There is immense irony in the way that we are told that T.'s father is actually an architect. For somebody who devoted his life and earned his living through planning and constructing buildings, there is something immensely perverse that his son devotes his energies and is so focused on their destruction. This of course helps us to understand more about T. and the way that he has such fascination to Old Misery's house. The fact that it was designed by Christopher Wren, a famous architect in England, would have been an added incentive to destroy it from his perspective. A house that would have been wondered at and admired by his father would be a perfect target for the repressed anger and rage that T. contains within him.
The irony therefore is based on the discrepancy between T.'s father and the actions and attitudes of T. The text focuses on the curious "beauty" that T. sees in such a pure act of destruction, and this is of course something that his father would have been completely opposed to.