Supporting Roof Rafters

[c.snyder]

Hello everyone. Hopefully this isn't as serious as i think it is but we'll find out. For a little background, i purchased this garage three years ago and just this year i've been getting around to remodeling it. The front part is typical 2x4 frame on slab and the back addition i'm dealing with is a post frame style building. The concern i have is with the rafters themselves. When i initially inspected them earilier this spring, i discovered that the builder had used two 2x6 boards to make up the span for each rafter tie on the bottom. His flaw was that he tried to join the two together in the middle with a small 2x4 and only a couple nails. Obviously the 2x4 split easily from the tension pulling on each 2x6.

To fix this issue i purchased enough 2x6's to fill in every other rafter he skipped so that they are now 24" OC and also i used a short 2x6 in the middle with four 1/2" hex bolts joining them together, two in each side. Each rafter tie is connected to the rafter at the wall with a single 1/2" hex bolt. This obviously isn't an issue now and the bolts were probably overkill. Yeah there's a slight sag in the ridge from the small amount the walls did push out but looking at the wall from the outside you can't notice any outward lean. If anything i believe the walls were leaning slightly inward to begin with since they are nearly level now. Given this i didn't try to mess with the rafters i just wanted to arrest this thrust issue so it didn't go any further.

Now the issue im dealing with is the span of the rafters themselves. Per my calculation, #2 SPF 2x6 rafters installed to handle roughly 10 psf of dead load and 20 psf of snow load should not span more than about ten feet to ridge. These 2x6's span 14 1/2 feet. Obviously these need support and i can tell they are beginning to sag. I've researched purlins and knee walls but from what i can gather these need to be installed in such a way they bear on an interior bearing wall. I understand you can't bring your braces down on the rafter ties as this will just sag the tie. My question is, what options do i have here to brace the rafters? There are no interior walls to brace to and the only other support i have under the rafter ties is at the mid span of the room. This is a double 2x10 beam that runs perpendicular to the ties and will be supported at each end by a 6x6 post down to footing. I'd like to figure something out before winter hits and there is a significant snow load on the roof. I added some pictures but i can get more if needed.

 

[PWC Repair]

So, are you saying that's 28ft deep with only a 2x6 rafter? And what about roofing, are there shingles up there?

 

[fury9]

I think you'll be fine as is. If it bothers you, split the distance from the top plate to the header, build yourself a strong-back (L shape) out of 2x6 and support your rafters off of that.

 

[Denwood]

The simplest solution IMHO would be to add truss webbing to your existing framing...essentially a build in place truss. If you spec a full support ridge beam under your truss ties, and support to your slab at both ends, (to replace the two 2x10s) then you could also run bracing up from that beam to the mid point of each roof stringer.

 

[c.snyder]

So, are you saying that's 28ft deep with only a 2x6 rafter? And what about roofing, are there shingles up there?

Correct. Roof sheathing is 5/8 plywood with a single layer of shingles on top.

I think those are both good ideas. I can get beams of pretty much any length or size so that's not a problem if i replace the 2x10's. Denwood I do remember seeing something almost exactly like your idea where they placed a beam in the middle of the span and ran braces to the middle of each rafter. If i remember correctly they were made almost like an upside down ridge where the opposing braces pushed against each other on the beam.

I'm trying not to make this too complicated. My boss already says im worrying too much about it lol.

 

[plott hound]

The simplest solution IMHO would be to add truss webbing to your existing framing...essentially a build in place truss. If you spec a full support ridge beam under your truss ties, and support to your slab at both ends, (to replace the two 2x10s) then you could also run bracing up from that beam to the mid point of each roof stringer.

what he said^

 

[drivesitfar]

I didn't see what the size of your pole building is. if it's 28 feet one direction is it about the same the other direction so a 28 x 28 foot building? Can you take more pictures from below looking up at the beams that are holding the tresses you just repaired up?

from the picture i see it looks like you have a couple 2 bys holding up the entire load and maybe another board that i can't see all of. so what size are they?

for that much space I'd like to see at least a 4 by and a post in the middle or a steel I beam to span that far which you could also use as a lift with a chain hoist.

i think you have good thinking going on to worry a bit especially if you end up with a few feet of snow on your roof. pictures from down below showing beams and supports would help those on the forum that are engineers instead of us that are retired Realtors or handy homeowners trying to help you.

 

[yfz 450]

Few options I would consider.
1. You could sister you existing rafters with another 2x6 rafter
2. Then you could put a girder under the ridge to push it up or make a stronger girder where the 2 2x10s are now and post up the the ridge to help the sag
3. Once you lift the ridge add more collar ties at about the mid point span of the rafters

If you could live with the sag I would just try and jack the ridge some and sister the rafters

 

[c.snyder]

Sorry it took me so long to get back with you guys. I've included pictures from below showing the support beam in the middle and the other end of the attic space. The back addition was built against what used to be the rear exterior wall of the original garage. The rafters were built over top of the roof up level to the original front roof ridge. The floor area measures 28'x21'. (Double 2x beam is thus 21' long). I was also mistaken on the size of that beam they are both 2"x7". Evidently someone cut a 2x8 down to 7 inches or something along those lines.

