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Magus2727 09-15-2012 03:41 PM

Modify Attic Truss for Attic Ladder and storage
 
I have a question about adjusting a single (out of 12 total trusses spaced at 24") attic truss that is in the shape as below:

http://www.homeadditionplus.com/imag...%20Truss_1.jpg

My trusses are all 2" x 4" construction. I am not making this into a livable space just storage space. The space between lengths of support from the center metal gusset and the bottom chord are 8 Feet. My plan is to lay down 23/32" tongue and grove OSB for a floor. Should I build up the floor with 2" x 6" in the lengths I am laying floor so its on the 2" x 6" and not the 2" x 4" of the truss? Guessing I should sandwich a 2" x 6" on each side of a single 2" x 4"? so of the 12 trusses I would have installed 24 8 foot lengths of 2 x 6?

The problem with the Attic Ladder:
The only problem is that the only location in my home/town-home that can accommodate an attic ladder (standard 22" wide 54" long) would hit about right in the middle where the two supports of the truss web meet on the bottom chord. and the truss is centered in the hallway so I will need to do some boxing between trusses as it stands.

how may I best modify this single truss? I was thinking of trying to make one side of it look like:

http://peaktruss.com/images/atticTruss.jpg

I was thinking of something like this:
http://i603.photobucket.com/albums/t...uss_Modify.jpg

The RED section would have 2" x 4" reinforcement on both sides
The BLUE section would have extra 2" x 4" sandwiched between the existing truss 2" x 4"

New 2" x 4" will be added to make up the corner using screw tie in plates.

This would move the tie in into the bottom chord (while keeping the tie into the top chord at the same point) enough to clear the attic ladder.

Thoughts? Thanks for any and all help!

inspectorD 09-15-2012 05:21 PM

well
 
This has been asked many times before, so I doubt you will get a different answer. And the answer is, you can not modify a truss, only an engineer can do this.
I'm not trying to be a damper on your ideas,You can do whatever you want in reality. But if you ever get snowloads, high winds or pressures you could have a roof collapse. We saw many of these a few winters ago where folks did things themselves.
My opinion would be to insulate the heck out of that attic and close it off. Find storage elswhere and save your money on the energy bills.

Magus2727 09-15-2012 10:26 PM

I was thinking with only 1 truss being modified it might be a little different. It also looked like on searching, other large projects (using Google search) if used the tipple up of 2 x 4 on either side of the truss would add the strength back in (if not make stronger). I also saw on another forum on a similar question where an engineer (claiming to be one) said as long as you kept the structure to be similar to what other common truss configurations are available you should be fine. but a lot can be said and people can claim all sort of things on the internet.

I wanted to get a full door (47 to 54 inch variety) but could always go with a ladder like:

http://www.homedepot.com/h_d1/N-5yc1v/R-203009104/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=Attic+Ladder&storeId=10051#specification s

nealtw 09-16-2012 09:54 PM

http://www.tra.org.uk/assets/file/pds8.pdf

joecaption 09-17-2012 06:08 PM

Plus 2 X 4 bottom cords were never designed to support any loads, even light ones.

Magus2727 09-17-2012 09:01 PM

So if it is done as it looks like in The PDF link 2 x 6 's need to be ran on the base. And all reinforcements need to be made prior to removing the "old" sections of the truss. Has any one followed up on this forum after contacting a structural engineer or architect to see what they have commented?

nealtw 09-17-2012 09:32 PM

I don't think anyone here thinks any of this is a good idea.

Wuzzat? 09-18-2012 03:37 PM

Quote:

Originally Posted by Magus2727 (Post 77075)
Thoughts?

Even if you know vectors and strength of materials and anticipated loading (concentrated or distributed) a manual truss design is laborious.
You will end up needing to know the force and thrust direction in each member, initially and after redesign.

What you propose may be overdesigned, underdesigned or just perfect, this last case being extremely unlikely.

I guess you could test what you already have by putting concentrated loads in different places and measuring deflections, and then rebuilding to not exceed those same deflections, but designing this test procedure may be worse than doing a redesign. And you should test your redesign in any case.

Your first truss picture looks wrong. That downward sloping strut is supposed at right angles to the roof rafter.
http://www.google.com/imgres?q=%22roof+truss+design%22+fink+king&um=1&hl =en&safe=off&client=safari&sa=N&rls=en&biw=1093&bi h=741&tbm=isch&tbnid=uLjxFWC4vvCW5M:&imgrefurl=htt p://mac6.ma.psu.edu/em211/p09a/probs/compare_04_05.html&docid=U1skq8558ONIaM&imgurl=htt p://mac6.ma.psu.edu/em211/p09a/probs/pr_04a.gif&w=435&h=236&ei=5y1aUKLNJurD0AHY_oCoCA&z oom=1&iact=hc&vpx=484&vpy=160&dur=3927&hovh=165&ho vw=305&tx=149&ty=92&sig=102793154617015424895&page =1&tbnh=103&tbnw=189&start=0&ndsp=20&ved=1t:429,r: 2,s:0,i:79

Magus2727 09-24-2012 01:29 PM

The first picture may be wrong, it was the cleaner picture I was able to find on Google images.

OK, so after more research and spending more time up in the attic and running some load bearing simulations at work I will not be modifying the trusses in anyway. I have located a location I can install an attic ladder and have it centered between trusses. Its not the optimal location I would have liked but will not require the cutting of the truss and relocating the webbing. I would still like to place a floor up there so my thoughts are as followed...

Install 2" x 6" x 8' (or 10') across each the bottom chord of each truss. I will have the new "beams" tie into the top 2" of the bottom 2 x 4 chord and where the truss webs meet the bottom chord (through a combination of wood glue and screws.

This would be enough support for a storage floor ( less than approx 100 per sq ft) you should think?

I already have blown in insulation in the attic and was going to add additional insulation by means of 2" thick insulation board to nail along the top chord of the trusses (so I have a good and unobstructed air flow from the eaves to the air vents along the center of the roof.). I was going to do a similar thing to "enclose" the area I have the floor for the upside down V in the center of the truss. I also was going to add an attic fan with the temp control switch to provide better airflow and cooler attic in the summer.

nealtw 09-24-2012 05:44 PM

I am happy that you no longer plan on changing any trusses.
Trusses are designed to carry the weight of 5/8" drywall and the roof and sheeting and what ever snow load you have in your area. As they are not designed to set any load on interior walls you will still be taking chances on saging. That sagging will show up on the ceiling the floor below the interior wall and the roof.
You should call your local truss company and see if they can make any suggestions.


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