Replace floating floor with flooring

[danped]

Hi,
I have a ground floor room with a floating floor, so some kind of softwood planks on timber joists. I want to tear out the softwood planks, insulate between the joists with 100mm of kingspan and then plan to use either some engineered wood flooring or some solid wood flooring to replace the softwood planks.

Is this a good idea or are there any gotchas? Do I need to do anything else to protect the flooring in anyway? Are there any guides anyone could point me to of a similar project?

Many thanks,
Dan

 

[Tile Tom]

You'll need a subfloor over the joists. Right now the "soft wood" tongue and groove is your subfloor.

Can you not insulate from underneath? If the planks are in good shape why mess with them?
If possible insulate from underneath and add a layer of plywood to stiffen up the plank and install finished floor on top of that.
If not possible then proceed with tear out and you'll have some framing work to do. You'll need to beef up your joists by adding blocking/ sistering to the existing system. Most likely around the whole perimeter. After that's squared away then you insulate. Then a good 3/4 t&g plywood and finally the finished floor.

This will be quite the project. How big is the area? It would be a multiple day project for a pro with a van full of all the right tools

 

[danped]

Thanks for the reply! The room is quite large - about 4m x 5m. the space underneath is only about 30-50cm clearance so I can't crawl under there. It is quite cold, hence the need to insulate.

I would be doing it over a number of weeks so I know it is a big project.

Sounds like I need to know a bit about blocking and sistering.

The part I don't quite get is if I am replacing like for like thickness and strength, why is a subfloor required?

 

[C.J.]

Subfloor is T&G installed perpendicular to the joists. Butt joints land on the joists but the side joints span the joists. The T&G locks the panels together and eliminates deflection between the panels themselves where they span the joists. A second layer of plywood on top of the subfloor is then called underlayment and is not required to be T&G. 3/4” T&G subfloor is generally thick enough unless your joists are farther apart than 19.2”.

As far as blocking and sistering, if you’re gonna open it up you might as well go all the way. Are your joists up to snuff? You can sister new 2x’s to them to beef them up or you can just go all the way and replace them. In my case the original joists were 2x8 spaced 24” apart. That’s just not gonna cut it so I opted to replace everything. Realistically it will run you about the same price either way. Then you can add blocking between the joists. That’s simple enough to do and helps to stiffen the floor system as well as distributes the load to neighboring joists.

Subfloor is installed before the walls so in your situation you will need to add blocking around the perimeter of the room. In the second picture you can see a 2x fastened to the exterior wall so the subfloor has some support at the edge as well as something to fasten to.

It seems like a lot of work, and it is, but if you break it down into bite sized pieces it’s more than doable.

 

[danped]

Thanks for that comprehesive reply! If I use an engineered board which has T&G and is 3/4" thick do you think that is still not sufficient to eliminate the need for a subfloor?

I'm not tring to avoid the work/cost, I'm actually thinking about the floor level and a step up from the carpet in the hallway into the room.

 

[C.J.]

Depends on your joist spacing but usually a single layer of 3/4” T&G is sufficient especially if you’re planning on going back with another floating floor or a nail down wood floor.

 

[Tile Tom]

Chris's picture is perfect for explaining adding blocking. See the one wall in pic 2? If you rip out the existing subfloor there's a good chance the joists go under the wall into another room etc. You will need to put blocking in between the joists do your new subfloor is supported between the joists. Not just laying on top with no support from underneath.
And as long as you have it all opened, you might as well beef it up. And get it nice and flat too.

If cost is an issue I would wait until you're financially in a good spot. These projects ALWAYS waterfall into added expenses. I don't care how much you plan, there will be some surprises along the way. You don't want to rip the place apart only to find out you have a foundation issue that will run another 5k and not have the 5k. You know?

 

[danped]

I am not seeing this blocking oin pic 2.. ? I thought blocking was the short perpendiculars between the joists like in pic 1.

I reckon I will have 2x8" on 18" centres. I don't mind beefing it up with blocking to get a nice solid floor and costs won't be a problem.

Is nothing required in terms of moisture protection if I am putting insulation between the joists?

 

[C.J.]

Usually the insulation has a paper side that is fastened to the underside of the joists. This acts as a sort of vapor barrier. The blocking between the joists helps to spread the load to adjacent joists. The other blocking we’re referring to is simply a 2x fastened to the exterior framing of the house, bottom plate? Sill plate? Framing?, whatever you want to call it, so you can fasten the perimeter of the subfloor to.

 

[DarisMulkin]

Usually the insulation has a paper side that is fastened to the underside of the joists. This acts as a sort of vapor barrier. The blocking between the joists helps to spread the load to adjacent joists. The other blocking we’re referring to is simply a 2x fastened to the exterior framing of the house, bottom plate? Sill plate? Framing?, whatever you want to call it, so you can fasten the perimeter of the subfloor to.

View attachment 13649

What about 6 mil visqueen over the dirt if that is what is there

 

[C.J.]

What about 6 mil visqueen over the dirt if that is what is there

Brilliance. I forgot all about that.

 

[danped]

My plan was actually to put the insulation boarding between the joists as I don't think there is clearance to get 100mm under the joists everywhere. Also it would be pretty difficult to get it under the joists. Appreciate it may not be as good for insulation but would this afect the wood in any way?

On the vapour barrier, just laying it down on the dirt/grit underneath sounds easy enough. I think that ground has been prepped aand probably already has a vapour barrier in it.

 

[DarisMulkin]

I think that ground has been prepped aand probably already has a vapour barrier in it.

needs to be on top and up the walls

 

[danped]

On top of insulation? or on top of earth floor? Is between joists ok for insulation boarding?

 

[C.J.]

Vapor barrier on top of the dirt and insulation between the joists just as you figured.