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Building a 2nd floor addition and have a problem

12 years ago

I'll try to make this brief. We are building a 2nd floor addition over the back room of our house. The main living area has a cathedral ceiling currently with 2x8 ceiling joists at 16" on center and a span of only 8 ft (the ceiling begins on an angle, it then goes straight, then comes down on an angle to the load bearing wall that is the entrance to the back room). So now, we are raising the wall to the entrance of the back room by 8'10" eliminating the slope of the ceiling. Here's my dilemma. The ceiling joists will now span a total of 36 feet. 19 feet to the first load bearing wall then 16 feet to the second load bearing wall (which are the new bedrooms). Code calls for R38 insulation which doesn't fit in 2x8 ceiling joists. Foam is not an option because of the expense. So here's my two questions. One, can I replace the existing 2x8's with 2x12's? And two, because of the great span, can I have a 19 foot 2x12 go from the one side to the first load bearing wall and then a 16 foot 2x12 to go to the next load bearing wall? Structurally will this work?

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Comments (5)

don92
12 years ago
I'm not quite following your post. Check the code book and see if 2x8's will make your spans, if so then just sister on what ever you need to give you the depth for the insulation. Wish I could be more help
User
12 years ago
Foam may not be on on your radar because of the cost, but it will probably be the only way you'll achieve the needed R value. And you'll be in the land of engineered beams rather than dimensional lumber for your needs as well. None of this is very DIY friendly and you need to be calling a contractor for this project.
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Thanks for the reply. I was planning to double-up the joists anyway. Actually, since what is there now are ceiling joists for the 1st floor, they are only 2x6. I was planning to sister a 2x8 along side each of these. Would that be adequate, or are you suggesting I would need double 2x8 joists? I don't really have the option to carry this load down to the foundation. Sicne there is alread a center beam, I'd have more posts in my basement than I know what to do with.
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jonnyp
12 years ago
Your best bet is engineered roof trusses. I think you will find the cost much cheaper for stock and installation. Most lumber yards can assist you in proper sizing and any other considerations. The only caveat is the loss of some attic space.
I can tell you for fact 3 guys,4 hours, framing and sheathing done. Make sure you are thorough in your objective(drawing) when you go to the lumber yard.
chibimimi
12 years ago
No engineering advice here, but a question: If you go with the 2x12s, would the extra 4" come out of the ceiling height on the lower level or would it raise the floor on the second? If the latter, and if you have existing stairs already in place, you might have to rebuild them to make them meet the new floor height correctly.
User
12 years ago
You mention ceiling joists but also roof insulation. Are you supporting a roof and a ceiling below it or just a ceiling? If this is a roof structure, you need to say where the project is located or say what the code required loading is. Is it a low sloped or a steep sloped roof?

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