new toilet floor

[str]

Currently have our downstairs toilet redone and the current flooring it old T&G floorboards.

plan is to tile the floor and don't want to raise it any more than I have to by adding ply ovr the boards then the tile.

its only a small area and plenty of joist to support the new floor, may even put in further noggins to tie the floor down but what thickness of ply would I get away with?

 

[Richard C]

Size is important but “Plenty of joists” doesn’t mean anything, what’s important is joist size, pitch & span.
Two choices;
if over boarding with WBP ply the BS standard is 15mm but 12mm is generally recognised as being the minimum in the majority of cases & will probably be fine in your case. Or use a tile backer board; these come in 6mm or 12mm varieties; for floors, many use 6mm staggered boards but, personally I would go with 12mm, so you’re no better off than using WBP ply. To avoid the threshold thing, the other alternative is to rip out the existing T&G & replace with 18mmWBP ply (my preferred option) which is generally enough to cope with most suspended floors; but you must fit noggins to unsupported edges.

Question; how are you going to put down additional noggins on an existing floor? If you’re going to take it up, you may as well replace it with something guaranteed to be more suitable!

 

[str]

thanks for the response.

Sorry, maybe wasn't clear! I was planning on ripping up the existing floorboards so that I avoid the height issues of WBP overlay or backing board under the tiles.

The room is probably about 1m x 1.5m, so I will be able to use a single sheet of WBP and as I am lifting the existing floor, can put in as many noggins as I need to.

My concern is that 18mm ply may still give me the threshold issue, was wondering if I could get away with 12 or 15mm ply if I reinforced the existing joists with plenty of noggins? Or am I deluding myself?!

 

[Richard C]

My concern is that 18mm ply may still give me the threshold issue,

Assuming the new floor will be at the same level, you’ll only have the tile/adhesive thickness which at most will be around 10mm; I don’t follow why it should give a threshold problem, you can get many different types of threshold plate to accomodate that & more. What type of flooring are you having the other side of the threshold?

was wondering if I could get away with 12 or 15mm ply if I reinforced the existing joists with plenty of noggins? Or am I deluding myself?!

I think you might be Sister joists will stiffen joists along their span but noggins won’t add much, they are mainly to provide support for cross joints.

if over boarding with WBP ply the BS standard is 15mm but 12mm is generally recognised as being the minimum in the majority of cases

Using less than 12mm for over boarding is just asking for a tile failure let alone using it for the floor itself; BS actually recommend 25mm for tiling but in most cases 18mm or 22mm is sufficient; 18mm is the minimum you should use for any suspended floor using a standard joist layout.

 

[str]

The toilet is on a qtr turn on the stairs so the threshold is the bullnose of the "stair" which in turn is level with the floorboards.

given that the boards are c.18 mm thick, replacing with 18mm ply will give me the tile finish being proud, which was what I had hope to avoid but it sounds as though this might not be possible!

 

[Richard C]

given that the boards are c.18 mm thick, replacing with 18mm ply will give me the tile finish being proud, which was what I had hope to avoid but it sounds as though this might not be possible!

That’s quiet normal & is good; in cases where over boarding is used the tile finish can be as much as 20-22mm proud & is why I prefer to replace rather than overboard.

I’ll ask again, what are you finishing the floor with up to the tiles there are many different threshold plates available to suit every taste.

 

[str]

I had wanted the transition between the wooden threshold at the stair to the tiled finish to be level, but I don't think that this is achievable.

I haven't looked at any threshold plates - where would be the best place to look at the options?

 

[Richard C]

I had wanted the transition between the wooden threshold at the stair to the tiled finish to be level, but I don't think that this is achievable.

So are you not putting anything on the floor outside then

I haven't looked at any threshold plates - where would be the best place to look at the options?

Try using Google search for "threshold plates"

 

[str]

wasn't planning to put anything outside - the door open out and its only a relatively small strip of timber, which has a bullnose that overhangs the step up - was just planning to leave this as painted.

 

[Richard C]

Are you saying you have a step onto the landing area immediately outside the door