# Insulation can save you money.

**Why Insulate Your House?**

Heating and cooling account for 50 to 70% of the energy used in the average American home. Inadequate insulation and air leakage are leading causes of energy waste in most homes. Insulation:

- saves money and our nation’s limited energy resources
- makes your house more comfortable by helping to maintain a uniform temperature throughout the house, and
- makes walls, ceilings, and floors warmer in the winter and cooler in the summer.

## 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.

Insulation Type | R-Value per inch thickness |

Fiberglass blanket or batt | 3.2 |

High-performance fiber glass blanket or batt | 3.8 |

Loose-fill fiber glass | 2.5 |

Loose-fill rock wool | 2.8 |

Loose-fill cellulose | 3.5 |

Perlite or vermilculite | 2.7 |

Expanded polystyrene board | 3.8 |

Extruded polystyrene board | 4.8 |

Polyisocyanurate board, unfaced | 5.8 |

Polyisocyanurate board, foil-faced | 7.0 |

Spray polyurethane foam | 5.9 |

- Let’s use an example where we have 6″ of cellulose covered by 6″ of fiber glass batts in the attic. We take the R-value of cellulose, which is 3.5 and multiply it by 6 to get 21.0. We then take the R-value of fiberglass batts, which is 3.2 and multiply that by 6 to get 19.2. Since the insulation is layered one on top of the other, we add them together 21.0 + 19.2 to get 40.2.
- If we live in a region where the recommended R-value is 38, we already have 40.2, so we do not need to add insulation. What happens though, if we live in a region that recommends 49-we need to add some insulation, but how much? That’s easy too! Take the recommended R-value, which is 49, and subtract what we have already, which is 40.2 (49 – 40.2 to get 8.8). We need to add an R-value of 8.8. The R-value of an inch of fiber glass batts is 3.2. Divide the amount we need to add, 8.8, by the R-value per inch, 3.2, to get 2.75. Batt and blanket insulation comes in several thicknesses. One of these is 3-1/2″. So one layer of 3-1/2″ fiber glass batt insulation added to what we have will give us a little more than what we need. It is always ok to add more insulation than is recommended. Just remember not to pack it too tightly because packing it can reduce its effectiveness.