Putting a basement under my garage (& back yard) ?

[Modern Jess]

Those last two posts were excellent! Thanks for the detail, and I'd like to cast my vote for continuing to post. I'm very eager to follow along.

 

[someguy11]

Truthfully, I haven't figured out what exactly we are going to do with all the space. I'm using one of the basement bedrooms in our house for an office. I'll probably move that into the bunker.

I'm thinking that I'd be fine using 22 x 34 of basement for my shop space. Any project that needs more space than that can spill over to the main floor of the garage.

I think we'll use 10x19' for household and shop storage. That leaves 30 x 19' for my office and whatever else we want to do with it. Our house has more than enough space for everything we want to do in it. I'd cut back on the size of the bunker, but it doesn't save a lot of money and who knows what other uses might become of it.

it would be nice to move our fitness room and the media room into the bunker, because of their soundproof nature, but then we'd have to heat the space to comfortable living temperatures and it would leave big unused spaces in the house basement.

The city has specifically asked me if I'm adding bedrooms or a rentable suite to this space. I've answered no, but I'm setting the space up for that eventuality anyway. The city disallows running any sort of business with customer traffic or employees in residences, but I've slightly bent those rules before.

Our house has 4 bedrooms on the upper floor, but one of those is a "study" which is only suitable for a baby's room. My wife might take that room over as an office. We have 2 nice bedrooms in the basement. I'm thinking that at least one of our kids is going to move downstairs when they become teenagers. That leaves us 1 guest bedroom, which is pretty much ideal.

 

[someguy11]

Those last two posts were excellent! Thanks for the detail, and I'd like to cast my vote for continuing to post. I'm very eager to follow along.

Really glad you liked them and found them useful !

Remember that none of this is gospel, I'm just fumbling my way through this and sharing as I go. Its like reality posting a bunker build, warts and all.

 

[someguy11]

I'm jealous of some of the nice, neat garages on this website and the hobbies the owners do in them. I've limped by forever with marginal garages, disorganized work space and I've generally hated working in the garages I've had, in spite of my love of building things. I'm really, really hoping this project comes to fruition and I get a nice garage out of it. Its long overdue.

 

[ez-duzit]

...
Labor
Myself + 1 helper for 3 months at $20/hour...
I can't help but notice that I'm no where near $200 or $300,000.

I can't help but notice you're nowhere near reality.

 

[someguy11]

I can't help but notice you're nowhere near reality.

Where specifically do you think my numbers are out ?

 

[ez-duzit]

You cleverly edited it out.

 

[someguy11]

Rough time estimate.

Lifting: 1 week.
Excavation: 3 weeks. Helper used only sporadically.
Footings: 1 week. Helper used full time.
ICF Block setup: 2 weeks. (17 feet per day)
Wall pour prep and pour: 1 week.
Floor prep and pour: 1 week.
1/4 roof cribbing and pour (375 ft^2). 1 week x 4 = 4 weeks total.

That is 10 weeks, with about 3 months of helper time. Should have the majority of the bunker completed ? Start mid September, finish in December ?

 

[someguy11]

You cleverly edited it out.

Huh ? I didn't edit anything since you posted. Check the time stamps.

 

[ez-duzit]

"Quote:
Originally Posted by someguy11 View Post
...
Labor
Myself + 1 helper for 3 months at $20/hour...
I can't help but notice that I'm no where near $200 or $300,000."

You + 1 helper for 3 months? Just laffin'.

 

[Playwme]

So here's a little twist. If you can build an underground insulated structure for $66 a square foot, imagine what cost you could do on a garage rebuild. I bet you could do it a lot cheaper than $50 per ft. Not having the garage in the way might bring down the cost of your basement a bit too.

 

[volleyball]

I could see the bunker as a pass through and storage. But as living space? I am thinking at least a window and maybe a door unless you like caves. Bilco type doors would allow easy access to the basement of the space and house.
I wonder if ICF walls will be the best choice for supporting the concrete roof beams? You could get pre stressed panels that could be craned into position once the blocks have cured and spread the load.
It would speed up the construction as you could start building on top sooner. Time is money. There are wall panels that are preinsulated and go in fully cured in a day.
Cannot say about costs. Without knowing the area, it is difficult. Maybe be tough to get $20/hr temp help that is willing to be reliably there and work that hard in million dollar neighborhoods.

