Digging out a basement

I'm currently in the process of digging out a basement under a 24x36 house. I wouldn't be doing it if I didn't have to. The main support beam and a number of the floor joist's are pretty well shot. The house is 50 years old and there is only about 12-16 inches of crawl space. I've owned the house for about three years, and after running a phone line to the computer about two years ago, I noticed the problems. The folks I bought the house from used 2x6's to strengthen the floor joists, and they aren't working. They didn't even attach them to the floor joists, there's about a 1 1/2 inch gap between the floor joists and the scabs. That's one problem, the other is that I want to replace the old galvanized plumbing with plastic, and possibly rewire. Since I'm not a little guy, I figured that digging a basement is my only option. I'm digging in hard red clay, any suggestions on how I should install some drainage and waterproofing.
I would also like to reduce the number of supports under the main beam. Would steel I beams, wood I beams or laminate beams would offer the greatest strength? If it's possible, I would like to have only one support in the middle. the span would be approximately 15-16 feet.

 

What a job. There are two ways to do this job. The easy way or the hard way. Only you have the answer to this. Do you want a basement ? This a yes or no question. Or do you just want to solve your problem. How much do you have dug out. ? Please respond. Thanks

 

Jack, thanks for taking the time to respond.
Yes, I do want the basement.
I'm about 1/8 into it so far. Will be renting a skid-steer shortly.
Sorry this is so brief, this is the seventh time I've typed a reply. Each time I go to post, it says I'm not logged in, so I have to start over each time. And I'm not a very fast typist.

 

It is easier to add space to your home by building out or up. Digging out a basement under an existing home poses the risk of compromising the integrity of the foundation and tends not to be a recommended way to go. I once read an article where I guy had some house movers come and jack up the house and put it on skids while he built a basement and new foundation, then replaced the house on the new foundation. Proceed with caution and don't hesitate to call in a professional for advice.

 

Thanks, Twelvepole.
I know it's a risky proposition. Most of my wife's and myself's families are in construction. I've ran this by most of them and each has had their own ideas of how to do this. I'm just looking to get some more input and maybe some things we all haven't come up with yet or thought of. Since I can get the block laid for cost, and just about everything else done for costs also, this is a pretty cheap way to almost double the size of my living space. I say almost, because I'll be staying about 2 feet away from the foundation as I'm digging. I'm digging in solid red clay, so it's rather stable soil, it's not very prone at all to collapse or cave. I'll also be bracing it as I go.

 

Bet a steer skid won't do it if you have hard clay. I'd go down each side about 4-5' inboard from the outside and crib it up either with 6x6s or steel I beam just like you were going to move the house.....in fact, you might want to hire a moving co to do it.

Then I'd hire a front load to run down both long wall and remove the old foundation while digging down to the level of new footers.

Then I'd pour new footers, lay the block up and set the house back down on the new outside wall. Then have the loader dig out the center dirt, pour the end footers and tie the end walls into the long walls.

This is a massive undertaking and I wouldn't mess around with anything but an all out assualt. You'll be money, time and grief ahead in the long run.

 

Klambpix, please keep us posted on this project!

Best regards,

 

Andy,
If I wanted to spend that kind of money to add 800 sq ft to my house, I'd have just put 25-30k into another house. I'll get this whole project done for less than 5k. The biggest expense is probably going to be the concrete footers and slab. I haven't figured out the exact amount of concrete that I'm going to need, but I'm sure it's going to be less than a grand, and that's including the crew to pour and finish the slab.

 

your orignal post:

"I'm currently in the process of digging out a basement under a 24x36 house. I wouldn't be doing it if I didn't have to. The main support beam and a number of the floor joist's are pretty well shot. The house is 50 years old and there is only about 12-16 inches of crawl space. I've owned the house for about three years, about two years ago, I noticed the problems."

SILLY ME....I THOUGHT YOU WERE DOING THIS >BECAUSE YOU HAD TO IN ORDER TO SAVE THE HOUSE

 

One thing about the advise you get off the internet.....it's often worth EXACTLY what you paid for it.

 

And I'm definitely getting my money's worth from you, Andy.

