Replacing Chipboard Flooring

[*Dan*]

I need to change out some chipboard flooring in the bathroom as its rotten due to moisture. The joists are at 600mm centres and the current flooring is 620MM wide (not sure on the thickness yet). The problem I have is both of the boards that need replacing go all the way under a partition wall so cant swap the whole board out.


The areas that I need to replace due to rotting will be able to go across the three joists that span the bathroom. I am planning on cutting out the original board just short of the joist and once most of the board is out I can then fine tune and remove the rest that sits on the joist itself. This can then be replaced by a fresh piece of floor and butt up to the other board on the joist. Is this ok to do with these boards or would they need extra support as they are not interlinking with the other board anymore on the joist as I will need to cut out the tongue from the other board to fit it in the space. The joists are I-Joist design and planning on screwing them down with minimum size 8 screws and not less than twice the thickness of the board I am using.


1st picture showing joist centres (red lines) with partition wall on the right. The first board under the waste pipe starts just under the tiles visible under the bath and goes all the way under the partition wall. I am planning on cutting this up to the third joist shown in the picture and relaying the replacement panel on this joist.

Second picture shows the first board where it joins together on the first joist.

Annoyingly the second floor panel in this picture is generally ok but there is a lip on the joins of around 5mm (blue circle) where the floor has warped so I was thinking of cutting this panel out and laying it on the second joist in the third picture (just to the right of the waste pipe) attached.

Thanks for looking any advice/suggestions welcome!

 

[JohnD]

the old boards look like 2440x610mm or 1220mm chipboard. You can get new boards of the same size which will make replacement easier, especially if you can get the old ones out more or less in one piece and copy any cutouts. 610 width is much easier to carry upstairs than 1220mm

As you will lose the old T&G, put struts (noggins) under all joins (long and short) to prevent them dipping when walked on, except where the joint falls on the middle of a joist. Your old board is probably 18mm or 22mm.

I recommend WBP ply rather than chipboard for your replacments. Seal all edges with copious paint or varnish before fixing, and preferably the faces as well, for water resistance.

18mm is the minimum acceptable. If you are replacing the whole floor, 22mm or 25mm is preferable.

If any of the joists show signs of damp, probe them for soundness. I favour applying a spirit-based wood preserver to all bathroom and kitchen joists.

Mark the position of pipes on the tops of the boards before screwing down, and definitely before using a drill.

Stainless screws are preferable in rooms containing water.

I disapprove of plumbing hidden inside false walls, but if you must have it, make the maintenance screws easily visible so your removable panels can be taken off when your leaks and other faults occur. Do not tile over them.

 

[*Dan*]

the old boards look like 2440x610mm or 1220mm chipboard. You can get new boards of the same size which will make replacement easier, especially if you can get the old ones out more or less in one piece and copy any cutouts. 610 width is much easier to carry upstairs than 1220mm

As you will lose the old T&G, put struts (noggins) under all joins (long and short) to prevent them dipping when walked on, except where the joint falls on the middle of a joist. Your old board is probably 18mm or 22mm.

I recommend WBP ply rather than chipboard for your replacments. Seal all edges with copious paint or varnish before fixing, and preferably the faces as well, for water resistance.

18mm is the minimum acceptable. If you are replacing the whole floor, 22mm or 25mm is preferable.

If any of the joists show signs of damp, probe them for soundness. I favour applying a spirit-based wood preserver to all bathroom and kitchen joists.

Mark the position of pipes on the tops of the boards before screwing down, and definitely before using a drill.

Stainless screws are preferable in rooms containing water.

I disapprove of plumbing hidden inside false walls, but if you must have it, make the maintenance screws easily visible so your removable panels can be taken off when your leaks and other faults occur. Do not tile over them.

The boards are definatly 610mm wide and most likely 2440mm long as not one of them can I see start and end in this room - they all end in another room which is the problem.

You mention noggins under the joists unless the joint finishes on a joist. I am planning of cutting out the old chipboard on the joists so that when I lay down the replacement panel it sits perfectly in the middle of the joist. Yes the tongue and groove will be cut out to do this but are noggins still needed if all the joins are on a joist? There is already one noggin on the joists but that’s because it’s at a room perimeter.

