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I have a house that has a two-story cathedral ceiling. I was thinking about adding a floor and turning it into new rooms in the house. However, a web page I read said "Vaulted ceilings create no floor space. In fact, they prevent you from ever building upward and into that space."

The author does not further explain this remark. Why would I be unable to build into the space? From a geometrical perspective I could still get 10 foot ceilings in the living room and at least 9-foot ceilings in the upstairs rooms, so there would seem to be no limitation from a headroom perspective.

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    I think the author was grasping for points to bolster the article. You can't "build into" almost any ceiling because it'll be too low. Maybe the author meant a bonus room built into the trusses. Who knows. – isherwood Oct 27 '18 at 16:20
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Generally nothing's really impossible, but a lot of things are impractical, usually due to expense.

Depending on the size of the room, changing a two story room into two stacked one-story rooms is a big job and will require an engineer's stamp, but nothing magic.

Essentially all you're doing is inserting a floor at ceiling height. You'll have to provide for a means of access to the new space - might be as simple as a set of stairs up, or cutting a door into an upstairs hallway.

The extra load of the structure (and the contents and the occupants) will have to be taken into consideration. For example it's possible that two opposite existing walls are strong enough to carry the additional load to the foundation, and the distance can be spanned by trusses.

There will probably be many possible ways to do it and doing a careful comparison of costs could save you a bundle.

There will be a million details to deal with - maybe redoing forced hot air ductwork, electrical, moving windows, etc. - etc.

It may be that it's not impossible at all, but an addition gives you much more for your money.

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Well, here it is two years later and I did it. There is now both a bathroom and bedroom where the "vaulted ceiling" used to be. To do the project required adding two additional lally columns in the basement. The floor was constructed by sistering two LVL beams to existing structural LVLs on either side of the space. Then joists were hung between the two LVLs. Even though the space was quite large (25x17), the resulting floor was quite solid once we installed bridging between all the joists. The ceiling in the bedroom space is a little weird because the valley of the roof cuts through it, so it has a loft-like look to it.

One problem we ran into was it was difficult to find enough area on the wall to install a window (required for egress) because a large chimney occupies that wall on the exterior. The space was too small for a double hung window, but we solved the problem by using a casement window.

Another issue is that both the bathroom and bedroom are somewhat cave-like, because of the lack of windows. I may install one or two skylights in the room to help alleviate this problem.

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"Why would I be unable to build into the space?" No idea.

You would have to frame into the exiting wall structure (which would require knowledge, or if you ever wanted to re-sell the property you should get an engineering design first). The requirement is that the existing wall structure could support the added weight of the new floor, furniture, and occupants.

You could also install structural support posts in your existing room, again, as long as they were supported from the floor, joists, beams and rooms below. The importance in this is that ALL load be carried down through structural components that carry weight ALL the way to solid ground.

Many people attempt adding rooms or doors, or removing walls and upend the structural integrity of a home causing sagging and movement of the remaining structure. It's not easy to fix these created problems once the home starts shifting, sagging, or moving.

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The addition of an intermediate floor in a 2-story cathedral space is problematic because the foundation, studs, and headers in the load bearing walls were presumably not designed to bear the considerable weight of an intermediate floor and the weight of people and furniture on the floor. And how would the introduced floor joists be connected to the load bearing walls?

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