Keeping Attic Heat and Moisture Under Control

By Mike Wood

Attic insulation and ventilation go hand in hand. They keep your home cooler in the summer, warmer in the winter, and free from damage caused by moisture.

Why is that important?

The main goal is to keep your attic temperature the same as the outside air temperature in the summer as well as in winter.

Summer: The concern in summer is heat. Extra heat build-up under the roof deck can cause your shingles to deteriorate much faster, sometimes cutting their life expectancy in half. In addition, your cooling system will have to work harder to keep your home comfortable. For example, when the temperature outside is 90° in the summer, attic temperatures can easily reach 120°-150°. This will make your air conditioning system stay on longer to keep the home cool, resulting in higher utility bills.

Winter: Our main concern in the winter is moisture. Warm and humid attic air combined with cold outside temperatures leads to condensation, which can form on any cold wood surfaces, metal nail heads, chimney surfaces, ventilation pipes, and even in the insulation. If left wet for an extended period of time, this moisture will cause wood rot, deterioration of the brick on the chimney surfaces, and can eventually cause mold to grow.

In addition to moisture, heat loss also becomes a major concern in the winter, since wet insulation has a lower R-value than dry insulation.

Where does all of that heat come from?

The heat typically comes from two sources:

Inside the home – The warm air is transferred from inside your home to the attic space through conduction (the transfer of heat between two materials in contact with each other, caused by a temperature difference between the materials), or through convection (the transfer of heat by the circulation or movement of air).

Conduction usually occurs when the ceiling materials draw the warmth out of the air in a room and passes it through to the insulation, and eventually into the attic air. It requires no movement of air for it to take place, and is usually a sign of inadequate insulation in the attic

Convection occurs when air escapes through small gaps around lights, outlets, baseboards, or any other openings in your walls or ceilings. This movement of air will flow through the wall cavities making its’ way into the attic, and is usually a sign that air sealing is required.

Outside the home – The attic space is warmed through solar radiation (heat gain caused when materials are warmed by the sun). Solar radiation can pass directly through your roof materials (also heating them up in the process) into your attic space and beyond.

What are some solutions to maintaining the correct attic temperature?

Insulation, air sealing, and ventilation all work together to combat these sources of heat and keep your home comfortable and energy efficient in our climate.
Since one of the largest forms of heat loss in a home in the winter is through the attic insulation, the U.S. Department of Energy has increased its’ insulation standards and currently recommends insulation levels that achieve an R-49 (16”) to an R-60 (20”) for our Northern climate zone. Many homes were originally built with only 4”-8” of insulation, but energy was cheaper when those homes were built and those were the standards at that time. Meanwhile, energy costs have risen, and insulation requirements have increased as well. To bring your home up to today’s standards, loose fill insulation is typically blown in on top of your existing insulation to increase the R-value.

Attic insulation is relatively inexpensive compared to other home improvements, and the costs will typically be offset by an improvement in your energy bills.

Fiberglass vs. Cellulose

There are two common types of attic insulation – fiberglass and cellulose – and they are similarly priced.

Fiberglass has a good R-value and works well in our climate. If it gets wet, it dries out easily, and since it’s inorganic, it won’t support mold growth. Fiberglass is fluffed up in a machine prior to installation and is guaranteed not to settle.

Cellulose also has a good R-value, but it is more susceptible to damage from moisture and will support mold growth if left wet over an extended period of time. Cellulose can also settle, which will cause a reduction in R-value over time.

Quick and Simple Installation

Callen uses blown-in fiberglass insulation. We utilize the Owens Corning AttiCat® system, which allows for a quick and easy installation. Most projects can be done in one day.

When we arrive, the AttiCat® machine is rolled into your garage. A wide hose is then run through your home into the attic. The insulation comes in compressed plastic bags, which are fed into the machine. In one step, the machine cuts the plastic, pulls the insulation, and fluffs it up adding millions of tiny air pockets that give the material its insulating power. It is then blown through the hose into the attic space. The AttiCat® system doesn’t generate any dust and distributes insulation only where it is needed.

The correct depth of the insulation is measured using cardboard rulers that are stapled to the trusses or rafters throughout the attic space. Unless there is mold or mildew damage, the old insulation is usually left in place. Working from the farthest corner, the installer blows in the required amount of insulation to the desired height on top of the old insulation, until a combined depth of 16”-20” is achieved.

