cut truss effects

[John Dirks Jr]

Can anyone post pictures that show negative effects of cutting engineered roof trusses?

I'm looking mainly for situations where trusses were cut to install pull down stairs or whole house fans.

[Matt Fellman]

Something like this? :)

[Michael Thomas]

http://www.energyefficientbuild.com/images/ImpN1-101-04a.jpg


Condo-Renovation_Structural-Integrity-Evaluation-Of-Cut-Trusses-2 (http://www.energyefficientbuild.com/Condo-Renovation_Structural-Integrity-Evaluation-Of-Cut-Trusses-2.html)

[John Dirks Jr]

Something like this? :)


Looks like they forgot the whole corner of the house on that one, foundation and all.

[A.D. Miller]

Something such as this . . .

[Jerry Peck]

Aaron,

That's from lack of, or improperly installed, temporary bracing during setting of the trusses.

[A.D. Miller]

Aaron,

That's from lack of, or improperly installed, temporary bracing during setting of the trusses.

JP: Yeah, I know, but it looked so good I just had to post it.:D

[Jerry Peck]

JP: Yeah, I know, but it looked so good I just had to post it.:D


I have, unfortunately, been a bystander observer telling the contractor that they need to get their men off the trusses until they install temporary bracing or the trusses will topple like dominoes, only to be standing there point that out and telling the superintendent or builder that and then actually watch as the trusses do topple over domino fashion and the workers fall with the trusses.

Each time, thankfully, no worker was killed, but some were injured and 911 was called, taking several of them to the hospital. :eek:

I think I have seen 3, maybe 4, of them topple like that. It is just stupidity, ignorance, or just not caring which causes it. :(

[A.D. Miller]

I think I have seen 3, maybe 4, of them topple like that. It is just stupidity, ignorance, or just not caring which causes it. :(


JP: Ignorance is simply stupidity deliberately cultivated by the man who does not care.

The only time I have seen a wholesale failure of an altered truss was back in the day when I was building and not just inspecting. The house next door to the one I was remodeling was being re-roofed after a hail storm. As is their custom here the roofers set about 8 squares of shingles up on the roof in one place - happened to be right over a two adjacent field-modified trusses - and the roof collapsed. No one was injured - other than their Latino pride - but the some of the bundles of shingles ended up in the laundry room . . . Needles to say, we took the opportunity to have a good laugh at their expense.:D

[John Kogel]

Can anyone post pictures that show negative effects of cutting engineered roof trusses?

How about some repaired trusses? This was a 1970's condo with manufactured trusses. A tenant said that while the roofers were replacing the roof, they also did some work in the attic, and that now it was stronger than ever. This spot is adjacent to the parking lot. I wonder if a pallet load of materials went through the roof here? :)

[Brandon Whitmore]

Picky Picky

John,
what's wrong with some oversized gusset plates :D

[Brad Peterson]

Good morning all

I was a builder / contractor in my pre -inspection life. I also owner a truss manufactoring plant in Northern Colorado for 6 years in the GREAT DEPRESSION of the early 80's. Anyway on with my comment. Most truss damage that I delt with was deliver caused. Trusses were either dropped of by a side dump or a roll-off method and at that time and the mear benting and twisting or being dropped off on uneven ground would cause truss plates to pop or get bent and chords to be cracked or broken. At plate location a typical engineered repair was a plywood not OSB gusset on both sides glued and nailed not stapled. The gusset was size a minimun of 10 to 15x's the gusset size (CYA) on the engineers side. So a 3x5 plate would have a 30" x 50" plywood gusset. We were instructed to convey to the builder that it was not the plywood gusset that would fail but the gusset size was need for the proper number of nails to equal the holding valve of the damaged gusset. So next time you see a truss repair with what we would thing are over sized plywood repairs just remenber an engineer came up with it and it is his stamp on the repair letter that was hopefully given to the builder / building department.