I am now tempted using WBP ply after some research but trying to get 610mm width otherwise I’ll have to just cut some down.

Checked where all the pipes are thanks to my endoscope camera.

I measured the floor thickness and it’s certainly not 18mm but seems to be around 24mm or 25mm (moisture resistant)

Thanks for help

 

[JohnD]

Yes the tongue and groove will be cut out to do this but are noggins still needed if all the joins are on a joist?

The boards have sides as well as ends.

I am now tempted using WBP ply after some research but trying to get 610mm width otherwise I’ll have to just cut some down.

Some vendors have a giant saw and will cut boards to your measurements. It will be a straighter, squarer, smoother cut than you can manage with DIY tools.

 

[*Dan*]

The boards have sides as well as ends.



Some vendors have a giant saw and will cut boards to your measurements. It will be a straighter, squarer, smoother cut than you can manage with DIY tools.

Doh yeah of course on the long edge I will need noggins. I am trying to find some clips that can attach to the joist to allow me to hang the noggins off. A lot of the clips seem to go over the top of the joist which will be tricky as the half of the joist will have the other board on still so won’t get it under.

I will contact them about getting it cut to the correct width and length as you say it will pay dividends come fitting time.

I will also loose the tongue and groove on the short side where I cut the wood to patch. The original panel will still be there but it will have lost its groove on that joist. Is this an issue loosing the tongue and groove on the short side (but keeping it on the long side).

 

[JohnD]

One way of doing struts/nogs is to skew-fix them

Drill pilot holes first or they will wander

Drill from the end of the piece at (say) 45 degrees, horizontally, so it comes out of the side. It helps to countersink the head end.

tap the nog tightly into position and hold it very firmly while you run a long screw through the diagonal hole into the joist (if you have a long enough drill to pilot hole for the screw tip it will reduce the risk of skidding sideways

then again from the other side

A carpenter would probably skew-nail but that's very prone to dislodging the nog from its proper place. They have to be a good tight fit.

If you have access to both sides of the joist you can screw through from the other side.

 

[*Dan*]

One way of doing struts/nogs is to skew-fix them

Drill pilot holes first or they will wander

Drill from the end of the piece at (say) 45 degrees, horizontally, so it comes out of the side. It helps to countersink the head end.

tap the nog tightly into position and hold it very firmly while you run a long screw through the diagonal hole into the joist (if you have a long enough drill to pilot hole for the screw tip it will reduce the risk of skidding sideways

then again from the other side

A carpenter would probably skew-nail but that's very prone to dislodging the nog from its proper place. They have to be a good tight fit.

If you have access to both sides of the joist you can screw through from the other side.

I will be able to get to both sides of the joist on one section so can just screw straight through as you say but the other two joists where the boards will finish I won’t so I will either have to skew nail or drill a pilot hole through at 45 degrees as you say then screw them on. Alternatively, I have been looking at these hangars which would save me screwing at an angle through the noggin onto the joist....

https://www.toolstation.com/mini-timber-to-timber-joist-hanger-trade-pack/p15789

Funny you mention about skew nailing - that’s exactly what has happened on some noggins I have seen in our house - the nail has split all the wood and you can see that the noggin is not completely flush with the floor board above it. I’m thinking of using 2x2 timber for the Noggins (which is what has been used on our house).

thanks

 

[JohnD]

you can pilot drill for nails as well as screws.

reduces risk of splitting, and of skidding around and getting out of place

2x2 should be fine

 

[*Dan*]

you can pilot drill for nails as well as screws.

reduces risk of splitting, and of skidding around and getting out of place

2x2 should be fine

I managed to find out the exact I-Joists I have and the flange is 47mm wide and 45mm high. Ideally trying to find some clips to attach onto the side of the flange to make fitting the noggins on easier and more securely.

There are z clips available but the top of the Z is going to be tricky to attach to the top of the joist where the remains of the other floor panel is. I would almost have to slide part of the clip under the floor which isn’t a great way of doing it. Maybe skew nailing/screwing is the best option if I can’t find any suitable clips - just want it to be extra secure!