Expert: Ted Barnhill (Principal, Design45 LLC) - 8/24/2009

Question
i recently purchased an old home that  has 6.5 ft ceiling on second floor.  i have rafters not trusses.  i plan on completely gutting second story but not roof.  can i just move the second floor ceiling joist up 1.5 ft?  i plan on moving joist up and putting hurricane straps from rafter to wall. and redoing collar ties but collar ties will stay in the top third of rafter.    greatly appreciate advise.

Answer
Ty,

In older homes, attic and roof framing tends to work as a system, with individual elements often undersized by modern standards, but still structurally adequate as a whole.  When finishing older attics, we normally find there to be two approaches:

1. Alter existing structure as little as possible, and finish "as-is".  (This might include moving collar ties up, depending on the rest of the geometry.  If your floor joists and rafters are both resting on the bearing walls in a simple gable roof, this might be fine.)  The bearing capacity of your floor joists must be verified (consult an engineer, ask your local building officials, or use an IRC span table).  It is always a good idea to have an engineer, architect, or experienced builder look at your structure.  In some cases, your roof will continue to move a little seasonally and under load, and you might experience sheetrock/tile cracking over time.

2. Bring the structure up to current code.  This is more costly, but will give you the peace of mind that your structure won't move over time.  Have an engineer size the structural elements; in some cases, your attic may be "overbuilt" and you won't have to do anything.  Frequently this will involve installing a ridge beam or other elements to allow for open spaces in your existing attic.

Good luck with your attic project.

Ted Barnhill
Design 45, LLC