Footings for sleeper walls

Discussion in 'Builders' Talk' started by legepe, Dec 5, 2017.

  1. legepe

    legepe New Member

    Hi
    I have a couple of questions about footings to support sleeper walls for suspended wooden floors - see pics
    1. Ive dug out the footings 40cm x 40cm to lay foundation blocks around 4" off wall to support the joists, is this over the top for sleeper walls? if so, should I fill with stones first?
    2. I calculate the volume I will need is 0.6 cu.m or 20.91 cu.ft. Is this mixable by hand or should I think about hiring cement mixer?
    3. One of the footings next to the wall where the kitchen is (lead pipe near by) has filled with water. I have dug another hole around 5" deeper at the rear of property (in extension) to test if it is the water tables limit and it hasnt filled with water. how can i know without ripping up the kitchen floor if this water is not simply coming from long term water leaks that are on the lead pipe running across the house but not under the kitchen?
    Any advice would be very much appreciated
    Thanks
    legepe
    ps: its a mid terrace house built pre 1900 i guess
     

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  2. yorkshireboy

    yorkshireboy Member

    Is there any reason why you can't put the new joists into the existing wall?
     
  3. legepe

    legepe New Member

    I guess they would rot much quicker if i put the joists into the existing walls, apart from that I would have a much harder job getting everything level.. not sure if im completely correct but Ive already dig the footings
     
  4. stevie22

    stevie22 Active Member

    Foundation: Assuming you have approved drawings, what do they say? If you don't then you need to ask BC what they want.

    Water: have you pumped out and seen if it comes back? Not uncommon to encounter isolated pocket of water in the groun
     
  5. yorkshireboy

    yorkshireboy Member

    Is this inside and you're replacing an existing floor or part of a new extension?.If you're digging a footing there is no exact depth,you have to dig down to the proper ground beyond any soil or any kind of fill,could be a foot,could be a long way down .Its unusual for water to appear that near the surface unless it's a leak.
    Fill your footings in put a layer of dpc and over site concrete over the underfloor and bolt a timber wallplate to the wall,to hang your floor from.
     
  6. Dr Bodgit

    Dr Bodgit Well-Known Member

    I'd hire (or borrow) a cement mixer...its hard enough work with a mixer let alone without.
     
  7. Simon74

    Simon74 Member

    Buy a water test kit, think they are about £20. Just used them on a job where water was pooling under floor of kitchen. Test indicated mains water which turned out to be a leaky old lead pipe, removed pipe and water drained.
     
  8. dobbie

    dobbie Well-Known Member

    It is a better job with sleeper walls and a wallplate bedded on top and the joists sitting on that.
    The joists can then be 4x2 if the sleeper walls are spaced correctly.
     
    KIAB likes this.
  9. KIAB

    KIAB Well-Known Member

    Totally agree, a neater way to do the job,easier than cutting pockets for joists, done a few like it over the years, but using 5x2 or 6x2 joists,plus you get better bearing for the joists,wallplate, also prefect oppertunity to insulate between the joists with Kingspan or similar rigid insulation, can nail tile batten to bottom of joist to support it.

    Also would get OP to remove, replace that lead pipe,one you disturb old lead pipe, they can cause all sorts of grief, probably the cause of the water pooling.
     
    Last edited: Dec 5, 2017
    legepe likes this.
  10. KIAB

    KIAB Well-Known Member

    And don't skimp on ventilation, make sure you got air vents unblocked & good air flow from front to back of house, otherwise you'll eventually will get damp,mould,rot, etc .
     
    legepe likes this.
  11. legepe

    legepe New Member

    Thanks everyone...
    The maximum distance between supporting sleeper walls will be 1762mm I was hoping that 4x2 joists would be ok?
    Not sure what you mean by "wallplate bedded on top and the joists sitting on that"? I was going to simply place new joists on top of sleeper walls with some dpc in between and if necessary some type of spacer if not level. is this not correct?
     
  12. KIAB

    KIAB Well-Known Member

    Like this.

    upload_2017-12-6_8-27-12.jpeg
     
    legepe likes this.
  13. legepe

    legepe New Member

    Thanks KIAB... thats how I was planning on doing it. I guess whats ment by wall plate is the timber across the top of sleeper walls (for joists to sit on)
    I know youve mentioned 5x2 and 6x2 but would I be ok with 4x2 joists? with the maximum span between walls of 1762 center to center
     
  14. KIAB

    KIAB Well-Known Member

    Not sure what C16 maximum joist span @ 400mm centres is from memory, but your close to it, not at home to have a look.
     
    legepe likes this.
  15. legepe

    legepe New Member

    Ive found the table http://www.rightsurvey.co.uk/joist-span-tables-for-floor-construction/and at 400mm its fine upto 2.08
    There are 4 spans to cross with this method of 4x2
    Now, if I were to build only the two sleeper walls at either end of floor and use an existing supporting wall in the middle, and span from end to middle(ish) I would need to span a maximum distance of 3.45m at one end and 2.65 at the other end, which would save me work and make much easier to level up, also provide easier airflow, however going by the table I would need to use joist size - 50-170
    Is this something you would recommend or should I stick with the first method?
     
  16. legepe

    legepe New Member

  17. KIAB

    KIAB Well-Known Member

    Yes, would be my preferred way to use exsisting supporting wall.

    Good air flow is very important with a supended floor.
     
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  18. legepe

    legepe New Member

    Thanks, now my only other concern with this method would be the strength of the middle footing to take the full weight of all the joists and flooring then whatever else goes in the room.. is this a valid concern? how would I be able to know what weight it could take?
     
  19. legepe

    legepe New Member

    Ah! Ive just noticed that the table shows a maximum joist size of 50x147 for GF and therefore gives a max span of 3.27 which is short of around 20cm.. at one end of the room... is this ok do you think?
     
  20. KIAB

    KIAB Well-Known Member

    Can't see 200mm making much of a difference, but if you middle sleeper wall is iffy, then I would go as far as laying new footings & build new, along with the other two new sleeper walls, then every thing is nice & level for your floor, can save you a lot of grief,been caught out myself leaving a old sleeper wall in place to save work, but ended up with more work as a result.
     
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