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Housing - Renovation: Renovating a suspended timber floor

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  1.  
    • CommentAuthorthebeacon
    • CommentTimeJul 8th 2019
     
    Hello,

    I am currently renovating a Victorian house with a suspended wooden floor. I recently lifted the floorboards to discover all the ends of the joists (about 200mm) where rotting due to the air bricks being blocked by previous owners. I will install new air bricks .

    I’m in the process of researching how to replace the rotting ends of the joists. Its been suggested to cut the ends of the joists off and sister new joists ends, making sure that the new pieces run at least 1 metre along the old joist and are joined with coach bolts. I will wrap the ends of the joists in a dpc to protect them. The joists are 3.5x2 inches thick and about 450mm apart; I was told that this is further apart than they should be for the thickness of the joist. To add extra support to the floor I will not only replace the ends of the joists and sister the new joist 1m along the existing joist, I plan to run the joists the entire length of the room about 4m. This means the new joists will sit on 3 sleeper walls. Should I still sister the new joists to the existing joists using coach bolts? Or as the new joists are well over the required 1m should I install the new joists independently from the original joists?

    I also have to replace 200mm of the ends of the 4 joists in the entrance hallway. The existing joists are too close to the wall for me to put a coach bolt through and tighten them. The new joists I lay will be 3 metres in length and will sit on at least 2 sleeper walls. Should I attempt to attached these to the existing joists, or lay them as independent joists.

    The plates also needs replacing. The old plate had not been wrapped in a dpc. I intend to add a new 4x2 inch tantalised/pressurised plate with a dpc wrapped around it and stapled. Should I place another dpc sitting under the plate and running up the wall a little? I will wrap the new joist ends in a dpc also.

    The old plate had scraps of wood balancing on it to level the joists, I have read that slate was commonly used, should I use slate or is there a more contemporary material used?

    Should the plate be attached to the wall is it sitting on at all? Should I attach the joist ends to the plate? Should the new joists be attached to the plates on the sleeper walls, if so what’s the best way?

    I will insulate and lay a plywood tongue and groove floor before laying the floor boards. I have seen when taking the original floor boards up that some have been leveled with thin bits of wood between the floor board and joist. What material should I use to ensure the plywood floor is completely level, and is it ok to put between the joist and plywood?


    Thanks,
  2.  
    <blockquote><cite>Posted By: thebeacon</cite>I’m in the process of researching how to replace the rotting ends of the joists. Its been suggested to cut the ends of the joists off and sister new joists ends, making sure that the new pieces run at least 1 metre along the old joist and are joined with coach bolts. I will wrap the ends of the joists in a dpc to protect them.</blockquote>

    Sounds about right

    <blockquote><cite>Posted By: thebeacon</cite>The joists are 3.5x2 inches thick and about 450mm apart; I was told that this is further apart than they should be for the thickness of the joist. To add extra support to the floor I will not only replace the ends of the joists and sister the new joist 1m along the existing joist, I plan to run the joists the entire length of the room about 4m. This means the new joists will sit on 3 sleeper walls. Should I still sister the new joists to the existing joists using coach bolts? Or as the new joists are well over the required 1m should I install the new joists independently from the original joists?</blockquote>

    According to my tables and assuming that the sleeper walls give you a joist span of about 1.3m your floor would support a dead load of up to 24kg/m2. I would sister the joists because you have to do that anyway to recover the rotten ends so a couple of extra coach bolts in the centre portion isn't so much.


    <blockquote><cite>Posted By: thebeacon</cite>I also have to replace 200mm of the ends of the 4 joists in the entrance hallway. The existing joists are too close to the wall for me to put a coach bolt through and tighten them. The new joists I lay will be 3 metres in length and will sit on at least 2 sleeper walls. Should I attempt to attached these to the existing joists, or lay them as independent joists.</blockquote>

    I would install them as sister joists and I would use galvanised threaded studding, available in 1m lengths in whatever dia. you need. Cut to length and assuming you can get your hand between the wall and the joist (typically there is enough space) then fit a suitably large dia. washer and then the nut and ensure that the studding is fully engaged in the nut and then fit a washer and nut on the other end and tighten from the inboard end whilst holding the outboard end (next to the wall) nut with a spanner.

    <blockquote><cite>Posted By: thebeacon</cite>The plates also needs replacing. The old plate had not been wrapped in a dpc. I intend to add a new 4x2 inch tantalised/pressurised plate with a dpc wrapped around it and stapled.</blockquote>

    I would put dpc against the wall but not wrap the timber up. If the timber is wrapped up any moisture that gets in can't get out.

