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Roof Truss Failures
August 3, 2009
11:23 am
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rickastoria
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The above photo can be reinserted rather simple with light tap with wood and hammer.

That way, the plate would be back in place as it was in the factory. They use a hydraulic press for uniform positive force and for speed.

August 3, 2009
11:14 am
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rickastoria
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Ok, JD. What do you suggest as a fix? Replace the trusses and rebuild the whole roof?

August 3, 2009
10:14 am
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jdrobysh
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George - What? No smiley face? 😀

August 3, 2009
10:07 am
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george roberts
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John Drobysh ---

I agree that an engineered solution is necessary.

August 3, 2009
9:17 am
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jdrobysh
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Rick -

Please stop. Most of the time, you provide over-designed advice to homeowners and I''m OK with that. A 4x14 Girder instead of a double 2x12 is pretty hramless, albeit more expensive.

But now you are giving dangerous advice about how to fix an engineered wood product that you clearly do not understand. Your suggestion in this case will not be harmless - it is potentially devastating.

There are ways to address this type of failure, but a hammer and wood block is not one of them.

#*^@ SPELLING!

August 3, 2009
8:38 am
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rickastoria
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Ok. You say it can''t be hammered back evenly so all the teeth has equal insertion depth. The hydraulic press that they use is like using a vice.

The pressure is to get the "teeth" inserted to a certain penetration depth which is full penetration depth. There is no special engineered pressure plan. There is always some conservative plan. You can not guarantee every truss will have plates equally inserted over life of truss. You have various wiggles room. Hammering it flush and tight or using a VICE clamp will do the same. Remember, you are dealing with wood that no single piece of wood is absolutely the same.

The factory used a hydraulic clamp to speed the job and makes sure that it was evenly done. It can be done with a hammer with skilled use of a hammer and if you use a piece of wood to hammer onto between the hammer and the plate and you hit dead center on the wood (and plate of course) you can get the plates inserted evenly.

The conserved pressure in the end is the same. Pressure is what drives the teeth into the wood. What is important is the teeth of the plate and all of them are fully inserted (not over inserted).

If you don''t hammer only on one side or corner - you be fine. The plate gets loose from the day it goes out of the factory at varying degree, every windstorm, earthquake and varying loads at varying points. The design can not be contingent on the original factory pressure insertion but on teeth penetration like any nail or staple and the bonding strength of the wood and the properties of the metal plates and its teeths.

How much shear can the teeth resist.

It is better to reinsert the plates carefully back tight and can be done with skilled use of a hammer and a wood block. The wood block is to distribute the concentrated point of force of a hammer over the plate surface. The plates aren''t always installed on both sides. Once you got the plates tight then it will be acting as it suppose to.

The bad thing is to do nothing and letting the plates fall off. JD: If you want me to prove to you that it can be done, bring me two pieces of 2x4 #1 or SS grade (what is the selected pieces used for trusses) - have it cut so two pieces will abut so the pieces join at 45 degree angle making a "V" and get one of those plates. Get a 2x6 that is 5.5" long. (5.5 x 5.5 x 1.5") Then I''ll hammer the plate back in that was partially inserted (the effect of what a plate that is popping loose). Also bring a little bit of a good bonding glue and couple Vice clamps.

August 3, 2009
5:37 am
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jdrobysh
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Rick -

Go back to the books, FAST! You CANNOT hammer the plates back in. That type of advice is what pisses off the DPRs on the board. Those plates are pressed simultaneously from both sides with uniform high pressure at the Truss manufacturing plant. There is no easy fix.

Many of these conditions are due to mishandling the trusses in shipment; at time of delivery; or during the erecting of the building. Some cases probably due to bracing issues.

I know contractors that have worked with these things as long as conarb, George and some of the others here. Many STILL don''t understand them and attempt the type of ''fix'' that Rick has suggested. Disaster waiting to happen.

August 3, 2009
12:33 am
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rickastoria
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hammer? Tap it. Maybe pour in some bonding epoxy and hammer the plate back tight with a bonding epoxy in between?

In your last part... (besides UB) the Tyvek deal... make the exterior wall frame with PT or "gree" alternative treated lumber (that is synthetic oil treating - similar to creosote). Then interior wood being standard wood. That should resolve much of the rotting issue.90 lbs felt between Tyvek and PT, I guess.

Tyvek gets a lot of flak these days. 😀

As for maintenance... that can be fun.

All these little "teeth" in these plates just needs to be reinserted back into the wood tightly.

BTW: That positive placement gun is just a pneumatic nail gun (or just nail gun). As for 30 year old wood... you are more likely dealing with a piece of ______ wood to begin with not douglas fir SS grade. Not old-growth either.