Happy inspections: Brad Peterson - Tri-City Inspection Agency, LLC

[Brad Peterson]

Good morning all

I was a builder / contractor in my pre -inspection life. I also owner a truss manufactoring plant in Northern Colorado for 6 years in the GREAT DEPRESSION of the early 80's. Anyway on with my comment. Most truss damage that I delt with was deliver caused. Trusses were either dropped of by a side dump or a roll-off method and at that time and the mear benting and twisting or being dropped off on uneven ground would cause truss plates to pop or get bent and chords to be cracked or broken. At plate location a typical engineered repair was a plywood not OSB gusset on both sides glued and nailed not stapled. The gusset was size a minimun of 10 to 15x's the gusset size (CYA) on the engineers side. So a 3x5 plate would have a 30" x 50" plywood gusset. We were instructed to convey to the builder that it was not the plywood gusset that would fail but the gusset size was need for the proper number of nails to equal the holding valve of the damaged gusset. So next time you see a truss repair with what we would thing are over sized plywood repairs just remenber an engineer came up with it and it is his stamp on the repair letter that was hopefully given to the builder / building department.

Happy inspections: Brad Peterson - Tri-City Inspection Agency, LLC
tricityinspection@juno.com

[Stuart Brooks]

Slight sags in roof surface are a little hard to capture with any definition. One inspection had a slight sag in one area of the roof due to a truss that was cut to accommodate a kitchen exhaust fan. I had another house that had two trusses cut to fit a heat pump in the attic. There was no obvious visual evidence on the roof. Another house that was too high to get on the roof had a slight "kink" in the ridge line at the gable end of the main roof that did not look right. In the attic there were three broken trusses in a row. The design had a center vertical web and it was this web that was broken. One had about 4 inches of separation between broken ends. The bad part about this inspection is that the seller had a pre-listing inspection and nothing was mentioned about truss damage or the ridge bump. Yep, another THOROUGH inspection by one of my competitors who stand on a step ladder, look up through the attic scuttle and say, "Attic, Check ; Insulation, Check" and quickly close the scuttle.

I know of inspectors here that don't recommend a structural engineer's assessment if the trusses are cut for pull-down stairs AND the enclosure looks "well framed in" to them. I guess they do load and stress calculations in their head.

[Jerry Peck]

We were instructed to convey to the builder that it was not the plywood gusset that would fail but the gusset size was need for the proper number of nails to equal the holding valve of the damaged gusset.

I was going to point out the lack of sufficient (what looked to be lack of) nailing for those large gusset plates.

You are correct, it is not just 'the size of the plywood gussets', it's more of 'how many nails' are holding it on.

Follow the engineer.

I looked at some today with a specified nail spacing of 2", and the installed nail spacing was 3", ... AND the gusset plate was WAY TOO SMALL and did not cover the area needed, which is why they could not nail it properly - not enough gusset plate to put enough nails in.

Sometimes it is both the gusset plate and the nailing (lack thereof).

[chris mcintyre]

We were instructed to convey to the builder that it was not the plywood gusset that would fail but the gusset size was need for the proper number of nails to equal the holding valve of the damaged gusset.


Since the issue is holding value, is there an adjustment for using screws instead of nails?

Also, it seems that the truss company would make a gusset that could be applied in the field. It would definitely be easier to install than a 4x8 sheet of plywood :eek: .

[Jerry Peck]

Since the issue is holding value, is there an adjustment for using screws instead of nails?

Typically, screws are not allowed to be substituted for nails. Screws are typically either more brittle than nails or have lower shear values.


Also, it seems that the truss company would make a gusset that could be applied in the field. It would definitely be easier to install than a 4x8 sheet of plywood :eek: .

They do, but it is easier to cut a piece of plywood and nail it on than to go down to the truss company, or wait for them to come to you, so you can make the repair. Also, those repair gussets require the old truss plate to be removed, the plywood does not.

[Marcel Cyr]

Can anyone post pictures that show negative effects of cutting engineered roof trusses?

I'm looking mainly for situations where trusses were cut to install pull down stairs or whole house fans.

Contents from Enzine;

The best advice I can give you, for any wood truss roof repairs, would be to contact the manufacturer and get a professional to look at the damage as soon as possible. If they don't respond in a timely manner, try to avoid using them in the future.
Unless you damaged the roof truss, they should be responsible. If you damaged the roof truss, you will need to accept responsibility and understand that you will be paying for these repairs.