This was the original rafter tie connector. Obviously nowhere near strong enough.

The 2x7 beams were cut at an angle on the end here where they rest and i'm not that comfortable with it. This is where i wanted to install a 6x6 post underneath to the ground. On the south end they rest on 2x4s which travel down to 4x6 posts. Whether this is okay i'm not sure. I can put a 4x6 or 6x6 here as well if needed.

I appreciate all of the suggestions so far. I don't think this will be too hard to get figured out. I've seen buildings far worse off.

 

[Denwood]

If you do decide to go with the 2x6 "sister" option then the beam you have beneath your truss ties could be removed (along with the truss ties) and replaced up top underneath the existing ridge beam as you have lots of room up there. This is what I did to remove 16ft of truss ties and create 10ft of headroom for the MaxJax hoist. The vault really increases the impression of space in my rather small 16x24 shop.

Before:

After:

The local truss manufacturer spec'd the versa-lam beams to "convert" my stick framed roof to a load bearing ridge beam design. This only took a few hours to do, with added time for bracing, adding support down to the slab etc. My span though is only 16ft, as I left 4ft at both ends for attic storage.

That split 2x4 on your truss tie is not a glowing testament to the original builder..wow. Your fix, on the other hand, looks great. If you beef up the beam and bit, run support down to your slab, and then run a support upwards to the middle of each roof stringer, likely all done. Not sure what you'd call it but perhaps "stick frame with inverse ridge beam integrating supplemental truss web thingy-do super duper roof system"

 

[yfz 450]

I would deff. Post something under were the double "2x7" lands. It is posible the boards were ripped down to that size but a 2x8 actual size is 1-1/2x7-1/4 to 7-1/2 so they could have shrunk over time depending how dry your area is. Those existing collar ties were doing nothing they were just put in as ceiling beams probably for storage. As I suggested before is probably the best options

 

[c.snyder]

Dennis that beam you installed is pretty sweet. It definitely does look a lot bigger in there. I'll keep this in mind if i do go that route. My span wouldn't be much bigger, right around 20 feet. I believe our local lumber yard can order these. I think they carry LP solidstart lvl.

Messing around out there earilier I was thinking about your idea regarding truss webbing. Would it be possible to install the web members in a fink design? Something similar to what i drew in here. The red denotes compression and green tension if i remember correctly.

I could also go the route you mentioned last running a brace from the 2x beam up to the mid point of each rafter although the brace would be installed at around 25-30 degrees from horizontal. I've read that they shouldn't be less than 45 degrees. In order to get to 45 deg i would have to bring one end of the brace closer to the ridge and rest the bottom on a ceiling joist about 20 inches from the 2x beam. The brace wouldn't be in the middle of the rafter but it would support it at the ten foot span distance. (from wall top plate).

It looks like i have all kinds of ideas to throw around but hey that's not a problem. You guys have been a big help. I should have tackled this before we had our awful winter last year when there was almost 20 inches of snow up there. It held okay then but i'll feel better getting it ready for long term.

 

[Denwood]

The Fink mock up you drew was exactly one of the ideas I was proposing. If you chat with a truss manufacturer locally, and give them your dimensions, they could likely do a drawing for you in minutes. With that solution, your beam underneath would not be required.

If you do support from the beam, going up with webs, they would each counter each other at your beam, and if you brace correctly, will keep the beam straight too. They would not hit the mid point of your roof stringers at 45, but as you calculated earlier, your max is 10 ft unsupported.

My preference doing a job like this is to consult with a structural engineer and fire these ideas by them. Your beam underneath gives you options (if beefed up) which takes your truss potentially from a full span, to half span if you web it correctly. Either way, I think you're wise to add in some support, particularly as weather patterns will tend to the more "energetic" in coming years.

 

[PWC Repair]

I think Denwood knows what he's talking about as he was in the same situation as you. If you don't need the overhead room I would keep the beam and web the trusses. Right now you have a lot of force trying to push your walls outward. I saw a lot of buildings like that come down this past winter around here. I'd really like to see that force directed straight down onto the walls instead.

 

[Denwood]

C, I was my own "general" contractor on our 9500 sq ft Cinevate build (ultra high efficiency building) and one thing I learned on that job is that in-place truss modifications can be done safely..something truss manufacturers may not have great experience with.

We had an architect as well as structural, mechanical, electrical engineers and stamped drawings etc on the job.

Truss mod 1 involved 60ft span trusses (8ft ceiling)that we recut to provide 11 ft vaults over 30 ft of each span. The vaulted section is reframed and clad both sides in plywood bonded to the frame.

Truss mod 2 was an area where we removed trusses entirely to create 3 clerestory windows (16ft up) for passive cooling. Existing trusses were reinforced similar to the studio vault.

So after the garage job I'm feeling a bit like an armchair truss guy. Ha. We do finite analysis on all of our products..but quite frankly the truss guys can do it in a fraction of the time as they have specific software at their finger tips.