HOME ENERGY SOLUTIONS

Weatherization Specification Manual

FLAT AND LOW-SLOPED ROOFS

FL 1.0—Introduction

Insulating low-sloped or flat roofs is technically difficult, and a wide gap exists between theoretical and field applications. Plans for retrofitting these roofs should be reviewed by the local building jurisdiction. Building permits and code compliance are the responsibility of the homeowner and contractor. All information provided here is for general reference only and Home Energy Solutions does not assume any liability for its use.

Exterior applications:

Any roof cavity shall be fully insulated (cavity filled) before exterior insulation is installed. Minimum exterior insulation shall be R-19 or a combined cavity, and exterior insulation total of R-30.

Ceiling cavity applications:

Ceiling cavity insulation shall completely fill cavity.

FL 1.1—Preparation

• Recessed lights in insulated cavities shall be IC or ICT rated.
• All plumbing vents, kitchen fans, bath fans, wood stoves, and other fixtures shall vent to the outside of the new roof and be adequately flashed and sealed.

If there is evidence of excessive moisture, including signs of mold, mildew, humidity, dry rot, or wood-boring insects, the following preparation is required before insulating flat or low-sloped roofs:

1. Seal holes in the ceiling, such as the gaps around fans and recessed lights.

2. Reduce interior moisture levels through use of bathroom fans, kitchen fans and dehumidifiers.

3. Install new 6-mil black plastic ground cover in the crawl space. (This may be required at the discretion of Home Energy Solutions.)

4. Provide a 0.5 perm vapor barrier between the insulation and the heated space. This may be accomplished through low-perms paints, faced insulation, or plastic if interior wall surface has been removed. Rotted or moisture-damaged materials shall be removed and replaced.

FL 1.2—Attic Configurations

The four scenarios below are guidelines and should be customized and approved by your local building official prior to starting any work.

FL 1.3—Flat Roofs

There are two options for insulating existing roofs while maintaining the existing pitch: one for vented roofs and one for unvented roofs.

Illustration FL 1.2

In the first option, the cavity between the roof sheathing and the existing insulation provides enough room for R-19 high-density loosefill installation. In this scenario, the existing vents would be sealed. All moisture-producing devices would be sealed and extended through the roof. Painting the interior surface of the ceiling with low-perm paint (0.5 perm cup) is strongly recommended.

Illustration FL 1.3

In the second option, rigid foam insulation, R-19 minimum, would be installed on top of the existing roof with all existing vents sealed. Fans would be extended through the new layer and sealed.

FL 1.4—Increased-Pitched Roofs

A licensed architect or structural engineer should review all additional dead load weights. Home Energy Solutions will not review any such proposed roofing additions. The ventilation for the new roof shall meet current state or local code.

One option is to remove the existing roof and add a new, pitched roof. Then baffle the existing soffit vents. Next insulate the attic to R-38, or greater.

Illustration FL 1.4A

Illustration FL 1.4B

Another option is to leave the existing roof intact and build a new, pitched roof on top of it. The existing roof shall have holes cut in it to prevent it from functioning like a vapor barrier. One square foot of old roofing shall be opened for each 150 square feet of roof area. In addition, there shall be a minimum of two holes in each joist bay.

The existing lower vents in the old roof cavity shall be sealed. The existing roof cavity shall be insulated, using a technique similar to installing loosefill insulation in walls. Additional insulation must be installed on top of the old roof so that the total R-value equals R-38, or greater. A minimum of R-11 shall be installed on top of the old roof, even if the total amount of insulation exceeds R-38.