Looking for examples of engineered truss repairs/capacity improvement alterations

[platinum_jello]

So I, like apparently many, ended up with a building with insufficient ratings on my trusses. When I told the builder I didn't want them to put a ceiling on, they took that as I didn't want to put any ceiling on. As a result, I ended up with what I generally refer to as a plain old barn truss. The BCDL rating is 4 PSF, and while arguments can be made that that can sustain a very lightweight ceiling, the options don't fall in line with my design intentions for the building (nothing crazy like storage or anything, just a sheetrock or plywood ceiling with some light capacity for overhead air lines, dust collection runs, fixtures etc)...

Boy this is getting wordy...

Anyway, I've read quite a lot of posts on this topic and have observed the very common recommendation is to enlist a structural engineer or the truss designer themselves to provide a certified reinforcement plan. My truss builder is unable to provide any assistance, and while I'm waiting for any of the dozen or so engineers I've reached out to to actually respond to my query, I thought I would post up and ask to see what kind of engineered solutions people have received/implemented. Now, I know there's a lot of backyard engineers who put their own gussets on and say that's just fine, and I'm interested in seeing those solutions as well, as long as they're called out as such, but I'm also quite interested to see what kind of solutions people have received from a paid consultancy.

All stories and pictures welcome, thanks!

 

[Rusted Nut]

Why won’t the truss designer help? Seems really odd, and unfortunate as they are really the only ones who can.

 

[loganb]

Pictures of what you have

 

[gsmith22]

adding load to the bottom chord does two things: 1) loads the bottom chord in bending and 2) adds load to the overall truss which will increase the axial loads in all members and their connections. you can increase the bending capacity of the bottom chords by adding a deeper sistering member adjacent to the bottom chord. That is the easy part. Upping the axial capcity in all members and connections requires you to know the current design loads and what the increase in loading does. Only your truss designer knows that or an engineer that you hire could quantify readily. There are a variety of things you can do to compression members like sistering them and adding additional lateral bracing to up their capcity but tension members will be your real hurdle because only additional area will help. And your bottom chord where you want to add the storage load is in tension. Don't think I could be any more specific than this which is why you need an engineer's help.

 

[Steve_P]

the problem with engineered trusses is that they don't want you to modify them in any way, or to add any load to them other than what was planned for. So, I'm not sure if you'll get any help from the company unless they need the business. I could make some recommendations on how to increase the moment of inertia, but I am not going to take the time to back them up with even a rudimentary calculation, so I'll defer

But if you look up "moment of inertia" for beams, you'll get some ideas.

 

[platinum_jello]

Why won’t the truss designer help? Seems really odd, and unfortunate as they are really the only ones who can.

Well, the place that built the trusses is a smaller shop that doesn't have an engineer on staff. They (like many) use design software from Alpine who makes the nail plates. Alpine lists engineering services on their website, so I called and called until I finally got a gentleman down in Florida to pick up. He explained that Alpine offers engineering services for truss builders like the one that made these (this is apparently a very common request), but in my conversation with the builder, I learned they don't pay for said services. So long story short... I'm SOL in that direction.

...where you want to add the storage load...

Just to be clear, I'm not looking to add storage loads, just a basic plywood ceiling and related support members along with the requisite insulation for Wisconsin. I point this out because I know a lot of people want to turn the attic into a storage loft, but I have no misconceptions about how undersized these trusses are for such a thing. I just need a few more PSF on the bottom chord and that space will be sealed up and hopefully never visited again.

I've had a lot of local folks say it'll be fine/not to worry about it, and frankly, they're probably right. I know there's safety margins built into these things, but I'd really rather have a properly spec'd repair. That's why I'm curious what kind of results people have had. Like I said, I've been led to believe that this is an incredibly common situation and I figured this would be a good place to see some examples/hear some stories.

In the meantime, I continue to wait for anyone to call me back, either from Alpine or the literal dozen engineers I've left messages with. Unfortunately I live in an area where there's no shortage of work, and getting folks in the building industry to respond is near impossible.

 

[platinum_jello]

Pictures of what you have

 

[gsmith22]

Well, the place that built the trusses is a smaller shop that doesn't have an engineer on staff. They (like many) use design software from Alpine who makes the nail plates. Alpine lists engineering services on their website, so I called and called until I finally got a gentleman down in Florida to pick up. He explained that Alpine offers engineering services for truss builders like the one that made these (this is apparently a very common request), but in my conversation with the builder, I learned they don't pay for said services. So long story short... I'm SOL in that direction.