August 2, 2009
8:57 pm
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constructionarbitrator
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I still don''t know how you are going top maintain gang-nail plates, when I was called in on the sagging roofs I went into the attics with a light and saw the popping plates, my first attempted fix was to bring my [URL=http://www.toolbarn.com/product/pneutools/RN-250/]positive placement gun[/URL] into the attic, clamp the struts straight to the chords and shoot through the plates. It didn''t work, in many cases splitting the 30 year-old wood badly. That experience makes me wonder about our new green building code and reusing lumber, but that''s another subject for another day.

If I can''t do it with all my men and equipment how do you expect a homeowner to do it? Bad enough that they have to pull their windows out every few years now and re-caulk them to keep the house from rotting out. I''ve often wondered why we have such thorough codes regarding structural safety, then allow temporary products to waterproof the building allowing all that fine structural work to rot out, we have inspectors counting and measuring shear wall nailing then let them put Tyvek over it so it rots out in a couple of years.

Stop Uncle Bob, Sewercide prevention line for building inspectors: 708-799-2300

August 2, 2009
5:37 pm
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rickastoria
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If you don''t know - how do deal with it?

Same about maintenance. If you don''t know anything about what needs maintenance, how often it needs to be done and about the need to inspect for maintenance and even the responsibility of performing routine maintenance and even the whole idea and concept never come to thought - how can you expect it ever to be done. In the 1800s it was part of basic "chores" - housekeeping. It was a regular thing just as it is to mow the lawn, eat food and drink and other basic routines in life.

Too many people just aren''t ready to live by the time they are 18.

August 2, 2009
5:32 pm
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rickastoria
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lol. Maintenance is part of owner''s responsibility to what they own. If you want your house to last like your car or anything else - you maintain it. Does it mean annual inspection or work. Not everything. But a prudent home owner makes sure its done. Whether they do it themselves or have a professional. Then we need to create better professionals.

Certain things needs inspections more then others and under certain situations such as after earthquakes and hurricanes - it is prudent to inspect or have the home inspected and not necassarily code inspected but inspect for needed repairs. More work means a person or business doesn''t need to charge as much. They can lower prices some because they can expect 25-50% more business.

Too many people don''t even know if when or even about inspecting or having the home inspected or maintenance done. They are totally oblivious and for the past couple generations, people ignored these things being talked about in school because they were too preoccupied looking at the opposite gendered persons in school or day dreaming.

Like so many people don''t know what to do in an emergency.

Especially if they aren''t use to regular earthquakes for example. Oregon coast will be a big disaster zone during the next big quake and tsunami because people will be ignoring emergency procedure and not know what to do when it really happens.

August 2, 2009
5:15 pm
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rosso
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Sometimes when I read this stuff; I just want to put my head in a manhole and commit sewercide.

Uncle Bob

August 2, 2009
5:11 pm
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rickastoria
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Have a contractor do it for you or a younger fellow do it.

A manual can provide a point to have a professional maintenance "handyman" do the job instead of yourself if you don''t want to break a leg.

Having it done does not absolutely mean that you have to do it yourself.

We just have to charge less money by having more continuous work. Contractors can charge less for work because they can stay busy. Making a years income to stay in business. Many charge more per hour because of the amount of down-time so in the end of the year, they are making a certain amount of money. Everybody wants their $100,000 a year you know. 🙂

It doesn''t all have to be annual.

Remember, in the 1800s, maintenance was a way of life and often you send a kid or younger gentlemen up there and get the work done. People worked harder, longer and faster and did alot more fancier stuff. We had craftsmen as a common thing not a specialty.

August 2, 2009
10:32 am
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constructionarbitrator
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I don''t understand the homeowner maintenance issue, what''s an owner supposed to do, periodically climb into his attic and see if his gang-nail plates are pulling out? If so what''s he suppose to do about it? Before I took those failing truss roofs apart I tried bringing a [URL=http://www.toolbarn.com/product/pneutools/RN-250/]positive placement gun[/URL] into an attic and shooting through the plates, all it did was split the 30 year-old wood making things worse. What about us septuagenarians, octogenarians, nonagenarians, and even centenarians, we own homes too? Do you really want us climbing around in attics checking our gang-nail plates?

This is as bad as windows installed with caulking as waterproofing, you should have seen the faces sitting around the conference table that day when a window company vice president testified that it was a homeowner''s responsibility to remove and re-caulk his windows "periodically".

Maybe we should all block out a weekend to climb into our attics and check and replace our roof trusses, and then remove re-caulk and replace our windows?

I repeat, I checked homes I built in the 50s with glued plywood gussets and there are no problems like twisting chords and struts, and the glued gussets are not coming off.

