Basement in "garage"

[Eaglescout94]

I'm still very early in my planning/ idea stage of home remodeling and am considering my options to get bedrooms. My current garage is on a sab connected to the house, roughly a 24'x24' garage then a covered porch on the back. Since I am considering converting my current gun room into a bedroom, I'll need a new gun room. My mind wandered to cutting the center of the garage slab out and digging down then pouring a floor and walls of some kind (cinder blocks, foam block with concrete fill) then framing the over the hole. The garage would then be converted to a master bedroom. I know my best/ ideal plan of attack is to talk to an engineer but how large in theory do you all think I could make said basement? I've helped deepen a basement before, so I have a vague idea what I'd be getting myself into. Thoughts?

 

[no704]

It could never be used as a garage again. And would still have to support the roof or anything else over it. How does your local planning department feel about it. No reason not to I guess. Just don’t forget to not park there! Might need some ventilation, especially if you are in a radon rich area.

 

[Eaglescout94]

The end use of what is currently the garage would be a converted master bedroom. I don't see how the roof has any bearing when it is currently free span the entire length/ width of the garage so just digging a basement in the center would be a non issue. I have no clue how the planning department would feel about it at the moment, I'm not within city limits and there doesn't seem to be much anyone has to say about building here.
I highly doubt I could make the basement close to the same footprint of the future bedroom but would a 12x12 room centered seem plausible and still allow enough structure under the exterior walls until the basement walls are built and everything filled in?

 

[loganb]

What's the timeline of you living in the house? Do you care about the resale value or headaches with selling it?

What you lay out is feasible, digging basements under existing structures is big business in locations you can't go up/out in...I think there is even a special on some streaming service about it in NYC. The challenge with it as a diy endeavor is future buyers, regardless of the level of care and lack of inspection requirements are likely to treat such a project as a significant red flag.

If you really need more bedrooms and don't have the easier to add options via converting existing rooms/unfinished space the, adding on is going to be a far more straightforward and long term value add solution then attempting to diy a partial basement addition.

You can look up in floor storm shelters which are often used in areas where basements aren't viable....similar concept as you're thinking but most are smaller then you're thinking.

 

[Eaglescout94]

I'm not planning on moving for a long time. Adding on for more square footage wouldnt be very simple either. I am surrounded by hills and the only direction I could feasibly build would be towards my septic system and require a complete layout change of the interior of the house. The basement add in would primarily be a storage room for my stuff or small work shop for reloading and storage of hunting/ gun supplies.

I had looked at the in floor storm shelters, I havent read the articles that I saw listed with a couple of them but there was nothing outwardly said about size being able to dig in place

 

[carlaisle]

If you do it carefully, you can dig out the entire basement. Underpin the exterior wall in sections until you have a full foundation underneath and you're done. General rules of thumb are heavily dependent on soil type. In a heavy, dense soil, a one to one ratio is generally fine i.e. stay 1' away from the existing footing for every foot you go down. As the soil becomes looser you need more spread for every foot of depth. i.e. it could be you can only go down 1' for every 2' away from the existing footing. It would be faster, far less work, and possibly even cheaper to completely demo the existing garage and slab so you can use appropriate equipment to put a full foundation/basement under it.

 

[duneslider]

Doing this sort of thing was fairly common in my area when I was a kid. Lots of garages turned into living space. The house I grew up in we turned a single car garage into a dining room but we did add on a big 2 car garage at the same time. Lots of people I knew dug under their houses to add basements, one friend even dug himself a "room" under the house one 5 gallon bucket of dirt at a time.

At work, we dig pits all the time to install equipment below grade level. We just saw cut out the area dig it down form it up and pour, not a big deal. We usually aren't close to footings and foundations though so no engineering is needed. If this were my place and I was going to get it done fast I wouldn't be too worried about digging within a few feet of the foundation, if this is going to be a DIY job that takes you months to complete I would be more cautious. We usually cut and dig the hole one day and the next day the concrete guy is doing rebar and forming and then we start pouring the next day, so it isn't much time anything is open. I would keep in mind that you want to figure out ventilation and heating and cooling.

I'm also one that doesn't take much account of making my house how someone else might want it to be should I ever move. I just make it how I want it since I am the one that lives there.