Just to be clear, I'm not looking to add storage loads, just a basic plywood ceiling and related support members along with the requisite insulation for Wisconsin. I point this out because I know a lot of people want to turn the attic into a storage loft, but I have no misconceptions about how undersized these trusses are for such a thing. I just need a few more PSF on the bottom chord and that space will be sealed up and hopefully never visited again.

I've had a lot of local folks say it'll be fine/not to worry about it, and frankly, they're probably right. I know there's safety margins built into these things, but I'd really rather have a properly spec'd repair. That's why I'm curious what kind of results people have had. Like I said, I've been led to believe that this is an incredibly common situation and I figured this would be a good place to see some examples/hear some stories.

In the meantime, I continue to wait for anyone to call me back, either from Alpine or the literal dozen engineers I've left messages with. Unfortunately I live in an area where there's no shortage of work, and getting folks in the building industry to respond is near impossible.

none of these outfits hire engineers - its all software and they will get an engineer to stamp a drawing if need be for a building department. its all garbage in /garbage out with the program and data imput person too. if all of you understood what goes on in the wood truss design and fabricaiton industry you would steer far and wide and never put one on a garage (or any other structure) again. i look at alot of manufactured wood truss failures every year, especially when it snows which is the primary load they are supposed to resist. Don't get too caught up in the "there are saftey margins" aspect too because these things get designed to a nats *** of failure with as many shortcuts taken as possible and if the programer screwed up the input, look out. comforting I know. my house and garage are stickframed. read into that how you like.

plywood (or drywall) and insulation probably amounts to a couple of pounds per square foot on the bottom chords. you can do the math yourself => weight of plywood (lbs)/(4'x8') = ? psf. you have 4 psf built into your design. I suspect you are fine. Its when the attic gets open to storage possibilities is when you are going to have a problem.

 

[gsmith22]

the printout of the truss you posted has all of the forces used in the design (on the right hand side) and has the design loads on the left. 4psf bottom chord dead load (BCDL) so I think you are good to add a ceiling. not sure what the original worry was about.

Edit: looking at that diagram a little furthur. these trusses are 8' on center? so you would need some sort of purlins to support a ceiling spanning between the bottom chords. But I see that the top chord dead load (TCDL) is listed as 4psf too. So in essecence the diagram indicates you could have the same sort of weight hanging from the bottom chords that you have sitting on the top chords. you can do the math, but I suspect 2xpurlins at 16" o/c with 1/2" sheathing (or gypsum) would be under 4psf. No live load included though so no storage possibility in the attic space.

 

[platinum_jello]

my house and garage are stickframed. read into that how you like.

Yeah, stick frame was my original goal, but the realities of budget and life being what they are, here I am.

Using reference figures for what the plywood, 2x6 framing and insulation would add up to put me about 4.7 or 5.2 psf, I don't remember the exact figure. Either way, it was over four, and that's not accounting for any metal brackets, fasteners, lighting fixtures, electrical, etc. That's where my neighbors look at me sideways that I'm getting a little too detail-oriented on the whole thing, but to your point, if this stuff is engineered that tightly, I don't need My roof coming in.

 

[gsmith22]

Yeah, don't give me started. Stick frame was my original goal, but the realities of budget and life being what they are, here I am.

Using reference figures for what the plywood, 2x6 framing and insulation would add up to put me about 4.7 or 5.2 psf, I don't remember the exact figure. Either way, it was over four, and that's not accounting for any metal brackets, fasteners, lighting fixtures, electrical, etc. That's where my neighbors look at me sideways that I'm getting a little too detail-oriented on the whole thing, but to your point, if this stuff is engineered that tightly, I don't need My roof coming in.

Failures tend to happen because somthing was completely overlooked (space used as storage but no LL included in design); an extreme event occurs like a series of snow storms every few days exceeding the design snow by 100%; or because a combination of things that alone wouldn't produce a failure but all happen/go wrong/align at the same time.

Presumably your roof has 2x6 purlins at 16", 1/2" plywood sheathing, and then asphalt shingle roofing (adjust as necessary). purlins are probably 1.5psf, sheathing 1.5psf, and roofing might be 2 to 3psf by itself depending on how good a shingle is used (longer warrantied shingles are thicker/heavier). so that is 5 to 6psf at your top chord with a design for 4psf. I wouldn't be concearned about this. Do the same for the bottom chord without the shingles gives you 3psf. So 8 to 9psf total (typical roof+plywood ceiling) when design was 8psf total. I think you will be fine.

