Attic mold is a moisture-control problem

Bad practice. Instead of exhausting moist air outside the house, this bathroom fan duct is dumping air into the attic. The black stain on the roof sheathing is mold. To fix the problem, energy technicians will connect the duct to a roof-mounted vent.

What happens when warm, moist air from a bathroom shower or from a pot of boiling water on the kitchen stove escapes into the attic and suddenly comes into contact with a cold surface?

The answer is "condensation." Cold air can't hold as much moisture as warm air, so when warm interior air leaks into a cold attic, droplets of water accumulate on cold attic surfaces like roof sheathing, rafters, and gypsum board. Wet wood and paper provide a perfect environment for mold to grow.

This problem can get much worse when the duct for a bathroom or kitchen vent fan blows humid air into the attic space rather than outside the house.

To eliminate mold in the attic, you have to air-seal the attic and make sure that all vent fans are ducted directly to the outdoors.

Attic air sealing: a must-do upgrade before adding insulation

Spray foam seals a plumbing penetration. Holes made in walls for plumbing, vents and electrical wires all provide air leakage pathways. Energy technicians typically seal these leaks with spray foam.

It's a common misconception that adding more attic insulation stops air leaks. The truth is that insulation filters air; it doesn't block it. For proof, you don't need to look any farther than the air filter on your furnace or air handler. It's made of fiberglass, just like fiberglass insulation.

To properly air-seal your attic, energy technicians need to move aside existing attic insulation and expose all the wall framing, can lights, soffits, vent fans and other details; then they seal all the holes, gaps and cracks they can find.

They'll also seal around the attic stair or hatch and around chimneys and chases for ducts, plumbing and wiring. Only then is it appropriate to proceed with adding attic insulation.

Attic access: stairways, folding stairs and hatches all need air-sealing attention.

There are several ways to get into an attic. In many historic houses, a conventional stairway provides attic access.

In houses built since the 1970s, a folding, drop-down stairway was often installed in a hallway or closet. Still other houses have an attic hatch (aka scuttle) --just a piece of plywood or drywall held in a framed opening.

No matter what access method is used, the opening that provides attic access needs to be air-sealed and insulated in order to prevent energy loss and compromised comfort.

If there's a conventional stairway into the attic, the attic door can be weatherstripped just like an exterior door. A drop-down stair (which is really more like a folding attic ladder) and an attic hatch can also be air-sealed and insulated using similar techniques.

Baffles and barriers keep attic insulation in place.

You can't add more attic insulation without making some provisions to contain it. Otherwise, you might not be able to enter the attic without having insulation spill down into the living space. Another problem can occur when attic insulation extends into the eaves, covering soffit vents and preventing them from working properly.

Also, if the attic has HVAC equipment such as an air handler, covering this equipment with insulation will limit accessibility for servicing. Insulation baffles or barriers (aka dams) take care of these problems. Different readymade baffles are designed for installation between rafters to keep ventilation channels open. In other situations, an energy technician will fabricate barriers from different sheet materials like plywood or rigid insulation board.

A radiant barrier is a smart way to reduce attic temperatures and cut cooling costs

Take a shine to energy savings. Stapled against the rafters, a sheet-type radiant barrier will reflect solar heat and save energy of cooling costs during warm weather.

When the roof of your house gets the full force of the summer sun, temperatures inside the attic can climb to 135 degrees and higher. The attic becomes a huge radiator pushing heat down into your living space, forcing your air conditioning system to work overtime. You can lower attic temperatures significantly and cut cooling costs by up to 17% by installing a sheet-type radiant barrier.

A radiant offers other benefits as well. By lowering attic temperatures, any items stored in the attic are less likely to be damaged. A radiant barrier helps the house to retain heat during winter months, but energy savings will be less than during the cooling season.

Finally, a radiant barrier is a smart investment if there's ductwork or HVAC equipment in the attic, since it keeps this equipment cooler during the summer and warmer during the winter.

Attic insulation: Blow-in fiberglass and cellulose are top choices

Blowing in a blanket. Blow-in fiberglass insulation is installed with a long, flexible hose connected to a machine that shreds and blows the material.

Most homes require additional attic insulation. The minimal levels of attic insulation required by local building codes aren't considered adequate today because of rising energy costs and increasing concern about the environmental damage caused by fossil fuel consumption.

If the attic in your house is insulated with fiberglass batts (many are), there's a good chance that this insulation can stay in place beneath a deeper layer of new insulation. Blow-in fiberglass and cellulose insulation are usually the best choices when it comes to installing new attic insulation.

Unlike fiberglass batt insulation, which must be brought through the house and put into place by hand, blow-in insulation can be installed faster, more uniformly and with less traffic through the house.