“In the attics of my life, full of cloudy dreams unreal.”
- The Grateful Dead
It is time to dispel the mystery and cloudy dreams unreal of attics.
Know thy attic and lower thy utility bills.
Your attic is probably not your favorite place to relax and spend time with your family. It is more likely a place you avoid and perhaps fear, especially as the temperature outside plummets or soars.
At their most romantic, attics conjure up dusty boxes full of hidden treasures, costumes, and old love letters. They may also be full of well-fed spiders, mischievous (and destructive) raccoons, or that pink stuff, otherwise known as fiberglass insulation.
Depending on the age and construction of the home, attics will have different shapes, different uses, and different options for proper air sealing and insulation. If you are a homeowner in Southern Ohio or Northern Kentucky, your attic probably falls under one of three categories.
Vented or Unvented
Balloon framing was a popular form of home construction into the mid-1950s in the Ohio River Valley. It is a form of timber framing popularized when lumber was plentiful; it uses long, continuous studs (framing members), and does not require highly-skilled carpenters. Boomtowns like Cincinnati were quickly built up with balloon framing. Neighborhoods like Hyde Park, Price Hill, Oakley, and Columbia Tusculum are full of balloon framed homes.
Platform framing replaced balloon framing after the 1950s. It is superior in safety and efficiency. If your house is platform framed, your attic can also be vented or unvented, and air sealing and insulating the attic are just as important.
The Stack Effect
The attics of balloon framed houses suffer from being directly connected to the basements or crawl spaces of the homes through the stud cavities in the wall. At its worst, this situation develops into what is known as “stack effect.” As air enters the home through the rim joist (or from the basement), it will actually gain velocity as it travels along the perimeter of the home, circulating and exaggerating the draftiness of the home. This is a problem both in the winter and in the summer, makes it difficult to heat and cool homes, and is a direct cause of high utility bills.
The solution is to create barriers between stories, blow in wall insulation and air seal and insulate the attic. In an unvented attic, the attic space becomes part of the conditioned air space through air sealing measures. An attic can also be vented with gable and soffit vents (or natural air infiltration). In this case, the attic must be sealed to separate it from the conditioned air of the living space.
Cape Cod style homes are popular in our area because, with their framing, the home can be divided into a lot of living space within an overall small and inexpensive home. Although the Cape Cod makes great use of space, they also are victims of heavy air infiltration and inefficiency.
Cape Cod attics are characterized by what is known as the kneewall, shown in the illustration above. Kneewalls present a logistical challenge for air sealing and insulation. The kneewall often has built in bookshelves, drawers, and closets, which can make it even trickier to establish a proper envelope.
The unique difficulties of the kneewall means there are multiple approaches to properly air seal and insulate the attic. One option is to air seal and insulate the entire roof deck with spray foam or foam board, or you can air seal and insulate around the knee wall. In either case, the top plate and attic floor should be sealed and insulated. If you air seal the entire attic floor, the sealing doubles as a low level of insulation. Blowing in R-38 level cellulose insulation on top of the sealed attic floor will maximize the protection of the upper portion of your home’s envelope.
The urban neighborhoods of Greater Cincinnati and Northern Kentucky are replete with narrow, often flat-roofed homes known as shotgun houses, railroad apartments, camelback or double barrel houses. They don’t all have flat roofs, but when they do, they are either vented or insulated. Their attic spaces are typically narrow cavities. A vented flat roof should have a finished ceiling, vapor barrier, dense packed cellulose insulation or foam injection, and an attic space with vents to the outside. In contrast, an unvented insulated flat roof will have 2-4” of rigid insulation and no venting.
Considerations For Your Attic
As discussed above, air sealing along the attic floor and roof is an important first step for an efficient attic and home. Air sealing stops stack effect and helps protect your home’s conditioned air space.
If you have fiberglass insulation that has gone from pink to black, it is an obvious indicator of air infiltration. As air leaks through your house carrying dust, particulates, and moisture, the fiberglass acts as an air filter and turns black with the accumulation of all those particles. The solution is to cover and seal leaks first, and then install insulation.
A natural flow of outdoor air to ventilate the attic’s unconditioned air space closest to the roof helps keep it cold or hot, which reduces the potential for ice damming in the winter, which can severely damage your roof. If your attic is properly air sealed and insulated, the warm air from the home living space should not be entering the unconditioned air space.
In the summer, natural air flow through a well-vented attic allows the super-heated air to move out of the attic, which again protects your roof and removes the threat of unwanted moisture in the attic. Keeping unwanted moisture out of the attic is an important home performance measure and health priority. Mold can develop on insulation as a result of condensation, leaky roofs, leaky pipes or flood damage, and it poses a serious health risk.
Gable and soffit vents should be kept clear of insulation by using baffles.
If you are not in the home performance industry, an attic bypass might sound like a good thing. It’s not! Any hole, crack or crevice that allows heated or cooled air to leak through and past insulation is known as a bypass. If bypasses are not sealed before insulating, the insulation only “filters” air on its way to the attic. Bypasses are commonly found in places that plumbing, electricity or ductwork has been installed.
Attic Access (Hatches)
We won’t bore you with the formula, but long story short, an uninsulated attic access such as a pull down ladder can reduce the R-Value of the attic by 55%. Creating an air sealed barrier around the attic hatch is the solution. Air seal the trim; air seal the hatch perimeter; insulate the hatch; and add fasteners to close it tight.
To learn more about this problem, there is a very useful article from the Green Building Advisor.
The Attic In Your Life
Don’t be afraid of your attic. If your home was built before 1985, chances are your attic needs attention. Whether it is an unsealed attic access, whole house stack effect or your moldy insulation, a qualified Home Performance Contractor can help you address your home’s attic and whole home health.