    <blockquote><cite>Posted By: thebeacon</cite>The old plate had scraps of wood balancing on it to level the joists, I have read that slate was commonly used, should I use slate or is there a more contemporary material used?</blockquote>

    Slate was used because it is thin, flat, hard and most importantly readily available to hand. The essence of packing pieces is that they should be at least as hard (non-compressible) as the material they are packing out

    <blockquote><cite>Posted By: thebeacon</cite>Should the plate be attached to the wall is it sitting on at all? Should I attach the joist ends to the plate? Should the new joists be attached to the plates on the sleeper walls, if so what’s the best way?</blockquote>

    I would copy what was done originally - but that's just a guess:shocked:


    <blockquote><cite>Posted By: thebeacon</cite>I will insulate and lay a plywood tongue and groove floor before laying the floor boards. I have seen when taking the original floor boards up that some have been leveled with thin bits of wood between the floor board and joist. What material should I use to ensure the plywood floor is completely level, and is it ok to put between the joist and plywood?</blockquote>

    any reason to use plywood rather than OSB? Re material for levelling, see comments above about spacers being as hard or more so than the material they are spacing. And yes I would put them between the ply (or OSB) and the joist.
    •  
      CommentAuthordjh
    • CommentTimeJul 9th 2019
     
    Posted By: Peter_in_HungarySlate was used because it is thin, flat, hard and most importantly readily available to hand.

    Slate was used because it is impervious to water and forms a capillary break. It is an early DPC. You can see a slate DPC course in some brick walls built prior to the invention/availability of engineering brick, which also serves as a DPC.

    I think current building regs require things to be fastened down. They also need to be held in place to stop them moving or twisting, but like PiH I'm just guessing.

    Plastic wedges are available for levelling. They are just one possibility.
    • CommentAuthorMike1
    • CommentTimeJul 9th 2019 edited
     
    Posted By: thebeacon
    the ends of the joists (about 200mm) where rotting due to the air bricks being blocked by previous owners. I will install new air bricks .

    You probably need additional air bricks too - I've not yet seen a Victorian house with airflow that we would now consider to be adequate, but if only the joist ends are affected lack of airflow may not be the (only) cause. The external ground level is often raised over the years, leading to the wall becoming damp. You may wish to remedy that, in addition to wrapping the new joist ends in DPC.

    Posted By: thebeacon
    The joists are 3.5x2 inches thick and about 450mm apart; I was told that this is further apart than they should be for the thickness of the joist.

    Typically that would just mean that the joists would deflect more than currently recommended - not normally a big issue unless it's causing a problem?

    Posted By: thebeacon
    I will insulate and lay a plywood tongue and groove floor before laying the floor boards.

    Why are you thinking of adding plywood? Aren't the boards adequate?
  5.  
    Some thing to watch out is the original joists are unlikely to match current standard timber section sizes, so if you mix modern with existing joists, it can be a nuisance to get them level with each other. Can be easier to stick with reinforcing what's already there, or completely replace it.

    Also it's good to position a joist in just the right place to support where the ends of the new floor sheets will meet, new metric boards are slightly shorter than the Imperial joist spacing.
    • CommentAuthorjamesingram
    • CommentTimeJul 9th 2019 edited
     
    If it was me I'd rip it all out and stick down 200-250mm eps on a well compacted blinded scalping subfloor, DPM and a 120-150mm concrete slab on top with 100mm PUR (celoptex) upstands round walls , leave room for batons if you want a wooden floor on top or just enough to self level with latex and stick floor finish down when fully dry.
    ok concretes not great but probably quicker and giving a several lifetime solution to a high insulated standard.

    If you want to go super 'eco' theres the limecrete on glaspor breathable solution but im not to sure about trucking all this NHL5 over from France is any better than local ready mix with OPC
  7.  
    Posted By: djh
    Slate was used because it is thin, flat, hard and most importantly readily available to hand.

    Slate was used because it is impervious to water and forms a capillary break. It is an early DPC. You can see a slate DPC course in some brick walls built prior to the invention/availability of engineering brick, which also serves as a DPC.

    Correct about slate being impervious to water and a dpc but between two bits of timber used for the purposes of a spacer the attributes of thin, flat, hard and available were probably more important.
  8.  
    Posted By: jamesingramIf it was me I'd rip it all out and stick down 200-250mm eps on a well compacted blinded scalping subfloor, DPM and a 120-150mm concrete slab on top with 100mm PUR (celoptex) upstands round walls , leave room for batons if you want a wooden floor on top or just enough to self level with latex and stick floor finish down when fully dry.
    ok concretes not great but probably quicker and giving a several lifetime solution to a high insulated standard.

