Often times decks are weakened by the way they are attached to a house. And a chimney should not be used to support the deck's structure. A chimney is not a structural member to attach to.
This house has two wood-burning fireplaces.
So, to accommodate both flues, which have to be independent, the chimney box is very wide.
The structure for these chimney flues is a mere wooden surround. It is basically a bump out, attached to the house's structure, but not a part of it.
There is no cantilever inside this chimney to make it a part of the house's structure.
And so decks are not supposed to be attached to them!
Approximately one third of this deck is attached to the chimney.
And not even very well! I only counted four bolts. And I'm not sure what kind of bolts they are!
Decks usually don't collapse downward. What usually happens is people go out onto the deck and congregate at the outer guardrail.
This places all the weight to the outside. Attachment to the house is CRITICAL to the deck's ability to stand straight and support that weight.
When decks collapse, it is most often by falling away from the house. This deck has been there a long time, but that doesn't discount the potential danger.
AND IT IS A DANGER!
This is one of the most common mistakes made by homeowner or unprofessional deck builders. What should have happened?
The two joist surrounding the chimney on both sides should be doubled up. And between them a double joist should run parallel to the chimney, but not attaching thereto. Then those perpendicular support joists can be properly, safely and securely, attached to that double cross joist assembly.
That is one way to tell that this deck was not built professionally.
Here is another way! --------->
The outside joists really ought to be doubled also. This provides strength to the deck "box," but also for the outside guardrail to anchor into.
But look. Not only is this (and the other) outside joist single, it is attached flimsily with a single angle bracket in the corner.
That bracket does not afford enough nail holes for proper attachment.
When they give way, and they often do, this is the result.
From above it is obvious that the decking in that corner has sunk a bit over 1".
AND VERY INSECURE!
So this "deck guy" was consistent in his inability to understand structure and attachment.
My recommendation: decks afford many opportunities for failure. They seem to be one of the things most-often attempted by nonprofessionals. They watch a TV show and bang, they can build one too! Look at the decks very carefully, see how wobbly the guardrails are, see if there is any sagging or if the joists are close enough. And don't walk out on a deck with high heels! You will appreciate that tip... pun intended!
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