An important part of the installation is making sure the attic intake ventilation is not blocked by the new insulation. To prevent this, baffles are installed between the rafters against the roof deck along the bottom edge. This holds the insulation back in those areas, allowing the air to come in at the soffits, flow past the insulation, and escape through the roof vents.

Air Sealing

In addition to insulation, you may want to consider air sealing at the same time, as it will be difficult to do this type of work once the new insulation has been installed.

Air sealing is a concept that involves sealing every potential source of air leakage from your living space into the attic. This includes recessed lighting, bath and kitchen fans, outlets, light switches, baseboards, holes in framing where plumbing pipes and electrical wires go through, and around your chimney chase. All of these areas, when added up, can lead to a large amount of heat loss that will creep past your insulation and get into your attic, often carrying higher humidity levels along with it. Caulk and expanding foam are two common products used for air sealing.

When combined, insulation and air sealing will keep your homes heated air where it was meant to be – in your home, not your attic.

Ventilation

Proper ventilation reduces heat build-up caused by solar radiation from the sun. Most roofs have shingles that are made of asphalt with ceramic granules to help repel the sun’s damaging UV rays, but asphalt absorbs a lot of heat, and this heat will transfer into your attic through the shingles, the roof deck, and into the attic space. Proper ventilation can help circulate the air, reduce the heat build-up in the attic, and keep down humidity levels.

The Federal Housing Administration has recommendations for the amount of ventilation you will need based on the size of your home. For an attic to be properly ventilated, it must also have a balanced system of intake and exhaust vents. The air comes in through the intake ventilation at the soffits. It then moves past the insulation through baffles installed on the bottom side of the roof deck toward the lower part of the roof. Once past the insulation, it mixes with the existing attic air. As it warms, it continues rising, eventually escaping out of the roof vents placed high on the roof carrying moisture with it.

Radiant Barrier

Another method of reflecting the radiant heat caused by the sun is through the use of a radiant barrier. A radiant barrier is a metallic film that can be used under certain roofing materials on the roof deck, or inside the attic on top of the insulation, to reflect heat back towards its source. This will reflect radiant heat from the sun back to the outside, and even reflect radiant heat from the home back in.

What can happen if my home is not insulated or ventilated properly?

The lack of ventilation or inadequate insulation can contribute to many problems, including high energy bills, damage to wood framing and decking in the attic, wet insulation, mold growth, reduced life expectancy of the roof shingles, peeling paint outside and inside the home, ice damming on the roof, and water spots on the ceiling.

The following is a story of a client that is an example of poor ventilation combined with inadequate insulation:

We were called over to look at the black ‘stains’ covering the bottom side of the roof deck boards. The client had four inches of insulation in the attic and no roof vents. When inspecting the attic space, we found frost on the exposed nail heads from the shingles. On very cold days the frost would appear on the bottom side of the roof deck boards as well, leading to a mold problem. We then showed the homeowner how warm, moist air rising from the home passed through the 4” of insulation by putting in three humidistats – one in the basement, one on the first floor, and one in the attic. The humidity in the basement measured 40%, the first floor was 45-50%, but the attic was 62%! The moisture was rising with the warm air of the home as it escaped past the insulation, and it was trapped in the attic because there was no roof ventilation. The solution was to install more attic insulation, do some required air sealing on the second floor, and install intake and exhaust ventilation in the attic.

What about ice damming?

Most homeowners look to the outside of the home to find a solution to ice damming. But the cause of ice damming usually comes from inside the attic space. A commonly held misconception is ‘snow melting off a roof is a good thing’. However, what that really means is there is not enough insulation in the attic – the home’s heat is rising up, heating the roof, and melting the snow. As the melted snow runs down the roof and hits the colder parts of the roof near the gutter, it re-freezes causing a dam. Any more water that runs down the roof will get stuck behind the ice dam and will find its’ way into the home as it backs-up under the shingles. The solution is simple – reduce the heat and you will reduce the melting snow, which will reduce the amount of ice damming.

Is there anything else I should be worried about?

In addition to the tips mentioned above, it is a good idea to do regular inspections of your roof and attic space. It is good to keep an eye out for any areas where moisture could find its way in, such as damaged chimney flashings or rubber flashings around the plumbing vent pipes on the roof. This year we have seen several cases where the recent draught and intense heat is causing those rubber flashings to dry out and crack. If you look at your plastic vent pipes and you can see the black seal split, you are seeing a source for moisture to enter your home. Since these areas are hard to reach, it is a good idea to have a professional do these inspections for you.

If you would like to discuss your home insulation or ventilation concerns, feel free to give us a call!