Levelling joists in upstairs bedroom - advice

Discussion in 'Builders' Talk' started by PoorbandTony, May 15, 2019.

  1. PoorbandTony

    PoorbandTony New Member


    I hope someone can offer some advice.

    Our upstairs bedroom has always been a little 'bumpy' across the room - so consequently the chipboard flooring squeaks like anything and the floor is very 'bouncy'.

    It's been like it ever since we moved in (so a good 15+ years ago) but it was made a little worse by having the downstairs kitchen below knocked through and installing an oak beam about 6 years back. It's not moved at all during that time so I'm confident there's no underlying issue - I think it was just a poor build.

    It's always bugged me so I want to sort it out. So here's my current plan which I'd like to run past you to ensure I've not missed anything.

    Basically I want to take up the floor and replace it with plywood once I've levelled. Against the joists, to level up the floor so it's consistent across the room, cut and glue 18mm plywood - cut just short of the height of the joist and offered up as cheeks along the joist on both sides, and if necessary cut, glue and plane ply between the new cheeks. I'm then intending to drill coach bolts to secure the cheeks every 400mm, alternatively top to bottom, side-to-side.

    I'm fairly sure this is how to tackle it, and as it's fairly labour intensive I'm happy to do it myself over time as we can move out of the room while I sort it.

    Once it's all level, I'd then fit ply flooring instead of going back to chipboard again.

    My main concerns are weight (though I suspect it'll actually strengthen the joists), and also would cutting the cheeks to 2 meters sections to make it more manageable to handle be ok? (timber yard can only cut to a max length of 2.65m anyway as the sheets come in that size). Finally is 18mm sufficient for the cheeks, or is thinner/thicker more appropriate.

    Really appreciate any advice.

  2. Pollowick

    Pollowick Well-Known Member

    Planing will be difficult as you will not be able to get right up to the walls.

    Many other ways to do it and my suggestion.

    Get some good quality 100x50 timber - ensure it is straight, or have some 50mm play cut into strips. If teh deviation is more than 30mm then go to 150x50

    Locate the highest point of the existing joists and use that as a datum.

    Screw/glue/bolt a strip to one side of the joist with the high point meaning the other end is lifted to match. Then using that joist as the start point, repeat on every other joist, fixing to the same side each time.
  3. stevie22

    stevie22 Active Member

    Shouldn't need to plane your ply: just get it ripped at your timber yard in 2440 lengths.

    I would centre the ply on the joist to maximise the stiffening effects and I'd just use decent glue and plenty of screws. As Poll says just start at the highest point.
  4. Mr Rusty

    Mr Rusty Well-Known Member

    When I've levelled a floor before I've done exactly as Pollowick says - fix some 2x4 or 2x6 to one side of the existing joists. I have always used coach screws but you need a good impact driver to drive them. Bolts are an alternative, but I find screws easier. Why ply on the floor? You won't have a T&G joint and the butt joint is always a potential source of slight movement against each other and squeaks. personally I would re-board using floorboards, fixed to the new sistered joists with proper flooring screws. The sistered joists will also reduce the bounce.
  5. Pollowick

    Pollowick Well-Known Member

    There is always extra flex at board edges - when I have done this, I have used a router and taken a touch over half thickness off the top on one and bottom of the next - around 10-15 mm back. The overlap stops the flex and provides a resonable seal.

    I too, would suggest T&G floorboards though - properly nailed or screwed down after being tightened through.
  6. PoorbandTony

    PoorbandTony New Member

    Thanks everyone - that's really helpful.

    So I'll probably go the 2x6 on one side of each joist, and T&G floorboards then. Just a couple of questions - any particular type of wood I should use, and as it's going on one side, I presume there's no potential issues with warping the existing joists with load, such as wardrobes etc.

    Sorry for sounding dumb - just want to be sure :) Really appreciate the advice.
  7. Mr Rusty

    Mr Rusty Well-Known Member

  8. dobbie

    dobbie Well-Known Member

    Fit noggins to them about 18" from each end and one in the middle,this will stop any warping.
  9. PoorbandTony

    PoorbandTony New Member

    Brilliant advice thanks all. 2x6 ordered :)

    I'm just about to order the replacement flooring. Joists are about 30-40mm apart so I'm looking at 18mm ply (it's currently 18mm chip). I'm not sure whether to use T&G or just sheets. I've done alot of reading up this afternoon and from what I can glean T&G is best but can be tricky to obtain. I know I can get 18mm hardwood ply from my local timber yard really easily.

