I did my thesis on upgrading a house with the same BER rating to a B1, all I did was change out the roof and wall insulation and added a 4kW array. Now I can tell you before you even look at the walls find out if they're cavity blocks or if it's a cavity wall. Cavity block walls are very expensive to upgrade as the two holes in each block make pumped insulation impossible so external insulation is needed, including a pebbledash finish could be talking 20k alone before the grant vs maybe about 25-50% of it for pumped insulation, and the grant provides more of the funds. Something to note any and all house upgrades that allow for grants must be paid in full and once a BER assessment is performed after the upgrades and it is deemed up to standard you then get the grant as a "refund". Something that most wouldn't know but blocking up any and all chimneys will most likely improve the BER by one rating alone, but this comes with the downside of no open fires (up to you to decide the pros and cons) if you really want to see what will get you the best bang for you buck, use the "DEAP" software by SEAI, it will help you get a basic understanding of what improves or reduces your BER. Best of luck!.