 

[someguy11]

"Quote:
Originally Posted by someguy11 View Post
...
Labor
Myself + 1 helper for 3 months at $20/hour...
I can't help but notice that I'm no where near $200 or $300,000."

You + 1 helper for 3 months? Just laffin'.

If you are so experienced, why don't you provide some constructive criticism. Please go through my time estimates and point out what specific part you think is wrong.

FWIW, I can add a second helper for $10,000, so its not like the labor cost is a deal breaker.

 

[someguy123]

So here's a little twist. If you can build an underground insulated structure for $66 a square foot, imagine what cost you could do on a garage rebuild. I bet you could do it a lot cheaper than $50 per ft. Not having the garage in the way might bring down the cost of your basement a bit too.

I've gone through the demolish/dismantle/lift scenario with a building mover, carpenter, designer and structural engineer. Everyone thinks its worth the pain to lift it in place and work around it rather than any other solution.

Exactly where would removing the garage save a significant amount of time or cost ? I've allocated 3 weeks for excavation. With the garage gone you can use a larger machine and it would go quicker, but I'd have to rent it rather than use my own machine. A larger machine would load the trucks faster, but there isn't a huge savings there.

Where it might pay dividends is if the weather turned against us and its impossible to excavate with the skid steer. In that case we might be forced to dismantle it and use an excavator. That might be our backup plan. But if the soil conditions are good we should be able to do it with a skid steer, leaving the garage in place.

 

[someguy123]

I could see the bunker as a pass through and storage. But as living space? I am thinking at least a window and maybe a door unless you like caves.

We are planning 2 windows in window wells where the basement meets the house. I haven't shared all the details of the design.

The bunker floor is going to be a bit deeper than the house basement floor. One thing you don't want to do is excavate near or beneath the house basement footings. So the bunker is going to have a wall 3 feet from the house, with only a hallway passage actually connecting to the house concrete. This allows the house basement windows to remain in tact as well.

We could actually pour a stairwell going down into the basement in this area too.

I wonder if ICF walls will be the best choice for supporting the concrete roof beams?

My structural engineer says the walls will be standard 8" reinforced concrete walls.

You could get pre stressed panels that could be craned into position once the blocks have cured and spread the load.
It would speed up the construction as you could start building on top sooner. Time is money. There are wall panels that are preinsulated and go in fully cured in a day.

You can't see from the pictures I've provided, but there is a power line along the street side of the property as well as along the others side of the back alley. Crane contractors will NOT lift anything into my back yard without de energizing both power lines.

Furthermore, it takes a huge crane to lift over the trees or over the garage. Like a 100' jib. You can't set up a crane that size in the back alley and besides the outriggers would be right next to the foundation we are working on. If you set it up on the street, the distance from the center of the crane to the wall on the property line would be about 75 feet. 10 feet for the crane, 4 feet for the sidewalk, 10 feet for the city's part of the side yard, 50 feet for my lot. The power line is right beside the sidewalk, so the jib angle would still be impossibly steep.

For these reasons, using a crane to lift material into the back yard is a total non starter.

Prestressed concrete panels are extremely heavy. Placing them in the basement would be complicated given the size limitations of the machines we could get in there, even with the garage removed.

The joints between them lack structural integrity unless they are tied together in a special manner.

 

[bczygan]

Rereading this thread, it is obvious the OP has a depth of knowledge about construction.

In addition, he is employing professionals to assist him.

Also using the wide ranging suggestions from GJ, he is employing the power of group think.

Very smart.

I have no doubt this project will come to fruition with finesse.

In any project, there are numerous decisions to be made on how to go about it.

In many cases, several ways exist to do a thing, and it's a matter of choosing one.

Looking forward to progress reports.

 

[homebuilt burner]

Very interesting build. One thing you mentioned was being unsure of heating and cooling the underground space maybe think about putting pex in the floor for future heating. Also, I did a project similar but much smaller 2 years ago I rebuilt my back porch and put a room under it I sealed the deck by laying rubber roofing material on the deck and repouring another layer of concrete over that no leaks yet(was suggested by a friend who owns a large concrete construction company).
When I was a young boy my father put a basement under our house by digging out one corner and pouring footings and laying up block then moving down the wall and repeating the process. Essentially, never really lifting the house only supporting it as he went along. He spent the whole summer doing this and we never had any cracking in the house and the hole was only about 8x10 the whole time. when finished with the exterior walls he excavated the interior and closed the last hole in the wall. Another option to the garage issue??
Good luck People are always telling me things won't work. My wife is still amazed at some of the things I have been able to accomplish.

