Garage to ADU Conversion Problems

When doing math it sometimes gets tricky in the conversions.  How many litres in a pint?  How many centipedes in a decibel?  Likewise it can get tricky converting a garage to an ADU.  Let's pretend that your local jurisdiction is not an issue and look at the inherent problems.  (Note, please always consult with your local jurisdiction and get a permit where required.)

Looks normal but the owners want more living space

The first issue would be the floor.  Most contractors would be happy to leave the floor as a slab and call it good.  Maybe put a carpet over it.  Nothing could be worse.  You have no idea what's under that slab.  It could be sand, gravel, or bare dirt.  There may or may not be a vapor barrier under there either.  Concrete is nothing more than a rigid sponge.  Placing a carpet over the top just gives latent moisture somewhere to make dank and moldy.  Don't do it.

Instead, consider laying some 6 mil vapor barrier down over the slab first.  There is likely no insulation under there either so a few inches of rigid foam insulation would help to keep the dewpoint away from your materials that are susceptible to mold.  After making sure all joints are sealed, overlay with a floating wood floor.  Looks nice too.

Hopefully walls and ceilings would be straightforward.  Always check for and mitigate any moisture in the walls, make sure the wiring is correct, and get inspected if necessary before applying sheetrock.  Fill the space with insulation before making it inaccessible.

Another big issue to consider is the street appeal.  The general rule of thumb is to throw some sort of window into the former garage door opening and frame around it.  This looks wrong on several levels.  First, the garage door header is generally not equal to other windows or doors.  If the garage is freestanding then this is less of an issue.  But if the garage door is near other windows and doors it can look discontinuous.

Slap in a window.  Well, it's functional at least.  Yeesh.

The expensive option is to cut out the header and make it the same as other headers on the front of the house.  Another option would be to consider something such as two 3/0x5/0 single hung windows.  The vertical aesthetic of the windows can help soften the horizontal issue.  Another option which happened near here was to remove the garage door but build an inside wall that looks like a garage door from the outside.  Windows were already on the side of the garage.  This looked really nice.  Unfortunately the local jurisdiction in all their wisdom required a window in the front.  In vulgar terms it looks really dorky now.  Perhaps a sliding glass door could be considered as another option.

This looks a little more purposeful...

A cabin perhaps?  May or may not work.

Another issue that can come up is the parking space.  If you have less than 16' in front of your garage to begin with you may lose an onsite parking space.  Some jurisdictions might think this a big deal.  Others won't.  A driveway going up to a blank wall does not fool the eye.  We have grown to expect a garage door at the end.  If that garage door is gone then the driveway needs to be reimagined in order for the eye to accept a wall at the end.

If there is room then landscaping or a bench will help soften the transition.  The amount of concrete in the driveway could also be reduced.  Leave a couple of 30" strips with 24" between them.  Everything else should be returned to grass or other low, resilient plantings.  If your budget allows, put in driveable molds or spaced pavers that allow grass to grow in between them.  Some folks may not appreciate the look of parking a car in grass but it may suit others' needs.

Sweet Stickley, can we live here?  That bay, that driveway.  What lovely lines!

If you are converting a garage into an ADU, Istockhouseplans would be pleased to give advice.  Send us an email or leave a comment below.