    So I guess my question is, is there anything I should know if I didn't go T&G? I realise I'll need to fit noggins to ensure that each cut has sufficient area to screw down into. If that's the case is there anything I need to know when fitting the noggins?

    Primarily I want to avoid creaks and squeaks! Some posts/articles mention gluing along the joists but that seems a little extreme. One of the biggest reasons I'm undertaking this exercise is the bl**y squeaking - it's driving me mad! :)
  10. Jimbo

    Jimbo Well-Known Member

    Screwed and glued ply will strengthen the floor and reduce bounce a lot. But is obviously a PITA when it comes to accessing a pipe or junction box or whatnot.

    Also worth considering adding 50 or 100mm of fibreglass on the ceiling boards as it’s all up. Will help reduce transmission of noise between the rooms. Wool would be even better - the ply acts as a reflector because of its mass and the wool an absorber, this is quite an effective acoustic strategy.
  11. PoorbandTony

    PoorbandTony New Member

    Thanks Jimbo.

    So I've got the floor ordered - hoorah! T&G 22mm Ply - so decent stuff. My final, final question and I'll leave you all alone! Securing the sister joists to the existing. Some of the joists are doubled up - so I doubt I'd use coach bolts to get through them as that's one long coach bolt! I'm thinking coach screws instead - been looking at these as an example : https://www.oscsales.co.uk/carpenters-mate/products/pro-hex

    How easy are these things to drive bearing in mind the gap between centres for most is 300mm so space is limited. Also, as I've gone for 2" (50mm) wide joists to join onto the existing, how long should I get the screws and any recommendations on pattern? I was thinking 90mm long but not sure if this is too long. The link above has decent PDFs so I can see clearly where and where not to place them.

    The bolts/screws are my last purchase, then I'm ready to go this Friday :)

    In summary, any recommendations on the diameter, length and type of bolt to use would be fantastic. If I could buy you all a beer I would!
  12. chippie244

    chippie244 Well-Known Member

    Turbogold coachscrews are good
  13. bigdan2019

    bigdan2019 New Member

    Is there any reason why you wouldn't just fit new joists in joists hangers inbetween the old instead or have I misread what you've ordered ?
  14. bigdan2019

    bigdan2019 New Member

    And if space is tight use a angle drill, was a lifesaver when I did a loft conversion.
  15. PoorbandTony

    PoorbandTony New Member

    Mainly from a confidence perspective and the amount of work. It's just to get the floor re-levelled as it's always been dipped and pretty bouncy. I don't have long to do it either as the other half is away next week so gives me time to get rid of the **** floor, relevel by sistering up taking the dip out, and then relaying the floor with decent ply. The only thing I'm not sure on now is the size of the coach screws to use to be safe.
  16. PoorbandTony

    PoorbandTony New Member

    Yep thanks mate - got one on hire as of Friday. Figured I'd need it given the space! :)
    bigdan2019 likes this.
  17. chippie244

    chippie244 Well-Known Member

  18. bigdan2019

    bigdan2019 New Member

    Okay , I presume it's just a little out in places then and nothing too major. For a second I thought you was doubling up every joist creating a lot more work for yourself. If there is some bounce and it's from the actual joists you could fit noggins/sprags to help balance it out before your ply goes down.
    Could always put service hatches in if any pipes or electrics need to be accessed later. And if space is tight then pre drill your joist before joining in situ . I've bolted mine with m12 just remember square washers and toothed timber connectors. M8 110mm coach will be fine though
  19. Pollowick

    Pollowick Well-Known Member

    You can get coachbolts in very long sizes ... I have some here at 300mm long.
  20. Mr Rusty

    Mr Rusty Well-Known Member

    I would use the flanged screws that chippie links to and forget washers. Might go up to 10s from 8s though - I always use 10s.

    Using toothed timber connectors is controversial. Many advocate that the friction between the surfaces is important and connectors risks stand-off. Others advocate using PU glue. I have used both nothing and PU with no difference noticed.

    Hmm. Not sure how you will get on. Never used angle drill for driving coach screws - not sure they are man enough, or the drives can stand the torque of coach screws. Quick look a ~£200 Makita angle drill has a max torque of 13.7Nm. My own model of bosch impact is 200Nm

    You really need a decent impact driver (knocky knock) - these are short and very powerful. e.g. https://shop.bosch-professional.com...mpact-driver-gdx-18v-200-c--46832--06019G4204

    Or, if you fancy a little exercise, you could just wind them in using a socket and ratchet bar on the hex head - you prob haven't too many to do, so wouldn't take long.
    Last edited: May 21, 2019

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