There are several options to choose from when laying new or replacing existing floorboards, but your final decision will depend very much on how you plan to finish the room (bare boards, laminate flooring, carpet, etc). Before you think about any floorboards, you should make sure your floors' structural elements (joists or concrete slab) are sound and ready to be laid over.
Floorboards are usually made of softwoods and are sold with either square or tongue-and-grooved edges. Choosing a narrow board will result in a much nicer finish and will reduce the amount of movement that happens to all new floors over time. Narrower boards obviously means you need to buy more and therefore the cost will increase. If money is no problem, and you want to create a superior finish which will be uncovered by carpet, etc, you should go for a narrow hardwood board such as Oak or Maple.
The next thing you should consider is whether the boards are Quarter-sawn or Tangentially-sawn. Quarter-sawn boards are cut from the centre of the tree to the outside edge, whilst tangetially-sawn boards are cut from the full width of the tree. The difference might sound minimal, but quarter-sawn boards will distort much less than tangentially-sawn boards, which tend to bow across their width. Quarter-sawn boards are usually significantly more expensive to buy than tangentially-sawn boards. If using tangentially-sawn boards, always lay them with the concave side facing upwards (look along the length of the board to see which way it bows).
Different types of Floorboard
1. Square-edged Softwood Board
As described above.
2. Tongue-and-groove Softwood Board
As described above.
3. Square-edged Chipboard
Cheap and easy to lay as it comes in large sheets. Chipboard will need to be covered by carpet, etc.
4. Tongue-and-groove Chipboard
Slightly more expensive than square-edged chipboard, but allows for a smoother finish.
5. Square-edged Plywood
6. Tongue-and-groove Plywood
7. Square-edged MDF
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