The honest answer is that there is no grant for the attic conversion build itself. Grants in this area, through the SEAI, apply to attic insulation as an energy upgrade, not to the structural work, staircase, fit-out or finishing that make up a conversion.
This is an important distinction. SEAI home energy grants are designed to improve the energy performance of your home, and attic insulation is one of the measures they support. That funding is aimed at insulating a cold, unconverted loft to reduce heat loss. It is not intended to help pay for turning the attic into a habitable room.
There is also a practical point. Once you convert an attic, the insulation strategy changes. A converted room is usually insulated at the slope of the roof rather than at the joists, because you need the space below to be warm and usable. That is part of the conversion build and is not the same measure the standard insulation grant covers.
You may still benefit from the Home Renovation angle on tax and VAT rather than grants. Renovation work by a VAT-registered contractor is charged at the reduced 13.5% rate rather than 23%, which is covered in our answer on VAT on attic conversions.
If your main goal is a warmer home rather than extra living space, our attic insulation page is the place to start. If you want the room, plan the conversion cost without assuming a grant; see the cost guide or book a free assessment.