Insulating Your Vented Attics For Performance

This article was originally published for remodeling projects, but these strategies apply to many new construction practices as well.

Just like a hat is essential for keeping folks warm in winter, attic insulation, a home’s hat, is critical in helping to keep a home warm in winter and cool in summer, and boosting the home’s energy efficiency. According to the Department of Energy (DOE), insulating ceilings is one of the most cost-effective energy efficiency measures. In addition to reducing heat lost to the outside in the winter and unwanted heat entering the home in the summer, attic insulation improves the homeowner’s comfort by bringing ceiling temperatures closer to room temperatures. This helps provide even temperatures throughout the house, eliminating drafty areas and cold spots.

Part of the attic insulation puzzle involves the framing complexity of the home, airsealing, and ventilation. Carefully considering all these pieces will help you to create a strategy for effectively bundling up your homes against the elements to reduce homeowner utility bills and keep them comfortable, two things that are sure to keep your customers happy.

Determine what kind of and how much insulation you need

Choosing an insulation material

Choose the type of insulation based on the design and framing complexity of the attic, your climate zone, and your budget. Loose-fill or batt insulation is typically installed in the attic. However, with the complex roof lines of today’s homes, many attics may incorporate a combination of loose fill insulation and batt types. Check out the DOE’s website on choosing insulation for more information.

It’s important to remember that no matter what type of insulation you use, the thermal performance is only as good as the installation. The fundamental strategy is to create a continuous air barrier along the ceiling plane by sealing all penetrations through the ceiling to stop air infiltration from the space below, and then add the insulation to stop heat loss through the materials.

Going beyond code

Local building codes often represent the bare minimum level of insulation required, which doesn’t necessarily make the home as efficient and comfortable as possible. To find the levels recommended by DOE for your location, check the Energy Savers R-Value map. You can also determine optimum insulation for your specific needs using DOE’s interactive ZIP Code Insulation tool. Both are available here.

Install depth gauges to ensure adequate loose fill depth

When you blow in loose fill insulation, ensure that the depth is continuous at its specified level for the entire space. Once you cover the ceiling joists or the bottom chords of the roof trusses, you won’t be able to easily tell how deep the insulation is. Use a gauge tape for quick, visual depth reference. If not provided by the insulation installer or manufacturer, create gauge tapes from scrap plywood or oriented strand board (OSB). They should be equally spaced along the length of a truss and repeated every fourth or fifth truss.

Keep the insulation continuous and seal any air leakage pathways

The attic should be insulated continuously without gaps to help keep the house warm in winter and cool in summer, but air leaking into the attic from inside the home can sabotage the benefits of an otherwise good installation. Controlling air leakage, however, can be tricky. Structural complexity and the many mechanical vents, ducts, lighting, and electrical elements penetrating the ceiling plane each introduce leaks. Key steps you can take to ensure you’re doing it right include:

• Seal top plates, pipe and wire chases, interior soffit spaces, dropped ceilings, and other chases. The goal is to make the insulation continuous, so seal around any penetrations through the ceiling to minimize air leakage, and then insulate over top of them.

• Ensure that insulation covers the entire ceiling of the space below that’s heated or cooled. Raised heel trusses, which allow more insulation at the critical roof-to-wall junction, should be used in new construction with low sloping roof trusses.

• Address heat-producing sources in the attic. When airsealing and insulating near heat producing items in the attic, such as exhaust fans, combustion venting, chimneys, and non-IC rated can lights, using appropriate materials and clearance will ensure a safe installation. See http://www.eere.energy.gov/buildings/documents/pdfs/26450.pdf

• Build a frame around the attic access with plywood so that the full thickness of insulation can be maintained up to the hatch or ladder edge. Also, the closure for the attic hatch should be insulated and gasketed.

• For a tray ceiling, or any other ceiling where there’s a change in elevation, build a frame up the sides with plywood and insulate to the edge to maintain insulation depth.

• Delegate clear walkways and remove obstacles to provide for easier maintenance down the road.

• If the attic is used for storage, build a raised storage platform to allow at least 75% of the full thickness of insulation. Build it as an open deck, with open sides and a slatted platform to allow the natural movement of moisture from the house to the attic. A raised deck will support stored items without crushing the insulation.
  

Ventilation

Most building codes require attic vents to expel moisture that could cause damage to building materials. While researchers are investigating whether attic ventilation is beneficial for all climates, chances are good that your local building codes require vents, so consider these points:

• Venting interior exhaust fans into the attic or soffit is a bad idea, as moisture is simply dumped into the attic, where it could condense on cold places and cause moisture problems. All ventilation fans should be ducted to the outside rather than into attic spaces with the shortest equivalent duct length.

• In order to insulate to the edge of the attic without compromising attic ventilation, install ventilation baffles to the roof deck first. Ventilation baffles will allow you to install the recommended level of insulation to the edge of the attic space without blocking the soffit vents.

A carefully considered and implemented strategy for attic insulation will help keep your customers comfortable and their utility bills low, two sure ways to improve customer satisfaction. Keeping the insulation continuous, sealing air leaks, and considering ventilation are key steps in ensuring the hat you put on your homes will be a quality fit.

Article courtesy of Professional Remodeler Magazine. Read the complete article by Jennifer Kent and Ananda Hartzell at: http://www.housingzone.com/topics/pr/cmaterials/pr04aa004.asp