Question

For a LEED Gold home, how much insulation is required in roof, walls, and floors?

Asked by Peter Strainer
Newburyport, MA

R factor for roof, wall, and flooring a LEED gold home?

Answer

Cynthia Phakos

Answered by Cynthia Phakos

Los Angeles, CA

Koffka Phakos Design

July 13, 2011

Before getting into the LEED requirements, we must first look at your local building codes.

The Massachusetts residential building code

I spoke to the Newburyport Building Department and they referred me to the Board of Building Regulations and Standards (BBRS) for Massachusetts. The Massachusetts’ residential code is comprised of the International Residential CODE 2009 (IRC) with an amendments package.

  • The IRC is a comprehensive code that creates minimum regulations for one- and two-family dwellings of three stories or less for plumbing, mechanical, fuel gas, energy and electrical provisions.
  • Massachusetts has amended the code by adopting the 2009 International Energy Conservation Code (IECC) for residential energy requirements.
  • An overview of 2009 IECC can be found online here which summarizes the Climate Zones, required residential and commercial energy efficiency requirements (R Values included).

The IECC is the code recognized by the federal law as the standard for energy-efficient residential construction and that the American Recover and Reinvestment Act recognizes for funding.

IECC 2009 Requirements for Your Climate Zone 5 (Massachusetts)

Ceilings (Roof) 38R
Wood Frame Walls 20R (or 13 + 5)
Mass Walls 13/17
Floor 30R
Basement Foundation Walls 10/13

Notes:

  • Wood Frame Walls: the 13 + 5 refers to two continuous insulations. (This is the sum of the cavity insulation plus insulated sheathing.) 20R is required for cavity insulation.
  • Mass Walls: the second R Value for the mass walls applies when more than half the insulation is on the interior of the mass wall.
  • Basement Foundation Walls: For basement walls the insulation must be from the top of the wall down 10 feet below grade or to the basement floor, whichever less.

LEED for Homes Requirements

There are two methods in the LEED for Homes Energy and Atmosphere (EA) section to evaluate the R Value for the insulation in your home.

  • EA1.1 is the Energy Performance Method and
  • EA2.1 is the Prescriptive Method.

EA1.1: The Performance Approach is recommended if you have incorporated passive design elements into the home such as shading or a green roof which will affect the heating or cooling of your home.

In this method the home is modeled with a software program and then when the home is built it is tested to verify that installations of various components meet the performance criteria.

As a prerequisite for the performance method, the home must be ENERGY STAR rated and points are awarded by the percentage you exceed this level. As of April 2011 you must follow Energy Star Version 3 for Energy Star homes. Version 3 refers to the 2009 IECC Code and so the R Values above would qualify as a minimum for the performance approach.

EA2.1: For the prescriptive method, the insulation must meet the requirements for your Climate Zone as a pre-requisite and if you exceed this by 5% you receive 2 points. LEED references the 2004 IECC under this section. I heard back from the USGBC that the code referenced should be the 2004 IRC, not the IECC.

The 2004 IRC is also referenced under Version 2 of Energy Star. The International Residential Code (IRC) and The International Energy Conservation Code (IECC) were developed by the International Code Council (ICC) in the year 2000 and are amended every three years, so I am not sure where one would find the 2004 IRC. It may be based on a version adopted by a state in 2004. I suggest that if you are using the Prescriptive Method than you go with the 2009 IECC.

As you are working toward a Gold LEED Rating you will probably want to go with the performance method.

  • For the insulation you should start with the required and then see how insulation with a higher R Value affects the performance of the home.
  • This allows projects to decide on the most cost effective strategies for their building to save energy.

Testing

Insulation is an important component of a comfortable, energy-efficient home.

It is not only about installing the right amount of insulation but also installing it properly.

LEED for Homes takes into account these two aspects and so LEED requires not only the appropriate insulation but then requires the proper testing procedures to insure its effectiveness.

In my research I found some interesting statistics (here) which point to the importance of testing the installed insulations.

“Recent studies have found that over a third of new homes have lower levels of insulation installed than specified and an additional fifth have serious installation problems that will result in significantly decreased effectiveness of the insulation. In addition, virtually all of the homes studied were found to have numerous insulation installation defects that reduce the performance of the insulation well below its rated R-value.”

 

For more information:

Read "Getting Started on Your LEED Home" a post by green builder Rick Goyette.

Tagged In: leed for homes

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