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Builders Websource Tech Note #021801-1


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With ever increasing costs of energy, proper home insulation is essential to ensuring long-term comfort and value. Furthermore, insulation also has significant sound proofing benefits that add peace and quiet to a personal residence or commercial structure. Based on research by the U.S. Department of Energy -- coupled with the latest information from NAIMA and leading insulation manufacturers, this Builders Websource Tech Note explores various types of insulation with special focus on fiber glass and related building systems that will ensure enduring comfort throughout a structure's life. In addition, an interactive online "R-value" calculator developed by the U.S. Department of Energy helps architects, building designers, contractors and insulation specifiers to determine recommended insulation levels for both new and existing construction based on postal zip code.

Table of Contents

Introduction: Why Insulate?
"Why Insulate" seems like a rhetorical question with an obvious answer: to save energy while providing long-term comfort inside a structure. However, what's not so obvious is that most homes are severely under-insulated -- either by design (to save building costs) or due to oversight in the design process. With escalating energy costs and increasing greenhouse effects, construction professionals have a responsibility to the end client -- as well as the environment -- to ensure that new designs reflect the latest insulation recommendations, even when these recommendations exceed local minimum code requirements.

Insufficient insulation exaggerates temperature swings inside a structure, causing uncomfortable draftiness. Summer days feel hotter...and winters feel colder when a home has insufficient insulation. Furthermore, under-insulated homes can cost occupants hundreds -- or thousands of dollars a year in higher heating and air conditioning bills. These costs are wasted year after year and the energy is non-recoverable. Whereas spending a little more up front pays dividends every year as the incremental cost of better insulation is amortized over the lifetime of the structure.

With so much information (and mis-information) about insulation, this Builders Websource Tech Note helps to educate designers, contractors and homeowners about this important subject by providing an in-depth look at insulation choices.

Furthermore, frequently overlooked are the sound-proofing qualities that insulation offers when combined with other sound-reduction construction techniques. Therefore, sound attenuation is one of the topics that this tech note explores.

Finally, the importance of proper home ventilation is also addressed which, if left unchecked, could result in unhealthy stale air inside tightly built new homes.

What is Insulation?
Insulation is any material or gas that provides a break in conductivity between any differing surfaces. In the case of electrical wiring, the outer jacket is also called insulation...since it prevents the conductivity of electricity from passing from the wire to a person touching the outer jacket of the wire, for example.

Insulation refers to special materials that impede the "thermal" conductivity between surfaces. Most of us think of traditional "blown in" type insulation or the colorful yellow or pink fiber glass or mineral wool "batt" insulation found at the local building supply store.

According to the North American Insulation Manufacturer's Association (NAIMA), insulation provides two primary comfort benefits:

    Insulation resists the flow of heat. Heat is a form of energy - it always travels from hot to cold - flowing outward in winter and inward in summer. By reducing heat flow, a properly insulated home uses less energy in winter for heating and less in the summer for cooling.
    Insulation is also an excellent sound absorber as well as an energy saver. When installed in the walls and ceilings, it can reduce the transmission of sound. Sound transmission is noise that travels from room to room - or from home to home - or from appliances such as washers, dryers, heating and air conditioning systems, phones, radios and TV's.
Where to Insulate
For maximum benefit, insulation should be installed in the following areas of the home:
Click for larger viewTOTAL INSULATION SYSTEM

Insulation must be designed as a total system, starting with the foundation, basement, crawl space, living areas and attic.

Drawing courtesy US Department of Energy
  1. In unfinished attic spaces, insulate between and over the floor joists to seal off living spaces below.*
    (1A) attic access door
  2. In finished attic rooms with or without dormer, insulate ...
    (2A) between the studs of "knee" walls;
    (2B) between the studs and rafters of exterior walls and roof;
    (2C) ceilings with cold spaces above;
    (2D) extend insulation into joist space to reduce air flows.
  3. All exterior walls, including ...
    (3A) walls between living spaces and unheated garages, shed roofs, or storage areas;
    (3B) foundation walls above ground level; 3C foundation walls in heated basements, full wall either interior or exterior.
  4. Floors above cold spaces, such as vented craw spaces and unheated garages. Also insulate ...
    (4A) any portion of the floor in a room that is cantilevered beyond the exterior wall below;
    (4B) slab floors built directly on the ground;**
    (4C) as an alternative to floor insulation, foundation walls of un-vented crawl spaces;
    (4D) extend insulation into joist space to reduce air flows.
  5. Band joists.
  6. Replacement or storm windows and caulk and seal around all windows and doors.

