Question:
We live in a cathedral ceiling home. There is a master bedroom upstairs with a small deck at the top of the stairs, and it is open to the kitchen and living room below. There are two 6×12 gluelams supporting the roof. We are wanting to put a loft to fill the rest of the upstairs from the first beam to the front of the house to the back. I want to put a post right next to the stairs under the gluelam to support that corner of the loft. I will do appropriate load bearing support underneath as well . The distance between the post by the stairs to the wall on the other side is just under 18′. My question is the beam for that distance along with the diagonal bracing under it , can I use the gluelam above it for support also if I use a post or chain between them. There will be another beam under the other gluelam and the lamps are only 8′ apart , and from the back beam to the back of the house is only 11′.
Answer:
Unfortunately it is impossible for me to provide a direct answer to your question, regarding structural support for a second floor loft, without actually seeing the situation and the conditions. However, I can offer the following suggestions.
It sounds like the existing glulam beams were used to accommodate the support of the roof, as well as provide a structural support to stabilize the open cathedral ceiling.
Glulam beams certainly have structural strength and integrity along their length, however in most situations they are not designed, nor intended to have specific point loads applied, such as a column sitting on the beam, or any type of substantial hanging apparatus suspended from them. In most cases, the glulam is designed as a header beam with the intended loading being uniform across the beam itself.
If you were to install a ledger board or individual joist hangers along the length of the beam, then the actual glulam might be large enough to accept the weight of a second floor, however, this can only be determined by a local structural engineer.
Obviously the installation of any type of column under the glulam beam will substantially increase their ability to carry additional weight, so this is a good thing.
I have to question your comment regarding the appropriate structural support under the new column. Unless you are a licensed structural engineer that is qualified to design this appropriate structural support, I would doubt that the local building department would approve the work or your design intentions.
It is important for you to understand that any additional loading on an existing beam, whether it is a glulam, a built up composite beam, a beam that is simply several pieces of framing lumber fastened together, must be evaluated by a competent structural engineer. If the beam was sized appropriately for the design of your home, it is unusual to find substantial additional capabilities in existing structural members. The obvious reasons are economics, why install a larger member if it is not required.
However, there is a strong possibility that these 6 X 12 glulam beams were installed due to aesthetic reasons and not simply structural considerations. If this is the case, then they may actually have the proper structural support necessary to perform the loft addition that you are intending.
Although, I would like to offer you some more definitive and logical answers, it is an impossible task without actually viewing the home, and calculating your intended loading of this additional space.
I would suggest that you contact a local contractor for their professional viewpoint, or if you are intending on performing the work yourself, contact a local structural designer or architect. You will need a sketch identifying the specifics of your plan to allow your building department to issue a building permit.
Good luck and I wish you well.