# Cutting the bottom chord of an attic truss



## timrev8 (Sep 15, 2008)

Yes I know it is an engineering sin.
i would like to challenge an engineer to calculate a fiesable way to cut the bottom chord to frame in some stairs

my own uneducated mechanical ability tells me this would be bullet proof and will stand the test of time…

lay a 4x8 3/4 sheet of plywood on each end of the truss on the bottom chord spanning to the two trusses on each side of the one to be cut. this is done to hold the bottom chord from pushing the wall out. 

head off the truss to the others with double 2x10 as normally done for the floor load and sheeth the floor

any thoughts? calculations?


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## Warren (Feb 19, 2005)

If only it was that simple.

So your going to support the bottom chord of the cut truss by the bottom chords of the adjacent ones? Wont those also require some beefing up?


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## timrev8 (Sep 15, 2008)

Yes, i plan to add 2x10 with bolts to either side of the metal gussets that are at the seems of each other bottom chord


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## Golden view (Feb 16, 2012)

Here's my calculation: 3 truss loads over 2 trusses. 3/2 = 150% load.


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## Warren (Feb 19, 2005)

timrev8 said:


> Yes, i plan to add 2x10 with bolts to either side of the metal gussets that are at the seems of each other bottom chord


You really need to call an engineer. Your thinking is ridiculous. Why are you using 2x10? How many bolts? How long will the 2x10 be? 

We recently converted some existing 30' common trusses into attic trusses. Just changing 3 trusses required over $1000 in materials and 4000 gun spikes. Most modifications are possible, but money spent on an engineer is well spent.


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## overanalyze (Dec 28, 2010)

Sure what's the worst that can happen...engineers aren't needed at all....come on man. Call either your regular truss supplier or an engineer. They can simulate the bottom cord being cut and then give you the required repair to said truss. It may be something along the lines of what you are thinking, but their idea will have the safety net of proper calculations and prints to back it.


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## timrev8 (Sep 15, 2008)

definetly calling the truss co. engineer in the morning but i am sure as usual his aditude will suck and he will tell me how i CANT do it and not how i CAN do it


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## timrev8 (Sep 15, 2008)

thanks for the replies guys


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## overanalyze (Dec 28, 2010)

You will always get better results with your engineers if you don't give them your ideas for the repair. If you have a big attitude when you go to them, they will most certainly give it back. Just food for thought.


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## timrev8 (Sep 15, 2008)

that is for sure thanks


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## Deckhead (Dec 9, 2010)

With our engineers I just tell them "X" happened and how do I fix it?

Your ideas are like a guy I used to frame with, he'd snap a compression member and just nail a 2X4 on it. Some trusses are incredibly complex and have crazy loads in places you wouldn't expect... Especially on the bottom chord.


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## hdavis (Feb 14, 2012)

Here is my thought. If you can't fit regular rafters in to replace the truss you're ruining, there is a good chance you can't fit a repair in, either.

No spans, no nothing on this one - nobody can give a better answer.


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## Young_Buck (Jul 19, 2009)

best answer, and only answer, call an engineer. There is no responsible way to do this on your own.


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## hdavis (Feb 14, 2012)

Young_Buck said:


> best answer, and only answer, call an engineer. There is no responsible way to do this on your own.


If it fits, he can use a prescriptive conventional rafter design for the bay(s) involved. What's done to the truss becomes almost irrelevant.


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## MTN REMODEL LLC (Sep 3, 2010)

Timer8....

Of course everyone's comment above is correct... I sure don'thave the correct/eng answer.... *BUT I think this is a great question by you*... 

It's something we all run into I think alot, at least me.

*I hope you'll keep us posted as to solution*......

Of course the solution won't be prescriptive.... and specific to your spec's.... but may teach us something or give us ideas.

In remodels in snow country, I seem to run into these issues fairly often. I happen to have a good truss company, that will work with me.

I will note that eng wise, I am often surprized at the solutions, probably because the truss engineering and load distributions are more complex and not as simple as a non-eng might think/conclude.

Good Luck

TIA


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## Bearded Wonder (Jan 21, 2011)

I worked for an old school New England carpenter for a couple years when I was 15-16 years old. I remember on one house he told me that you "never, ever ever, ever, cut a truss. Period. Ever. Unless you just have to".... 

He then proceeded to cut 8 feet out of one truss for a stairway to the attic. I think he spread the load over 4 other rafters by gluing and nailing 4x8x3/4 plywood sheets spanning the vertical members of the truss that were right close to the stair opening. When he was done, it was solid as a rock and looked great to me, but I've always remembered the "never ever cut a truss" part, and I think I've only done it a couple times in the 20 years since then.


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## Marven (Jul 15, 2013)

Why do you want stairs to the attic? Storage? The attic is not built for it. Contact the truss manufacturer and tell them what you want to do and what you want to store. They will do the numbers.


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## NCMCarpentry (Apr 7, 2013)

Marven said:


> Why do you want stairs to the attic? Storage? The attic is not built for it. Contact the truss manufacturer and tell them what you want to do and what you want to store. They will do the numbers.


x2

If this is the case you have to make modifications to all the trusses that will be carrying a load on top of the bottom chord as well. You'll need an engineer on this one for sure.


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