I really appreciate all the replies, much food for thought. Below I will try to elaborate on a few things. I do have a design that I will post here in a minute.

This house would be in a Northern climate (Northern British Columbia), heavy snow loads. Wind is not a huge factor there. I am told helical piles are a great solution to soil in the area due to the amount of water in the soil and frost. Shallow foundations heave easily, while piles are set deep and in solid ground.

The roof would be rafters with a 1-2 ft overhand. 20ft or so 2x8 rafters, 16oc.

To clarify, the 'great room' would be in the 1st floor. The issue is just supporting the attic. Without an attic I wouldnt have a problem. I understand that the floor joist connections to the walls are key to hold the walls from spreading outwards. Connections would be stronger than recommended, overkill, if you will is what I would aim for. Heavy duty joist hangers and any other product I can find.

If I do proceed with this project, I do intend on consulting a professional. :)

Let's say I want to build a 30x30 great room in a 30x50 house (with a full attic). How would you cover a wide space overhead while supporting a usable attic. Walls being 8ft high, 2x6 throughout, interior walls 2x4.

Assuming the roof is a 12:12 pitch. Attic walls are 4ft from the wall top plate. The attic being largely one continuous space. Not many walls or heavy loads planned to be along the center.

How could I keep that 30x30 room open concept or mostly? A post in the centre of the room with two 15ft beams along the length? 30 foot I-joists? is this even possible?

For the post and beam option. The two beams would be triple 2x10s, 6x6 post, 6x6 diagonal bracing, joists 2x10s for this room to cover 15ft span (or 2x8s 12oc?). A helical pile directly below the 6x6 post.

This picture below is my original layout with 2 posts to be safe, which is what I would most likely go with. 1 post was a bit of a reach perhaps.

rough 2st floor layout - 2 beams - 10ft apart

  • 2
    Looks like homework assignment.
    – JACK
    Jan 14 at 12:48
  • Are you planning the great room in the attic(above) or removing walls on the floor and want to give attic support? Either way this sounds like a job that needs an engineer to design, since you would be changing the support structure of the house. Will probably need at least one post, if not two, to keep the size of a beam down.
    – crip659
    Jan 14 at 13:03
  • 2
    Also keep in mind that while 8' is pretty standard and seems plenty big enough in a smaller room - e.g., 10x20 - when you get a lot bigger it will feel "low". Jan 14 at 13:05
  • 1
    This is far too broad a question for this site.
    – isherwood
    Jan 14 at 14:04
  • 1
    An edit to make it much more specific could rescue it, but it's likely this will be closed for being to broad ("Needs more focus").
    – FreeMan
    Jan 14 at 14:32

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