New floorboards will result in a 6mm drop in floor level...

[PreferNotToDIY]

I plan to have the original, but badly damaged, 1 inch thick (26mm approx) floorboards ripped out and replaced in certain rooms of a Victorian property. The new floorboards will be 20mm thick solid oak floorboards. These days it seems impossible to get floorboards thicker than 21mm, and because the original boards are so thick, a simple swap will mean the new floor will be about 6mm lower than the original. This is a problem because it will create unsightly gaps between the bottom of the skirting (and door architraves) and will not align neatly with rooms where the original 1 inch thick boards are remaining.

My thoughts were to lay a 6mm thick sub-floor on top of the joists (in ply say) in order to raise the height ready for the new 20mm boards. However I understand that this is not a suitable thickness for a true sub-floor where the recommended minimum thickness is much greater. However, given that the boards themselves are capable of carrying the load, is it acceptable to lay a thinner sub-floor simply as a means of achieving the desired height?

I would appreciate opinions on this and other suggestions regarding best way to solve this problem?

 

[ursamajor]

I'd be worried about the new boards squeeking against a full subfloor. Would it not just be easier to have one piece of 6mm ply cut into strips 2" wide which can then be nailed/screwed on top of the existing joists?

While the floor is up, you should consider putting insulation between the joists for both sound and heat purposes.

 

[PreferNotToDIY]

...I'd be worried about the new boards squeeking against a full subfloor. Would it not just be easier to have one piece of 6mm ply cut into strips 2" wide which can then be nailed/screwed on top of the existing joists?

I simply did not consider that but it seems like a nice solution. With the floor boards up there is a nice opportunity to sort out the pipework and electrics and, as you say, insulate.

 

[Richard C]

Would it not just be easier to have one piece of 6mm ply cut into strips 2" wide which can then be nailed/screwed on top of the existing joists?

That’s what I’d do; doesn’t really need to be ply either.