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Making an access hole through a concrete foundation wall

S

Stan in Oly, WA

Well-known Member
There is a job I have to do which I have been avoiding for years. There is a small area in the most inaccessible part of the crawlspace under my house which has no access. It is enclosed by concrete walls on every side. It is under a bathroom and it has both supply and drain plumbing in it. My basement garage is about 40" below grade and there is a place in the garage where I can open a wall which is on top of the house foundation and look into the inaccessible space between the ends of 2X10 floor joists. I always thought I would cut through a different concrete foundation wall in the crawlspace to get access to the area, but that would be a nightmare. Because of furnace ducting down the middle of the crawlspace, getting to the place I need to work means crawling 25' in the opposite direction, then 50' down the other side and another 25' across. Imagine having to low crawl 100' with equipment to bore or cut through a concrete wall, and then having to do the work lying on your stomach. Now imagine doing it when you're old and tired.

Recently it dawned on me that I can cut through the foundation wall in the basement garage to get into that space. It's eight inches thick and it was poured in about 1950. I could get through an opening 24" wide and 16" high, but it might as well be at least two feet by two feet. There's no advantage to skimping. I think I have to remove the concrete without disturbing it too much, like by bashing it with a sledge hammer. I can't think of a way to support the floor joists above that space before I get into it. What should I use to cut through the concrete?

Stan
 
I was going to suggest renting a partner saw, but they can get heavy and awkward. Never seen a concrete chainsaw so I looked them up. That's the way to go, no doubt.
Though I would suggest not cutting the entire opening in one large piece.
 

Stan perhaps you should hire these old fellows ?

https://www.dailymail.co.uk/news/article-3052184/Big-squeeze-Gang-60m-Hatton-Garden-gem-heist-drilled-concrete-steel-wall-create-hole-just-25cm-high-45cm-wide.html

Or at least follow their practices , :)
The Hatton Garden heist has become almost legendary in the few short years since it occurred .
 
MJMJ; That's good advice. I'm not a fan of using LOL, but I did actually laugh out loud when I read it. A chunk of concrete 24" square and 8" thick would weigh 400 pounds, and it would be just about my speed to overlook that little detail when I cut it. Eventually, though, I'd notice.

Stan
 
Stan I would use a hammer drill and drill holes every 3/4 inch. Draw a line on the foundation where you want to cut it out and start drilling, a half inch concrete bit and hammer drill will make quick work of it. After you have the holes start swinging your sledge hammer, the concrete will break out and more or less follow the drill holes
 
Hire someone who does this for a living. It will be a decision you won't regret. They will do as much or as little as you want them to do. Good luck.
 
You can probably just hire someone to do the work in the crawl space and skip cutting a hole in the concrete wall. They can dig a hole under the duct work for more direct access.
 
Concrete chainsaw would be well worth renting if you do it self. They can cut through rebar and make a good clean cuts.

Get one that a water hose attaches to for dust control. If not atleast wear good protective gear and be prepared to clean up one heck of a mess.

As far as the joist go. A flat plate or angle can be used on top of the foundation to support them.
====

Could you not open a hole in the floor and work from it?
 
Stan, before reading any of the responses, first thing that came to mind was a concrete chainsaw.

Hands down, you were given good advice below. One of the more difficult tasks I have seen done with these was trimming the ends off 5000 PSI prestressed concrete plank, steel strand reinforcing included. These plank were the deck or buildings floors and the precast shop drawings or placement were off. This was an elevator shaft and had to be correct, concrete chainsaw made short work of it.

I hired it out and there has to be a concrete core drilling/cutting outfit in your area that would typically have all of the concrete cutting tools and could do the job for you. Make 2 cuts to lower the weight of the piece taken out. Cut bearing points for a steel lintel to carry the overhead load. Only issue with doing that is fastening the lintel, but say with a return angle with holes spanning far enough into the wall each side to maintain fastener edge distance, expansion anchors could secure it.
 
Charles; They don't work for less than 15 million pounds a day. Even with the US$ strong right now, that's going to run over my budget.

Stan
 
Michael; Since this foundation wall supports one end of a 12' span of floor joists , I'm not comfortable with the idea of breaking a section of it apart with a sledge hammer. In my experience there's a very high likelihood that even if some of the wall came apart and left a void under one of the joist ends, the mud sill would hold it up. But what if it didn't? What if it sagged and caused the ceramic floor tile in the room above to crack? I see no reason to take a chance when there are more peaceful ways to do it, and I can afford them.