 

[homebuilt burner]

I have heard behind every successful man is a surprised mother-in-law.

 

[Tyberius]

I look forward to this project progressing. September seems like a long way off!

 

[someguy11]

Very interesting build. One thing you mentioned was being unsure of heating and cooling the underground space maybe think about putting pex in the floor for future heating. Also, I did a project similar but much smaller 2 years ago I rebuilt my back porch and put a room under it I sealed the deck by laying rubber roofing material on the deck and repouring another layer of concrete over that no leaks yet(was suggested by a friend who owns a large concrete construction company).

The roofs are probably going to get poured in 2 lifts. The roof under the garage is probably going to be thicker than the roof under the back yard. I'm not sure if its allowed to put a sealant between the layers of concrete. I think doing that decreases the strength of the slab because the top layer can slip against the bottom layer. Its stronger when they can't slip against each other.

I'll ask my SE.

 

[someguy11]

Very interesting build. One thing you mentioned was being unsure of heating and cooling the underground space maybe think about putting pex in the floor for future heating.

For sure I'm going to run pex in the bunker floor. I can't believe how comfortable the basement is in our house due to floor heat. Its the first time I've ever owned a house with a heated basement floor. I wouldn't own another one without it.

Having said that, I'm not sure I need that level of comfort in the bunker ? I'll prep it for it, not sure I'll install the boiler and circulation pumps.

Basement floor heat is excellent for keeping a space warm, but it doesn't react heat the air above it quickly. What I typically do in our house is turn on the floor heat for a day and then turn it off. Once the floor is heated up, it stays warm for a couple weeks. Its amazing. Our house basement has forced air ducting from the main floor furnace. I'll probably install a small direct vent natgas furnace in the bunker with some minimal ducting to handle warming the air. I could duct some of the warm air up into the garage space to heat it too.

I'm still working out the details. As long as I properly prep the space for various options, I can decide this stuff after the bunker is built.

 

[someguy11]

I look forward to this project progressing. September seems like a long way off!

There is so much prep to do to pull this off, its going to be very tight to get started in September. My family expects me to take holidays this summer !

Its really helpful for me to have the discussions in this forum. You guys bring up various stuff that forces me to think, reconsider and justify. It builds my confidence.

I was totally overwhelmed when I started thinking about this project. The more time I spend planning it, the more realistic I think it is to do.

I don't want to curtail discussion. If someone sees a hole or flaw in the project, I want to hear about it. 100 sets of eyeballs and brains are better than one.

 

[Fishplate]

I'm not sure if its allowed to put a sealant between the layers of concrete. I think doing that decreases the strength of the slab because the top layer can slip against the bottom layer. Its stronger when they can't slip against each other.

That makes sense...but I wonder if there's a way to key it so they won't slide? Like a beveled edge on the underslab, and the top having a turned-down edge? That would keep it from sliding, but still allow for drainage from the inner membrane. You would still have to engineer the edge for proper strength of each layer.

Tricky proposition without overbuilding...

 

[Fishplate]

My family expects me to take holidays this summer !

Tell them they are going to the beach - then send them out in the back yard with pails and shovels, and tell them to build a castle!

 

[readhead]

As I suspected there are no real deal busters here. Looks like you have covered everything. One suggestion I would make is to hire a house mover to lift the garage. You supply the beams and they supply the cribbing. They have all the stuff and can do it more quickly.

The jobs like this that I have been involved with did the roof in two pours. First was structural, then the water proofing, then the final slab to protect the water proofing and in some cases provide a finished, exposed slab.

This will be a deep hole so you will have to shore the walls or bench the walls if you have room.

 

[DeadSock]

But if the soil conditions are good we should be able to do it with a skid steer, leaving the garage in place.

Reading through this, IMO the critical issue is going to be the stability of the soil (during winter). The decision of how to deal with the garage depends very much on the soil conditions.

For example what's the plan for shoring the soil during excavation? If none, have you planned for a 45* slope from the finished footprint?

