Can you install natural timber flooring over Formply?

[PTB]

I have an old house built in the 50’s.

The current timber floor is not level. It varies in height up to 25mm.

In a years time we have plans to knock the front of the house off to extend and build a balcony.

The back end of this same level is to have a kitchen installed ASAP.

I want to level the timber floor in the kitchen area and build the kitchen now.

The family and I also have to live in this while I’m doing this work.

I am thinking I could take up a section of the floor level the joists, then lay a sheet of some product like formply, repeating until I’ve got an area big enough for the kitchen.

I was then going to build the kitchen on top of the formply.

Then level the rest of the floor in the same fashion with the formply sheets.

Later when the extension (I’m a year or two away from getting to this job) is done I would lay the natural timber floor over the top of the formply.

I’d have to factor in the height of the natural timber flooring when figuring the kickboard height.

This level of the house is the top level, so I’m thinking this might also help with noise below.

Questions I have:

1. Would formply stay flat and straight/ resist cupping?
2. Will the natural timber floor I eventually install fix OK to the formply?
3. Is there a better product to use instead of formply?
4. Is there a better way?

Thanks in advance for any advice!

[JacobZ]

Hi @PTB,

Thank you for your question and welcome to the Bunnings Workshop community, it is fantastic to have you with us.

The method of removing the current flooring, planing the joists so that they are level and then reinstating the floor is going to be the way to go. 

Instead of form ply, I'd suggest using STRUCTAflor General Purpose YellowTongue as it is designed for this exact application, is tongue and groove for easy installation and is perfectly capable of having timber flooring attached over the top. 

I'd suggest having a look at How To Level a Subfloor and How To Lay Chipboard Flooring for some guidance on this.

Also, allow me to tag some of our helpful members to see if they have any advice, @Dave-1, @Nailbag, @ProjectPete, @DIYGnome.

Let me know if you have any further questions.

Jacob

[Dave-1]

Evening @PTB 

Now that sounds like a good bunch of projects! And you helped me out with the dip I have in my floor just now as I was following your steps to level your floor I agree with your thinking about how to level the floor.

Definently yellowtounge as @JacobZ has suggested and I do think it will help with noise insulation once you lay floorboards over it towards the end.

Finding that sweet spot where you can start your level may be interesting. Id maybe go for the high point of the floor that way tou can adjust the beams height without shaving any of the joists off.

Please take a bunch of photos as I think this will be a really interesting project.

Dave

[Nailbag]

Hi @PTB 

Definitely use yellow-tongue flooring as @JacobZ suggests. But before laying get your joist levels right. This will be by using a long straight edge/level to highlight high and low points. Plane the highs and pack the lows with masonite packing strips.

If you have easy access to under the subfloor, the packing can be done/completed after laying the sheets down by tapping in the same packers or these which give you more options of a perfect fill. This method will eliminate the need for expensive self-levelling compound.

Leave the kick boards off until the floating floor is down. It will be a much neater finish and easier install to fit these on top of the flooring. The standard height to set the cabinet legs is 145mm. So take it up 1-2mm above the height of the floorboards and any underlay. Its the same method I use with any final floor thats going in after the cabinets are installed.

Nailbag

[PTB]

Thanks Jacob.

The videos and advice make the job seem much more doable for me.

[PTB]

Thanks Nailbag!

Great advice, and the pictures help reinforce my plan.

Great to know that is also the same way someone that knows what he is doing does.

[PTB]

Hi Jacob and all,

Just a follow up question.

I did suspect Yellow Tongue would be the product of choice.

However I’m worried about  this.

It will be some time (maybe a year or year and a half before the subfloor gets covered with timber floorboards.

In that time I have to live on the subfloor with 4 kids that spill stuff and a Labrador with a drinking problem (more water gets spilt than gets drunk) I’m worried that the chipboard will swell in areas where spills occur.

I was thinking that Formply with its coated surface might hold up better under these conditions.

I could perhaps rout a groove in the edge to hold a yellow tongue connecting strip too.

Would there be any downside to this choice in terms of the Formply not remaining flat or being capable of holding nails when installing the timber floor?

Thanks again for the advice.

Feel free to say it’s a stupid idea!

[JacobZ]

Hi @PTB,

While Yellowtongue is not fully waterproof, it has a waxy coating that is water resistant, so as long as spills are cleaned up in a reasonable amount of time, you shouldn't have any issues with swelling. It is actually designed to withstand full weather exposure for up to five months so it can withstand the periods in house construction where a floor is needed but the roof isn't on yet.

Aside from this, Yellowtongue is designed for this specific purpose and is warranted for use as flooring, formply is not.

It is not a silly idea at all, but it wasn't really designed for this purpose, so it's best to use the product that is.

Let me know if you have any further questions.

Jacob

[PTB]

Thanks again Jacob.

That all makes a lot of sense.

Pete

[Nailbag]

Agree with @JacobZ the yellow tongue will easily with stand the riggers of a family for considerably longer than its external exposed to the elements of 5mths. Plus Formply has a very smooth and extremely slippery coating that wouldn't be practical or safe as a long term temp flooring solution.

Nailbag