Understanding your home's thermal envelope

Posted By Proud Green Home || 25-Jun-2015

Building a new home or making an existing home more energy efficient presents several challenges. One has to not only think about the size and shape of a building but also how that construction will be heated and cooled. Making sure it has proper insulation by using the right materials with the correct thermal properties will help create an environment that is comfortable and efficient.

When sealing a home for efficiency purposes, addressing the building’s envelope is primary. This is the layer that separates a home’s conditioned living space from the outside or unconditioned space. In simple terms it is the home’s heat-flow control layer.

Often when referring to a home’s thermal envelope, one is discussing the space where heat rises in a home and is trapped—usually a ceiling. The attic space in a home is generally considered to be outside the thermal envelope. However, correct attention to sealing and insulating this space in a home can mean big returns for the homeowner in value and coziness.

Director of Building Science for Demilec, Brian Metrocavage, shares some insights about how choosing the right insulation and air barrier can provide great returns for increasing efficiency in a home. Using practical examples, understanding how air works can help homeowners and builders alike make solid choices.

“In the winter you put on a hat because the heat escapes through the top of you. The same kind of theory applies to your house. The more that you utilized good air barrier work in conjunction with good R-value based on your climate zone, it increases the efficiency of your home.”

Because of increased efficiency in the airflow, a homeowner may find that the size of the HVAC system in the home does not need to be as large, which provides cost savings in the energy bills for the home.

When building a high efficiency home or increasing the efficiency of an existing home, several practices should be taken into account. There should be attention given to purchasing the best insulated windows, correct sizing on the HVAC system and perhaps one of the most important components, adding the right insulation—particularly in the attic space where heat often escapes or is trapped outside of the usable living space. The best insulations should be one that best fits the home and with the highest R-value.

The R-value is the unit of thermal resistance. The higher the R-value, the higher a building’s thermal resistance. In simple terms, the higher the R-value number, the warmer or cooler your home will remain.

“What happens when you’re utilizing spray foam insulation is if utilizing closed-cell foam, you can get about an R-7 rating per inch. Now, as you go up the law of diminishing returns applies. At a certain point in time all the insulation you add doesn’t really make a whole lot of difference if you don’t use air barrier work appropriately,” Metrocavage illustrates.

“We’re eliminating the infiltration of unauthorized air from the exterior. If we look at it from that respect, we’re going to size our HVAC more efficiently, since we’re not relying on air leakage.”

Air barrier and insulation should not be confused. Both are integral pieces of adding efficiency to a home. The benefits of spray foam like those from Demilec are one way that these two issues can be addressed in one application.

“An air barrier prevents or helps prevents unauthorized air from entering the building and conversely it prevents conditioned air from escaping a building. With Spray Foam insulation, the upside is that it can provide an air barrier and gain thermal resistance.

Another benefit of providing a home’s thermal envelope with good insulation is providing the home with effective sound barriers. Using these same tools to create comfort can do so in other ways. Sound pollution in a home can be damaging to a families’ wellbeing. From outside noise to the sound of people talking in the next room, the level of noisiness in a house matters to its level of comfort.

The use of open-cell spray foam can assist in eliminating or greatly reducing the amount of noise that happens in a structure. The ceiling or attic space is a good place to start, especially for those who live near an airport.

Deciding on the proper insulation takes a bit of research, but choosing the correct type will prove invaluable in providing the most efficient environment for living and working.

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