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single story extension advice

Discussion in 'Building' started by d.kenny, 5 Jan 2016.

  1. d.kenny

    d.kenny

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    hi all

    im new to the site but always find myself directed back here when searching for info on the net so thouight id sign up to clear a few things up in my own project that i plan on doing as much of the work myself on to keep the costs down!

    the extension will just be the standard 3m on building regs

    iv had a plan and calcs done for the steels to make the back of the house open plan consisting of 2 posts and a beam to support the rear of the house and then bolted to that anopther beam and a post in the centre of the house to support the upstairs joists

    now i wanted to do the footings and underpin what i can, then build shell for the extension, then break through, dig for the posts and then pour concrete for that and install the steels...can someone confirm that this is the correct order or should all concrete go in at once thus meaning the house will be in pieces at the back until shell is built to make watertight again?

    im trying to avoid the mess and disruption where possible!

    cheers in advance for any advice!!!
     
  2. tony1851

    tony1851

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    Why have you got steel posts everywhere?
    Can't the remaining walls hold the beams up?
     
  3. d.kenny

    d.kenny

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    It was that or build pillars

    Steel seemed less intrusive internally and i thought it would be more simple

    3 posts and 2 steels so a T suspended by 3 posts

    The 2 main ones supporting back wall/roof to be sat on a foundation /pad 900x800x450 deep and the third on 600x600x450 pad

    Do i dig and pour the pads then have the steels made to suit i take it?
     
  4. tony1851

    tony1851

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    Is your rear extension also going beyond the side of the house - ie is it a 'wrap-round' - or is it
    just an extension on the rear?

    If it is just a rear extension, I fail to see why your SE has specified 3 steel columns.
    They are expensive and the pads for them are large. Even if it's a large wrap-round where overall stability has to be considered, you shouldn't need the third column supporting the secondary beam.

    The usual practice is to allow the existing walls and foundations to carry the beam loads, which they
    almost always will without re-building and new pad foundations.
     
  5. d.kenny

    d.kenny

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    No just single to rear not a wrap around

    I cant support the upstairs joists off the internal wall as its only 100mm and is studded next to it so would have to create a corner for the support

    The rsj would be resting right next to studding hence the reason a steel post is needed
     
  6. d.kenny

    d.kenny

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    The pads though

    Are they literally 900x800x450 holes dug, filled with the correct spec concrete then the steels are measured up and resin bolted into the concrete or do i have to set steel feet into the pad stones that im creating and then bolt from the steel post to the steel foot?
     
  7. tony1851

    tony1851

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    Are you able to post a plan drawing for this?
     
  8. d.kenny

    d.kenny

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  9. d.kenny

    d.kenny

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  10. RonnyRaygun

    RonnyRaygun

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    Certainly looks like pad 3 and post 3 could be avoided if the nearby wall has a decent foundation.

    You need to ensure your pads are the correct depth for the ground conditions, and set top of concrete to the correct level - probably the same as the strip foundations. Ideally you need a couple of sections drawn to ensure you set everything to the correct levels.

    You don't cast the posts in - you should get the fabricator to weld on a base plate and resin fix some bolts into the ground. As there shouldn't be any moment or uplift on the bolts four M12 anchors with 100mm embedment and a suitable resin should be adequate, but ask your designer as they should specify.
     
  11. d.kenny

    d.kenny

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    Instead of studding the wall i should of bricked up but gro t room plastered etc now so tough luck i think haha

    So within reason the pads can be varying heights and steels can compensate for height differences i take it

    They are pretty simple then

    Just concrete slabs that the steel posts just bolt to like you say with resin bolts

    I though post and pad 3 was avoidable but would need a pillar building anyway so for the work on footings its just aswell to fabricate from steel

    I cant decide to do out of blocks now anyway i dont think as will need re calculating

    Ball park for the steels what am i looking at really price wise?
     
  12. tony1851

    tony1851

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    @R.R; agree entirely regarding post 3; if the wall between the dining- and lounge is brick or block, there is absolutely no need for a steel post there - beam 3 could go direct onto the wall with a suitable padstone.

    With regard to the other 2 columns - I was sceptical at first but, seeing the plan, presumably they've designed it for lateral stability as well as supporting the back wall.
     
  13. d.kenny

    d.kenny

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    I think that is just how the regs are

    Post 3 has a stud wall right on the edge so cannot have padstone and would need underpinning

    Architect said used to work to failure value of 4 or something but its 8 now so prob why it looks a lot beavier than usual??

    Either way thats what the se says and what building control will be referring to and im not going to argue it

    My main concerns are

    Can i dig footings and build shell

    Then acro building

    Knock walls through once supported

    Dig padstones

    Have steels made and then install

    Or do the footings and padstones need doing at the same time so will cause major disruptions to living?
     
  14. RonnyRaygun

    RonnyRaygun

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    Yes, the pads can vary slightly, but try to keep them within an inch or so, as then you will be able to use a cementitious grout to bring up to level. Get the columns all cut the same length and use the grout to make up for any discrepancies.

    Yes, you would need the foundation to be checked and a pad stone designed - might be cheaper than the extra steel and footing...

    Not a builder / fabricator, but I reckon you will be looking at £2.5 - £3.0K for supply and fabrication of steelwork.
     
  15. tony1851

    tony1851

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    @op, sorry, just noticed your post re the studwork :oops:
     
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