[Scleros]

I have an older home with a 6 foot basement ceiling. I'd be willing to repour the concrete floor to gain some inches and I'm wondering what, if any, drawbacks to, considerations for, or ways of having the floor at or below the footer level of the outside foundation walls if the floor is kept independent and doesn't make contact with the footers. Bad idea/why? Comments?

[21boat]

What I have been doing for years to solve that old farm house basement is dig down past the footers and underpin it doing a tooth out system. The other option which at times is used with the first is to encapsulate the old footer with a mini Knee wall of concrete. This holds back the undisturbed dirt under the old footer and allows for a lower floor.

[Scleros]

Thanks for your response. Could you point me toward additional information on these techniques with perhaps an illustration of what a tooth out system is?

Edit: HOW TO: Dig Out Your Basement or Cellar describes the knee wall option?

[21boat]

I don't have any pictures but I can explain it. The site you posted came out way to far into the basement.
Divide the wall up into thirds. This way you are only taking out 1/3 of support to underpin on phase 1. Keep in mind 2/3 for support to remain and roughly 24" wide tooth outs . We dig under the old footer or under the dry laid rock. When you get to the lowest evaluation you need to dig back into the dirt several inches to get width out there as an extended footer. When you look at it the outside dirt is flush to the outside wall but 8" up from the bottom it goes back further in the dirt as if you poured a wide footer and laid narrower wall on that.

Inside is a bit tricker. You need to form up min 3" above the wall and min 8" out from the wall. This allows enough room to get Crete in form and the form is high enough so when you use a concrete vibrator gravity works in your favor to completely fill the void right under the old foundation. I also use 1/2" rebar in towards the bottom of the footer. I actually jab them in the dirt parallel to the foundation. This reinforces the footer and the rebar in the dirt doesn't get coved with that pour so when you add the next tooth there is clean rebar sticking out from the first pour to ties in the second pour after the dirt is removed digging put the second adjoining tooth. Forming up and holding the form is the hard part. Do this right and you can keep reusing the panels you make up. I don''t know how much you need to dig down and that would help me on the forming directions. Get back on that.

[Scleros]

I Googled quite a bit yesterday and found some other descriptions of underpinning. What I gathered is you basically you dig out sections under the old footer in sequence and fill them with concrete or a concrete/non-shrink grout combo until the whole foundation has been filled under. Your technique sounds like it yields an inverted T or L shape, wider at the bottom than the old footer. It all appears to be very labor intensive.

One of my basement rooms has a gravel floor that I need to concrete and the rest is concreted but isn't the best concrete, so originally I was thinking going inches lower to avoid having to duck piping and refloor the entire basement, but given the effort involved another foot to two feet would allow room to run some A/C ducts and I'd only want to do this job once. I also have a floor drain to a dry well that would have to be addressed with a sump or such. Alternatively, if house movers do brick structures, I could raise the house, but that would involve more plumbing rework, and add entry structures. I could also gut the interior walls upstairs and run ductwork from above and dig out less below. How does one decide which route is best? Guess I could get quotes for all three. Is the digging part a DIY job? And do you build a temporary support wall to reduce the load on the active foundation wall segment you're working on? I also see you are in PA, what's your service area?

[21boat]

Sorry Its not Virginia.

It is labor intensive and that's the big cost. It is an inverted T for the finial look. I moved houses already and also Jacked up 2 story barns but a house is a different matter. Much cheaper to underpin walls. I would like to know some of the lengths of the wall and how thick they are.

another foot to two feet would allow room to run some A/C ducts and I'd only want to do this job once. I also have a floor drain to a dry well that would have to be

The big difference is hauling out the dirt in the rest of the basement floor area. I lean towards More depths to get the bang for the buck.

And do you build a temporary support

A lot of that depends on the integrity of the wall itself, cracks/leaning/bulges... Put it this way. You can build a house on pillars and the footer below them are not Huge compared to what it carries. The other aspect is think of the "Arch" effect. Your house has pretty much settled. Unless there is sinking problems there already.

When we knock out a 7' or 8' section of a wall we only need to support the joist under that area because the knock out it is all the way up to the plate. You are leaving the wall in and by doing so you create the Arch effect to transfer loads. To prove My thinking, We very Seldom if ever add to a footer new widths where an opening is in a wall on a continuous footer.

The one 1 third 2 thirds for support is way within parameters of a post and beam structure. Once you wrap the brain around that then it makes structural sense.

