Mine would be a bonus room which is media room, bar and gym but since it has plumbing, toilet, sink etc. it does not qualify as a bonus room. No clipped ceilings. Steps to this room are via a landing between garage and main house. I put the room above the front garages because it is opposite end from the master. I can watch action movies with sound turned up and listen music at deafening volume without disturbing DW or anyone else. In our previous home in NJ I had this setup in the basement and it shook the whole house when I turned up the volume. Lastly the room looks just nice there, it is approximately 1000sf.

I think they go over the garage because it is inexpensive to build there and it maintains some exterior symmetry to the building. I also think that they are always cold/hot

As noted above, there's already a foundation there. Furthermore, zoning limits heights and even the number of floors, so where else is there to go?

The big mistake comes in finishing the space when the ceiling below is inadequately sealed and insulated.

Sound of garage door and transmission of sounds out of the room can be minimized if floor, joists and wall framing are suitably sound proofed as we intend to for instance using joist isolation and rubber underlayment beneath finish floor above.

PineBaron it's wonderful that you can throw all the money you want to do whatever is needed to make your house so special, but you seem to forget not everyone is as fabulously successful as you are. For most people who buy a tract home with a bonus room, they don't have the options you are using.

There you go again cpartist, you just can't help yourself, cool down please. There are options and not everything needs a lot of money to get it right in new construction, one needs to see how much is acceptable or enough. Joists would benefit from using joist gasket tape; $25/100' roll. It can also be used for ceiling and wall studs, it reduces (not eliminates) sound and can give a room a softer feel. Next option, yes it is expensive but if budget permits would be to use Green Glue Damping Compound, two tubes per 4x8 ply sheet, roughly $16/tube. There are different levels and stages to sound proofing; one would set a budget and invest accordingly since we are not all building recording studios.

By the way rubber underlayment can be bought between 32cents/sf for 2mm and $1.6/sf for 12mm and everything in between. I'll use 5mm which is 69c/sf.

I thought bonus rooms originally didn't count as finished space so you didn't pay taxes on it. But now they're finished in initial construction so there's not much bonus to it.

The law where i live (ny) is that the assessment is based on value. An unfinished bonus room has some value and a finished bonus room has more value. So both would increase your assessment and thereby your taxes.

Bonus rooms are not built, they happen. At some point of time a home designer did not think about putting usable space above a garage and realized there is space below the roof above the garage and they called it a bonus.

An overhead garage door and opener are suspended from the floor above so resilient tapes, underlayment and glues would not be as effective as resilient isolation hangers at support brackets and nylon rollers that can be installed after the house is finished.

Resilient floor underlayment is intended for reducing footfall noise and joist tape prevents squeaks. A more appropriatebette underlayment in this case would be mass loaded vinyl but the best method for reducing the transfer of airborne sound to the room above is resilient channels supporting a 5/8" drywall ceiling with spray foam against the bottom of the subfloor and mineral fiber batts below the foam.

But the best solution is to avoid bedrooms above garages if family members use the garage when others are sleeping above it.

Since I live in the SE, let me throw a couple of things out.

Like has been said the foundation and roof are there so it is cheap space to add. Traditionally bedrooms are upstairs. The sound of the garage door makes a bedroom above not ideal - so a bonus room goes there instead. Could be a laundry room, craft room, media room. Doesn't really matter. In our market, a bonus room is just a non bedroom that isn't a kitchen/living/dining room. Could be an office too.

Our temps are mild so the room does not need extreme measures to be comfortable. My garage gets below 50 without insulation on rare winter nights. It doesn't be above 100. So yes insulation is needed but it isn't that bad.

We don't have basements since we don't need to dig deep for a foundation so they represent a large added cost unless the land is sloped significantly. Our market is filled with northern transplants who expect a basement. So a bonus makes sense.

CO is lighter than air so worry about your main floor just as much if not more than the bonus area. Worry more about your behavior if you leave a car running in the garage. It is not a common means of death to have CO from car running in the garage getting to the main house. Now the garage is another story.

CO is only slightly lighter than air and quickly becomes evenly dispersed in a space. That's why a door from a garage is not allowed to open into a bedroom.

JDS

An
overhead garage door and opener are suspended from the floor above so
resilient tapes, underlayment and glues would not be as effective as
resilient isolation hangers at support brackets and nylon rollers that
can be installed after the house is finished.

