Pouring pad foundations underneath existing wall and pier

Discussion in 'Builders' Talk' started by Turbine, Aug 9, 2018.

  1. Turbine

    Turbine New Member

    There’s been a big problem with my building works.

    Hoping some of you have some ideas, with the promise of a large amount of beer for anyone who saves the day.

    I’m knocking through the load bearing wall between my living room and kitchen/diner in my newly bought 1930s terraced house.

    I didnt want party wall issues, so I got my structural engineer to take the opening close to the party wall, but without using the party wall to support the beam. She inspected and came up with a steel goalpost structure, with the steels sitting on the existing foundations.

    My builder (a great guy) was surprised we weren’t using additional pad foundations. He opened up the floor and saw there was a dwarf wall under the wall we are removing that supported the floor joists. He advised that it would be impossible to put the steel columns in without removing this wall and lifting the joists, which would be a massive job.

    So my structural engineer put together another plan (she’s dedicated - she’s on holiday but is still coming through). She called my builder to ask about it and on hearing the foundations were all concrete, came up with a revised plan - the steel sits on a pier on the party wall side and is supported by the existing single skin wall on a padstone on the other side. The steel is converted and dry packed into the wall and pier.

    My builder finished, while there was a slight false start with a wrong size pier and some difficulties with the concreting, he solved them quickly and professionally. It looks great. He did an amazing job.

    Building control come. They’re not happy about the pier. They reviewed the calculations and told us we need additional pad foundations. Builder drilled a test hole - existing foundations are 120mm. Structural engineer agrees we need additional pad foundations poured.

    My builder has been trying to come up with a way of putting in the pad foundations without knocking down the wall and pier, repositioning the dwarf wall, cutting the joists and rebuilding everything. But he can’t think how.

    He has 25 years experience and I trust him. But I’m down 3k so far to get the steel in, and am looking at a LOT more than that if we have to do what looks to be required.

    So I wanted to check in with others - can any of you think of a way we can pour foundations under the pier and wall without removing them first? If we can, I’d save thousands, and will ensure anyone who comes up with an idea that works in practice and gets past my structural engineer and building control gets rewarded with a large amount of beer.

  2. Isitreally

    Isitreally Well-Known Member

    Can't you underpin it. ??

    If not what about putting a pad on either side building walls up to required height and bridging with a RSJ that the goal post steel could sit on.

    Or even use steels to form something like this but smaller to suit.


    With your steel goal post sitting in the middle.
    Last edited: Aug 9, 2018
  3. KIAB

    KIAB Well-Known Member

    Very difficult one.

    When builder found dwarf wall under the wall, everything should have stopped until your structal engineer had a nosey.

    Had similar were we end up putting rsj needls through wall to support,while foundation were sorted & new ones poured,not for the fainted heart.

    There are firms who do internal underpinning.
    Last edited: Aug 9, 2018
  4. Turbine

    Turbine New Member

    Thanks. I’ll ask my builder about underpinning. Just to be clear, the current design doesnt involve a goalpost as my structural engineer revised the plans once she found out about the dwarf wall.

    Unfortunately she couldnt attend the site as she was on holiday, and it sounds like there was a misunderstanding about the adequact of the foundations that were uncovered.

    64B1040D-3EB7-4712-A487-C856B211B6A5.jpeg A45D45E6-57A2-4B54-9651-F48B2E33350C.jpeg
  5. Turbine

    Turbine New Member

    And a picture of the dwarf wall

    Attached Files:

  6. stevie22

    stevie22 Active Member

    Can you put up a diagram. I think Isitreally has a good idea here. Another possibility is to dig a section of trench foundation parallel to the floor joists to form the additional bearing. Would need to remove a short section of the sleeper wall but the trench could be undercut a bit to get whatever area your SE & BCO agree on
  7. Jord86

    Jord86 Well-Known Member

    Right, bear with me on this one, it's more a brainstorm than a scenario I've ever had to do. Open up the floor both sides of the load bearing wall/dwarf/honeycomb wall underneath to expose the joists, at least 3 feet back each side so you can physically drop down into the void.

    Prop the joists both sides of the piers a couple of feet back from the wall both sides, so four points in total (however many joists you need to cut to cast a concrete pad whatever dimension is determined underneath the wall) once supported, cut the couple of foot section of joist out.

    Now, before using either acrows size 0 or acrow trench struts (whatever height suits) disc cut a 100mm square then drill a series of holes through the bottom of the pier just above the floor level leaving a course of bricks gap underneath the needle (check needle sizes first), clean up then insert a steel box section needle right through both sides, then Jack the acrows up tight so no movement can occur. Remove the section of dwarf wall underneath the needle to the size of the concrete pad required. If the acrows are kept back far enough I would think your builder would be able to shutter and cast pads in situ without too much problem, kept down the course of brick depth I mentioned earlier, then once the concrete has cured fully fill in the remaining bricks either side of the needle, jam slate in the joints tight as possible, remove the needle, then infill the last couple of bricks where the needle was, again packed tightly with slate.