 

[Eaglescout94]

I should atleast talk to my friend that I helped dig a deeper basement and get their thoughts on it. I believe one of their dads is an engineer so could be a more experienced opinion even if he’s retired.
There will be plenty of planning ahead of time to do it, if I do, in as timely a manner as possible.

 

[nadogail]

The definition of “A long time” is open to debate. We have been in our present home for 37 Years and it doesn’t seem to have been that long ago that we moved here.
Converting your garage to a bedroom is the first step in loosing your workshop. I am a firm believer in “never give up the garage”. Either add on to your existing house, maybe a second story but IMHO never give up the garage.

 

[Eaglescout94]

Hopefully would be short term, how ever long that ends up being. A pole barn is definitely on the list so I have shop space that I can fit my trucks in. Right now just trying to plan living space to get a room for everyone

 

[bassJAM]

Is adding rooms by extending out from another area of the house not an option? I know people convert garages to living spaces (my wife and I have even briefly discussed that) but digging into the foundation to add additional living space and shoring that up seems like a lot of cost for little benefit.

 

[OccupantRJ]

A 24x24 is a big *** bedroom If just for a bedroom. Could you not build a long narrower gun room along one side? I have a gun nut friend with a safe room/gun storage/ loading room in his garage like that. He has it well laid out and is only about 8 feet square.

 

[Eaglescout94]

Don’t really have the option to build out because of the interior layout.

It may be 24x24 but I’m planning on a large walk in closet. My current gun room is 12x12, I think, with a corner work bench, toolbox and a couple safes. It holds all my guns, reloading, gun smithing and hunting stuff.

 

[Just Puttering]

Digging under slabs and buildings is common but extremely expensive in dense cities. Some folks have put multi car garages under an innocuous looking 2 car garage with car elevator access. You can even dig under the house iteslf with enough $$ and engineering.

Cutting part of the slab out is easy, but as soon as you start digging down more than a couple of feet (depending on soil type) you will have to start underpinning the remaining slab edges which gets costly ad you start getting to 8’ depth. Waterproofing and drainage of the room could also be a concern.

It can certainly be done, but makes for a very expensive gun room.

 

[Mezz2006]

My opinion, but your room under the existing garage could in reality be as large as the garage itself depending on the foundation. My parents house has a workshop under the existing garage. There are 3 rooms in the ~24x24 space.

 

[PoorUB]

I'm still very early in my planning/ idea stage of home remodeling and am considering my options to get bedrooms. My current garage is on a sab connected to the house, roughly a 24'x24' garage then a covered porch on the back. Since I am considering converting my current gun room into a bedroom, I'll need a new gun room. My mind wandered to cutting the center of the garage slab out and digging down then pouring a floor and walls of some kind (cinder blocks, foam block with concrete fill) then framing the over the hole. The garage would then be converted to a master bedroom. I know my best/ ideal plan of attack is to talk to an engineer but how large in theory do you all think I could make said basement? I've helped deepen a basement before, so I have a vague idea what I'd be getting myself into. Thoughts?

Does the garage have full depth footings?

Personally, I would just rip out the slab, dig the basement and semi-finish it, then frame in the floor structure with typical floor joists. IMO, it would be easier and might cost less in the long run.

 

[dcg9381]

I know my best/ ideal plan of attack is to talk to an engineer but how large in theory do you all think I could make said basement? I've helped deepen a basement before, so I have a vague idea what I'd be getting myself into. Thoughts?

Engineers don't like small one-off jobs, so that may be "difficult" (expensive) to get done. And generally engineers are engaged where a stamp is required (permit inspection).

I know there are basements in IL, but for the rest of the world it's way cheaper to build UP when you can't build out... YMMV. Interested to see what you come up with though.

 

[Eaglescout94]

From the perimeter that I have dug around for a parling pad next to the garage it seems like its just a slab. A very thick slab but just a slab. There are a couple holes drilled in the floor, and they appear to be 6" or so of concrete but I haven't checked with a light and hook.

I still need to talk to my friends to see what they have for input or direction. It would be super handy to have the space below the future master bedroom but cost will for sure factor in.