Insulation Fact Sheet

Insulation Fact Sheet

Contents:

Introduction

  • Why Insulate Your House?
  • How Insulation Works

Which Kind of Insulation is Best?

  • What Is an R-Value?
  • Reading the Label
  • Insulation Product Types

Insulating a New House

  • Where and How Much
  • Air Sealing
  • Moisture Control and Ventilation
  • Installation Issues
  • Precautions
  • Attics
  • Walls
  • Design Options
    • Insulation Fact Sheet
    • Crawlspaces and Slabs
    • Advanced Wall Framing
    • Metal Framing
    • Insulating Concrete Forms
    • Massive Walls
    • Structural Insulated Panels
    • External Insulation Finish System
    • Attic Ventilation or a Cathedralized Attic
    • Adding Insulation to an Existing House

      • Where and How Much
      • How Much Insulation Do I Already Have?
      • Air Sealing
      • Moisture Control and Ventilation
      • Insulation Installation, the Retrofit Challenge
      • Precautions
      • Attics
      • Walls
      • Basement Walls
      • Floors and Crawlspaces

      Resources and Links

      About This Fact Sheet

      Which Kind Of Insulation Is Best?

      Based on our email, this is one of the most popular questions homeowners ask before buying insulation. The answer is that the ‘best’ type of insulation depends on:

      • how much insulation is needed,
      • the accessibility of the insulation location,
      • the space available for the insulation,
      • local availability and price of insulation, and
      • other considerations unique to each purchaser.

      Whenever you compare insulation products, it is critical that you base your comparison on equal R-values.

      What Is an R-Value?

      Insulation is rated in terms of thermal resistance, called R-value, which indicates the resistance to heat flow. The higher the R-value, the greater the insulating effectiveness. The R-value of thermal insulation depends on the type of material, its thickness, and its density. In calculating the R-value of a multi-layered installation, the R-values of the individual layers are added.

      The effectiveness of an insulated ceiling, wall or floor depends on how and where the insulation is installed.

      • Insulation which is compressed will not give you its full rated R-value. This can happen if you add denser insulation on top of lighter insulation in an attic. It also happens if you place batts rated for one thickness into a thinner cavity, such as placing R-19 insulation rated for 6 1/4 inches into a 5 1/2 inch wall cavity.
      • Insulation placed between joists, rafters, and studs does not retard heat flow through those joists or studs. This heat flow is called thermal bridging. So, the overall R-value of a wall or ceiling will be somewhat different from the R-value of the insulation itself. That is why it is important that attic insulation cover the tops of the joists and that is also why we often recommend the use of insulative sheathing on walls. The short-circuiting through metal framing is much greater than that through wood-framed walls; sometimes the insulated metal wall’s overall R-value can be as low as half the insulation’s R-value.

      Reading the Label

      No matter what kind of insulation you buy, check the information on the product label to make sure that the product is suitable for the intended application. To protect consumers, the Federal Trade Commission has very clear rules about the R-value label that must be placed on all residential insulation products, whether they are installed by professionals, or whether they are purchased at a local supply store. These labels include a clearly stated R-value and information about health, safety, and fire-hazard issues. Take time to read the label BEFORE installing the insulation. Insist that any contractor installing insulation provide the product labels from EACH package (which will also tell you how many packages were used). Many special products have been developed to give higher R-values with less thickness. On the other hand, some materials require a greater initial thickness to offset eventual settling or to ensure that you get the rated R-value under a range of temperature conditions.

      Insulation Product Types

      Some types of insulation require professional installation, and others you can install yourself. You should consider the several forms of insulation available, their R-values, and the thickness needed. The type of insulation you use will be determined by the nature of the spaces in the house that you plan to insulate. For example, since you cannot conveniently "pour" insulation into an overhead space, blankets, spray-foam, board products, or reflective systems are used between the joists of an unfinished basement ceiling. The most economical way to fill closed cavities in finished walls is with blown-in insulation applied with pneumatic equipment or with sprayed-in-place foam insulation.

      The different forms of insulation can be used together. For example, you can add batt or roll insulation over loose-fill insulation, or vice-versa. Usually, material of higher density (weight per unit volume) should not be placed on top of lower density insulation that is easily compressed. Doing so will reduce the thickness of the material underneath and thereby lower its R-value. There is one exception to this general rule: When attic temperatures drop below 0°F, some low-density, fiberglass, loose-fill insulation installations may allow air to circulate between the top of your ceiling and the attic, decreasing the effectiveness of the insulation. You can eliminate this air circulation by covering the low-density, loose-fill insulation with a blanket insulation product or with a higher density loose-fill insulation.


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