Hardwood flooring questions

[mikepower]

Hi All,

My first post, so apologies if this has been covered in depth before. I am having a hardwood floor installed next weekend, and as I know nothing about it, I thought I'd get a few second opinions.

The guys laying it say they will not need an underlay - but I thought this was necessary. I have taken a look under the carpet and the floor is currently joist, laid on top with some kind of plasterboard, then tongue and groove thick chipboard.

The oak flooring itself is T&G, and is 18mm.

Alos, if only the centre planks are nailed down, what stops the floor from sliding about?

Many thanks in advance of any replies.
mp

[thedoctor]

Underlay is always required on liaminate flooring but not on solid hardwood. Hardwood floors can be laid floating or fixed. Timber expands and contracts a great deal and to allow it this movement stops the planks cracking where fixed by nails, adhesives or screws. The weight of the boards and good fitting, keeps them in position is a large area.