And compliments of:

http://homerepair.gregvan.com/roof/roof_truss_repair.htm (http://homerepair.gregvan.com/roof/roof_truss_repair.htm)

http://homerepair.gregvan.com/images/roof-repair.jpg




http://homerepair.gregvan.com/roof/roof-truss-repair.jpg

http://homerepair.gregvan.com/roof/roof-truss-repairs.jpg

Hope this helps a little. :)

[James Foy]

JP: Ignorance is simply stupidity deliberately cultivated by the man who does not care.

The only time I have seen a wholesale failure of an altered truss was back in the day when I was building and not just inspecting. The house next door to the one I was remodeling was being re-roofed after a hail storm. As is their custom here the roofers set about 8 squares of shingles up on the roof in one place - happened to be right over a two adjacent field-modified trusses - and the roof collapsed. No one was injured - other than their Latino pride - but the some of the bundles of shingles ended up in the laundry room . . . Needles to say, we took the opportunity to have a good laugh at their expense.:D

I will be stealing this. Thank you.
[quote=A.D. Miller;109270]JP: Ignorance is simply stupidity deliberately cultivated by the man who does not care.

[A.D. Miller]

I will be stealing this. Thank you.
[quote=A.D. Miller;109270]JP: Ignorance is simply stupidity deliberately cultivated by the man who does not care.

JF: Steal it if you must, but let me correct it first by changing the positions of the two words "stupidity" and "ignorance". I must have been in a hurry when iwrote that . . .:(

[Bob White]

I don't have any pics of the effects of cut trusses, but here is on showing one effect of removing the braces from the walls supporting the trusses ----

[Dan Harris]

Six or seven years ago I inspected a new home that had eight out of ten webs cut to make room for two furnaces, above the kitchen.
The attic space was low.
The effect, on that one. The customers were moved out and put up in a motel for a few days, the roof on that area of home, cut trusses, cabinets and drywall were removed, and replaced.

[Jerry Peck]

JP: Ignorance is simply stupidity deliberately cultivated by the man who does not care.

I state it, and define it, slightly differently, but the same overall intent and result.

Ignorance and lack of knowledge are different in that a person lacking knowledge is willing to learn when presented with new knowledge, whereas ignorance is either the inability to recognize new knowledge or the desire to ignore new knowledge.

Aaron, changing 'ignorance' and 'stupidity' does not make it read right.

"Ignorance is simply stupidity deliberately cultivated by the man who does not care."

versus

"Stupidity is simply ignorance deliberately cultivated by the man who does not care."

I contend that you were correct the first time, that stupidity cultivates ignorance, not that ignorance cultivates stupidity.

I do agree, though, that the latter wording is similar to my ending wording of "or the desire to ignore new knowledge".

Normally, one would not but "ignorance" and "deliberately" together as the ignorant person does not do much "deliberately", more by happenstance than anything else.

[Jim Hintz]

Ok Everyone,
What are your opinions on these single purlins with the rounded edges?

[Bob White]

Over on TIJ, a WTCA engineer replied to questions regarding this type of truss:




Thanks for contacting WTCA with your question. Rachel Smith is no longer employed here, so hopefully I will be able to address your questions. The following information should help you and your fellow inspectors regarding the quality criteria for metal-plate-connected wood trusses using round cut webs. The general use of round cut webs do work within the framework of the Truss Plate Institute's (TPI's) Quality Assurance Program. Around 2000, TPI's Technical Advisory Committee rendered an interpretation to the then metal-plate connected wood truss design standard ANSI/TPI 1-1995 Section 4.6.4 that the wood-to-wood joinery gap tolerances (maximum and average) applied only to cut to bear wood members, and were not intended for round cut web applications. However, as TPI began working through the revision process to ANSI/TPI 1-2002, there appeared to be a growing consensus to assign a small tolerance for wood-to-wood point contact tolerances using round cut webs. So, ANSI/TPI 1-2002 included the following language:

