Sistering A Truss Joist

 
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Old 10-05-2011, 07:07 PM   #1
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Sistering A Truss Joist


I'm new to the forum and could use some structural advice. I'm moving into a new construction home in West Palm, Fl; and will install a laddered attic-access door from a scuttle hole that's too small for my needs. Attic access is in the garage, and will be not be insulated to R30, as wil be the air conditioned ceiling elsewhere in the home.

Currently the joists (truss joists) are 24" OC and I'm considering installing the door in such a way to require removing approximately 5' of a joist to gain wider access. I realize that truss joists which support the roof's weight are not to be compromised as can regular ceiling joists.

From what I've been able to gather, sistering the joist I'm to cut through is the way to do it. I'm unfamiliar with exactly how this is done. I'm thinking that after cutting away the section of the joist I need removed; I only need to frame in the new rectangular opening in such a way as to ensure the compromised joist can move neither outwards or inwards. I'd accomplish this by doubling-up on 2x8's and framing in a box to accomodate the new door. I'd glue and screw and use joist hanger brackets; most likely.

I'm an electrician and have fair knowledge of stucture, but am not a structural engineer. I'd like to know if I have the concept right, and if my proposed step sounds safe.

Thanks to all.

Larry.
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Old 10-05-2011, 07:10 PM   #2
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Re: Sistering A Truss Joist


Incorrect and unsafe. If the house is in fact new, contact the truss manufacturer and ask for an engineered change. Anything else is a crapshoot even for a seasoned pro.

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Old 10-05-2011, 07:11 PM   #3
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Re: Sistering A Truss Joist


A trussed joist you don't want to mess with without engineering right from the truss manufacturer. Probably not a huge deal, not like the place is going to fall down or anything, but more than likely the truss designer will tell you what you need to do without charge. Could you possibly move the one truss over?
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Old 10-05-2011, 07:21 PM   #4
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Re: Sistering A Truss Joist


Thank you both. I've read more than once in my searches to contact the manufacturer or hire a structural engineer for assistance. I suppose I had a pipe dream that someone would say something like, "oh, that's fairly straightforward, just. . .. (do this), but as I suspected, my original searches yielded rational information. I'll take my own advice--that I give to apprentices and, "do it right." Three words that so many can't fathom. It's just not as cut and dry as I suspected it might have been. I can accept defeat.

Thanks again, all.
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Old 10-05-2011, 07:27 PM   #5
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Re: Sistering A Truss Joist


The problem with messing with trusses, is that every web does so many different things. Thats why you see 40' long trusses made from just 2x4's. Working together the way they were designed, the webs make the whole truss work. Any modification moves stress points to spots they were not intended. I have seen some truss modifications that seemed really minor that were actually quite involved.
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Old 10-05-2011, 08:25 PM   #6
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Re: Sistering A Truss Joist


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Originally Posted by sparkyjw View Post
I suppose I had a pipe dream that someone would say something like, "oh, that's fairly straightforward, just. . .. (do this), Thanks again, all.
It is fairly straighforward - go get an engineer! There, your dream come true
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Old 10-05-2011, 09:31 PM   #7
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Re: Sistering A Truss Joist


Is it really a truss joist or is it a TJI?
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Old 10-06-2011, 06:21 PM   #8
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Re: Sistering A Truss Joist


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The problem with messing with trusses, is that every web does so many different things. Thats why you see 40' long trusses made from just 2x4's. Working together the way they were designed, the webs make the whole truss work. Any modification moves stress points to spots they were not intended. I have seen some truss modifications that seemed really minor that were actually quite involved.
Again, I've no experience with structural items, but I suppose like many, I feel I can look over a system and figure out the significance of a layout. My roof truss system that also make up the attic floor looks simple enough--but I'll trust that it's most likely ME that's simple, and not the system.

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It is fairly straighforward - go get an engineer! There, your dream come true
I'll probably do just that!

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Is it really a truss joist or is it a TJI?
It appears to be a bare-bones truss joist system. I see no provisions for an engineered floor in the attic. The attic "floor" would simply be the lowermost, horizontal section of roof truss, comprised by the 2x6 that spans the home, and nothing more.

Last edited by sparkyjw; 10-06-2011 at 06:23 PM.
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Old 10-06-2011, 06:44 PM   #9
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Re: Sistering A Truss Joist


After reading Rusty's response, I waited to hear from you as to what you had, since he did point out that there may be some confusion, and I still think that there is a little.

Just an FYI for future reference:

These are I-Joists. Many will call them TJI's, which is a company called TrusJoist International and will just get shortened to Trus Joist. Most will understand what you mean when the material is right in front of you, but talking about it on a forum can create a little confusion.



These are trussed joists, or open webbed floor trusses. This is what I felt that you were talking about.



After reading your last post, I think you may be talking about either plain ol' trusses (though I have not seen 2x6 bottom chords) or you are referring to attic trusses

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Old 10-06-2011, 07:45 PM   #10
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Re: Sistering A Truss Joist


Thanks for the replies, all. Perhaps some pictures will help. These are pics of the place during construction. The shots taken from the ground are a bit confusing due to plane of reference.