*Well-insulated attics, crawl spaces, storage areas, and other enclosed cavities should be ventilated to prevent excess moisture build-up.

**For new construction, slab on grade insulation should be installed to the extent required by building codes, or greater.

Types of Insulation

In the form of batts or rolls, blankets are flexible products made from mineral fibers. They are available in widths suited to standard spacings of wall studs and attic or floor joists. Continuous rolls can be hand-cut and trimmed to fit. They are available with or without vapor retarder facings. Batts with a special flame-resistant facing are available in various widths for basement walls where the insulation will be left exposed.


Loose-fill insulation includes loose fibers or fiber pellets that are blown into building cavities or attics using special pneumatic equipment. Another form includes fibers that are co-sprayed with an adhesive to make them resistant to settling. The blown-in material can provide additional resistance to air infiltration if the insulation is sufficiently dense.


This type is made from fibrous materials or plastic foams and is pressed or extruded into board-like forms and molded pipe-coverings. These provide thermal and acoustical insulation, strength with low weight, and coverage with few heat loss paths. Such boards may be faced with a reflective foil that reduces heat flow when next to an air space.


Reflective systems are fabricated from aluminum foils with a variety of backings such as kraft paper, plastic film, polyethylene bubbles, or cardboard. The resistance to heat flow depends on the heat flow direction, and this type of insulation is most effective in reducing downward heat flow. Reflective systems are typically located between roof rafters, floor joists, or wall studs.If a single reflective surface is used alone and faces an open space, such as an attic, it is called a RADIANT BARRIER. Radiant barrriers are sometimes used in buildings to reduce summer heat gain and winter heat loss. They are more effective in hot climates than in cool climates. All radiant barriers must have a low emittance (0.1 or less) and high reflectance (0.9 or more).

Comparison of Insulation Types

(source: USDOE/CE-0180)

Physical Form Install
Blankets: Batts or Rolls
  • Fiber glass
  • Rock wool
  • Mineral wool (MW)
Friction fit between studs, joists and beams

Staple flange to stud edge
walls, floors and ceilings DIY

Suited for standard stud and joist spacing, which is relatively free from obstructions
Loose-Fill (blown-in) or Spray-applied
  • Rock wool
  • Fiber glass
  • Cellulose
  • Polyurethane foam
Blow into place or spray apply by special equipment

(Also, BIBS - Blown In Blanket System) which uses nylon netting
Enclosed existing wall cavities or open new wall cavities

Unfinished attic floors and hard to reach places
Commonly used insulation for retrofits (adding insulation to existing finished areas)

Good for irregularly shaped areas and around obstructions
Rigid Insulation
  • Extruded polystyrene foam (XPS)
  • Expanded polystyrene foam (EPS or beadboard)
  • Polyurethane foam
  • Polyisocyanurate foam
Interior applications: Cover with 1/2-inch gypsum board or other building-code approved material for fire safety

Exterior applications: Cover with weather-proof facing to protect from ultraviolet
Basement walls

Exterior walls under finishing (Some foam boards include a foil facing which will act as a vapor retarder.

Unvented low slope roofs
High insulating density per inch of thickness

Mitigates thermal short circuits when installed continuously over frames or joists.
Reflective Systems
  • Foil-faced paper
  • Foil-faced polyethylene bubbles
  • Foil-faced plastic film
  • Foil-faced cardboard
Foils, films, or papers: Fit between wood-frame studs joists, and beams Unfinished ceilings, walls, and floors DIY

All suitable for framing at standard spacing. Bubble-form suitable if framing is irregular or if obstructions are present

Effectiveness depends on spacing and heat flow direction
Loose-Fill (poured in)
Vermiculite or Perlite
not currently used for home insulation, but may be found in older homes
How Much Insulation Is Required?
How much insulation is required depends on where you live and the expected temperature extremes. Insulation is identified and labeled according to its R-value. "R" is resistance to heat flow. Higher R-values provide greater insulation. For example, R-19 insulation provides 72% more insulating power than R-11.

The US Department of Energy defines six national zones for optimum insulation efficiency.

Drawing courtesy NAIMA

The following table adapted from the U.S. Department of Energy outlines the minimum recommended insulation values for new construction, broken into 6 nationwide "insulation" zones. Zones 1 and 2 generally cover the Rocky-Mountain, Upper Midwest and Northeast states (including Alaska), whereas Zone 3 covers the Pacific Northwest and much of the Southwest, lower-Midwest and Southern states, with Zone 4 covering the California Central Valley, Southern Texas and Florida, with Zones 5 and 6 covering the mild California coastal regions from San Francisco on south to San Diego (Hawaii is Zone 6).

