Expert: Cary Simmons - 1/16/2010

Question
QUESTION: We have discovered horizontal cracks between the ceiling and the crown molding in 4 out of 6 rooms in our 2 and 1/2 year old house. The house is on crawlspace.  It is brick veneer construction and doesn't appear to have any cracks. These ceiling cracks just appeared this year in very cold weather in middle Tennessee.  What could be the cause?  How do we repair these cracks?

ANSWER: Diane:

I don't detect alarm in your question, and there is probably no resaon to be alarmed.  I need to get a bit more information in order to narrow the possibilities and propose suitable, permanent repairs.  I assume that the house is wood-framed beneath the veneer.

1.   Are the cracks continuous over the entire length of the walls on which they appeared?
2.   Are they exclusively on interior walls?
3.   Are they of uniform width?
4.   Can you identify a distinction for me between the rooms that have displayed cracks and those that do not?  (lower floor, lower heat, north side of house, two or more exterior walls, etc)
5.   What is your heating system and, if a furnace or boiler, where is it located within the house?
6.   Are any of the exterior walls not faced with veneer brick?
7.   To the best of your knowledge, of what material are the crown mouldings made?

Depending on your responses, it's likely I'll need to know a bit about the home's floor levels (one or more?)and roof framing--stick framed or trusses and whether the ceilings where cracks have appeared are supported by floor joists, attic joists, trusses or something else.

---------- FOLLOW-UP ----------

QUESTION: The cracks are not continuous and they are on interior walls only. They are not uniform width. The house is one story and the cracks are in every room except the bathrooms.  We have a heat pump.  All the exterior is brick veneer over wood frame.  All the crown molding is wood. Unfortunately I know nothing about the ceiling support system.  There is an attic/storage space  

Answer
There are four facts that you mention that tend to point to the same cause.  They are (1) that the house is quite newly built, (2) wood framed, (3) the cracks showed up during a heating season and (4) they have not appeared on exterior walls or bathroom walls.

All wood framing starts losing moisture as soon as its milled, generally starting around 20% moisture content and curing to around 5%, depending on exposure and climate. This moisture loss results in shrinkage.  It is not uncommon for a single-story frame wall to lose as much as 1/2-inch in height from shrinkage in the sill and top plates and minimal shrinkage in the studs.  This curing is most noticeable in the first years after construction, and is accelerated when the heat is on.  Bathrooms and exterior walls, and usually kitchens, will shrink less due to the greater amount of moisture available when compared to other spaces.

I suggest that this is the prime cause, but perhaps not the only cause.  If the roof and interior ceilings are supported by trusses resting on the exterior walls, and those walls shrink less than interior walls, cracks will predictably develop between the ceiling and the interior walls.  However, you indicate that there is an attic.  If the attic floor and interior ceilings are not supported by trusses but rather by simple joists, it is probable that some of these joists are in turn supported by interior walls which would cause the ceilings they support not to separate from the walls beneath.

I would not anticipate noticeable shrinkage from the wood mouldings unless they were improperly stored after being milled, and even then, the shrinkage would be uniform on exterior and interior walls.

Try to determine if the roof and interior ceilings are supported by trusses.  If you look into your attic and see (1) symmetrical wood "sticks" extending diagonally from each roof stick to
floor members and (2) metal plates at the points where the diagonals meet the roof and floor members, you have trusses and the shrinkage you describe is predictable and we can move on to the issue of remedy.  In either event, please do this and let me know the results.  if you can take a picture, so much the better.