Building Insulation

Insulation is not the most attention grabbing building component, but it is essential to both the performance of the building and health of the occupants. Without sufficient insulation, large portions of the energy used to heat or cool a building will be lost to the outdoors.  Insufficient insulation can also lead to mold problems as heated air rapidly cools and causes water vapor to condense. Historically, mud, asbestos, and cork were used as insulation materials for buildings and pipes.  The insulation products available today are much more effective, especially in conjunction with air sealing and ventilation.

How It Works

Insulation, which contains many tiny air cavities, slows heat transmission when installed on a building’s interior or exterior surface, or in building cavities.  Each type of insulation material receives an R-value rating, which is a measure of its thermal resistance.  A higher R-value indicates a better insulator.  The R-value of materials changes with their density, so especially when installing loose-fill insulation, the appropriate density is needed to achieve peak R-value.  Appropriate insulation depends on regional climate and a building’s mass size.  Check Pennsylvania building codes for up-to-date minimum R-values for ceilings, walls, crawlspaces, and other building features. 

Historically, mud, asbestos, and cork were used as insulation materials for buildings and pipes.

The best way to insulate a building is to have a well-defined thermal boundary.  The thermal boundary of a building separates the conditioned (heated or cooled) spaces from outdoor or unconditioned areas.  A building should be insulated continuously around the thermal boundary, including corners and edges.  The surface of ducts and furnace cabinets that lie outside the thermal boundary, such as in an unfinished basement, should also be insulated.  A common problem that arises when creating a thermal boundary is thermal bridging, which happens when conductive materials span across a barrier and allow heat to flow from one side to the other.  For instance, when insulation is placed between wooden studs but not behind or covering the studs, the wood will continue to conduct heat through the wall.  Avoid thermal bridging by minimizing use of conductive materials such as wood, steel, and aluminum, or by including thermal breaks so that conductive materials are not in contact with each other.  A building’s heating load can be calculated by taking into account the various materials in each wall in order to see how insulation affects savings.

One of the main misconceptions regarding insulation is that it is automatically an air barrier.  While some types of insulation can act as a moderately effective air barrier, such as extruded polystyrene or spray foam, this generalization cannot be assumed.  In particular, insulation batts and blankets do NOT serve as air barriers.  Air flowing through or around insulation is actually one of the biggest causes of energy waste.  Therefore, it is imperative to install both a thermal barrier and an air barrier, usually in full contact with each other.  Another important step is to seal all insulation seams with insulation tape or spray foam to make the thermal and air barriers continuous.  Even gaps that take up a tiny percentage of wall area can cause major inefficiencies.

A home’s basement and attic require special consideration when insulating.  Either may be left unfinished, which most often corresponds with exclusion from the thermal boundary.  Homeowners must consider the space’s intended purpose, as well as conditions such as how much of a basement is above grade.  In basements, moisture control measures should not be overlooked.  A damp basement can lead to mold problems, structural damage, or rotting insulation.

Types, Cost, and Installation

Insulation comes in many forms, including batts, rigid boards, spray foam, and loose fill.  Insulation’s R-value varies depending on its quality!  Better insulation will cost more upfront, but in the long run will pay off with substantial energy savings, as well as less wear and tear on HVAC systems.

Photo credit: flickr-Logantech

Insulation batts (flickr: Logantech)

Flexible batts and blankets, composed of loosely bound fibers of fiberglass, mineral wool, denim, or natural fibers, are the most widely used insulation in the United States.  Most are faced with foil or kraft paper.  Make sure the desired brand does not use formaldehyde as a binding agent.   Blankets are not pre-cut, whereas batts come in sizes that fit easily between studs or joists spaced at 16 or 24 inches.  Batts should be cut or split to fit around obstacles, not squished.  Likewise, they should be cut exactly to length to fill a cavity.  If a batt is not in continuous contact with the adjacent surface, its R-value can be substantially diminished.  Batts and blankets typically have R-values between R-2.5 and R-4.5 per inch.


Rigid board insulation (flickr: Martin Pettitt)

Rigid board insulation (flickr: Martin Pettitt)

Another common type of insulation, foam board, is highly water-resistant and serves well as a thermal break because it covers entire walls, including framing.  Foam board is sold in 4’ x 8’ sheets ($10-$60 per sheet) and its R-value depends what material it contains.  For instance, expanded polystyrene (EPS) has a similar R-value to insulation batts, between R-3.6 and R-4.2 per inch.  Extruded polystyrene (XPS) is denser and has a higher R-value of around R-5 per inch.  Polyisocyanurate board has one of the highest R-values of any building insulation material on the market, at R-5.6 to R-7 per inch.  Extruded polystyrene and polyisocyanurate boards are useful in applications with limited space because of their high R-values per inch.  Other rigid insulation boards such as fiberglass or mineral wool board can also be found, but they do not share all the properties of foam board.

spray foam insulation

Spray foam insulation (flickr: ilovebutter)