3.7.6 Wood Member-To-Member Gaps

3.7.6.1 Except as indicated in Section 3.7.6.2, maximum gaps in all joints except floor truss chord splices shall not exceed 1/8'', where the gap is measured at each edge of the metal connector plate for joints in which the plate edge is within the scarf, and measured at the end of the scarf for joints in which the plate edge is outside the scarf. Scarf is the portion of the joint in which it is intended that there be wood-to-wood contact between two wood members. The maximum gap for floor truss chord splices shall not exceed 1/16" across the entire scarf. For joints designed with single points of contact between adjacent members as shown on the Truss Design Drawing, the maximum gap between all contact points shall not exceed 1/8". (See Figure 3.7-3)

http://www.inspectorsjournal.com/forum/uploads/hausdok/200821882150_DexterTemp.JPG

Figure 3.7-3 Wood Member-to-Wood Member Gaps

3.7.6.2 Where a metal connector plate is designed to carry all compression load at the joint without buckling of the plate steel section, the allowable gap shall be that amount of gap used in sizing the metal connector plate as specified on the truss design drawing by the Truss Designer.

What you are illustrating in your photos are a system of standardized webs with standard end cuts, and, in most cases standard ends and standard lengths. The reason for using these standardized webs is that they reducing web cutting labor, truss assembly time and web lumber. But there are reductions in the metal plate connector's design values when the webs are standardized. These are engineered and will handle the loads the trusses are designed for. You mentioned Turb-O-Webs as an example - Turb-O-Web trusses have been used in the United States since 1999. Specific questions regarding the Turb-O-Web System can be answered by calling them at 888-TURBOWEB.

Ryan Dexter, P.E.
Director of Technical Projects
WTCA - Representing the Structural Building Components Industry
6300 Enterprise Lane
Madison, WI 53719
rdexter@qualtim.com
608/310-6744 (direct)
608/213-1527 (cell)
608/274-4849x144
608/274-3329 (fax)
SBCA - Structural Building Components Association (http://www.sbcindustry.com)

The Voice of the Structural Building Components Industry

WTCA is the voice of the structural building components industry. Please support SBC Advertisers and BCMC Exhibitors who support our industry and make SBC and BCMC possible.

[Jim Hintz]

Thanks for the diagrams and info Bob. I am still concerned, as the diagrams did not show single purlins / web members with rounded edges. Wouldn't the support provided by this configuration be minimal, if any at all, due to the purlin not actually pushing / pressing on the roof truss? In your diagrams I can see where 2 rounded edge purlins / web members would work and stay in place because they push against each other. But the plate on the single purlin in my photos appears to only be suspending the purlin / web member. BTW, the place was built in 1973. Your thoughts please.

[Jerry Peck]

I am still concerned, as the diagrams did not show single purlins / web members with rounded edges. Wouldn't the support provided by this configuration be minimal, if any at all, due to the purlin not actually pushing / pressing on the roof truss?


Jim,

This is the crucial part, which you may have missed, in the text accompanying the drawings:
"But there are reductions in the metal plate connector's design values when the webs are standardized. These are engineered and will handle the loads the trusses are designed for."

Which simply means that the truss designer took the reductions in the truss plate load capacities into consideration when designing for the rounded end web diagonals.

Or, at least 'was supposed to' take those reductions into consideration.

And, if the truss engineer did take those reductions into consideration, then the truss plates should be strong enough and all is okay.

I can imagine the reductions were significant, so the truss engineer simply uses a larger, or heavier gage, truss plate to do the same job. Basically, the trade off is less wood bearing strength for more metal strength.

[Jim Hintz]

Thanks for explaning it Jerry, I appreciate it - Happy Thanksgiving to you and yours - Jim

[Roger Hankey]

Trusses are typically so strong that unless two adjoining trusses are cut, there is often little deflection in either the roof or ceiling. Here are two photos: One of a truss with 3 webs cut for a triple wall metal chimney, and a photo of a very good truss label, which I wish appeared on all trusses instead of only a small percentage of trusses.

[chris mcintyre]

Trusses are typically so strong that unless two adjoining trusses are cut, there is often little deflection in either the roof or ceiling.


I disagree, trusses are typically 2' on center, so a cut cord in effect leaves you with a 2x4 rafter/ceiling joist in a 4' span.

