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nikademous 05-20-2010 03:05 PM

reinforcing second floor joists
my house is 31 ft x 24 ft one story. i would like to take off old roof and put a second floor on. the building inspector says that the exisiting joists
2x5's 16" on center my not be enough support. i need to know if i can sister more 2x5 next to the exisiting ones. the joist run from side to side spaning 24 ft. will sistering joists support 30 pds per inch? i plan on reinforcing everything with beams running vertical to joists.

jklingel 06-11-2010 02:47 PM

tough one
Extremely tough for anyone to answer w/out all the specs on the house. You better see a qualified engineer, because you may well need to HAVE INSTALLED LONG AGO a foundation wall under whatever is going to support those beams you are adding in. If I read correctly, you are taking a clear span and now halving it by supporting the ceiling members w/ beams; excellent idea for them, but what will the beams sit on? Sistering is fine, but it only doubles the load carrying capacity of the member; you may need to add height, as in trusses, to keep the clean span. I see big red flags. GL. j

jklingel 06-11-2010 02:55 PM

What you described implies a flat roof. Are you sure you don't have normal trusses and you are just looking at the bottom cord? That is an unbelievable span for a 2x5 (did you mean 2x6?), or even a 2x12.

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