Spray foam is an effective and versatile type of insulation.  Its two components are mixed at the tip of a spray gun, forming a liquid foam that will expand and harden on a surface.  Polyurethane is the basis of most spray foams, although compositions vary.  Check to be sure the desired brand of foam does not contain HFCs or HCFCs, which are greenhouse gases.  Spray foam is ideal for irregular surfaces and small gaps, cracks, or seams, but it can also be used to insulate large areas such as walls, ceilings, or even roof exteriors.  Protective gear must be worn when installing spray foam insulation and often the best strategy is to hire a professional.  Spray foam comes in open-cell and closed-cell variations, with a few key differences.  Closed-cell foam has an R-value of R-6 to R-7 per inch rather than the R-3 to R-4 per inch of open-cell and many other types of insulation.  Open-cell foam should not be used in moisture-prone areas.  It is cheaper than closed-cell, although both are significantly more costly than batts.  Spray foam does serve as an air barrier, which helps eliminate additional costs.

Loose fill insulation is useful for closed spaces (i.e., retrofitted walls), as well as attics.  It may be made of blown fiberglass or mineral wool, blown cellulose, vermiculite, or perlite.  Vermiculite and perlite are particularly good for cavities with rough surfaces where blown insulation might get caught and obstruct the installation, but make sure to look for brands that are asbestos-free.  Typical R-values for loose fill insulation lie between R-2.5 and R-4.5, and R-values for blown insulation are optimized when it is installed according to its ideal density.

SIPs (flickr: jsbarrie)

SIPs (flickr: jsbarrie)

Two relatively recent insulation technologies, structural insulated panels (SIPs) and insulated concrete forms (ICFs), are gaining a lot of traction in the green building market.  SIPs are a multifunctional material made of rigid foam insulation sandwiched between two structural boards, generally oriented strand board.  The foam core is typically expanded polystyrene, polyurethane, or polyisocyanurate.  SIPs serve as structural components, insulation, and an air barrier in buildings.  They are quite sturdy and prevent buildings from warping or sagging.  The panels are made to order for each building, so they come in a variety of dimensions (up to 8’ x 24’), thicknesses (4.5”-12.25”), and even shapes.  Because they are prefabricated, using SIPs can save both time and labor costs compared to other methods of framing and insulating a new construction project.  They can even be purchased with window openings pre-cut and electrical chases already installed.  SIPs also result in extremely airtight buildings, so a good ventilation system is needed.  The R-value of a structural insulated panel depends on its thickness, ranging anywhere from R-14 to R-45, but it’s notable that SIPs with relatively low R-values may still outperform other insulation types with slightly higher ratings because, for SIPs, the R-value already takes the whole wall into consideration.  SIPs are more expensive than traditional materials, but they combine several functions.  Overall, they are no more difficult to install than other framing and insulation, but do require certain knowledge and equipment.  Projects built with SIPs must be carefully planned ahead of time to avoid mistakes, last-minute changes, and delays from needing to order additional panels.   Alterations to SIPs are best done with specialized tools and a crane is also needed to lift upper-story and roof panels into place.  Panels are held together with a special adhesive and, once they are in place, seams are taped, caulked, or sealed with spray foam.  Particular methods are employed for installing recessed lighting, plumbing, exterior cladding, and roofing in a SIPs building.  SIPs must be protected from exposure to moisture.

Insulated concrete forms begin as individual blocks with two sides of foam held together with plastic spacers.  The blocks, which come in different shapes for corners and walls, fit together to make hollow foam structures.  Builders then pump concrete into the interior and the foam-insulated concrete walls are complete.  ICFs are incredibly strong, more resistant to moisture than SIPs, fire-resistant, and noise-deadening.  They are particularly useful for basements or areas that need strong reinforcement.  ICF walls are typically around R-12 and, because of their high thermal mass, they help improve energy performance in locations that regularly have hotter days and colder nights than the desired indoor temperature.  Passive heating may be possible.  On the other hand, ICF buildings require a large amount of concrete and are hard to renovate once they are built.  They are more expensive than traditional types of insulation, but, like SIPs, they serve several purposes in a building.

Lastly, an unconventional insulation method involves the use of straw bales, which are another dual-purpose insulator and structural material.  Building with straw bales makes use of a waste product to create an easily customizable space with thick walls insulated up to R-35.  Like many insulation materials, straw is susceptible to moisture damage.  Usually covered in stucco, clay, or plaster, straw bale buildings are fire-resistant and can last a long time when properly maintained.  Construction or demolition waste is biodegradable.

Insulation may contribute to new homes meeting the requirements for general energy-efficiency tax credits (for homeowners and builders) based on reduction of energy use relative to the International Energy Conservation Code 2006 baseline.

Advantages of Good Insulation

  • Conserve energy used to heat and cool a building
  • Save money on energy bills, HVAC equipment, and even dehumidification
  • Enhance comfort by reducing interior temperature variability
  • May also serve as a noise, air, and/or vapor barrier or may add structural strength

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