You are usually responsible for carrying out any repairs or improvements once you have bought your home. It's very difficult to get grant approval from the Housing Executive to help you with the cost of repairs. These days, this type of grant will only be awarded if the Housing Executive believes the condition of the property is likely to cause a very real and very serious risk to the life of the person living in it.
You may need to get planning permission and approval from Building Control at your local council if you are going to carry out improvements or alterations.