    Sounds like a good plan
    • CommentAuthorthebeacon
    • CommentTimeJul 10th 2019
     
    Thanks for all the feedback,



    Posted By: Peter_in_Hungary

    I would put dpc against the wall but not wrap the timber up. If the timber is wrapped up any moisture that gets in can't get out.


    Ah, yes that’s a great call.


    Posted By: Peter_in_Hungary any reason to use plywood rather than OSB?



    Posted By: Mike1Why are you thinking of adding plywood? Aren't the boards adequate?


    Is OSB better to use rather than ply? The joists downstairs run in both directions, one way in the kitchen and the other in the rest of the downstairs. For the majority of the downstairs they run in the opposite direction to upstairs, by boarding over them we can run the floor boards in the same direction throughout the entire house.



    Posted By: djh Slate was used because it is impervious to water and forms a capillary break. It is an early DPC. You can see a slate DPC course in some brick walls built prior to the invention/availability of engineering brick, which also serves as a DPC.

    I think current building regs require things to be fastened down. They also need to be held in place to stop them moving or twisting, but like PiH I'm just guessing.

    Plastic wedges are available for levelling. They are just one possibility.


    This is really useful to know. Would you recommend sticking with slate to level the plate and the plastic wedges to level the boards on the joists?

    I was considering using restraint straps: https://www.metrofixings.co.uk/main/product/productinfo/24428/Simpson-Strong-Tie-H05B15-Heavy-Duty-Lateral/1

    Screw them to the lower part of the wall below the base plate and to the top of the base plate with galvanised screws. It shouldn’t create a bridge.



    Posted By: Mike1You probably need additional air bricks too - I've not yet seen a Victorian house with airflow that we would now consider to be adequate, but if only the joist ends are affected lack of airflow may not be the (only) cause. The external ground level is often raised over the years, leading to the wall becoming damp. You may wish to remedy that, in addition to wrapping the new joist ends in DPC.


    Currently we have 2 tiny airbrick that are blocked at the front, we plan on have 3 or 4 by the time we are finished. Indeed, the external ground level has been raised over the years. Currently we have concrete and paving slabs in the front garden, the plan is to dig a 150mm deep air trench around the front of the property, will probably put a galvanised grate over it to limit the debris falling in and slope the rest of the garden away from the house to encourage water run-off. The air bricks will probably now be external periscopes so they can get come in under the plate and insulation.


    Posted By: WillInAberdeenSome thing to watch out is the original joists are unlikely to match current standard timber section sizes, so if you mix modern with existing joists, it can be a nuisance to get them level with each other. Can be easier to stick with reinforcing what's already there, or completely replace it.

    Also it's good to position a joist in just the right place to support where the ends of the new floor sheets will meet, new metric boards are slightly shorter than the Imperial joist spacing.


    This is true, I discovered this when looking for some new joists. I have sourced a timber yard that will cut C24 tanalised timber to the required dimensions and lengths.

    I will sister the new joists to the existing joists using toothed timber connectors and square washers. Do you think M8 bolts would be suitable for the joists? If I go too thick they will weaken the joists. And when sintering the new to the existing joists, should I bolt every 450mm? and top, bottom, top, bottom etc?

    Thanks for all the advice! It really helps!!!
    •  
      CommentAuthordjh
    • CommentTimeJul 10th 2019
     
    Posted By: thebeaconWould you recommend sticking with slate to level the plate and the plastic wedges to level the boards on the joists?

    I don't have a recommendation, I'm afraid.

    I have sourced a timber yard that will cut C24 tanalised timber to the required dimensions and lengths.

    Make sure it is tanalised *after* it has been cut. There's no point in the tanalised bit being on the waste pile!
  11.  
    Posted By: thebeaconThis is really useful to know. Would you recommend sticking with slate to level the plate and the plastic wedges to level the boards on the joists?

    I don't think there is any advantage in using different spacers in the different places. Use which ever is easier to obtain. If you have access to a saw you can also use hardwood spacers cut to any length and thickness needed. I wouldn't use soft wood. I don't see any advantage/need to use impervious spacers between two bits of wood.

    Posted By: thebeaconIs OSB better to use rather than ply?

    Price /performance. OSB is much cheaper than ply for the same performance. Either way you will need a reasonable thickness to fix the boards as you probably won't be able to reliably hit the joists with the fixings

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