In the description of the exterior of the house of Usher, which words suggest the presence of decay in the structure itself?

The narrator experiences a strong feeling of dread as he approaches the house and sees the desolate, blighted landscape, but it is not until he draws closer that he discerns distinct marks of decay in the structure of the building itself. As he gets closer, he stops and looks carefully at the exterior of this unusual house. He sees that the outside is discolored. He notes that "minute fungi" grows over the whole exterior and...

The narrator experiences a strong feeling of dread as he approaches the house and sees the desolate, blighted landscape, but it is not until he draws closer that he discerns distinct marks of decay in the structure of the building itself. As he gets closer, he stops and looks carefully at the exterior of this unusual house. He sees that the outside is discolored. He notes that "minute fungi" grows over the whole exterior and hangs in "a fine tangled web-work from the eaves." We can imagine the fungi hanging down like the Christmas icicles people string up during the holidays --but this is fungus (mold). The individual stones of the house seem to be crumbling, although as a whole, the building is holding together. The house reminds the narrator of "old woodwork which has rotted for long years ..." He also sees a very thin--"barely perceptible" fissure that runs down the wall from top to bottom in a "zigzag direction." 

If I had to pick out words that indicate decay, I would choose the following: "discoloration," "fungi," "crumbling," "rotted," "extensive decay," "fissure." I have copied the relevant passage below:

The discoloration of ages had been great. Minute fungi overspread the whole exterior, hanging in a fine tangled web-work from the eaves. Yet all this was apart from any extraordinary dilapidation. No portion of the masonry had fallen; and there appeared to be a wild inconsistency between its still perfect adaptation of parts, and the crumbling condition of the individual stones. In this there was much that reminded me of the specious totality of old wood-work which has rotted for long years in some neglected vault, with no disturbance from the breath of the external air. Beyond this indication of extensive decay, however, the fabric gave little token of instability. Perhaps the eye of a scrutinizing observer might have discovered a barely perceptible fissure, which, extending from the roof of the building in front, made its way down the wall in a zigzag direction, until it became lost in the sullen waters of the tarn.