions about your home's building envelope:

How does the house perform from a thermal standpoint?
How does it perform from a moisture-management perspective?
How comfortable is the home?

The thermal aspect of the building envelope plays a big role in energy efficiency. This means every quality envelope has to be sealed up properly (figure E) and have a high resistance to the outside temperatures.

"Insulation is a key component of the building envelope," Chuck Chippero, general manager of Pulte Home Sciences, said. "Both insulation and sealing the whole house." The technology that Pulte Homes utilizes is Structural Insulated Panel (SIP) systems (figure F) -- for more information on SIP, please see Episode DBBH-101 (hot link, above), Segment 3 ("Building Off-Site"). SIP is basically continuous insulation with a minimal number of cold joints in the walls because the panels are continuous.

Traditionally, rolled fiberglass batt insulation is used in-between framing studs (figure G), but because the studs themselves provide very "little" insulation you still get what is called a cold joint. This means cold air can transfer from the exterior sheathing of the building envelope through the stud to the inside of the house.

Note: SIP walls, on the other hand, provide the "continuous insulation" barrier with fewer cold joints in the house.

"It [SIP walls] also provides a highly accurate fit and finish detail that allows us to install windows very accurately and also fit the wall panels together very accurately," Chuck said. "We put insulation foam in-between all of our joints, both on the floor and attaching walls. This allows us to provide a very well-sealed envelope."

SIP walls perform approximately 50-percent better than conventional construction, which allows the builder to provide an energy-efficient building envelope.

Figure H

Moisture, Moisture, Moisture

Air penetration isn't the only concern when it comes to creating a tight building envelope; moisture is also a threat to any house. Many better builders create a draining plane on the exterior of the building envelope. Underground is a different approach.

"In our foundation systems, we use an exterior insulation process (figure H)," Chuck said, "to prevent moisture from coming inside the foundation, but it also allows us to eliminate the potential of condensation in the basement."

When looking at the efficiency of your home's performance, it's not only from a structural integrity standpoint, but performance in terms of how the house behaves relative to swings in thermal temperatures, changes in outside conditions as it relates to humidity, rain, snow and all of these factors, which lead to a higher efficiency building envelope.

A quality building envelope results in a more responsible use of natural resources and cost savings to homeowners.

In the next segment find out how even the government encourages quality building envelopes with the Energy Star program.