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loftezy 02-22-2011 03:17 PM

Floor Joists on Concrete
I am planning to start my next home improvement project soon and will be submitting my plans to the building department next week. However, I'd like to get a little input on one issue before I talk to the plan checkers at the city.

I am planning to make changes to an existing room (small 7'x12' office type room) to turn it into a third bedroom. To do this, I need to move a wall, and raise the floor and ceiling to match the height of the rest of the house. The floor of the room is currently on a concrete pad (I think it is an old patio that was enclosed a long time ago) but the rest of the house is on a raised foundation. To raise the finished floor height in the room, I will install floor joists that will match the height of the adjacent joists. The problem is that I won't have much clearance (if any at all) from the bottom of the new joists to the concrete pad.

I am proposing to use pressure treated joists since I may be resting on the concrete but I'm not certain how to address the ventilation issue. Once I add the floor insulation, there won't be much space left to have cross ventilation under the floor. Would a vapor barrier be appropriate here? (Vapor barriers aren't very common in my area of California).

Like I said, I'll get my final answer from the plan checker next week but I'd like to hear from anyone who has had to deal with an issue like this before. I've attached a cross section of my house so that you can get an idea of what I'm talking about. The existing floor in the room sits directly on the concrete pad. The new walls and joists that I am going to add are shown in bold.

Gary in WA 02-23-2011 04:09 PM

The problem with most similar additions is converting from a patio to a screened porch to a 4-seasons room to a habitable room without changing the foundation. Windows, doors and walls need a foundation- usually concrete, floors and roofs need structural support. Contact the local B.D. now, and ask for a pre-construction inspection, to find what they require and go from there....


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