[Ron6519]

I have an addition that was built in early 1900's. THe addition is aprox. 12' X 15' 7", The current ceiling joist are bowed and twisted, due to water damage. Unfortunatly once I opened up the ceiling (Removed all the 1 x 6 x 5/8, tongue and groove) I found that the joist were 30 to 34 inches apart from each other. They are running the 12' length. I know that they should have been at 24" (MIN) on center.

My question is shoulden't they have been 2 x 6 rather then 2 x 4's?

Since I am going to have to replace them (Builders permit requires inspection prior to covering) and actual length is 12'-10.25", so I will have to get 14' is 2 x 4's enough? It has a flat roof on this addition. Roof Rafters are running 24" on center.

The oppiset side of the house has a 12' X 32' addition. Ceiling joist are running 24" on center, but they used syrafoam for the ceiling I want to use 1/2" sheet rock or 5/8" sheet rock, will the weight cause me problems on this ceiling as well?

Thank You

I'd sister 2x8" to the current joists and fill in between them so the framing is more standardized.
You don't mention the roof rafter size or where you live. The structure has been up for 100 years, so it can't be that understructured.
Do you have snow loads?

 

[AGWhitehouse]

You said it is a flat roof with the rafters at 24" o.c.. It sounds like the 2x4's you speak of are only there to hold up the ceiling finish. The only load they are carrying is the ceiling finish. 2x4's at 12" o.c. or 2x6's at 16" o.c. or 2x6 at 24" o.c. to carry sheetrock at the span noted.

 

[Redbeard71901]

Roof Rafters

Everything is done in 2 x 4 to include the roof rafters. Wall joist are running 34 t0 37 on center. I am also redoing them to 24 oc.

Just my opinion seems 2 x 8's would be over kill enless I ran them across the 15-7 ft width of room. But I have been known to be wrong.