Also a lot of homeowners (and sad to say some builders) think that if you have a truss roof, that you are free to tear out as many interior walls as you like. They must be installed exactly as designed, and are often designed with the interior load bearing walls in mind.

I am not a big fan of trusses, there are applications where they are a must, but I feel it is a delicate system that is easily compromised during installation and especially after.

[Roger Hankey]

Chris,

I did not say cutting only one truss was good. What I left out of the remark about little deflection was "under typical light loads". I cannot think of any circumstance where I would not report a cut or modified truss as an adverse condition and recommend a correction designed by a qualified truss engineer.

[Jerry Peck]

I am not a big fan of trusses, there are applications where they are a must, but I feel it is a delicate system that is easily compromised during installation and especially after.

I disagree with that description.

Trusses are not "a delicate system that is easily compromised during installation and especially after".

Trusses are designed for a safety margin *above and beyond* maximum design loading, and even after design loading ... i.e., hurricanes ... I have seen very few actual truss failures EVEN WITH missing webs.

The failures were typically the loss of roof sheathing and or gable ends being sucked off or blown in (which was a result of missing diagonal bracing, not a fault of the trusses).

In my opinion, I have seen many truss system which have been butchered during installation and afterward, and still performed admirably considering the extent to which they were butchered. "Admirably" meaning that everything was still standing and no evidence of sagging or failure.

[Marcel Cyr]

It might have been more accurate in saying compromised during installations, period.
Trusses are very fragile on a one on one basis.
When they are installed and complete with their sheathing and lateral bracing in, they have become a system diaphragm and are rugged indeed.

Install more than one truss, and the handling becomes easier and less apt to comprise.

http://i373.photobucket.com/albums/oo171/mcyr/Main%20Street%20Station/SDC10445.jpg

http://i373.photobucket.com/albums/oo171/mcyr/Main%20Street%20Station/SDC10447.jpg

http://i373.photobucket.com/albums/oo171/mcyr/Main%20Street%20Station/SDC10446.jpg

:)

[chris mcintyre]

I disagree with that description.

Trusses are not "a delicate system that is easily compromised during installation and especially after".

Trusses are designed for a safety margin *above and beyond* maximum design loading, and even after design loading ... i.e., hurricanes ... I have seen very few actual truss failures EVEN WITH missing webs.

The failures were typically the loss of roof sheathing and or gable ends being sucked off or blown in (which was a result of missing diagonal bracing, not a fault of the trusses).

In my opinion, I have seen many truss system which have been butchered during installation and afterward, and still performed admirably considering the extent to which they were butchered. "Admirably" meaning that everything was still standing and no evidence of sagging or failure.

O.K. Jerry, point well taken.

My opinion has come from the fact that AHJ's and the truss manufactures flip out at the slightest deviation.

Examples: The rafter for the cathedral ceiling is only bearing on the interior wall 3", it should be 3-1/2", so you will have to get that stamped.
The attic stairs is suppose to start at truss A-12 and you started it at truss A-11 (when truss A-1 through A-20 are identical!) So you will have to have that stamped.
The HVAC unit is suppose to be over trusses #.................
Oh yea, I almost forgot about the 4'x8' sheets of plywood needed to replace 6"x8" nail plates.

Of course the truss company's "engineer" will always need to evaluate($), issue a repair($), and inspect to see that it is done properly($).

So I may have to change my opinion to be:
I am not a big fan of trusses, there are applications where they are a must, but I feel they are a cash cow for the SE's :D .

[chris mcintyre]

Marcel,

Very impressive, but on a scale and budget far different than mine :) .

[Marcel Cyr]

Chris, try this, and save some time and be a little safer too!

Truss-Me-System

Truss-Me System For Setting Trusses (http://longspantruss-set.com/trussme.html):)

[chris mcintyre]

Chris, try this, and save some time and be a little safer too!

Truss-Me-System

Truss-Me System For Setting Trusses (http://longspantruss-set.com/trussme.html):)

Garages are one of the main reasons we use trusses, and by "we" I mean my company, not builders is general.

Very good link. Thanks!