Even 'if the soil conditions are good' it seems little has been considered regarding safely excavating 9' in tight quarters.

 

[Strouty]

For sure I'm going to run pex in the bunker floor. I can't believe how comfortable the basement is in our house due to floor heat. Its the first time I've ever owned a house with a heated basement floor. I wouldn't own another one without it.

Having said that, I'm not sure I need that level of comfort in the bunker ? I'll prep it for it, not sure I'll install the boiler and circulation pumps.

Basement floor heat is excellent for keeping a space warm, but it doesn't react heat the air above it quickly. What I typically do in our house is turn on the floor heat for a day and then turn it off. Once the floor is heated up, it stays warm for a couple weeks. Its amazing. Our house basement has forced air ducting from the main floor furnace. I'll probably install a small direct vent natgas furnace in the bunker with some minimal ducting to handle warming the air. I could duct some of the warm air up into the garage space to heat it too.

I'm still working out the details. As long as I properly prep the space for various options, I can decide this stuff after the bunker is built.

I would make this a top priority, the floor heat will help keep things dry. I really do not like radiant heat in a shop space, because when I open the big door, the heat is gone so quickly and it takes forever to recover. One of my Dad's shops was that way, we ended up adding forced hot air in that bay as well, just to keep things on an even keel.

 

[someguy11]

Reading through this, IMO the critical issue is going to be the stability of the soil (during winter). The decision of how to deal with the garage depends very much on the soil conditions.

For example what's the plan for shoring the soil during excavation? If none, have you planned for a 45* slope from the finished footprint?

Even 'if the soil conditions are good' it seems little has been considered regarding safely excavating 9' in tight quarters.

This hasn't been forgotten, its on my list of things to address. I was hoping that my structural engineer was going to handle the geotechnical aspect, but now that I'm moving the bunker wall to the property line, he wants me to bring in a geotechnical expert.

If we excavate to the property line, there is no opportunity to do any benching. I understand the safety concerns. I am investigating how we can do a safe excavation and create a safe work site. FWIW, 2 infill houses were build across the street from mine in the last year. Both had 9' or deeper basements. Both were built next to existing houses. Neither excavation used shoring or benching. Not saying that made it a safe work situation, just saying that is what happened.

I'll comment more on this once I have a geotechnical engineer on site. At the moment I'm spending as little as possible until I know the funding is in place to do this project this fall. I bought a few hours of structural engineering because I needed to know a few of the concrete parameters in order to get a rough estimate of building costs, in order to finalize a go/no go decision from the construction point of view.

 

[someguy11]

I would make this a top priority, the floor heat will help keep things dry. I really do not like radiant heat in a shop space, because when I open the big door, the heat is gone so quickly and it takes forever to recover. One of my Dad's shops was that way, we ended up adding forced hot air in that bay as well, just to keep things on an even keel.

Just to clarify, the floor heat would be in the bunker floor, not the garage floor (aka bunker roof). The garage floor is a stressed member and from what I understand we don't want plastic pipe floating around in that concrete making it weaker. The garage is going to have to use forced air heating. Luckily I can locate the furnace in the basement.

 

[Strouty]

Just to clarify, the floor heat would be in the bunker floor, not the garage floor (aka bunker roof). The garage floor is a stressed member and from what I understand we don't want plastic pipe floating around in that concrete making it weaker. The garage is going to have to use forced air heating. Luckily I can locate the furnace in the basement.

That was where I was talking about. The basement would inherently be damp and the in floor heat will help it out. I was just ranting about my past experience and forgot to tie it together.

My point was in a basement, the heat is contained with no large exit. This makes it very efficient and I think it is the best choice.

 

[volleyball]

This is one place I would double think the floor heat. You don't want heat under big crates and such in the storage area. And while you may have a plan, well plans change. Or maybe you need to put in a pier because the engineering/ products used were not up to snuff. I'd make the floor lower and put a walking floor on top. Sort of like a computer room floor just not the 2x2 tiles. But a space you can run or move the heat pipes in.
I've done excavating deeper than and right next to existing footing. You do need to have the right soil, rock or whatever. Do we know what is existing? That info might quell fears or bring up new questions/ ideas?

 

[Strouty]

I thought this was going to be workspace or man space, not storage, did I miss something?

 

[DeadSock]

If we excavate to the property line, there is no opportunity to do any benching.

