One man's struggle to take it easy
Cabin: Windows, Door, and Second Floor Framing
Tuesday, Aug 17, 2010
Last week I finished taping the seams on the Zip Systems wall sheathing and installed the front entry door. This past weekend I cut out and installed the first floor windows. There are three windows on the first floor, plus the window in the door. I limited the number of windows somewhat to provide more wall space for cabinets and storage.
Yesterday I finished framing the loft floor. The first floor ceiling height is 8 ft. and the loft floor is framed with 2x8’s leaving a 2-1/2 ft. knee wall in the loft. I used 2x8’s for the loft floor rather than 2x10’s because there will be an interior wall running most of the length of the floor for support. The span tables indicate 2x8’s would be acceptable even without the support wall but would be at the limit of their span rating. The 8’ ceiling on the first floor provides enough height to avoid feeling cramped in such a small cabin.
Rather than weaken the wall studs by notching them for a let-in ledger to support the loft floor joists, I attached the ledgers directly to the studs using 5” “Ledger-Lok” screws which are supposed to have the same shear strength as 1/2” lag bolts. Calculations showed 1/2” lags would provide acceptable shear strength. The joists were attached to the ledger with standard joist hangers. The stairwell opening uses double joists.
"LedgerLOK can be used to replace the 1⁄2" Lag Screws called for in Table 502.2.2.1 of the 2009 International Residential Code (IRC) or Table 507.2 of the 2012 IRC."
Of course that code is referring to decks and not second floors. The consensus seemed to be that using a let-in ledger or installing jack studs to rest the joists on without using a ledger was preferable, but I took the easy way out.
Note that the issue in my case isn't just the load bearing capability of the joists, but also their ability to act as rafter ties to keep the walls tied together. Also note that I'm not a code expert and most of my decisions are based on random scraps of info found online, although I did generally try to over-engineer vs. make do.
Hope that answers your question.
Thanks again!
Using the 2x8's I don't have any noticeable flex in the loft floor. It seems very solid. You should really consult a span table or calculator which will tell you exactly what distance you can cover with your joists. It varies somewhat with the type of wood you're using and the loads you'll be supporting.
My joists are 16" OC but if you really want to use 2x8 and are worried about the span, you could always go 12" OC which should be fine.
Here's a span calculator that will give you exact info: http://www.awc.org/codes-standards/calculators-so...