    Fix a doubled up small trimmer joist to the nearest full uncut joist with a joist hanger, then either house it into the party wall or bolt another small joist to the party wall and fit the trimmer in between with joist hangers, then fix the cut joists into this with joist hangers, bolt another small length joist to your new concrete pad with thunderbolts and infill the small 2 foot or so void section with joist offcuts I.e. deep noggins. Once floor structure is reinstated remove the acrows/props supporting the rest of the floor structure and replace the previously removed floorboards.

    I hope that makes sense, and that I haven't missed something obvious, otherwise that's a lot of beer time wasted typing pointlessness.
    KIAB, Dam0n and Turbine like this.
  8. Turbine

    Turbine New Member

    Thanks very much all. This is the plan.

    Attached Files:

  9. sospan

    sospan Well-Known Member

    TBH I think you were on a losing start with Building Control when they saw the brickwork on the pier. It does not look the best. No pad stone and the end of the beam has been bricked up so they can't see the full bearing on the pier.

    I would have removed the plaster and put the brickwork against the wall.

    As Jord mentions it is seems a relatively simple thinig to support the RSJ with Acro props with the base of the prop on timbers /steels at 90 degrees to the RSJ.

    To support the pier it is relatively simple to make a timber cradle or brace to support it while it is underpinned.

    I would have expected the pier to be tied into the wall with mechanical fixings which will also assist in it slipping

    Just saw the diagram - I would be surprised if 150 mm thick foundation will be acceptable to the BCO.
    Last edited: Aug 9, 2018
  10. Turbine

    Turbine New Member

    And a picture of the dwarf wall prior to the removal of the main bit above it.

    Attached Files:

  11. Turbine

    Turbine New Member

    Jord, that sounds like it might just work! I guess the principle is the same to cast the pads under the existing wall. I’ll speak to my builder in the morning.

    Sospan, thanks. The bricks on the steel itself were a solution to the structural engineer’s call for the steel to be dry packed into the pier and concreted into the existing wall, which my builder thought was impossible in practice.
  12. Jord86

    Jord86 Well-Known Member

    Good luck, keep us posted, be interesting to see how you overcome it.
  13. sospan

    sospan Well-Known Member

    I think it is time to have a think where you are going with the structural engineer and builder.

    It isn't acceptable to rely on a few bricks placed on the web of the RSJ to hold it in place. It either has to go into a pocket into the party wall and be concreted in. Concreted in on a much wider pier or bolted into the party wall with angle brackets fixed to the RSJ.

    I would suggest that the RSJ is propped up, demolish the pier for a second time, cast a much deeper pad than 150 mm and then rebuild the pier
    KIAB likes this.
  14. Isitreally

    Isitreally Well-Known Member

    The brickwork on that pier is awful, I hope the rest of his work is better.
  15. Turbine

    Turbine New Member

    Sospan, we wanted to avoid putting any load on the party wall (to avoid a party wall agreement) so the structural engineer took that into account. The bricks and concrete on the webbing are just to prevent lateral movement, not to take the primary downward load.

    Isitrreally, is it really? Or is it just cosmetically a bit rough? The pier will be boxed in with plasterboard, so as long as it is straight and strong, I am happy. My builder got a bricklayer in to do it rather than doing it himself.
  16. KIAB

    KIAB Well-Known Member

    Spot on, & you explained it better than I could.:D
  17. jonathanc

    jonathanc Active Member

    i'd agree with that - its about my standard of brickwork and i freely admit i'm **** at it. No pride in that job at all
  18. KIAB

    KIAB Well-Known Member

    Agree,but sadly doesn't surprise me,you see it a lot,it's the 'it's being plastered/boxed in,so appearance doesn't matter' attiude.
    I'm old school, even if brick/blockwork is out of sight, it has to be neat.:oops:
  19. stevie22

    stevie22 Active Member

    With respect to your SE this is a rubbish design.

    Fair enough to not want to mess about with PWA but why oh why not just a steel post against it to hold the beam up. Post 50 deep (RHS or PFC) would do, certain to fit onto PW foundation (which I don't believe for 1 minute would be only 150 deep) whereas this great lump of mediocre brickwork is taking up space and causing the problem.
  20. sospan

    sospan Well-Known Member

    The advice you have on the Party Wall is wrong. Any structural work near the boundary is covered by the Part Wall Act and you are liable for any damage to your neighbours property for 7 years from when the work started.


    You should have notified your neighbours and gone through the process. Normally, Building Control will check for a PWA being in place on their first visit. They do have the power to stop all works until it is place.

    If there is no download force on the pier what is taking the weight of the RSJ and structure above if there is no goalpost ?

    At the moment you are on the wrong side of the Building Control Officer, I have never, ever had one reject a Structural Engineers calcs (a message there itself). The poor state of the brickwork on the pier, is a clear red flag to them that things aren't quite right.

    Before you sink a lot more money in to the project , I would get a second opinion from another Structual Engineer and see what they say
    KIAB likes this.

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