 

Keep us all posted. I want to do the same thing to my house. The wife says I'm crazy but I think it's a workable way to add some space. I like the idea from andy about the backhoe, but my house is brick on the outside and if I cribbed up the floor joist and removed the earth and block that incorporates my existing footer. I would lose my brick ledge and then my brick. so by backing up inside the existing foundation I don't have a linear perimiter foundation but I saved the brick and the cost to re side the house. My house is 24X52 with a sloping crawlspace from 36 to 48 inches high. So the excavation would only be 4 1/2 to 5 1/2 feet to have a full 8 foot ceiling. I would end up with 20X48 and enough dirt to fill in all the low spots in the yard too. Did you check with the local building officials as to codes or permits. Would this impact a persons ability to sell the house in the future, would an appraiser sign off on the design. Please post back and give us the details and your progress.

 

Klamb....you're quite welcome. Since you have all the answers already, I can't figure out why you bothered asking for advise in the first place. Seeking confirmation of your way of doing it ??

OK...you're right.....besides...I can't see it from my house

Joe:

With brick veneer, it does get a bit tricker, but I've seen a local house moving company move houses with brick still attached !
They even moved one BIG two story a couple years ago that had a chimney on both ends and didn't remove them either !!

The problems I see with leaving the leaving old crawl space foundation in place are:

--Waterproofing the new one. With the old one and it's drains above the level and outboard of your new one, water is going to be hard to keep out.

--If you lay block all the way up 2' inboard, how do you ever access floor joists, plumbing, heating ducts, etc in that small space between the old foundation and new one.

 

anna2


--If you don't lay the wall all the way up, and stop at the height of the footer of the old one, you have this silly ledge all the way around the new basement to contend with.....and it looks like just what it is......a poorly done retrofit.

No, all around, if I was trying to just gain space ( and that wasn't how klamb started off his post), I would pop an addition out the back or one end and just accept the fact the original builder went the cheap route with a crawl space.

I made exactly the same mistake with my first house....and money was the issue.....but decided that crawl spaces are just a place for critters to collect. All houses I built since then ( about 50) have either been full basement or on a slab. My own current house is a combination of full basement and slab.

 

Well, Andy, I'm just trying to kill two birds with one stone. Gain access to fix my floor joists, main beam, and plumbing. Sorry if I started off this thread the wrong way, it's the first one I've ever posted. I was just trying to get some ideas on the waterproofing. To see if all these experts out there had a better way of waterproofing than I did. Guess not.

Yes, I could lift the house up and bring in a loader, and the loader wouldn't cost me a thing. But if I jacked up the house to excavate under it, where would I be living while all this work is going on?

As far as permits, I don't need one in my area, this is considered remodeling.

I can't add onto the back of my houes because it would then be over the septic lines. The only nice tree I have in my yard is a large maple on one side of the house, don't want to cut it down for an addition on that side. On the other side I have plans to add a large addition, that's down the road a couple of years.

As for the ledge, I may frame it up with removable sections, so I can get to any portion of it I need to. Pop off a piece of trim, remove a couple of screws, no problem. The only ones that will ever know it was done that way are you guys and whomever is helping me work on it. Or I may just leave it as it is, it'll give the cats a nice high vantage point of the entire basement. Since I have a chimney to take out of the middle of the house I thought about running one of those tube type skylights down to the basement.

Since I didn't get any input from you guys about the waterproofing, which was my original question. I've discussed this with other builders/contractors and family in construction. So far the best thing I've come up with is to cover the clay walls with a good thick plastic, put the thin slotted drain tile into the outside edge of the footer for the new walls, cover with a little gravel, and pour the footer over the drain tile( I'll probably under cut the clay wall about six inches so I won't have to pour concrete over the drain tile) Lay six inch block with jewel wire every 2-3 courses, and put the black waterproofing on the outside of the block(this will have to be done every course or two as the block is layed.) After waterprofing the block, I'll backfill with gravel also.
Put a couple coats of Dry-Loc on the inside and I should be set.
and yes, I'll run the drain tile out to a point where it will drain correctly. In my case, this'll probably be a couple hundred feet. My lot doesn't slope much. but this will be a dual purpose trench. I'll be installing my own geothermal heat pump, which is another crazy idea I have. If it doesn't work, I'll only be out a couple hundred bucks worth of pipe. If it does, I'll have a very cheap source of heating and cooling. That's not going to cost me 10-15 grand.

