One type of underfloor

Explained in another post using the correct underlayment (with floating installation method) has to be the start of your enjoyment of the end result.

When you have one area containing two (or more) types of underfloor you have to start with other preparations: making sure you have one type of underfloor. Example: extension with new concrete underfloor connected to a room which has existing floorboards. Both types of underfloor (can) have a different temperature or moist content and your natural wooden floor will react accordingly: one part of a board when laid on both types could 'go-all-over-the-place' and you could end up with a cupped or warped floor.

Simplest solution in this situation is to install plywood or OSB sheets (cut in small sheets 30 by 60cm maximum) in the whole area. Glue the small sheets with flexible adhesive to the concrete and nail them into existing floorboards. On the plywood/OSB (=sheet material) use a foam or rubber underlay for sound-insulation and your underfloor is ready for the wooden floor.

Comments

[Dave]

HI,

I am planning to lay an oak floating floor in front and back room of my terraced house, the 2 rooms are connected by double doors. one is concrete floor, the other has floor boards (terrace is built on a hillside). You suggested using ply or OSB glued/nailed down, and then foam or rubber underlay, but didn't mention any DPM. Won't the concrete area require a DPM? Also, could I use Fibreboard instead of ply or OSB?

Many Thanks,

Dave.

[Karin H.]

Hi Dave, welcome

You'll have to use either plywood or OSB, the fibreboard is an underlayment and not a stable or suitable subfloor.
And no, when you glue or screw ply of OSB to the concrete floor you don't need an extra dpm.

Wood You Like Ltd

[Paul]

Is this the case with engineered floors too?
And the size of ply, can i not lay sheets of 8x4?

[Karin H.]

Hi Paul

Yes, wood-engineered flooring is all wood too (be it in a combination of wood-types).
If you lay very large sheets your subfloor could echo due to unevenesses in the underfloor. And trust me, smaller sheets are much more 'handy' to work with.

Wood You Like Ltd

[julie2933]

We recently removed a ceramic tiled floor which was defective to find that it had been laid directly onto green, 25mm floor grade, chipboard. The chipboard is a floating floor and is in 2400 x 600mm boards underwhich is approx 50mm polysterene then a damp proof membrane. Having scrapped most of the remaining adhesive from the chipboard, can an engineered board be put down on top and if so, what preparation? I know ideally it would make sense to remove the chipboard altogether but we are talking around a 120 metres/2 and all the stud walls are built over it and compounding the problem we would have to seek LB consent to remove and replace any internal studwork, so best avoided.
Julie

[Karin H.]

Dear Julie

If the chipboard subfloor is stable and sound you can install the wood-engineered boards using the floating method. All you have to add is 3mm foam underlayment between chipboards and wood floor and glue all T&G's correctly.

Hope this helps

Wood You Like Ltd

[Craig Stephenson]

Can I ask if this can be laid straight down on timber joists at first floor level, or do i need a subfloor of particleboard?

[Karin H.]

Hi Craig

Yes you can as long as:
your new floorboards are load-bearing (18m thick at least)
the new floorboards connect with at least 3 joists
and the joists should not be further apart than 35 - 40 cm

Wood You Like Ltd

[Steve Rowland]

Hello experts Help required,
My son has recently purchased a house built in the 1950's, and the downstairs rooms and hall have oak parquet flooring. In places the blocks have lifted and underneath there appears to be a 2" layer of a soft powdfwery substance like plaster on what appears to be stable concrete. Does anyone know what this layer on the concrete is? Is it an insulating layer, and how can I repair it to obtain a level sufrace to refit the oak blocks to? Thanks, Steve.

[Karin H.]

Hi Steve

We've never encountered this and will "ask around" for you and your son. Are you sure it is not deteriorated chipboard?

Wood You Like Ltd

[Carl]

Hi there,
I want to fit a Floating style solid brushed & oiled floor in a house with Two types of sub-floor (Floorboards & concrete screed)But as the floorboards sit 4mm lower than the concrete I was hoping to put a DPM (vinyl sheet)on the screed and then a 2mm foam underlay: To build up the floorboards a DPM again to prevent moisture from below and then a 6mm fibreboard underlay. Then I wanted to lay the boards by gluing the toungues all sides. I am aware of the idea of ply boarding the whole area and forgoing the DPM but have limited ceiling height and am working in a grade II terraced house,So don't want to raise the floor any more than necessary! Is it a lost cause or can it work like this???

[Karin H.]

Hi Carl

Do not place a DPM over your existing floorboards no matter what. This will prevent the normal and necessary ventilation and could cause rotting joists etc.
Also I don't think 2mm foam (especially not the one more suited for laminated floors) is sufficient. 3 or 4mm would be better. The fibreboards tend to create a wobbly floor, so best would be to create a level underfloor first, perhaps with hardboard/plywood of various thickness and then lay a 3mm underlayment over the whole.

Hope this helps

Wood You Like Ltd