I recall looking at the prints and seeing the term "truss joists." I saw my trusses staged on the ground before they were mounted above the block walls of the house. I noticed that the joists to which the drywall ceiling would be mounted were the truss bottoms I saw on the ground. Hopefully I'm not creating confusion by using incorrect terms. Hope the pics help.













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Old 10-06-2011, 07:52 PM   #11
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Re: Sistering A Truss Joist


No "H" clips on plywood in Florida? Is there a ridge vent? I know this has nothing to do with your question, I was just curious.
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Old 10-06-2011, 08:03 PM   #12
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Re: Sistering A Truss Joist


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No "H" clips on plywood in Florida? Is there a ridge vent? I know this has nothing to do with your question, I was just curious.
No on both counts, Warren.
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Old 10-06-2011, 08:14 PM   #13
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Re: Sistering A Truss Joist


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No "H" clips on plywood in Florida? Is there a ridge vent? I know this has nothing to do with your question, I was just curious.
Could be T&G. That is done often here.

Those are regular trusses sparky. No attic trusses. You are going to need to call your truss manufacturer to see even if there is even the slightest possibility that they have any options for you. But no, do not cut any part of the truss.

About all you can do would be to move it over, but then you'd need to head it off, which usually requires a girder truss. And being in Florida....you may be out of luck.

I don't think I've ever seen a cinder block home before. Garages, sure....but not homes. I can understand the reasoning with the hurricanes you guys have.
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Old 10-06-2011, 10:31 PM   #14
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Re: Sistering A Truss Joist


Looks to me like you're stuck with a maximum 22-1/2" wide attic stairs.
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Old 10-07-2011, 12:24 AM   #15
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Re: Sistering A Truss Joist


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Could be T&G. That is done often here.

Those are regular trusses sparky. No attic trusses. You are going to need to call your truss manufacturer to see even if there is even the slightest possibility that they have any options for you. But no, do not cut any part of the truss.

About all you can do would be to move it over, but then you'd need to head it off, which usually requires a girder truss. And being in Florida....you may be out of luck.

I don't think I've ever seen a cinder block home before. Garages, sure....but not homes. I can understand the reasoning with the hurricanes you guys have.
Not T&G either. I'm quite sure it's run of the mill () 1/2" ply. I don't know if it's typical, but maybe it passes inspection because it's an S-Tile roof, and there's generally no walking on these roofs?

It's becoming more common to see homes entirely built with CBC in Florida, and yes, hurricanes are the reason.

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Looks to me like you're stuck with a maximum 22-1/2" wide attic stairs.
I suppose I can live with that, txgencon. As I stated above, if it was a no brainer scenario, I'd cut away; but that's not going to be the case, it seems. I'm not looking to change things if I run the risk of compromising the structural integrity of the house.
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Old 10-07-2011, 01:33 AM   #16
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Re: Sistering A Truss Joist


Don't cut those trusses. I always install 5/8" ply on roofs, but I usually overbuild on most things anyway. You still need the H clips up there walk on it or not. How did they vent the roof with no ridge vent? Gable end vents?
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Old 10-07-2011, 05:51 AM   #17
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Re: Sistering A Truss Joist


I wouldn't mess with the trusses unless you talk to an architect or engineer. Each truss is designed support the span and the load they will carry. Right now you have a small access opening in the garage which is used for minimal storage or it could be a fire access depending on the local code... installing pull down stair will mean that you plan to create a larger storage space then it was designed to be, which means you will add plywood, you will be walking up there and who knows how much stuff you plan to put up there... therefor you will exceed the DL and LL on that trusses they meant to support and chances are the system will fail or ceiling will sag or collapse.
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Old 10-07-2011, 08:12 AM   #18
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Re: Sistering A Truss Joist


Who stood up those rafters and layed them out

10th post- 4th picture- 2nd 3rd and 4th rafters to the right of roof centerline.,

WTF! Looks like an electrician framed that area
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Old 10-07-2011, 09:30 AM   #19
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Re: Sistering A Truss Joist


Personally I don't like 1/2 sheeting on a roof, around here no one even uses H clips, why I don't know. Used 3/4 T&G when I did my own house.
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Old 10-07-2011, 09:53 AM   #20
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Re: Sistering A Truss Joist


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Who stood up those rafters and layed them out

10th post- 4th picture- 2nd 3rd and 4th rafters to the right of roof centerline.,

WTF! Looks like an electrician framed that area
My house is the one right of the home you speak of. I snapped the pics of the adjoining homes in my external shots for sequence reminders (the homes are painted immediately before the roof tile is laid, etc.). FWIW, I'm pretty sure those out-of-level trusses you note are tacked in place for continuation of the job the next day. You can see furring strips in that pic that later came down.

BTW, did you mean to say Stevie Wonder framed that area?


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