August 2, 2009
6:00 am
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drp
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You aren''t going to have access to many trusses or all the connections of any truss... floor, scissor, heeljoints.

The Elmhurst document is not specifying a connection it is calling for a cover, what is the purpose of the cover? fire, withdrawal? Is there documentation of its purpose and the cover''s suitability for whatever that purpose is? Has their "solution" been tested in any way or is the BO using "common sense" here? "Glue" is a mighty loose term, correctly glue comes from hooves, hides, blood, milk and the like. Also don''t forget that "truss" is a broad catagory, I drive across a steel truss bridge daily, a covered bridge is a truss. I''ve installed trusses made from oak 8x12''s with wood pegs connecting them and glulams with plates and bolts, these are but one form of truss.

Were Conarb''s trusses designed for the correct dead load? Were his site built trusses designed? Are the design assumptions the same, was the resistance to the applied loads handled in the same way?

Required nail penetration is based on diameter to develop full lateral load resistance or penetration for withdrawal. These are small diameter "teeth" so would not require penetrations that use the same common sense logic we might be used to. I believe metal plate connected wood trusses have proprietary testing for their connections through an ESR. FPL has a paper on withdrawal due to moisture cycling. Reaction wood does move more than "normal" wood, don''t know if that is part of the equation. Density of the wood plays a large role in fasteners as well. The FPL tested red maple trusses several years ago. I talked to one of their technicians at a conference who tested softwood and hardwood trusses to failure. Where softwood trusses failed by the plate pulling out of the wood, hardwood trusses failed by the metal plate itself tearing.

Not an attemt at answers, just more questions.

August 1, 2009
11:45 pm
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rickastoria
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Chuckle...Peach, I agree. The design, calculation and specification for the building is the responsibility of the designer of responsible charge for preparing the documents and not just the project. There is Project Designer of Responsible Charge and also a Document Designer of Responsible Charge - (the latter being consultants like Engineers, ect.) This has important meaning and a consultant holds responsibility for their drawings - especially that prepared by an engineer.

Sometimes, it can be the same person.

Now, the number of braces depends on many factors. Where is the shop drawing on this?

I''m not 100% sure but the penetration depth into the wood doesn''t seem a whole lot. It is like it is no better then using perferated metal plate and staples. Nails usually penetrate the wood deeper. Usually 1/2" to 1" (depending on member size). This looks like maybe - 1/4" max penetration. I would want to see 1/2" an plate fully fastened to the point that the flat part of the plate is in contact with the wood. Full surface contact.

I''m still use to standard metal plates with using standard nails. Otherwise - wood plate.

Trusses are good systems to use when properly design, assembled, installed and maintained. The problem that we have in this day and age is that houses often has many owners. First owner may have a manual guide prepared. Existing houses are like used cars. You might not have all the manuals that goes with the car.

A solution is that we could require at the city among submitted documents to have a "Suggested proper Maintenance Manual for the house - especially maintenance of trusses and other specialized structural and infrastructural systems" as well as the original owner. A subsequent owner who may bought the house 10-20 years from now could go to the city/county office and obtain a copy of Maintenance manual and any blueprints of the house if they don''t have one when house was bought or it was lost or destroyed. So, in the future, this can be resolved and recorded as a record retention.

This is one of those many issues that can be resolved as part of documentation submitted. Kind of like a Owner''s Manual for a Car. A copy should be submitted into city records for certain things. Trusses, certain Mechanical and Plumbing systems may need that in my opinion.

How that would work... I don''t know. It is food for thought.

Peach, I agree, it is my or my consultant''s (or Truss Manufacturer''s truss designer''s/engineer''s) responsibility for the truss design. I have responsibility for everything else and in some cases choosing the right truss.

August 1, 2009
2:58 pm
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peach!!
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like all pre-manufactured components, they are supposed to be inspected in the factory before they are shipped..

having said that, those truss plates aren''t a miracle product, and I suspect most inpsectors don''t look at them for damage (or separation at the plates) when they are installed. Combine that with insufficient bracings (yes, trusses need more bracing than shown on the shop drawings, and that''s the building designer''s responsibility)..

time will tell, I guess... personally, I''d use rafters

August 1, 2009
2:29 pm
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dave w
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Standard maintenance inspection? What a concept, I agree George except home owners never inspect the structural integrity of their home, let alone receive something (Home Owner Manual) indicating maintenance requirements of their homes.

I would wonder if this also applies to floor trusses as well.

It?s ironic that we are more informed about our vehicle (17K) than our home (250K) where we expect to be safe.
:p

August 1, 2009
12:26 pm
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george roberts
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Standard maintenance should find and correct these problems.