You might open up your attic and find bare joists with fiberglass or cellulose insulation between the joists.
Attic conversion ceiling joist loft framing.
Lining walls and ceilings with a double layer of acoustic plasterboard can also be very effective as can laying a carpet over thick rubber underlay.
At least 50 of the usable area calculated above must have ceilings of at least 7 feet.
There are many ways of altering roof structures for loft conversions but they all have one common element the ceiling joists will almost certainly be inadequate as floor joists.
Fortunately this is a fairly easy fix.
Joists insulation and boarding.
Existing loft joists are designed only to support ceiling boards so a structurally sound floor is needed.
In other words if your attic has 200 square feet over which the ceiling is at least 5.
Loft floors loft floor construction.
You can sister the joists by cutting 2 x8 boards the same length as the joists applying construction adhesive and affixing each to a joist with nails.
This means that new floor joists are fitted alongside them slightly raised above the ceiling plasterboard to avoid contact with it.