Building Homes or Extensions/concrete ceiling

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Expert: - 9/14/2010


Question
I am designing a earth contact home with the dimensions of 36'x66'. The lower level will be completely underground. The upper or second level will be mostly underground, with contact on 3 sides. My question is; I want to  have concrete as the floor between the levels and concrete as the roof of the upper level, with dirt put on top of the roof. Can a "regular" concrete crew, who normally does traditional foundations and flat work be capable of this project? And am I asking for something that is going to be unreasonably expensive compared to a traditional floor and roof? What about special forms or supports?  

Answer

elevated slab formwork
Hi Bill, I like this type of home design myself.  Basically the exterior walls would be done like any basement foundation.  The floors and roof are nothing more than structural slabs and depending on the spans shouldn't require anything too out of the ordinary regarding reinforcing steel and finishing.  But you will need to find a contractor capable of the formwork and shoring unless you are doing the formwork yourself.  To form an elevated slab isn't that difficult but it would be cheaper for you to find someone that has the forms capable of doing the job.  It requires a grid work of posts and beams topped with joists set close together.  I am including a simple drawing to illustrate.  The formwork can be reused for each level, one use for the middle slab, then reuse for the roof slab. You will also need to reshore the second floor slab while forming and pouring the roof slab since the shoring and formwork for the roof slab is supported by the second floor slab. This is done by adjustable post shores spaced under the slab in a 6'x6' grid pattern and left in place until the roof slab reaches 85% design strength. To achieve a more open design you might want to think about prestressed concrete beams, they make a great floor and roof system and allow greater open spans without columns or supporting walls. I hope this information helps, please feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

Bruce E. Johnson

Expertise

I can answer any construction related question in regards to carpentry, concrete, drywall, masonry, structural elements of any type of building, residential or commercial. Interior or exterior.

Experience

Custom Commercial and residential buildings. Churches, theaters, schools and auditoriums. Most recently I am working with the Catholic Church on several design build committees. I have a website related to scheduling and project supervision. Although my expertise is more related to multimillion dollar commercial, educational and theatrical projects my generous credentials in residential and remodelling construction make me a viable source of information regarding all forms of building questions.

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