If there are I-joists above a basement space (including a garage) they must be protected by a drywall ceiling or the I-joists must have a fire-retardant (intumescent) coating.

If the joists have a coating and there is a habitable space above the garage, the garage ceiling must have a layer of drywall.

So, if I understand correctly, the joists above the basement garage must have both the coating and drywall? The IRC mentions 1/2” drywall or 5/8” OSB or plywood. Would those work in lieu of the drywall?

Usually living space above a garage will be hotter/colder than other parts of the house, so I would not skip that layer of insulation and drywall.

Is it too late to talk you out of a garage under plan?

Our first house had one and we swore we would never have one again, and we haven't. Garage under homes also sell for less than a comparable home with the garage on the same level as the main floor.

No, if there is a code compliant garage ceiling. the joists don't need a coating.

What section says OSB can be substituted for drywall? That sounds like fire blocking, not fire separation of the garage from the house.

In the 2015 IRC the requirements are in section R302.6. What year is your code and in what state? Have you read the amendments? The amendments in my state consist of 100 pages and amend the section we are discussing.

What is the real issue here? Are you trying to avoid a ceiling in the basement and garage? You could use treated joists in the basement but there must be a ceiling in in the garage. You can't create a fire separation with exposed wood or a coating.

This might not be what is required in your jurisdiction but the only difference would be whether the drywall is 5/8" Type X rated or regular unrated 1/2" drywall.

Thanks, RES! I was erroneously looking at the 2012 code.

@chispa, we will have an upstairs carport (large). The basement will be for our boat and for when weather is harsher. It won’t be primary. We’ve had basement garages before and have found them extremely beneficial.

I think the garage resale and usability issues are extremely variable.

I would not be without a main level garage because I want cars in the garage at all times. It isn't a weather thing. I just think cars (as attractive as they can be) mess with the peaceful elevation of a house. I also want cars routinely hidden for security - so no one can tell when the house is occupied.

So I would not buy your house if the plan is using a carport on a routine basis and Chispa (I think) would not either. So strike 2 buyers off your future list. Just a thought even if a really minor one.

I am guessing you don't want drywall because it hides ducts, plumbing, etc? That really isn't a big deal. If you have to get in, you can probably get away with access points to cover - either way code man will be long gone.

We live in an extremely rural area on 1000 acres so resale and basement garages aren’t really issues to consider. Our needs and wants are different than most folks. In fact, our area doesn’t even have permitting and Codes enforcement except for electrical. Our builder, however, builds to Codes but seemed a little fuzzy about how to handle the basement garage ceiling and why.

I just didn’t want to spend money on something I didn’t have to upfront since we plan to finish the basement at a later date DIY.

We have a suspended with drywall / fire rated panels that are also vinyl coated to meet the flame retardancy requirement. It's worked well for 20 years.

The purpose of the code requirement for a basement ceiling under I-joists is to extend the time of collapse so it is roughly equivalent to a floor constructed of 2x10's for the safety of fire fighters. In your situation you can choose what you think is appropriate: unprotected, a protective ceiling or a factory intumescent coating depending on the likelihood that fire fighters or you would be fighting a fire in your basement.

The protection of living spaces above the garage is more important. Are any of those spaces bedrooms? If you add a ceiling, it should be drywall but you might consider omitting the joint taping so it could be easily removed later. In any case, I would spray the bottom of the floor deck with closed cell foam to protect living spaces above from CO in case a car is left running.

IMO future access to plumbing is not so important that you need to expose the pipes and the same goes for ducts. Electrical wiring and data cabling can be snaked later.

@User, I had asked our contractor about if the drywall required joint taping or not and again, the answer was fuzzy. We will definitely insulate the ceiling as the master bedroom and bathroom and part of the living room will be above that garage space so spraying closed cell foam makes sense (but will be much more $$$$). Both of our previous houses that had basement garages were "grandfathered" in so this isn't an issue we've ever faced. I like the idea of being able to unscrew a drywall or OSB/plywood panel to be able to have access so that may be the route we take. I guess, technically, the rest of the unfinished basement should have some sort of protection but I had to spend $$$$ on putting up drywall or OSB/plywood temporarily if we plan to finish it within a year or so of completion.

I have a basement garage and I love it! My car is never too hot or too cold Yes, the bedroom and library above can be colder in the winter, but a small space heater keeps the library toasty and I prefer the guest room to be cooler for sleeping.

My ceiling is plaster and yes, it's a pain if repairs much be done beneath it as it then needs re-plastering. But it does look nice!

Fire tape. Pay attention to required fire blocking & fire stop.

The last fire job I was involved in started in the garage. When it broke through the master closet floor above the family had already escaped.

They were lucky as the fire had found a gap at a ceiling plug and another gap at the garage wall missing fire stops allowing it to climb up through the 2nd story attic immediately.