Planning to excavate to the property line is a mistake or possibly a disaster in the making, IMHO. (I'd also ditch the idea of increasing the garage footprint, the extra few feet isn't worth it).

FWIW, 2 infill houses were build across the street from mine in the last year. Both had 9' or deeper basements. Both were built next to existing houses. Neither excavation used shoring or benching. Not saying that made it a safe work situation, just saying that is what happened.

Find the geotech engr for that and hire them next.

I'll comment more on this once I have a geotechnical engineer on site. At the moment I'm spending as little as possible until I know the funding is in place to do this project this fall. I bought a few hours of structural engineering because I needed to know a few of the concrete parameters in order to get a rough estimate of building costs, in order to finalize a go/no go decision from the construction point of view.

My point is that the soil conditions may make the go-nogo decision as well.
You may also need to have the condition tested during the season you doing construction which may delay your plans a year).

 

[Strouty]

Soil conditions can vary designs huge. I do towers and if we have sand it could be three times the amount of concrete because the sand offers no real resistance like gravel or clay would. If the engineer is worth anything, he will have soil borings taken so you know what you have. They probably won't be that expensive to do, they will be cheaper than the engineer, that is for sure.

 

[someguy11]

I thought this was going to be workspace or man space, not storage, did I miss something?

Goal #1 is to provide a space to store all the stuff I have in my garage in the bunker. Lawn mower, snow blower, spare engine, 2 transmissions, bolt bin, steel rack, project lumber, yard tools, sports gear, snow tires, welding supplies, etc. It all goes in the bunker. I want a very clean, uncluttered garage main floor when I am done. I might bring projects up to the main floor, but I want the option of taking them into the bunker whenever I want.

Goal #2 is to provide a clean, uncluttered work space for my big tools. Lathe, CNC mill, a table saw I don't own but always wanted, etc. My below ground work shop. If I need to do anything dangerous or smelly, I'll do it on the main floor - welding, painting, etc.

Goal #3 is to solve a drainage problem we have in our back yard. Truth is, our garage needs to be lifted whether or not I put a basement underneath it.

Goal #4 is to free up a downstairs bedroom from being my office by moving my office into the bunker.

Goal #5 is to re landscape and redesign the back yard. Its not great right now.

Goal #6 is to add a patio onto the front yard.

I don't have a big need for a man cave space per se. The basement of our house is nearly 2,000 ft^2 and has room for a nice sized media room, fitness room, pool table area, etc. I don't need much more in the way of man space. What I am really missing is a place to store stuff in an organized manner that is now stored in the garage and a nice warm, dry, uncluttered workshop area.

Will my workshop area grow to take up the entire 1500 ft^2 in the bunker ? I can't see it, but maybe as I grow older and have more hobby time it might. The thing is that one doesn't save a lot of money by reducing the size of the bunker by a third.

 

[someguy11]

Soil conditions can vary designs huge. I do towers and if we have sand it could be three times the amount of concrete because the sand offers no real resistance like gravel or clay would. If the engineer is worth anything, he will have soil borings taken so you know what you have. They probably won't be that expensive to do, they will be cheaper than the engineer, that is for sure.

The soil is very stable around here. The only thing the soil stability changes is the size of the footings under the walls and how hard it is to excavate and work safely.

My designer suggested moving the walls out to the property line. They do this on one side of all the infill garages now.

 

[DeadSock]

Infill designs/issues are VERY different than what you have. Erase those from your head.

 

[DeadSock]

What's the setback for the houses (yours and neighbor) which both have full basements?

I'm guessing the slab garages you both have are 3' back?

 

[someguy11]

Infill designs/issues are VERY different than what you have. Erase those from your head.

Not so.

 

[someguy11]

What's the setback for the houses (yours and neighbor) which both have full basements?

3 feet.

I'm guessing the slab garages you both have are 3' back?

My garage has a frost wall and is 3 feet back. I don't know what my neighbors garage has. It is actually encroaching and illegal. He is about 2' back.

Don't get your ******* in a knot about the geotechnical and excavation issues. We'll figure them out once we get the facts. Right now I'm assuming that we can do like most of the other excavations/builds in the area. If I find out differently, I'll modify the plan to suit.

I'm really happy that I got answers to most of the construction questions this week.

One step at a time.