Expert: Bruce E. Johnson - 8/18/2009

Question
Hi:

I have a 20'x20' detached wood-frame & stucco garage. The house was built in 1956 and has so far withstood two 6.6+ magnitude earthquakes (we're in Los Angeles if you haven't guessed it).  I would like to finish the inside of the garage, but make sure nothing falls down during the next big one.  Main use of the garage is for tinkering on stuff and working on cars – we will not be living in it – but since it gets quite warm here, I am planning on insulating it.

My question is about hanging drywall from the ceiling and adding vertical supports. My neighbor had his garage done and I went up into his attic to see what they did, but didn't have a chance to measure things.  They had a lot of new vertical supports that I originally (incorrectly) called purlins, but I couldn't tell if they had beefed up the joists.  In my garage, besides the walls, from lowest to highest point in the roof framing, there are (2) 1x6's in an X pattern that tie in near the corners of each wall..Then there are (4) 20' long 2x4's running widthwise approx 40" o.c.  Next up, there are (3) 16' long 2x4's running lengthwise (perpindicular and above) approx 50" o.c. that have about a 6' overlap brace over two of the lower perindicular members.  There are two 1x6 vertical supports tied into the 2 center-most 20' 2x4's running widthwise and they tie into the rafters near the peak of the roof.  Rafters are 2x6 16" o.c. Roofing was redone recently and includes plywood sheathing with comp shingles.  There are also a couple of other random 2x4's toenailed in between the lowest 2x4 members here and there to support the all-important Xmas and camping stuff storage.

The (4) 2x4's running widthwise will probably be what we flush the drywall against.  Should I put additional 2x4 joists between them and how far apart should they be?  (24” oc?)  And what do you suggest that I do about lateral supports to the roof?  We would like to continue to use the attic area for storage, so I was thinking about putting some 5/8” plywood sheets up there (perhaps 1-2 4x8's) for an attic subfloor.  I will be putting insulation in the ceiling and there is a Pro 3 attic fan with active louvers to blow out the hot air.

Also, what are your thoughts on those drop-down ladders?  That would add a lot more weight and require more framing, but might be worth it since it seems like the ladder is always buried behind some other unfinished project that's taking up the middle of the garage.  Plus, the wife can go up there on her own without me, so that might be worth all the extra work.  Thanks for your input!

Brian

Answer
Hi Brian, I have to say, that is the wierdest sounding roof structure I have ever heard of.  I don't get the 1x6 X bracing unless it is being used to laterally support the structure from swaying.  And 40" centers for your ceiling joists?  It just doesn't make sense.  Can you take a photo of it and send it to me?  For some reason I just can't picture what you are describing. A normal roof structure would consist of 2x4 ceiling joists located beneath or alongside each rafter.  At mid spans of the rafters you would have a vertical strut of 2x4 connecting the  ceiling joist to the rafter. It is hard to compare this standard structure to yours. I need a photo if you can provide one. As far as an attic space for storage and a drop down ladder from what you describe I wouldn't recommend putting any kind of weight up there at this point. Sincerely bruce e johnson