Strange Wood Framing | Concerns

[bookowski]

See attached photo. I was looking at this building for something unrelated to the framing shown.

The photo is of roof framing: 3x10s @ 16" o.c., spans around about 15ft. from walls to center steel beams. To pitch the roof the original builder built a series of 2x4 stilts off the framing which in turn support flat 2x4 (@16 o.c.) to support the pitched sheathing. These 2x4 posts vary from 0" to about 12" in height. The building is a two story brick masonry residential, late 1800s but the framing shown is obviously much newer (1990s).

My work was not related to this framing so I am wondering what kind, if any, of upgrades to the framing I should recommend - or should I leave well enough alone? The joists are obviously not braced by the sheathing. There also is an issue of the diaphragm not being connected to anything. Since this is an existing condition I don't want to go overboard and recommend major fixes if they are avoidable. I was thinking of solid blocking between the joists, providing post installed ties from masonry to the joists, and was also considering some diagonal struts up from the blocking to provide a lateral path for the diaphragm. The roof/roofing is not being worked on so ideally all work is from below and does not penetrate the roof. Any thoughts/recommendations?

 

[BAretired]

Are the 2x4 posts bearing on top of the joists or are they nailed to the far side of the joists?

BA

 

[bookowski]

Bearing on top - I haven't been up there yet to see if they are toenailed or connected in any way, I am guessing that they are as the framing is fairly neat/clean even though it's strange.

 

[msquared48]

Looks like a way to get Mechasnical and electrical laterally across the wood purlins without having to drill holes to me. Lots of carpentry work, but it works...

Mike McCann
MMC Engineering

 

[BAretired]

Might be a good idea to recommend adding 2x4 @ 4' continuous on top of the joists and normal to them, with two nails to each post and possibly a framing anchor to each joist if the toenail connection is deemed inadequate. Looks like the joists are Douglas Fir so nailing to them could be difficult.

BA

 

[Ron]

Looks like the entire structure was built from scrap. I would X-brace from the top of the stub 2x4's to the joists.

 

[MikeHalloran]

What's most unusual is that the joists are individually replaceable (given temporary holes in the exterior wall at their ends, or maybe room to swing them aside enough so they can fall through the diagonal of a rectangular opening).

Okay, replacing them individually would be kind of a pain, but maybe installing them that way in the first place was less so.
E.g., maybe the joists and stilts were installed to replace some prior support system, maybe a truss, without severely disturbing the purlins or the actual roof.

The stilts are short enough to be sort of self-bracing if they are cut square, and they could be used to adjust the local roof pitch by cutting them a hair oversize and hammering them into place.

In short, I think that we are looking at a specific solution to a specific problem, but we don't know what the problem was. There must be an interesting story there.

Before sending up a flare, I'd chat up the older or former tenants of the building, as informally as possible of course, and check with the AHJ for stored permits and plans. Okay, that last is a long shot, but somebody somewhere must get permits, once in a while, right?


Mike Halloran
Pembroke Pines, FL, USA

 

[ztengguy]

Unless you see something that is structurally inadequate, and it wont keep you up at night, I would let sleeping dogs lie.

 

[ACtrafficengr]

As well as providing pitch, it is probably someone's idea to make up for the fact that the wood joists aren't as deep as the steel beams.

Are you in a high wind area? Would uplift be a concern?

 

[BobNeng]

Solid block the joists max 7' o.c. Two rows would be nice, especially since the joists aren't blocked at the beam...just sittin' there. How these guys lay their subfloor without rolling joists and breaking their necks is beyond me sometimes.

 

[SLTA]

Was it done to raise the original height of the roof? Look at the wall and see if you can tell. What a mess. But, as I always remind folks - it must be working somehow, or it wouldn't be there anymore.

 

[Archie264]

It seems like I've seen that very scenario somewhere, I just can't remember where. That's not helpful, of course, other than to say that it might not be as rare a situation as you think. That doesn't make it right, but I've long since quit being surprised at some of the things I've seen on residential projects. I've come to believe there are houses out there being held together by a combination of the wallpaper and electrical wiring.

I've learned to refrain from telling a residential builder, "that won't work", as he will have likely seen such a configuration "work" many times in the past and I then loose credibility with him. (Of course, for him "work" means that it hold together long enough to get the structure built, not hold up under full design load.) In any case, now I try to remember to say things like, "well, in order to fully brace it..."

 

[bookowski]

Low wind and low seismic area. Still, the diaphragm is sitting on the 2x4 posts but there is no perimeter connection to the walls so it's not much use - and the parallel joists aren't anchored to the walls either. The whole place is a mess.

I am thinking that I'll anchor the parallel joists to the wall, specify solid blocking @6ft o.c., and provide some diag 2x4 struts up from the new blocking to the 2x4 posts and purlins and call it day.

 

[Compositepro]

To me it looks like this may be a fix for a sagging shallow pitch roof that was causing ponding, without having to replace the old roof.

 

[mpocius]

Lot of good information posted in here already. Since you effectively have no load path from the diaphragm to the structure below, I would suggest adding cont. 2x4 blocking along the top and bottom of the stilts at every other or every 3rd joist. A few properly located nails from the blocking into the stilts top and bottom would help them to act as a frame like a shear panel and transfer diaphragm forces into the structure.

 

[chicopee]

The attached picture invoke a style found in Rube Goldberg contraptions. Also, I have never like the idea of notching wood joists as I have seen to many situations where joists where splitting lengthwise, also it is a waste of material.

 

[BAretired]

What attached picture?

BA

 

[chicopee]

It is in the JPG attachment.

 

[BAretired]

What attachment?

BA

 

[hokie66]

I imagine he means the original attachment by bookowski, but that thought is only after scratching my head.