# Large truss roof open span question.



## Hodgepodge (Apr 9, 2020)

Just skip to the end if you don't want the background... I am working up a renovation plan for a large South Carolina ranch home built in the 80s. The main section of the house uses very large 46 foot 6/12 pitch roof trusses with obvious load bearing walls at the perimeter (3 foot overhangs) and one or two interior partition walls. The homeowner wants to remove several walls, some of which will leave several trusses unsupported except for the perimeter walls. I know that, in general, truss roofs need only be load bearing at the outside walls, but I've never dealt with any trusses this massive before. I do not know the exact type of trusses but believe they are WW or KK style. There are currently one or two interior partition walls to remove but I have not yet checked to see how they are made or if they line up with supports in the crawlspace. Obviously not something I want to guess on. I will have the plans and site checked before and during construction, but a qualified answer to this question will help with the design direction. Two questions: 1) Even this 46 foot truss roof only needs load bearing support along the perimeter, correct? 2) Should I expect any sag in this truss roof cieling once the interior walls are removed? Thanks for reading and for your response!


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## griz (Nov 26, 2009)

Unless there are continious load bearing walls across the interior the trusses are clear span.

If you suspect an interior wall is loadbearing it should have footings under them.


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## Rio (Oct 13, 2009)

Climb up in the attic and take a look.


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## META (Apr 9, 2015)

Truss deflection could slightly increase even if rated for clear span. It's generally "ignored" accept for cosmetic reasons like drywall joint cracking. 

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## Golden view (Feb 16, 2012)

All I can contribute is that 46' is not a "difficult" or "rare" span to see. Probably doesn't really cost more to make with or without intermediate support.


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## Hodgepodge (Apr 9, 2020)

griz said:


> Unless there are continious load bearing walls across the interior the trusses are clear span.
> 
> If you suspect an interior wall is loadbearing it should have footings under them.


This is also what I was thinking. I will be checking for footings when I get back to the site.


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## Hodgepodge (Apr 9, 2020)

Golden view said:


> All I can contribute is that 46' is not a "difficult" or "rare" span to see. Probably doesn't really cost more to make with or without intermediate support.


I agree but I have not had to create an open space that large in a remodel before. Better safe than sorry.


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## We Fix Houses (Aug 15, 2007)

You may see 2x6 , 2x8 fillers where the angle supports meet the bottom chord with a clinch plate around all. Same at perimeter wall bearing if present. If not, that's good sign along with no footing / beam it's a clear span.

SC... what size bottom chord and is it SYP #1, Select / Structural...these are confidence builders ?

Add a run or two - 2x6 strong backs maybe before taking anything out below.


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## Railman (Jan 19, 2008)

Typically bearing interior walls will be dbl plated, non bearing single plate. Bearing openings will have a solid 2x6 to 2x12 header depending on opening width, non bearing not. These can easily be checked for without damaging walls. If these aren't present, they will be clear span trusses. The only exception to clear span trusses I've ever seen are 2-part (mono half) trusses that have a center bearing wall beneath.

I was also thinking the same as We Fix Houses that adding strong backs to either center post, or angled webs near center would be a good idea to help prevent any undo movement.


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## Big Johnson (Jun 2, 2017)

Railman said:


> Typically bearing interior walls will be dbl plated, non bearing single plate.



:blink:


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## Joasis (Mar 28, 2006)

A word of caution: I use a lot of trusses, and most of mine are designed to the plan, meaning they can catch support from interior walls, as well as where they land on the exterior plate. Another is where the main plan is a rectangle, and has an inset porch. The trusses designed for the inset will be modified. 

Not all is black and white.


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## META (Apr 9, 2015)

Designated truss load points are typically tagged, but you never know...

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## Railman (Jan 19, 2008)

Johnson,
Around here lumber yards stock 2x4's at 94 1/8" non bearing, & 92 5/8" for non bearing walls. I'm guessing in your parts all walls are dbl plated?


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## TheConstruct (Dec 8, 2017)

Interesting. Never heard of single top plate studs and all our 8' wall studs are 92 1/4".


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## Calidecks (Nov 19, 2011)

Non bearing interior walls I've seen single top plates. Drywall guys may not like, then again we don't jamb the walls under the trusses and oftentimes use 1x as the doubler. After the roof is stacked of course. Tied with a truss clip. 


Mike.
_______________


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## griz (Nov 26, 2009)

Calidecks said:


> Non bearing interior walls I've seen single top plates. Drywall guys may not like, then again we don't jamb the walls under the trusses and oftentimes use 1x as the doubler. After the roof is stacked of course. Tied with a truss clip.
> 
> 
> Mike.
> _______________


never seen it...

fvcking value engineering...

i would not be involved in a job that was built like that...

old dog thing i guess....


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## Calidecks (Nov 19, 2011)

griz said:


> never seen it...
> 
> fvcking value engineering...
> 
> ...



Can't have interior walls tight to the trusses or they can bind with settlement. Even if the roof is stacked first. That's why truss clips are slotted. 


Mike.
_______________


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## Calidecks (Nov 19, 2011)

It's done that way to allow the use of 94-1/4" stud lengths without jamming the walls under the trusses. 


Mike.
_______________


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## griz (Nov 26, 2009)

Calidecks said:


> Can't have interior walls tight to the trusses or they can bind with settlement. Even if the roof is stacked first. That's why truss clips are slotted.
> 
> 
> Mike.
> _______________


well aware, i came from 250 lb snow loads and am well aware of trusses tied to interior walls...

i just refuse to go along with ANY value engineering bs...

you can't afford to build it right do something else...


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## Calidecks (Nov 19, 2011)

griz said:


> well aware, i came from 250 lb snow loads and am well aware of trusses tied to interior walls...
> 
> i just refuse to go along with ANY value engineering bs...
> 
> you can't afford to build it right do something else...



Oh I agree. I always double plate interior walls. But as a youngster I've seen many things (some real doozy's lol) that I learned much better ways later on in the trades. 


Mike.
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