Wood Framing - Truss roof to cathedral ceiling conversion & remodel 2

[bobharsh]

YOung engineer who often forgets which way up is designing own house remodel...

Any help here would be mUcH appreciated! I feel competent enough to size beams and columns -> I am concerned I am overlooking major design flaws.

I am converting a truss roof system into a cathedral ceiling the whole length of the house. I am using a system of columns and structural ridge beams to support the roof. I am also gutting the entire house/moving majority of walls around.

1st question: I would like to concentrically load the columns @ the basement level by aligning columns on the first floor. Am I creating a hinge here? Do I need a moment connection/do I need to use a continuous column to achieve this concentric load path? The 1st level floor is 2x8 joist @ 16 on center. (see attached BH_house 2 model) Due to 2x4 stud wall framing - I have sized a HSS3x3x3/16 column - is this over kill? I understand that sheathing will act to reduce the le dimension in the strong axis -but- the amount of sheathing in several areas is limited.


2nd question: Diaphragm question -> I am removing the majority of ceiling joist in the center of the house. Do I need to add any chord elements across the living area here? There are areas of low roof in the bed rooms(attached is low roof framing plan).

Thank you for your time. ~ Bob

http://files.engineering.com/getfil...f-bc28-6da1c6be5f45&file=Binkley_low_roof.pdf

http://files.engineering.com/getfil...-a2e6-e0ba564e65f8&file=Binkley_1st_floor.pdf

http://files.engineering.com/getfil...-ae81c26165b7&file=Binkley_basement_floor.pdf

http://files.engineering.com/getfil...f-8316-d5395a11a127&file=BH_House_2-Model.pdf

 

[oldestguy]

While you may be doing this yourself, do you plan to get an approval by another engineer (PE) in order to get a remodel building permit? How about the lending agency (assuming you have a mortgage)? Of the building inspectors I have run into, some of them might be difficult to work with. Just wondering about some of the roadblocks that may come up. Any questions about suitable insulation in the roof system? What does the local building code require under upgrades? Was this a prefab coming in as two units?

 

[XR250]

The floor diaphragm will brace the hinge so you do not need a moment connection. You gable end walls may be unbraced at the old ceiling level now which would require reinforcement.

 

[bobharsh]

Youngest guy(bob) -> Oldestguy; I am meeting with a PE next week to discuss/review the project. I have the financing figured in, and will be pulling permits. The inspection as you have stated WILL be a pain the my derriere. As far as insulation goes - I will be sistering 2x10's to the now 2x4 truss rafters and using faced batt insulation 8 1/4"(r30). This will leave air space for sofit to ridge ventilation. The house was not prefab. trusses were built on site. Thank you for the response!

XR250 - Thank you for the reply! This was my first assumption (floor diaphragm bracing against the hinge) but I started to talk myself out of it. Good point on the gable wall end... I have decided to run a 6" stud wall down the middle of the house and used (3) 6x2 LVL as column above 1st floor. I will do the same at the gable ends and extend them past the top plate. I am not sure what is currently there (top plate wise) and will re analysis once it is opened up.

If I do like fore-mentioned and run (3) 2x6 to bottom of structural ridge beam do you think this will be enough to brace the gable wall? There will be low ceiling the full length on one gable end and half length on the other. Since this is a remodel I am trying to figure a way to run a strap across the gable ends to tie in my chord element. Since this wall is 2x4 construction this will be an issue. -> Do you think I can get away with using (3) 2x4 LVL column post to support ridge beam(less than 4kip load) and brace against lateral forces acting @ gabels?

Would running continuous 2x4 @ 1/3 points to bottom of ridge brace the gable wall? House is located in Nashville TN - not high wind area, also brick clad.

 

[txeng91]

2x4’s suck as columns, especially when you start getting over 10’, but you might be able to get away with it if your loads or low enough. Might also consider using a solid section like a PSL for added strength. As far ss the gable ends go, you probably need to add multi-ply full height stud columns down the length of the gable, in addition to the ridge support for it to be wind rated. It will depend on the capacity of the columns and how far your top plate can span. You would just cut the top plate to let in the columns and strap across with a coil strap after they are installed. Would also need to make sure your connections from the top plate to the column and the columns to the floor and roof diaphragms are taken care of. Other than that I would just double check the basement framing if the roof load distribution is changing, I can’t tell if your roof trusses were previously supported in the center of the house or not. Also probably worth making sure any uplift on the ridge is transferred through the columns down to the foundation.

 

[HouseBoy]

A few thoughts:

If you are maintaining the the ceiling at one end (am I right in understanding your use of the term "low roof"?) why do you need to run the new structural ridge all the way across the building?

Having those ceilings at the gable ends would alleviate the need for added studs there. If not, it look like you have brick exterior so... make sure the end walls are sufficiently stiff.

At the interior columns a steel column is more robust that necessary but 2x4's will be too slender at 12 ft tall. Engineered wood columns are available and it should be simple enough to build up columns using 2x6's (full height pieces), just make sure you fasten them adequately. NDS provides good guidance for that and some structural screw makers have good alternatives to nailed built-up columns.

At the gable end walls (again, assuming you will have the ceilings in there at least on one half of the gable end) just make sure the column is proportioned for axial and bending. Seems like "bracing" at the ceiling level will be most helpful.

I'd be curious about the available heal height and how much of a notch there will be on the bottoms of the 2x10 rafters. Looks like 2x6 "rafters" in there now so, if the new and the old are married together enough, that might be fine.

With an adequate ridge, I would not expect that the "chord element" you are asking about is needed.

Seems like temporary shoring while you get he structural ridge in place will be a chore.

Steve