Zone Energy Type Ceilings Walls/Floors Basement
  Gas Heat
Attic Cath Wall
Flr Crwl
Int Ext
1 x x x   R49 R38 R18 R25 R19 R8 R11 R10
1       x R49 R60 R28 R25 R19 R8 R19 R15
2 x x x   R49 R38 R18 R25 R19 R8 R11 R10
2       x R49 R38 R22 R25 R19 R8 R19 R15
3 x x x x R49 R38 R18 R25 R19 R8 R11 R10
4 x x x   R38 R38 R13 R13 R19 R8 R11 R4
4       x R49 R38 R18 R25 R19 R8 R11 R10
5 x       R38 R30 R13 R11 R13 R8 R11 R4
5   x x   R38 R38 R13 R13 R19 R8 R11 R4
5       x R49 R38 R18 R25 R19 R8 R11 R10
6 x       R22 R22 R11 R11 R11 (c) R11 R4
6   x x   R38 R30 R13 R11 R13 R4 R11 R4
6       x R49 R38 R18 R25 R19 R8 R11 R10


(a) R18, R22 and R28 exterior wall systems can be achieved by either cavity insulation or cavity insulation with insulating sheathing.

For 2x4 walls, use either 3-1/2" thick R15 or 3-1/2" thick R13 fiber glass insulation with insulating sheathing.

For 2x6 walls, use either 6-1/4" thick R19 or 5-1/2" thick R21 fiber glass insulation.

(b) Insulate crawl space walls only if the crawl space is dray all year, the floor above is not insulated, and all ventilation to the  crawl space is blocked. A vapor barrier (e.g., 4- or 6-mil polyethylene film) should be installed on the ground to reduce moisture migration into the crawl space.

(c) No slab edge insulation is recommended.
R-Value Calculator
(US Only)
For a more precise assessment of the US Department of Energy recommended insulation values, the following R-Value calculator provides a DOE-certified recommendation that you can use for design purposes. These values may vary from local codes. You should always consult you building department to ensure you are following the more rigorous standard. A more advanced version of this calculator is available by clicking HERE.
Simplified R-Value Recommendation Form

Home Type:

Fuel Type:

US ZIP Code (first 3 digits):

Owens Corning Fiber Glass Insulation

Owens Corning PINK Fiber Glass Insulation

  R-Value Thick Wide Long Sq. Ft./
R-11 3.5" 15" 93" 155.00 Interior walls Noise Control
R-13 3.5" 15" 93" 125.00 Finished attic
Basement walls
Exterior Walls
R-15 3.5" 15" 93" 67.8 Finished attic
Exterior Walls
R-19 6.25" 15" 93" 77.5 Crawlspace
Finished Attic
Basement walls
Exterior Walls
R-21 5.5" 15" 93" 67.8 Finished Attic
Basement Walls
Exterior Walls
R-30 9.5" 16" 48" 53.3 Attic
R-30c 8.25" 15.5" 48" 56.8 Cathedral Ceilings
R-38 12" 16" 48" 42.7 Attic
Basement Walls
R-38c 10.5" 15.5" 48" 41.3 Cathedral Ceilings
Noise Reduction Techniques
When included as part of an overall noise reduction system, insulation plays a key role in minimizing sound transmission between interior rooms.

Most leading manufacturers offer special insulation targeting sound attention applications, such as Johns Manville ComfortTherm®, CertainTeed NoiseReducer®, or Owens Corning QuietZone®, for example.  While some of these batts are unfaced, others are faced or fully sealed in a special poly-wrap exterior surface that seals in the fibers, reducing airborne insulation fibers during installation.

Contractors and consumers should be aware that sound attenuation batts are generally the same product as standard insulation, repositioned to highlight the special noise reduction properties of insulation. A leading insulation manufacturer points out that there are virtually no acoustical differences between sound attenuation batts and regular batts:

"The only difference between [sound attentuation batts] and R-11 or R-13 batts is that the [sound attenuation batts] have not been tested for R-value. The vapor barrier has no effect on the sound control quality of the insulation."

Rather than focusing too much on the insulation alone, which only adds a few dB improvement in sound transmission control, Owens Corning emphasizes overall sound reduction system, comprising special stud construction, insulation, acoustical caulking, and double-layers of drywall. When used in combination, the QuietZone® system reduces perceived sound transmission by up 80%. Uses four techniques, sound to control noise in your home – it absorbs, blocks, breaks and isolates it.


Acoutstic sound attenuation batts reduce noise through absorption. The absorption method converts sound waves into energy that is captured by insulation.


