Why a post on the fabled diagonal crack in drywall?
Simply because during home inspections I often get questions as to drywall cracks - are they bad? Are some worse than others?
They all have a source! It could be poor fitting together of two pieces. Or tape without enough joint compound (AKA mud) underneath. Even normal expansion and contraction of wood.
Truly, some drywall cracks happen because of a structural issue. But some structural issues are worse than others.
This is during a one-year inspection of a new house.
These two photos are of a double door between the master bedroom and bathroom.
The vertical crack over the left side of the double door is because of what is causing the diagonal crack over the right side.
The wall is 16' long in the bedroom.
It is not a load-bearing wall.
But underneath this wall is over the ceiling between the kitchen and family room. That span is 21', and would be represented by the L in the diagram below. That is a long span.
From the bedroom it is possible to see a slight bulge downward under the right side of that door. In the diagram below that location is in the Moment Critical Zone, and it can flex. It can also bounce!
In the bathroom, to the left of that door is one of the bath sinks and cabinet. To the right of that door is the shower.
I suspect that underneath this wall is an array of supportive floor I-beams, wide to be sure, but singular in their array and spacing. And it is likely that the distance between them is 16".
Even though this is not a load-bearing wall in the bedroom, it is still a long wall. Possibly the support underneath needed to be doubled up, with two I-beams sistered side by side. If that wall rests between two I-beams, then each it rests between probably should have been doubled up.
A singular I-beam underneath would have sagged somewhat, hence the diagonal crack. The vertical crack to the left is the joint between two pieces of drywall. In that location the joint is properly done, but cannot withstand the flexible movement to its right and has separated a bit.
Over time can these cracks open up wider? Maybe, at least a little. But there will always be something of a bounce where the bulge is happening under the door and repairing that diagonal crack may be hard to do. It will "want" to reoccur. The structure probably needs shoring up under that wall! But what to do is not my department. I observe and report, and maybe give what verbal evaluation I can.
My recommendation: sometimes evaluation needs to be a combination of observation and experience, coupled with a little knowledge as to structural components. In this case the structural components visible in the basement are composed of floor I-beams and paralaminate beams and posts. Those same components are likely used in the structure above. When used in a maximum span arrangement floor I-beams can bounce! And if I had to say, my opinion is that this is what's happening and causing that diagonal crack above!
Jay Markanich Real Estate Inspections, LLC
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560