Finishing Attic Space above a Garage

Large Attic Garage Space can Frequently be Finished to Create a Bonus Room or In-law Apartment

By Mark J. Donovan

If you have an existing garage with a large attic space you may want to consider finishing the attic to create extra living space in your home. Or, if you have garage addition plans, you may want to think about finishing the attic space as part of the garage addition project.

Due to the typically large footprint of a garage addition, e.g. 24’x24’ or larger, garage additions frequently have large enough attic spaces to support some finished living space. 

Consequently, it is worth contemplating adding some additional features to the garage addition plans to support a finished garage attic.

One key feature is egress/ingress into the garage attic space. For example you may want to include a staircase from the first floor level of the garage to access the garage attic space. Alternatively, you may want to punch a door opening from the main house into the garage attic space. Depending upon the garage addition and main house elevations the door could be installed either from the second or first floor of the home. For example, in one of the homes I built, the gable addition attached to the gable side of the home.

This allowed the garage addition roof peak to be centered on the gable side of the home, in perfect alignment with the second floor hallway. By punching a hole from the back of the gable side of the home, I was able to create a doorway from the second floor of the home into the garage addition attic space. I was able to then create a 3rd bedroom on the second floor of the home above the garage addition.

The next major key feature you may want to consider when finishing attic space above a garage addition is the inclusion of a dormer, either a shed or a dog dormer, to bring in natural light into the attic space.

Room Addition over Garage Addition Bid Sheet

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A shed dormer is much larger than a dog dormer and thus will enable much more wall space for windows. A shed dormer in a finished garage addition attic also helps to create some additional standard headroom space in the attic. For example, your finished attic space will include knee walls along the sides of the garage addition to help “square up” the room. Typically the knee walls will be 3 to 4 feet in height. The useable cathedral ceiling or standard flat ceiling height area may only represent 25 to 30% of the attic footprint.

By adding the shed dormer, e.g. bumping it off the back of the garage addition, you may be able to increase the standard flat ceiling height by another 25%.

Another key feature to include in your garage addition plans, if you plan to include finishing the garage addition attic, is skylights. Consider installing skylights on the roof line side that doesn’t have a dormer. This way you have natural light on both sides of the garage addition roof. In addition, you may want to include a window on the gable side of the garage addition that is not attached to the home.

 Finishing Attic Space above a Garage

If you plan to include plumbing in your finished attic space above the garage addition you will need to meet with a plumber during your garage addition planning stage to see how best to do this.

Attached garage additions can present some plumbing challenges. Routing supply lines and drain and vent pipes into the existing drain and vent stacks can be difficult to do. In addition, supply line pipes need to be properly insulated and protected from cold garage areas to prevent freezing.

You’ll also need to consider how to heat and cool your finished attic living space. Attic spaces can be particularly challenging to cool during the summer months. Again, talk with your plumber or an electrician to see what your best heating and cooling options are.

Finally, when contemplating finishing an attic above a garage you need to think about safety. This includes having to insulate and drywall the lower level garage area.

In addition, you will need to meet the local fire codes on the drywall thickness and/or drywall type to use on the garage addition ceiling and garage addition walls that are adjacent to finished living spaces. Typically you will need to use fire retardant drywall or 5/8th inch thick drywall in these places. 

In addition to the drywall, you will need to include fire and carbon monoxide sensors in the garage and finished attic space above the garage. 

For more information on building a garage addition see the Garage Addition Bid Sheet from The Garage Addition Bid Sheet includes an extensive questionnaire (Request for Quote) that a homeowner can provide to prospective general contractors and subcontractors for bidding the garage addition. In addition, the Garage Addition Bid Sheet also includes estimated costs and time intervals for constructing a garage addition as well as a list of key home material manufacturers. Finally, the Garage Addition Bid sheet includes an extensive set of helpful tips and advice on making sure the garage addition is built properly and on time and budget.

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