No such problem here; it will be taken care of by side mounted garage door openers, hence no ceiling mounts for the opener or noise :)

That would be the expensive solution that would be difficult to get a developer to do that CP mentioned. You would be wise to seek more professional advice for the airborne sound abatement.

There you go again cpartist, you just can't help yourself, cool down please. There are options and not everything needs a lot of money to get it right in new construction, one needs to see how much is acceptable or enough.

That's true Pinebaron, but my point is when you do post, it's to show how big and over the top you do everything.

The main advantage of jackshaft (sidemount) openers is that they free ceiling space, allowing for overhead storage and vehicle stacking systems, which are increasingly seen in tight urban builds.

***

A common problem in cold and very cold environments is poorly sealed and insulated garage ceilings. Before I learned better, I tried batts, poly and drywall, multiple layers of XPS boards and even supply and return air systems.

The only truly effective solution is ccspf.

Jackshaft openers are extremely quiet. If bonus room noise is an issue, these can save costs on noise abatement material required otherwise.

it does not qualify as a bonus room

Some rooms have actual "qualifications"; for example, a room cannot be a bedroom unless it has a window for egress and a closet ... but I don't think bonus rooms have actual definitions. They're typically FROG: Finished Room Over Garage.

My friend's house plan had a two-story great room ... she finished it as an upstairs den for her kids. It's a bonus room, though it isn't over a garage and doesn't have the sloped ceilings.

The term Bonus Room is marketing jargon for an upsell

Yes. When I was a kid, people built Rec Rooms ... now they build Bonus Rooms. The name gives the idea that it's a freebie, which it isn't.

No such problem here; it will be taken care of by side mounted garage
door openers, hence no ceiling mounts for the opener or noise :)

If noise is a serious concern, I'd say go with a detached garage or a garage attached with a breezeway.

mrspete: I love it, will try and remember it, single level home with a FROG; hope it does not offend other Frogs in our pond :)

"...Why are bonus rooms mainly built above the garage?..."

Because it's harder to put them anywhere else and still make them habitable. And they aren't "bonus rooms". They're left over space. With problems, often not over come.

Jackshaft openers are very quiet. However, belt-drive openers are super quiet too. Damn chain-drive operators will rattle the whole house... Then you can always mount rubber pads between everything etc etc.

I saw Tom Silva on This Old House take a few strips of rubber and screw them between the garage opener motor mounts and where the tracks were screwed to the ceiling joists. It did the trick. Instant sound and vibration reduction.

Here is a kit the works well if you need serious sound reduction in the room above. There are many others available.

Why are bonus rooms built above garages? Because most people don't understand the negative impacts on indoor air quality.

Just as with vented crawlspaces, ducts in vented attic, ventless fireplaces and atmospherically vented gas water heaters, unhealthy construction practices are so entrenched that enlightened building professionals have a hard time convincing clients that safer and healthier solutions are worth designing for.

Most CO poisoning goes undiagnosed and there are plenty of other pollutants making their way into an attached home from the garage.

While building a bonus room above a garage, even if conditioned space, one needs a different approach to installing insulation, blocking, drywall etc. and even more so when exposed to the elements on multiple sides. One would not want the room to overheat or be very cold.

I only heard the term from House Hunters. It seems to be that the house was so poorly designed that there is no clear use for the space. Found on the 2nd floor, it is too small or unzonable to be a bedroom, and not isolated enough for a playroom, office or home theater. And they are open to the rest of the house which makes them a poor choice for a (usually messy or noisy) hobby room.

Oh, and newer belt-drive garage door openers are substantially quieter than older chain driven ones. If noise/vibration is an issue that'd be my first suggestion (only a few hundred installed, generally).

Its far easier for pollutants from a garage to enter a house through the shared wall and door than through the ceiling so you should put attached garages higher on your list of unhealthy design practices than bonus rooms.

I agree JDS, mainly because of garage-to-house door leaks at weatherstripping and jambs to rough framing but usually it's mudsills needing the most attention. Bonus rooms often share garage walls (mudsills) and the stack effect can be more effective at sucking garage air up, than wind or exhaust fans at sucking the air sideways into the house.

Spray foam at garage ceiling/bonus floor is a good suggestion to prevent this but also pay attention to the airtightness of garage wall cavities. Standard construction practices of fiberglass batts and not proving airtightness with a blower door is sure to result in poor separation of garage air and bonus room (house) air.