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-   -   Ceiling span 3 foot on center (http://www.houserepairtalk.com/f109/ceiling-span-3-foot-center-614/)

Porter418 04-07-2006 06:54 AM

Ceiling span 3 foot on center
 
Renovating an old saltbox style house (1850's). Found the second story ceiling was bowed. The plaster had been removed and covered with sheetrock at some point. A crawl in the attic revieled 4X4 joists attached to the rafters, which are 3 feet on center, about 6.5 feet up the slope, with a span of 15 feet (no wonder they bounced) They were then filled with blown in insulation. Removed all the insulation and pulled down the sheetrock and lath.

Two questions:

1) I would like to move the ceiling joists up about six inches for more headroom and replace the 4x4's with 2x8s.
Is this feasable as they are not attached to anything structural ?


2) Can I run furring strip perpindicular every 12 inches on center across the joists (remember they are 3 foot on center) and hang new 5/8ths sheetrock without it bowing?

Square Eye 04-07-2006 09:00 AM

I would remove and replace them one at a time. They may be holding more than they appear. Then I'd run at least one vertical member from the peak down to the ceiling joist. A 2x4 would be strong enough.

Even better would be two. Divide the length of the joist by 3 and mark it. run one framing member to each mark from the peak. This will help tie the thing together without losing the triangulation that makes a roof strong.

I'd then use 2x4s for laths to hang the drywall on, 16" on center.

All of this will get heavy, make sure that the joists are secure. A couple of bolts in the ends would be a worthy investment

Porter418 04-08-2006 04:19 AM

Thanks for your quick reply. Kind of confirms what I suspected.

manhattan42 04-08-2006 08:43 AM

Structrual Engineer
 
This is not something you should try without getting the advice of a structural engineer and a stamped design.

What you propose can significantly weaken the roof system and will affect the structural integrity of the entire second floor and perhaps the entire house if not done properly.

Raising cross laterals (the ceiling joists) above top bearing plates reduces the bearing and spanning capacity or the rafters and makes the roof system more unstable.

Also, depending on the saltbox design, raising the cross laterals can increase the span of the 'long' rafters of the saltbox beyond their ability to bear wind and snow loads.

This is not something to take lightly and not something a DIYer should tackle without professional oversight.

Square Eye 04-08-2006 09:39 AM

Oh be serious.

Read the original post. The house was built in 1850s, the ceiling joists are attached to the rafters like collar ties. He's only raising them 6 inches and he's going to a dimension of lumber that will dramatically increase strength of the joists AND give him more surface area to attach the ceiling joists! Raising 6 inches will not reduce the strength of the long rafters enough to affect the snow loads in this application. An engineer would recommend so much more than is necessary (to cover his tail) that this project would become more than just the ceiling. An engineer would have him tearing out walls and installing brackets and gussets everywhere. Possibly removing his roof and replacing it all with new rafters and sheet decking to prevent racking.

I realize that homeowners can destroy the structural integrity of their home quickly and innocently. BUT, this is not one of those cases. Removing the floor joists from the top plates of the wall below is a big old double dog NO-NO, but that's not what he's talking about here. I'll bet that the current 4x4 ceiling joists are barely hanging, toe-nailed into the rafters, OR, nailed from the rafter side. If he uses bolts to attach the new 2x8s, once again he is far the better.

This is not a major structural engineering problem. Pull the old joists one at a time, replace it, then move on to the next one.

Tom in KY, not that big of a deal.

Porter418 04-08-2006 10:22 AM

Correct, the joists are basically collar ties/rafter ties and they are nailed to the SIDES of the rafters (w/ what looks like a few 10 penny nails) at least four feet up from the kneewall and have no support from the rafters above. I could pull them down by hand at this point. I'd install the new 2x8s a few inches above the existing joists before removing the old ones. Keep in mind this has held plaster and lath for who knows how long AND a layer of sheetrock as well as six inches of blown in insulation.

If these were attached to the sillplate I wouldn't even be considering this.

Porter418 04-08-2006 10:24 AM

Oh yeah. And calling these timbers 4X4's is being generous. This stuff had to be the culls left around. At some points there more like 3.5 X 2's, some still have the bark attached in spots.

inspectorD 04-08-2006 02:44 PM

Opinions , opinions
 
I have to agree with Square Eye on this one. You sound like you have an idea about what you are doing.
One thing you can do that will help a little is to install another set of 2x4's above the ones you are putting in . It's a cheap insurance to help from spreading.
I'm guessing this is a post and beam home ?
In that case it would not matter to much.
I can understand the other guy getting the engineer but not with something such as this. A competent person can do the updates and not harm the building.
I have seen things that I could not understand What was holding them up....

Post us some pictures of what your doing..
InspectorD

Porter418 04-09-2006 05:54 AM

Thanks all. Yes this is a post and beam home. And Inspector I know hust what your talking about (regarding damage done by other people). On the first story I've torn out the interior walls. There are 12 x 16 beams spanning the structure every four feet (no other floor joists just pine plank layed on top of the beams for the second story floor). They are 20 feet long and are moritsed into the second story sills. At one point they must have had a fire which destroyed one of the support posts (also a 12 X 16 by looking at whats left hanging) so they substituted a single 2x4 as a support. How everything stayed up is beyond me:confused: . I have not replaced it yet (just started interior demolition on this house about two weeks ago). I'm going to support both sides of the missing column with two 4x4s prior to attempting any replacement.

This house has had nothing (and I mean nothing) done to it since the 50's. We bought it only because its across the street from our home and we picked it up cheap. Oh, and I misspoke whan calling this a saltbox. Further investigation into the structure tells me this was probably an eyebrow colonial and had a later addition of two first story rooms added on. The rafters appear to me mortised into the sill for the second story and the first story additions rafters are attached to the outside of that sill so there are no "long rafters".

I've completely remodeled our house which was built in the 1790's and expanded in 1820. Unfortunately it suffered from some "renovations" prior to my getting hold of it. The outside was original but the inside was "circa 1980 condo". Way out of touch with with it's colonial heritage.

Square Eye 04-09-2006 07:48 AM

Sounds like an education within itself. Finish those two houses and you may be a pro. Heh-heh. Some of the best learning tools are demolition experience and repair. None of us know as well as you do what you have.

Carry on Porter!


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