Building a continuous barrier that stops air movement reduces airborne sound transmission. Acoustic caulk reduces noise using the principle of blocking airborne noise paths through cracks, holes or gaps in a wall.


Interior and exterior walls, ceilings, floors, and the studs and joists holding them, all allow sound to travel between and through them.  Resilient sound channels or specially designed studs with metal spacer clips break up sound waves as they travel through the structure.


Acoustic floor mat deadens noise and isolates or confines it

To provide better breaking, Owens Corning and Trus Joist™ have jointly developed a framing system that not only offers unique construction and superior strength, but also superior acoustic performance.

Sound vibrations readily permeate conventional wood stud framing. QuietZone Acoustic Wall Framing comes with a built-in acoustically resilient metal clip. The clip attaches between two sections of engineered lumber and causes sound vibrations to be greatly reduced between the two walls before exiting.

  • Wall floats to absorb sound vibrations and reduce transmission as sound enters the wall.
  • Sound vibrations from walls are greatly reduced when dispersed by metal clips.
  • Wall is attached to the top and bottom framing plates, securely grounding the wall and reducing sound transmission.

2x4 QuietZone Acoustic Wall Framing has limited load-bearing capabilities and should be used on interior walls only.

* 2x6 QuietZone Acoustic Wall Framing has load-bearing capabilities similar to standard 2x4 wood framing.

JM Comfort-Therm Sound Attenuation Batts

JM ComfortTherm ™ Encapsulated Batts and Rolls

Facing R-Value Thick Wide Long Batts/
Sq. Ft./
Poly R-11 3 1/2" 15" 93" 16 4 155.00 B001
Poly R-11 3 1/2" 15" 93" 16 4 155.00 A001
Poly R-11 3 1/2" 15" 40" 1 12 50.00 B006
Poly R-13 3 1/2" 15" 93" 12 4 116.25 B002
Poly R-13 3 1/2" 15" 40" 1 12 50.00 B007
Poly R-15 3 1/2" 15" 93" 7 4 67.81 B003
Poly R-19 6 1/4" 15" 93" 7 4 67.81 B004
Poly R-19 6 1/4" 23" 93" 7 4 103.98 B008
Poly R-19* 6 1/4" 15" 48" 14 4 70.00 B023
Poly R-21 5 1/2" 15" 93" 6 4 58.12 B009
Poly R-25 8 1/4" 15" 18" 1 12 22.50 B005
Poly R-25 8 1/4" 23" 18" 1 8 34.50 B012
Note: Rolls are stretch-wrapped, batts are strap-wrapped.
* Reversed vapor retarder for under floor applications.
Refer to Product Availability Sheet for latest
and most complete product offerings.
Moisture and Ventilation
While there is no question that well insulated homes provide energy savings and comfort, there is increasing evidence that super-insulated homes can result in poor indoor air quality. Older homes breathe more easily without heavy insulation and housewrap vapor barriers common today, increasing the hourly air exchange rate in cubic feet per minute. To feel air movement for yourself, simply stick your hand near an electrical socket on a cold night and you can feel the air passing through.

However, if the home is so well sealed that it cannot breathe, then indoor air pollution can rise to unhealthy levels. Moisture from bathrooms and cooking, as well as fumes from fireplaces, furnaces and water heaters can quickly combine into an unhealthful mixture, not to mention other sources of air pollution such as the gradual outgassing of furniture, paint, carpeting and other building products. Together, these lead to poor indoor air quality, many times worse than the outdoor air quality that normally commands our focus.

As a result, when building a super-insulated home, proper attention must be given in the design of the HVAC system. It is essential to provide for a filtered fresh air intake, coupled with an air-to-air heat exchanger. This fresh air intake, when mixed with the re-circulated air inside the home, will provide an on-going supply of healthy air for the occupants.

The heat exchanger will help to minimize heat loss by pre-warming the incoming fresh air with the outgoing stale air. This process often results in condensation which must be drained to a suitable outside location away from the foundation. Never drain condensation into a sewer line directly, as this will provide an immediate path for sewer gases to penetrate the house, which is not only dangerous, but further aggravates indoor air pollution and odors.

Insulation is essential to providing long-term thermal and acoustic comfort in residential and commercial structures. Fiber glass insulation is the most widely installed insulation today. Standard widths are available for both wood and steel framed construction. With continually increasing costs of energy, new more rigid recommendations require more insulation than ever to keep occupants comfortable while minimizing costly gas or electricity for heating and cooling. Proper ventilation is essential when designing a well insulated home in order to prevent unhealthy indoor air quality. Contents

ASTM International