But you can see how the designed to nats *** of failure happens. I doubt there would have been any price premium to design for DL of 10psf at the top chord and 5psf at the bottom chord, given you wiggle room, and potentially give the trusses a slightly better saftey factor for that extreme event or concurence of non extreme events. All this because everyone is searching for the bare minimum of pricing forcing any and all "conservatism" out of the design. Don't fret, all the same problems exist in the butler style steel buildings too. Look at lots of those falling down as well

Edit: I should note why I wouldn't worry. You have a design with a top chord live load of 30psf. So 1psf here or there on the chords won't matter for the overall truss when it is dwarfed by that top chord live load. It seems like a conservative assumption too because Roof Live load is usually 20psf or less (reduced when roof is sloped for instance) and the snow load is shown as 23psf so again lot less than 30. Your ceiling seems like it will be less than 4psf so no local bending issue on the bottom chords either.

 

[Tbender78]

Is it too late to add more trusses? Instead of spacing them 96”. Space them at 48”. Just a thought, not an engineer but have been in a similar situation.

 

[Hank11]

Adding more trusses can work. They don’t have to be identical to what is there now, just designed to help hold up your ceiling, not the roof. Could likely slip them onto the top plate and roll them into place. Then strap the bottom of all trusses and attach ceiling.

 

[theoldwizard1]

Why won’t the truss designer help? Seems really odd, and unfortunate as they are really the only ones who can.

Not at all !

If OP does find and engineer to do the job, it will cost him and arm and a leg to get approved drawings. Not much good anyway, without a certified truss builder.

 

[manwithtools]

Adding more trusses can work. They don’t have to be identical to what is there now, just designed to help hold up your ceiling, not the roof. Could likely slip them onto the top plate and roll them into place. Then strap the bottom of all trusses and attach ceiling.

I kind of like that idea, I wonder if putting two I-joist's equally spaced in between each truss would be another route?

 

[BillK]

What spacing are the trusses at ?

 

[Bert_]

Instead of changing the trusses I would change the ceiling.

Tin with a deeper profile can span 8', support insulation, and probably stay under 4psf. Someone else would have to run numbers to be sure

 

[BillK]

I am not a construction engineer but unless my math is way off I come up with:
1/2" plywood or drywall at 1 1/2 lbs per sq ft
12" fiberglass insulation about 1/2 lb per sq ft
2x6x8 joists hung between the bottom chords at 2 ft centers about 1 lb per sq ft

Thats 3 lb per sq ft and should leave you plenty of leeway for lights, wiring and paint.

I think you are overthinking it.

 

[billconner]

I kind of like that idea, I wonder if putting two I-joist's equally spaced in between each truss would be another route?

Can TJIs span 36'? I had this written but thought I should find out and found they seem to top out around 32'. Maybe I didn't find the right products. I also looked at flat floor trusses, but also not 36'. And I though bar joists were too much.

 

[manwithtools]

@billconner You might be right, probably can't span more than 32' in a floor joist application with a LL rating. I imagine an engineer would have to get involoved with this use case. Could be it won't work at all. I was thinking out loud to some extent.

BTW, trusses are at 96" according to the drawing.

 

[Hank11]

I kind of like that idea, I wonder if putting two I-joist's equally spaced in between each truss would be another route?

I was thinking floor joist trusses. Probably lighter and easier to install. OP has a pretty long span and the new trusses will be pretty heavy, so he'll want the lightest thing available.

 

[billconner]

Some question if the top of wall headers will support these between trusses trusses.

 

[Zeke]

Some question if the top of wall headers will support these between trusses trusses.

Add a stud?

 

[Hank11]

Or studs and more top plate if needed.

Its only wood.

 

[loganb]

I am not a construction engineer but unless my math is way off I come up with:
1/2" plywood or drywall at 1 1/2 lbs per sq ft
12" fiberglass insulation about 1/2 lb per sq ft
2x6x8 joists hung between the bottom chords at 2 ft centers about 1 lb per sq ft

Thats 3 lb per sq ft and should leave you plenty of leeway for lights, wiring and paint.

I think you are overthinking it.

Swap the plywood or drywall for metal liner panel, save even more weight and get to skip the crappy job of painting a ceiling

 

[billconner]

Add a stud?

I thought it was post frame? I agree no problem if continuous footing and stud wall.

 

[Zeke]

I'm unclear. Re-read and don't see where he said exactly. No pics as ususal.

 

[billconner]

I guess the trusses being 8' on center made me think it's pist frame. Seems like a less common choice for stick frame, at least in my experience.