Is a D1 good or bad?
On the lower half of the scale, a D1 home is costing more to heat than it needs to, and is a strong candidate for a grant-aided upgrade.
How to improve from D1
Homes at this level usually benefit most from attic and wall insulation, better heating controls and, where heating is oil or solid fuel, a heat pump. Moving up even one band noticeably cuts heating bills and improves comfort.
The typical measures are grant-aided by SEAI. See the grants, or estimate your own home to get a tailored list.
See what your own home is likely rated
Four questions, real data, the grants that apply.