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Replacing Roof Trusses with Rafters

CLawNC's picture

I'm walling in a front porch and removing the old exterior wall.  That old exterior is one of two support points for the roof trusses.  The new horizontal span is 14 feet.  I want to add 2x6's or 2x8's as rafters beside and attached to the existing trusses to move the load to the new external wall and safely remove the old exterior wall.  The roof pitch is 8/12.  The new unsupported horizontal span is 14 feet.  The existing trusses are 24 inches OC.  I have room for a maximum 2x8 rafter size.  Could I safely put double 2x6's beside each truss (24" OC) and provice adequate support for the roof?  The bottom member of the existing trusses will remain as ceiling joists (and rafter ties).

(post #65899, reply #1 of 14)

could you provide a sketch? I'm not totally clear on what you're doing, but I don't think you can do it the way you describe - a truss is an engineered member, and can't be altered without an engineered plan.

"Down these mean streets a man must go who is not himself mean, who is neither tarnished nor afraid...He must be, to use a rather weathered phrase, a man of honor, by instinct, by inevitability, without thought of it, and certainly without saying it." - Raymond Chandler

(post #65899, reply #2 of 14)

Not only no, but HELL NO.

What you're proposing isn't even CLOSE to being acceptable.

The shortest distance between two points is how far apart they are

(post #65899, reply #3 of 14)

New canidate for the Darwin awards................


I Love A Hand That Meets My Own,


With A Hold That Causes Some Sensation.


yourcontractor@aol.com

 

 

"When the spirits are low, when the day appears dark, when work becomes monotonous, when hope hardly seems worth having, just mount a bicycle and go out for a spin down the road, without thought on anything but the ride you are taking." — Sherlock Holmes, 1896

(post #65899, reply #11 of 14)

Not that bad - Darwinigans don't bother asking

 

 


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We did the best we could...

(post #65899, reply #4 of 14)

Hey Boss, it's the guy's second post.


Could you elaborate on the specific reasons why it is not valid? Would that be because of the new forces that would be put into play on the opposing truss side of the roof?


Thanks. 




sobriety is the root cause of dementia.

 

(post #65899, reply #5 of 14)

He's trying to extend the span of his trusses by scabbing 2x6 to the sides of the chords to bear on a new wall some distance from the one the currently rest upon.


At the very least he would need a header at the current location of the wall to carry the trusses. But still doesn't get him a roof over the new porch. Don't have Boss' knowledge to guess if he can scab a shed roof or do a layover on the trusses to the new outside wall of the porch.


Needs and engineer.


Eric


I Love A Hand That Meets My Own,


With A Hold That Causes Some Sensation.


yourcontractor@aol.com

 

 

"When the spirits are low, when the day appears dark, when work becomes monotonous, when hope hardly seems worth having, just mount a bicycle and go out for a spin down the road, without thought on anything but the ride you are taking." — Sherlock Holmes, 1896

(post #65899, reply #6 of 14)

"Could you elaborate on the specific reasons why it is not valid?"

O.K. He didn't tell us what span of truss he was dealing with. So I'll assume a 26' existing truss to use as an example.

Assuming I understand his post, he's trying to add 14' to the span of the existing 26' trusses, so he'd have an new clear span span of 40'.

For starters, that would put a TREMENDOUS amount of bending stress in the rafters he wants to scab alongside the existing truss. There's no way a 2X6 or 2X8 would handle that kind of bending.

The connection between the rafters and the truss would be all but impossible. There's just no way you could get enough nails and/or bolts in there.

And you'd be adding a lot of stress to the truss that it wasn't designed to handle. Even if the lumber was of adequate size/grade, virtually all of the plates would need to be reinforced.

So that's it in a nutshell. I could try to run some numbers if anyone was seriously interested, but may not have time this afternoon.

I always wanted to be a procrastinator

(post #65899, reply #7 of 14)

Thanks



sobriety is the root cause of dementia.

 

(post #65899, reply #10 of 14)

your turn to be grumpy today, eh?

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #65899, reply #12 of 14)

"your turn to be grumpy today, eh?"

Oh shut up.

(-:

I was just trying to make a point in my first post that it wasn't even CLOSE to working.

If it weren't for pickpockets I'd have no sex life at all.

(post #65899, reply #13 of 14)

Just for the mental excercise, it would be nice if he came back with a sketch and photographs to be able to see what he is talking about more specifically

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #65899, reply #8 of 14)

Realistically, there are two ways to deal with this:


1.  Replace the structural function of the old exterior wall with some sort of beam.  If it's wide enough, you may have to use a post or posts to divide up the span of that beam. If the look of the beam and post(s) is unacceptable to you, then the best option is:


2.  Sell this house to someone who will be happy with it the way it is.  Buy or build a bigger house.


Without proper engineering, what you propose will collapse the whole house.  With proper engineering, it might collapse your bank account.  Bottom line, you'd probably be better off to sell the house and buy what you want.


 


-- J.S.


 


 

 

 

-- J.S.

 

(post #65899, reply #9 of 14)

You really do need some on-site engineering from a pro.

If your description is ruight - the way I read it, you now have a house that is only eight or ten feet wide. with a porch that is four or six feet wide.

I think you are assuming that some center wall is bearing load from the truss and that your house is more like 22 to 26 feet wide at this point. your actuall clear span would then be the total. Or - it is possible that the beam on the porch is the load bearing structure for these truisses and no modification whatsoever is needed.

by way of explanation - there is a tremendous liability in any engineering of structural work and a lot of details are needed that are missing in your information. Tbhis is not to be hard on you, but the way you present the info hints that you don't quite know what to look for in the beginning and have made some potentially dangerous assumptions.

Trusses are very carefully designed and Boss is a truss designer. he has seen all the errors at one time or another. The thing you ARE doing right here is aasking FIRST. A lot of people wait until the failure happens and then ask why - or how do I fix this...when it is already too late.

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #65899, reply #14 of 14)

you cannot remove the end support without replacing it with something.cut off the tails and install a flush beam so that the truss end is hanging off the beam.beam will have to be engineered,as it will act as a girder.new rafters can be added on top of the truss as long as you provide support from the new beam to the underside of the new rafter.either way , get an engineer involved .


 


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