Stan
 
wgm; I'm leaning that way. The concrete chainsaw rental is $95 a day, and I would have to buy the chain/blade for $275. Since there's a good chance I'd never have any use for it again, I'm not keen on owning it. A local concrete cutting company gave me a ballpark estimate which sounded pretty good. I wouldn't mind not being the one to do it.

Stan
 
Concrete chain saws would be initially my thought have used them a bunch until I demoed a husqvarna cut and break saw. That was probably about 10 years ago and I have never used a chain saw since. That would be my tool of choice. It?s worth a YouTube or google search but I would also cut a vertical cut down the middle to give some room for the pieces to come out
 
How about finding a spot, say in a closet above the crawl space and cut and build yourself a floor hatch that is framed off to support cut joists in the floor, and allow you to access the crawl space.
It would be much easier.
Loren
 
PS If this is a house that you bought rather than built, perhaps there is an existing floor hatch that you do not know about. Perhaps you need to go exploring. I can not imagine a crawl space would have been built without an access.
Loren
 
ss55; The space I'm trying to gain access to is surrounded by concrete walls. The idea that I had to go through the one I could get to in the crawlspace seems crazy to me now that I've realized that I can go through a wall that is easy to get to. Sometimes I get an idea in my head and it blinds me to other possibilities. That must be what happened here.

Stan
 
Mule Meat; I've been persuaded that a concrete chainsaw is the way to go, but I'm leaning toward paying someone else to do it. Every floor in that part of the house is covered with ceramic tile. That's too bad. I'm experienced at carpentry, so I'd have no trouble concealing an access panel in the floor, but this would be my first time using that tool to cut through vertical concrete.

Stan
 
Does sound like a project to be hired out. Too many variables it sounds like you don?t know about. Be cautious.
 
Billy; Good plan. My plan differed only in that instead of a lintel with short returns for fastening, I though I'd fab up a complete frame and mortar it in place. If I'm lucky with the location of the plumbing behind the wall, I should be able to put a 24" wide opening where it will only be under one joist. If I can leave at least six inches of concrete in place at the top I shouldn't have to jack it up to support it.

Stan
 
During remodel here we needed two openings cut, one making the coal chute opening into an egress window for a basement bathroom, the other a new opening into a newly added crawlspace like Stan has. Our concrete contractor or general knew of a concrete sawing company from about 50 miles away, they agreed to swing by when down here for any other job.

Dad was here that day, said it took far longer to get the saw off the truck than to cut the holes- 24" diamond circular saw that fastened directly to the wall, operated by remote control and truck-mounted pump. Total time was under an hour, slicing through poured wall, block wall and bricks. Finished cut is smooth as silk. I think we paid $300? Really glad we had the loader to remove the chunks!
 
Adirondack case guy; I can't come up with an explanation of how an area under the house got closed off---particularly since it has plumbing pipes running through it. As far as providing access through the floor, there's no way to do it that wouldn't be more disruptive than cutting through a concrete wall. I've worked on every inch of floor that is over that space---a lot. If there were any access I'd have found it. The house does have quirky features, though. There's a fallout shelter under the concrete floor of the basement garage, and a four foot high sort of anteroom to the attic of the main part of the house which you enter by using a fold down stairway.

Stan
 
bmack518n; I agree. When I have to do something I haven't done before, I prefer to have a couple of test runs somewhere where it doesn't matter as much. I hate to be responsible for bad work that's out where people can see it. I don't like to have to look at it, either.

Stan
 
K Effective; Nice story. I don't think it would even be possible in my situation. The place I need the concrete cut is about ten feet inside my garage. I'll need to move things out of the way, including a washer and dryer. I'll probably hire a guy who has a small company (probably just him) that does this. He would do it with a wet cut concrete chainsaw, so I might have to devise some kind of temporary trough to direct the runoff water out the door rather than let it run further back into the garage. There won't be much to it if I don't have to do the cutting myself.

Stan
 
IMHO there is only 3 things to know about concrete, 1. It gets hard, 2. It cracks, 3. (The most important) Hire it done!
 
I recently had to install two windows in a basement wall and hired someone to cut the concrete. His words "When in doubt, sub it out". Before all these concrete saws the normal method to do what you are doing was to drill holes all the way around the opening as close as possible then break out the concrete. I have done it this way with a pneumatic drill and jackhammer, not a fun job. Those chainsaws work well.
 
Cutting a hole in the wall might be a lot of grunt work but what I would be concerned with is what is above it and what you might do to the structure of the house by cutting the hole. You might need to get an engineer to evaluate where to cut the hole. It might be necessary to put a steel beam over the hole. The engineer could tell you if a beam was necessary and what size and type of beam would do the job.
 