 

Klambpix: I have not responded again because I wanted to see
what other great pieces of advice you got. You sure got some, all negative. I have one crew and this is all they do, everyday. dig basements under houses. We do not raise the house. We do not wiggle the house, and most people do not even think it can be done. YOu and your relatives are on the right track. I will not go into all the construction details and your relatives can supply these, but I will just throw in a few items for thought. Pick the side or end of your house you want to dig from. Get a backhoe to dig down along the side of the house about 8' wide, and then dig your ramp for your bobcat. If your soil is real hard put a set of forks on your bobcat to bust up the clay. Then put on the bucket to take out soil. Off and on, off and on, you know the routine. After you are under your house about 8' dig out an area
abot 12 wide, and begin installing a tempoary post and beam wall. When you finally get to your old foundation footings, dig past them about 2 feet, and lay drain tile on the outside as you go along. About every 8 to 10 feet, stop, and pour your new footings. Let harden, and then pour your new wall. You just keep moving around your house 8 to 10 feet at a time. So at some point in time, you will have a basement under half of your house and the other half will not have been dug out yet. Dig, move your forms, pour, dig pour your forms, pour. You will p[robably have to install several post and beam setups by the time your are done. When your all done, pour your floor. contrary what others think, this is not expensive. Probably $10,000 at most and you get double floor space. Good Luck PS Went back and read your last post, and yes, you can use blocks instead of pouring an interlocking wall. In fact it may be easier. Put your drain tile in and attach the black plastic (6ml) to your house and it goes over the top of the drain line. Back fill with pea gravel.

 

Thanks Jack. It seems as if we're on the same page. I've already had the ramp dug and a temp cellar door type covering over it. I'm already into it about 16' with a 6' ceiling. the bobcat was delivered this week. Called every rental place around and finally got what I think is the best deal for me. $18.00/hr that it's used. Since I do have a full time job and can't put 40hrs/week into it, this was the kind of deal that would suit me best. As soon as it dries out I'll start digging with the bobcat, taking the floor down another 3'.

Do you think it would be a good idea to put 2" styorfoam on the outside of the block wall? And fill with pea gravel between the styro and plastic covered clay? My thoughts are if I insulate the outside of the block, I can just finish the block inside with Dry-Loc and paint, that way if I do have moisture problems in the future, they will be easier spotted and fixed.

 

Your idea is right, but just in the wrong order. Cement Blocks, styro(the pink kind)plastic (6ml) this is also on top of the drain, pea gravel, then your dirt. If you wanted, it would not hurt to put some dry lok on the outside either. Your choice.

 

Could you keep us posted on how this goes? I am fascinated by all this.
One question: I know people who have spent small fortunes on 'french' drains' to take care of water in basements, who say it works great. it doesn't sound like you are doing this; have you considered this?
Another question: and I ask with all respect, why did you buy a house without a basement?

 

J66,
No I didn't realy consider the french drain. Didn't want the gutter running all the way around the perimeter of the basement. the drain tile around the footers will work just as effectively if not more so, it'll get rid of the water before it gets inside.

We bought a house without a basement, because all the others that we looked at in our price range were much worse off than this one. And the location is great for the two of us. five minutes from town and work. No brown bagging it or McDonald's every day, just ride home for lunch.

 

Thanks for the answer; I don't know a lot about basements. I just thought if they were a good idea, this is the time to install them, and no-one else had mentioned them ...

I never knew there were houses without basements until I was well into my twenties, so I still find the concept startling. When house-hunting I looked at a house that had a basement added, and it (the basement) looked great, but the plate glass in the doors had cracked.

 

Probably 70% of the homes in the USA do not have basements.
French drains will only work with certain soil conditions. He has what is called a hard clay. With this type of soil, your goal is to keep water off it. A French drain puts water into it.

 

Jack,

I'd disagree with the 70% figure, as most every home built in the north and northeast has one due to the depth the ground freezes. In order to get the footers below the frost heave line, if you have to go 5-6', you might as well put a basement, and they do. It's only when you get into milder climates that basements become optional, or if you get into FLorida where the water table is about 1' down, slabs dominate.

