Expert: Dan Griffin - 3/6/2009

Question
QUESTION: I would like to add a 12 x 8 loft from our 2nd story over the living area, which currently opens up to 18 foot ceilings. The loft will be supported by the second-level floor joists and I would like to mount the other side to an exterior wall made of concrete block. I am wondering exactly how to go about this. What specific hardware and materials will I need to ensure appropriate load bearing capacity?

ANSWER: Eric, your subject line is misleading.  The outside walls you intend to tie to all have footings.  I'm not sure if your interior wall has a footing, but if it is carrying 18 foot walls, I suspect it does also.  I am a bit lost though about this living room.  Will this new loft go completely across the living room?  Is the living room just 12' across? Is there a balcony/mezzanine at the second floor level now?  Things don't jive in my mind.

If the new joists don't go all the way across the living room, some method of supporting the loft will need to be created, whether carried by knee braces from the wall)s), hung from an overhead beam, or using some type of post/column.

The issues will probably need the services of a structural engineer who can see the issues and propose some possible solutions.

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

QUESTION: Thanks for the quick response. The loft will go across a portion of the living room that is 12 feet across. I do not want to place any posts/columns underneath the loft in order to maintain an open flow beneath it.

I guess my concern is whether the loft can be held securely by the second-level floor joists and with knee braces from the two walls. The second floor does have a balcony that the new loft will be extended from.  

Answer
Eric, it makes a bit more sense now.  The existing balcony joists are probably cantilevered over the wall.   There are fairly short allowances for cantilevers, and I suspect your balcony is using every bit of it.  It would be best to get your loft beam to bear on that same wall the joists are cantilevered over.  The block wall across the living room is probably fine to carry the loft joists out to the beam.  You can use a ledger band stagger fastened to the block wall.  It would be best if the wall is slushed solid for this fastening, though epoxy and sleeves should be able to provide plenty of hold.  I'm guessing your balcony at about 4 feet, so you are spanning about 16 feet with the beam.  that should be well withing the characteristics of an LVL beam on the lead edge of the loft to carry the 8' joists.  You will need well designed fastening for the block wall end of that beam and the balcony end may need additional 2x4's in the wall to support the LVL.

As you develop this plan, you may want to solicit the services of a structural engineer.  The city will probably require his stamp anyway.