The house next door is having an addition put on and access via hole to 4 ft "crawl" space, per code, had to be made. House was built in late 30's/early 40's so concrete is well cured. Two gents, father and son, did the job. Cut a hole, probably 2 block wide by 3 or 4 high. Did it with chain saw,diamond teeth and water, fed off garden hose. It was new to me, so I watched. Impressive. Arrived at 8 and done by 10:30. Made 3 cuts, pushed the block out and it flopped onto some wood the protect the concrete floor. Not much mess, goo slop shoveled up and shop vac for other clean up. Price was ?$300 maybe $500, can't recall. Still a deal. Clean straight finish on cuts. Sounds like what you are looking for.
 
I had to do that thru my foundation wall to gain access to the crawl space--rented an electric jack hammer from home depot and had the job done in 4 hrs.
 
dpendzic; How neat was the opening you were able to make? One advantage for me of having somebody cut it with a concrete chain saw is that if they can cut a rectangle with straight sides, I can have lengths of steel plate ready to set in place and weld (or weld and set in place), and be done with it the same day. If the opening is ragged, as it would be if I made it with a drilling or impact tool, I'd have concrete work to do before it was done. I've got the time for that, but I'll be uneasy until I've put back the support that will be compromised by making a hole under at least one floor joist.

Stan
 
George by Geneva, NY; It does sound like what I'm looking for. And that price range is about what it would cost me to rent the equipment (but have to buy the blade), and do it myself. And since I've got no concrete walls to practice on, it's unlikely that my first attempt would be as pretty as one done by someone who does it for a living.

Stan
 
Stan---it was a bit rough--maybe + or - an inch or so. I assume the joist is on the far side of the wall. Is there a face beam nailed to the end of the joists? Do the joists sit on a sill plate?
If your going 24 inches wide and the joists are 16 inches on center can you place your opening so one joist is 8 inches from one of the side cuts and not in the middle?
 
Pete in MD; It might be possible, but it would be a challenge. There's no rim joist, so when I open a section of the framed wall above the concrete foundation wall, I'm looking at the ends of the 2X10 floor joists. That means I could have one, two, or three 9.5" X 14.5" openings to work through. The concrete floor of the basement garage is 40" below the top of the foundation wall. The ground level on the other side is about 10" higher. Trying to set up a bottle jack on an uneven surface which is beyond arm's reach, and which I can't see except with a mirror, all through a hole (or two holes, or three) about the size of a long manila envelop, would definitely give my creativity a good workout. I like a challenge, but it might not be worth the trouble. I'll look, though.

Stan
 
dpendzic; The only factor which might affect the placement of the access hole in relation to the joists would be the location of plumbing pipes. Unobstructed access relative to pipes would outweigh optimum placement relative to joists. There is no face beam/rim joist, which is fortunate. It's relatively easy to open the wall so that I can look through between the joists. If there were a rim joist, I'd have to cut through it to look inside. Putting that wall back together is simple. There is a 2X6 sill plate which will provide some additional support and spread the load of the joist that is over the hole through the concrete. The load on the joist ends at that point could be significant---it's a bearing wall and there is another story above the basement garage. I'm guardedly optimistic about it, though. I've moved houses before, and jacked up many more. Frame houses hang together surprisingly well.

Thanks again for your advice and comments.

Stan
 
Stan---sounds like you have it well thought out--the one option that might work for supporting that joist on the other side is to work thru the joist 16 inch space and get a vertical timber under it before you cut the concrete out?
 
Hi Jim; Water supply lines for the bathroom that's above that space and the laundry area beside it run through there, as well as the supply for a hose faucet on the outside of the house. If any of those lines sprung a leak or broke, there would be no way to stop the leak or the flow except by turning off the water at the meter. Then the house would be without water until I could get access to that area to fix the problem. I can do it now when it's reasonably convenient for me, even though it may never become necessary, or I can do it if it becomes necessary even though it's unlikely that it will be convenient then. Some people, maybe even most people, would judge that problem to be too unlikely to worry about. I'm not like that, though. I'll feel better when I've dealt with it.

Haven't heard from you in a while. How have you been?

Stan
 
dpendzic; That was my thought, too. I'll see what I can do, just as I'll see if I could get a bottle jack under it as Pete in MD suggested. I actually kind of like problems like this because there usually is a solution, particularly if you don't fixate on one possibility and ignore all others. I could spend quite a bit of time dealing with it and still come out ahead compared to the time it might take me to repair the floor in the bathroom if the joist sags and it pops loose or cracks any of the 14" ceramic tiles in there.

Stan
 
I would jack up 3 floor joists and slip a 6"x 6"x.25" by 3' piece of angle iron in to hold up the joists.
Leave it there.
 
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