ALso French drains .....a trench filled with gravel and sometimes drainage pipe for those that don't know what they are......ARE used quite a bit here in the southeast where we have predominately clay soils. The clay is almost waterproof, so if the home is built into a sloping lot, the French drain is a defense against water running down a slope and in against a house...it is not always possible to grade the yard to shed water away. You'll find these drains on the upslope side, sometimes with a light cover of topsoil and grass.

 

im doing the same job right now. I dug out a ramp int he back of the house so i could drive the bobcat right in. My house was built on fieldstone. I bought the house 3 months ago and noticed that the floors are slanting on the second floor. I too only had a crawl space ranging from 2ft to 3.5 at the deepest point. I now have the basement dug out to a depth of 9 ft. Now comes all the tricky stuff and i guess my question to whomever. I want to dig out under the fieldstone but only in a small section at first so i can put a support beam eventually taking out out all the fieldstone and supporting the house all the way around with beams then pouring the foundation once the house is supported. Please write back with some comments or questions.

 

thisjobsucks,

Be careful! It's not clear from your post how close you have already dug to your foundation. I hope you understand that the load on your foundation is not transmitted straight down from the fieldstone. The load spreads out in a conical shape down into the earth.

If you have already dug close to your foundation on all sides, a slight mistake at this point could cause your house to collapse. I recommend professional on-site support. But I'm looking forward to what Jack has to say, since he has quite a bit of experience in this area.

 

Thanks for the reply John. I did not dig a straight line with the wall i left an A shaped decline. But today i am getting ready to dig under the foundation by about 3 ft so i can put a jack there and then cement that 3 ft section. Once that dries I plan on finishing that side of the wall and so on around the house if this strikes you as odd write me back with some other ideas. Thanks again!!

 

Please consult a structural engineer or architect for goodness sake. That's the best investment.

 

Any suggestions as to taking on this kind of project if your house is built of concrete block from the footings straight up to the ceiling? The floor joists are let-in to the block walls.

 

Ok guys: I am going to answer several issues here. Tn Andy, my 70% might go downward to 65% but no less. Most of the US with the exception of the east coast and NE area are in a high water table. Yes, 4' frost for foundation footings, with a 2 or 3' crawl space. Now to This Job Sucks, Only take out enough Flagstone to put in a post. I would do this about every 8 feet and once you have2 of them i, put a beam under your mudsill.
Do not take out alot of flagstone at one time or you will have one great big problem. Now for the cement blocks the entire wall. This is easy. You sillis only hooked to your wall with bolts, which can be cut off. Just start at one point, take out no more then 8 feet of wall, fill it in and continue. The alternative of jacking up the whole house is expensive. Good Luck to all. PS We got the knee wall problem solved also.

 

On the concrete block house, the sill is not bolted to the wall- the joists are pocketed one by one into the masonry.

 

hello everyone, just an update on how things are going for all those who care. I have finished one wall it took about 90 bags of concrete along with the fieldstone that i was using. I'm using quikcrete 5000 it dries to 3000 pounds square inch in just 24 hours and after 28 days it's rated at 5000 pounds "..".
I have 2 more walls and the floor to do. It will probably take me a month or so to finish. This is hard ass work. If you guys have any questions or if you aren't sure of what exactly im doing reply.

 

KC-76
You are correct in some cases, but however, in many states, bolts must be anchored into the concrete blocks before the sills or plates are attached, and they are then bolted to the wall.

 

I realise that. However, this house was built sometime in the mid 30s, most likely by a weekender and without a permit. There are no plates or sills because it's not platform framing- the concrete block wall of the crawlspace extends straight up without a break and is also the outside wall of the house. The joists are pocketed into the block wall one by one, with brick nogging inbetween.

 

Just a quick update.
Got everthing dug out with the skidsteer. A tooth bar made all the difference. Spent about 30 hours on it getting about 25 dumptruck loads out. Getting ready to form and pour the footers.
Also got the main beam reinforced with two 1 3/4 x 14" laminated beams. So far I've only spent about $1300, got about another $1500 or so to go. Moving pretty smoothly so far. Hope to have the walls done in a couple of weeks.

 

It sounds like everything is right on track. Good Job.

 

Just an additional thought, instead of using blocks, it might be worthwhile to look into one of the new Insulated Concrete Forms.
I'm getting ready to do a project like this with them. They worked real well on the basement I just poured for my log home.They will also give you an R45 or greater!!! E-mail me with questions about them?