[Scleros]

I would like to know some of the lengths of the wall and how thick they are.

The approximate wall plan is shown and the outside dimensions are 30+ something feet I'd guess. I measured once but have forgotten. The exterior walls are concrete (12"?) with block and brick above except for a block section under the upstairs fireplace. The interior walls are block. The house was built in the 40s. There are no obvious continuing sinking or bulging problems, few cracks though.

You are leaving the wall in and by doing so you create the Arch effect to transfer loads.

Makes sense.

[21boat]

Just curious is it a one story or two. The other thing I forgot to mention is you Need down weight to pin the wall to the footer to begin with. If the house is jacked up and the ground is wet you run a big risk of the foundation now being a retaining wall to hold back the dirt pressure. Just a FYI

The house post will be the first attack. There you will need to brace on either side to remove steel post to lower its foot print

Since there is brick veneer it could also be a 10" wall then 6" block right below grade which allows the brick ledge.

Just to let you know How I get my information, I started as a professional Mason ( 30 + ) years and a G.C. for 25 years

I don't normally post that but its hard enough to find a real mason let alone an old school Contractor. Luckily this site has some good tradesmen and not reading answers out of a book. And or have done the research as well as doing the trades

You are in good shape here since it's a newer house from the 40s. Most of the underpinning we do is on houses built in the 1800/1900s that are basically dry laid stone at this point with No footers.

Since you have a block wall with a footer you essentially have a concrete footer that becomes a concrete lintel once the dirt is removed to tooth it. Just for FYI because of it being block you can do bigger sections to underpin.

Here's how that works. Look above the area you want to dig out. That last full block becomes the "Keystone" to the imaginable arch. Just look at the head and bed joints and trace that down like a pair of steps snd this id Exactly where the weight transfer will end up.

The pure science for an arch to fail can only happen 3 ways. The "keystone: crushes and fails. The bottom ends of the arch horizontally kicks out, Or the arch all falls in or out. The Romans got it right.

Just on a side note, The masonry trowel is one of the oldest hand tools used on a daily basis and hasn't really changed since the Romans invented it.

[Scleros]

just curious is it a one story or two.

Two.

The house post will be the first attack. There you will need to brace on either side to remove steel post to lower its foot print

The two columns are a stack of single block with a course of brick on the top supporting triple 2x10 or 12 beams running down the center of the house.

Since there is brick veneer it could also be a 10" wall then 6" block right below grade which allows the brick ledge.

The upper exterior walls are block too with brick.

...but its hard enough to find a real mason

I took a stone masonry class a couple years ago at the local technical school. The instructor apprenticed in Europe and learned from a Japanese master and she's worked on some non-traditional stuff (Earth Pods). If not herself, I think she could recommend a local mason.

I'll take some photos this weekend and post here in case you have any other thoughts to FYI me. I'll take all the information I can get. For instance, would removing the interior walls and putting in glu-lams or steel I-beams be feasible to open the space up? I have some windows, but there is no exterior door which would probably have to be cut in first to get the beams in.

[21boat]

The instructor apprenticed in Europe and

That reminded me when I turned down an Invite to go to England and Europe to do stone work I also worked as a stone mason back in the 70s. Kudos to you for taking that course...

glu-lams or steel I-beams be feasible to open the space up?

very feasible. Here's the skinny there. A steel I beam can carry more weight then wood but it has its limits on clear span to size ratio. Basic I beams in a house is usually w8x18 or w8x24 When it comes to micro lambs it gets Real Expensive Quick. Also they are higher in height to load ratio then I beams. All this will need to be engineered and specked out.

I'll take some photos this weekend and post here in case you have any other thoughts to FYI me

That would help all here that visits this post. I will keep a watch on it to see if I have more thoughts on it.

Japanese master

I always wonder why we call a skilled tradesmen a "master" when it a Japanese. Good sales... in the west. Not thinking less here. Japan has some beautiful Architecture to say the least. And Highly skilled tradesmen. The "Master" is the kicker.

When you post picture be clear on what walls you are underpinning.

[toddmanqa]

Here is a step-by-step article on how to do underpinning of basement walls:

http://www.jlconline.com/cgi-local/v...170a32100a0631

If the link doesn't work, go to JLC Online - Home and search the Archive for: lowering basement. Its in the October 2009 edition.

Some other things I've read in other places:

1. You need to vibrate the concrete to get full psi strength on the concrete.