A 1940s attic fire compromised the integrity of the ceiling joists in my 1909 bungalow. I’ve torn down the lathe & plaster from several rooms and now need to replace the ceiling joists. I think the old ones were undersized. Can someone help me determine what size to put back in? They will be 16″ oc.
They sit on wall plates at each end and also act as rafter-ties. The roof pitch is 7/12 so they are angle cut where each end sits on the wall plate (I will attach them to the sides of each of the rafters). The attic space above them is not useable – will only have R50 in cellulose – no foot traffic other than an occasional crawl through to tend to something. I will hang 5/8″ drywall on the new joists. The two room spans are: 16 feet and 11.5 feet.
What size joists do I need? Thanks in advance for your help!
Edited 2/26/2004 3:29:53 PM ET by Robinson
Replies
3/4" rock? I need guys like that on my crew.
I'm assuming you have 2x4 existing. You probably want to go with 2x6 @ 16" O.C. for your new joists. Some houses have 2x4 spanning that far--I had a house like that and the attic crawl was pretty spongy. You probably do have some usable space under a 7/12 roof and in the future someone may store something up there.
Thanks for the reply. I'm sure I meant 5/8" drywall, right?!
I'm surprised with the 2x6 for a 16' span. I would have guessed beefier.
Edited 2/26/2004 3:43:32 PM ET by Robinson
I am sure that you know this, but if they are rafter ties, don't take them all down at once...
I learned that the hard way. On my first starter home, I opened up the attic to give more headroom in the room below. Took all the ties out. The rafters sprung about an inch. Used come-alongs bolted through the exterior brick walls to pull it back in (which didn't work - but at least it served to pre-stress the new ties I put in). Thanks for the reminder!
There's a SYP span chart for ceiling joists here:
http://www.southernpine.com/tables/9.htm
A friend of mine confused her valium with her birth control pills. She had 14 kids, but she doesn't really care.
That's a great resource. Thanks kindly!
When I angle-cut the joist ends (where the 7/12 roof rafters meet the wall plate), does that alter the span capability of the joists?
Boss Hog's table is for southern yellow pine. Where I work we ue fir 100% of the time and couldn't get SYP if we wanted to. What type of framing material will you use?
7/12 is a 30 degree cut and will mean that the top of the cut is off of the top plate, but I don't think that means you need to upsize.
I guess it's worth saying that you're in the engineering realm with this question and project, and advice you get here on line may be worth only what you paid for it. Never hurts to consult a structural engineer (well... it does hurt your wallet).
16' could easily be spanned by 2x4 or 2x6 .. if you drop struts from the rafters to break the span.. turning it into a site-built fink truss ( the basic "w")...
i'd then furr that ceiling sytem with 1x3 @ 16" oc nailed with 8d common.. this will give you a strong ceiling to support your R50 insulationMike Smith Rhode Island : Design / Build / Repair / Restore
16' could easily be spanned by 2x4 or 2x6 .. if you drop struts from the rafters to break the span.. turning it into a site-built fink truss ( the basic "w")..."
That changes the forces in the roof system. You then would have more compression in the rafer, and it might not be well enough connected at the outside wall to resist the added forces.
The connections would also ahve to be adequate to resist the forces put on them.
I know, maybe I'm being a bit anal. But I'm trying to amke a point. No sense putting in grossly overspanned members and trying to cobble something together like that, when you can just put in the correct members in the first place.I have the best lover in the worl .I can only hpe that she and DW don't run into each other.
Please replace your joists alternatly so the walls don't get pushed out.