Almost all houses have a space between the ceiling of the top story and the roof's underside. This space is commonly called the attic. Attics come in a wide range of square footage, heights, and configurations.
The attics of flat-roofed houses typically span the home's full length and width but have very low ceilings. Many modern homes with peaked roofs can have their attics developed into bedrooms or playrooms, usually with cramped heights and sloped ceilings. Older homes -- especially Victorian, Cape Cod, and Italianate styles -- tend to have large, high-ceilinged attics that can be transformed into dramatic living spaces.
No matter what type of house you have, it's important to know what you can -- and can't -- do with your attic space. Your attic's dimensions and construction determine whether it can be finished for living or storage space or must remain empty, wasted space at the top of the home. In the remainder of this article, we'll describe the five varieties of attics, identify which types of attic construction allow for storage and living space, and discuss the pros and cons of ventilating and insulating your attic. Keep reading to learn all about attics!
1. Scuttle Attic
Any attic space that does not have a permanent staircase for access is considered a scuttle attic. A typical scuttle attic has a trap door and requires you to climb a ladder or a pull-down staircase to get up into it. Some homeowners use their scuttle attics for storage, but most leave this space empty and only go into the attic if they need to perform maintenance or repairs. Of course, because scuttle attics do not have permanent staircases and traditional doors, you cannot legally use them for living space.
2. Unfinished Attic
The major difference between an unfinished attic and a scuttle is that the unfinished attic is accessed via a permanent staircase rather than a ladder and trap door. The floors, walls, and ceilings of an unfinished attic have not been upgraded to livable conditions. In most cases, this means that the wall studs and ceiling rafters are exposed. Floor joists are usually covered with plywood, making unfinished attics ideal for storage. Unlike scuttles, most unfinished attics can be upgraded into living space.
This unfinished attic space can be used for storage. If your attic is too low for a living area, it can still prove an efficient space.
3. Partially Finished
The difference between a partially-finished attic and a fully-finished one is based on the percentage of the attic's area that is up-to-code for living space. Partially finished space applies to attic areas equal to 20% - 39% of the home's main floor square footage. In A-frame homes, which feature long and steeply sloped roofs, the portion of the attic with enough headroom for living space may be quite small. In other cases, homeowners may choose to finish only enough of their attic for a bedroom, study, or playroom and use the remaining storage space.
This finished space's size is less than 40% of the square footage of the ground floor.
A tiny, "unusable" space behind the kneewalls is transformed into a charming nook.
4. Fully Finished
A fully-finished attic has a livable area equal to 40% - 54% of the home's main floor's square footage. Like partially-finished attics, this may mean that the owner chose to finish only part of the livable square footage in the attic or that, due to a steep roof, much of the attic is simply not usable as living space. Many Cape Cod and Tudor homes fall into the latter category: their steeply sloped rooflines render much of their attic space too small and cramped for people to safely and comfortably use.
The finished area in this attic is just over half the size of the ground floor.
Bookshelves along the kneewalls make great use of low-headroom space in the attic of a Cape Cod.
5. Full Fin Wall HGT
If an attic area equivalent to 55% or more of the main floor's square footage is finished to livable standards, the attic is labeled Full Fin Wall HGT -- which stands for Fully Finished Wall Height. Most attics that earn this designation are entirely, or almost entirely, finished, with perhaps some small unfinished storage areas under the eaves. Full Fin Wall HGT attics often include not only the electricity and HVAC required in all partially- or fully-finished attics but also plumbing, dormer windows, and/or skylights. Using the building's roofline as an attractive architectural feature, Full Fin Wall HGT attics can be transformed into dramatic living spaces.
The entire attic is finished, with square footage identical to that of the ground floor.
In this modern loft, the peaked roof makes a dramatic statement.
Difference Between Rafters And Trusses In An Attic
The construction of your attic -- specifically, whether the roof supports are rafters or trusses -- determines whether you can finish the attic area for living space, use it for storage, or leave it empty. Rafters are the traditional method of framing a roof; trusses are a newer innovation but are more common in new construction.
Rafters are typically 2"x8", 2"x10", or even 2"x12" lumber. They connect to the ridge board at the roof's peak and to the top plate of the wall framing. Each rafter is supported by two horizontal boards: a collar tie just below the roof's peak and a joist just above the top plate of the wall frame. The joists also frame the ceiling of the room below the attic. The rafter-and-joist structure is strong enough to support placing finish flooring atop the joists, thus allowing the attic to be used for storage and/or living space.
Trusses are 2"x4" lumber connected in triangular webs, prefabricated in a factory. They are less expensive than rafters and can support approximately the same weight load. However, the webbed construction of trusses makes it impossible to finish any of the attic spaces for living purposes, and it is difficult even to use the space for storage. Because the bottom pieces of the trusses are composed of 2"x4" lumber (rather than the bigger, stronger joists used in rafter construction), you should not even store heavy boxes on them.
To Vent or Not To Vent - What's Best for the Attic
Most unfinished attics, and even some finished ones, have air leaks, insufficient insulation, and/or poorly fitted windows. This allows the house's warmed or cooled air to leak out and outdoor air to infiltrate. Because warm air rises, the attic tends to be hotter than that in the rest of the house. So, in the winter months, heated air escapes from the attic; in the summer, cooler air sinks to the bottom of the house and out, pulling hot outdoor air into the attic. You can choose to ventilate your attic to help control the warm air buildup or leave it unvented.
Modern homes typically have attic ventilation built-in. This includes some combination of a ridge vent at the roof's peak, soffit vents under the eaves, and/or gable vents built into the walls below the roof's peak. These vents keep the attic cooler in the summer and keep moisture from building up throughout the year. However, they also allow heated air to escape in winter and cooled air to exit in the summer. Venting is appropriate only for unfinished attics.
An unvented attic is best if you use it for living space and/or if your HVAC system is located there. To convert a vented attic to an unvented one, you must include the attic space in the home's thermal envelope. This means air-sealing and insulating the attic walls and roof and installing HVAC ducts to keep the temperature of the attic space relatively close to that of the rest of the house. In winter, the roof insulation prevents warm air from escaping. In summer, it keeps cool air within the home's envelope.
How Do You Air-Seal And Insulate An Attic?
Air-sealing your attic stops the infiltration of outside air and the exfiltration of indoor heated or cooled air. Use caulk to seal any small gaps, leaks, or joints in the walls and roof. Be particularly thorough in sealing knee walls, odd angles, and spaces around pipes or chimneys.
After your attic is completely air-sealed, move the thermal envelope of the house to the roof deck. Accomplish this by first removing any insulation between the ceiling of the top story and the attic floor. Then install insulation valued at a minimum of R-38 in the walls and roof. This will keep warm air from bleeding out of your attic in the winter. It will also shield your home from absorbing the sun's heat during the summer.
Finishing your attic can help make your home more comfortable and convenient. It can also raise the value of your house. Understanding your attic's construction helps you determine whether you can use it for storage or finish it for living space. If you're considering finishing all or part of your attic, you'll also need to air-seal and insulate it. Following the guidelines above will help you turn your attic into a beautiful and functional part of your home.
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