Removal of roof truss cross-members, to make for easier attic storage access...[??]

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Background: I'm trying to modify my attic a little bit in order to store some things up there. Currently I'm busy fastening 3/4" plyboard over the ceiling rafters (so objects to be stored won't crash thru the drywall ceiling). However movement/activity up there is hampered by the fact that the roof is supported by factory produced 2x4 trusses, as these are composed of many cross members that switch back-and-forth at oblique angles between the upper and lower rafter sections of each truss. It would certainly make my attic storage efforts easier if some of these cross-members could somehow be removed out of the way (that is... in such a way as to not compromise the structural integrity of my roof, of course).
Therefore I'm requesting feedback on the following idea: 'Sistering' (i.e. reinforcing with) 2x6s to the topmost rafters, followed by removal of some of the supporting cross-members of said trusses. Not being a carpenter or structural engineer of any kind, I'm seeking informed comments/advice from others before going further with this.
Thanks.
Ken
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You need a Structural Engineer. TB
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It seems like you're being careful about this; which is good.
"Never trust a truss" is what many firefighters say. When any of the support members of the truss are compromised the strength of the entire truss is compromised.
Trying to build attic space in a web of truss supports isn't going to be easy. You'd probably have a safer project if you just put your shelving boards in the spaces on the trusses where possible. You don't want to start cutting on any truss. I believe there are issues with doing anything to stop the flexing of the bottom member of the truss (probably the ceiling joists for you). There needs to be some room for movement with temp and humidity fluctuations.
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Ken Moiarty wrote:

What you are suggesting would require re-engineering of each and every truss you are killing. All the parts of a truss work together so if you eliminate one, you have in essence eliminated them all.
--
Joseph Meehan

Dia duit
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Ken,
Work with a truss manufacturer and their truss engineers. They have truss design software that can run your project inside out and upside down. A normal engineer can do it, but the truss manufacturers have the software to work up calcs easily.
You might have to pay for this engineering, since you are not buying a truss set.
David A.
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David, If I gave a truss manufacturer a careful drawing of an existing truss, a manufacturer could tell me what loads it could support? TB
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snipped-for-privacy@bellsouth.net wrote:

A manufacturer will probably not even give you the time of day.
And I doubt they have a CAD system and/or expert that does finite element analysis on the stuff they do make.
Look. They churn out the same stuff day in and day out. They're not going to have expensive computer software (and an even more expensive engineer) on staff to basically twiddle his fingers. They don't change their designs often enough to warrant that sort of cost. Wood trus engineering was worked out decades ago. It's not rocket science.
For liability issues no-one is going to look at your drawings and give you a thumbs up or down.
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Some Guy ( snipped-for-privacy@Guy.com) said... [talking about truss manufacturers]

This really has no idea what he is talking about.
While truss manufacturers will do some business "churning out the same stuff" for subdivision builders, they also do a substantial amount of work for custom built homes that are one-off projects.
As one who had to source out a truss manufacturer for our custom built home with some rather unique roof components, they most certainly do have this sort of capability.
Now, whether they would bother with looking into an alteration issue as the original poster has, is a whole different question.
--
Calvin Henry-Cotnam
"Never ascribe to malice what can equally be explained by incompetence."
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Better think again

Wrong again
They don't

Wrong again

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That's what civil engineers are _for_.
--
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
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In a previous post Chris Lewis says...

Sure. You just have to find one willing to do so.
As I said before, this is not cost effective. The price a homeowner is willing to pay for services is not commensurate with the liability exposure.
Are you willing to pay more than $1000 so you can store some stuff in the attic. If you are, then I might consider doing the work.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
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Chris Lewis wrote:

The civil engineers that I use don't do structural.
--
Robert Allison
Rimshot, Inc.
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Maybe a terminology difference. Here, I believe there isn't a "structural engineer" designation per-se, it's a specialty in civil. My dad was a civil, and he did structures, tho, his main work was in other stuff.
--
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
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In a previous post Chris Lewis says...

The designation of "civil" vs "structural" engineer will vary by state. The requirements for becoming a "Structural" engineer also vary by state.
In Washington State, you must be a licensed PE (civil, mechanical, mining, etc.) before you are allowed to sit for the structural exam.
A summary of requirements goes like this:
1. 4 years college or appropriate work experience 2. Take and pass the Engineer-in-Training exam (8 hours) 3. 4 years work experience for a total of 8 years counting college 4. Take and pas the PE exam in an appropriate discipline (usually civil) 5. 2 more years work experience 6. Take and pass the NCEES Structural I and II exams (16 hours) 7. Take and pas the Western states seismic exam (8) hours)
So to be a licensed structural engineer in Washington State you must have the following minimum requirements: a. 10 years appropriate work experience b. take and pass 32 hours of examination
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
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In a previous post says...

Tom:
Most likely they won't take the time to deal with it. This is a common problem, but the truss manufacturers don't really want to deal with a homeowner on a single project where they are not going to sell anything. The possible profit to them is too small, so they won't consider it. This is especially true if the existing trusses are not ones that they built in the first place.
Most structural engineers (including me) don't really want to be bothered with this type of problem either. The liability is high for a very small return. I'd do it for a regular client, but only then. The cost of engineering services to analyze the truss and its connections, then design a fix is simply not worth the money in my view. You could rent a lot of storage space or buy and build a small storage shed for the same amount of money.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
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If you're a half decent carpenter and you throw enough 2x4's at it, you'll probably end up with something stronger than you started with.
If you use 1/4 bolts with fender washers and (or) #12 or #14 wood screws and pre-drill the holes (and not nail anything together) you'll have something stronger than the existing framework.
I bet your existing wood is full of splits because of the hack job that is usually done when cutting rafters and pounding over-sized nails in.
Do yourself a favor and make sure each and every rafter space is ventilated out to your soffit overhang. Don't stuff the insulation in there - let it breath.
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Some Guy wrote:

<snip>
Now I have seen some bad advice in this forum before but this ranks right up there with the worst of them.
Harry K
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Some Guy wrote:

I wouldn't bet on that. The odds of him messing up the structure are very high.

Stiffness attracts load. You stiffen up one section of the truss and another area, maybe on the opposite side of the house, will have its loads drastically affected. You're intentions are good, but you're not helping this guy.

The house is built with trusses. No one was cutting any rafters. And the trusses are, dollars to donuts, held together with the gangnail plates.
R
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Some Guy wrote:

I have to add my professional opinion that this is very bad advice. There is no way that I would give any advice on modifying trusses where the work is going to be done by someone I don't know, much less without even seeing the situation in person.
Trusses are built with enough strength to hold up what they are designed to carry and no more. Even storing stuff on them is considered to be forbidden by the engineers that I use. One of my PEs will not sign off on a job if there is decking down on the trusses because he knows that something is going to eventually be stored there and he will NOT let you leave it. For him to sign off on the job, decking must be removed except where it is necessary to access equipment.
The thought of modifying trusses is not a scary thought to me, because I have done a lot of work that involved modification and I have worked with a lot of engineers on what to do, and I have 30 years of experience in construction. The thought of advising someone else on doing it sends chills up and down my spine.
Like the time I went to look at a job where the garage trusses were failing and looked in the attic to see ENGINE BLOCKS stored up there! I got the heck out of that place as fast as I could.
--
Robert Allison
Rimshot, Inc.
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Oh, come on, it's easy. The proper way to modify a truss for load bearing is to run posts up between the existing trusses, put beams across just over the top, and build a deck on the new beams. No problem. You can ADD anything you want, you just can't take anything out, and nothing that you add is allowed to touch the existing system.
--Goedjn
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