Room addition over garage

[Finger]

I have been wrestling with this project since I bought my current home in '06. 

The home has a great sized flat roof over the garage that would be ideal to build an addition on.  I replaced the flat roof a few years ago with EPDM and sloped insulation (to prevent pooling) and now I am looking to tear up half the new roof and build a 10x14 foot addition.  I have a few questions that someone more engineering/architecturally savvy may be able to help me with.

1- Should I make/order roof trusses or use a ridge board and rafter combination?
2- I need some help sizing a header beam that will support one of the walls.

Some specs:
The addition will be built over the garage, the north-face and south-face will be built over the garage walls. The garage walls are 2x4 16" o.c. walls with 2x10 16"oc rafters.  I had an engineer visit and certify the foundation will support an addition (required for the permit).  The north and south walls are 10' and the west wall is 14'.  The fourth wall is the existing exterior wall of the house.

I envision a 4/12 roof slope (match current roof), likely using trusses (see #1 above), with a 2 foot soffit for a total of 9 feet from the roof center to the end of the soffit.  We live in Virginia Beach, VA (not sure what snow loads I need to use, suspect I would get that from the codes office?).  The walls will be standard 2x4 construction with a few windows - nothing huge - with T-11 board siding.  I will probably use ceramic tile, and the space will be classified a sleeping room for live load consideration.

Biggest challenge:  The south wall will not be framed over an existing wall and will be parallel to the existing floor joist.  To support the load of the roof, wall, live load of the addition (not really sure how to do this yet either), I know that I will need to add a header beam in the garage ceiling.  The header beam will need to span 12 feet, and will rest on the perpendicular top plates from the existing walls (likely need to support the top plate with additional 2x4s).  The span is longer than the new wall (12 vs 10 feet) because the existing 2nd story wall is not aligned with 1st story bearing wall (cantilevered ?).

From what I have read, dimensional 2x10s will not support the load.  Engineered lumber looks to be a better option, but I need some advice for selecting and sizing (three joined 1 3/4 x 9 1/2 LVL are the current frontrunners).

I have thought about contracting out the framing and reinforcing aspects of the job and just doing the finishing and interior portion, but the economy is strong right now and I am getting no interest from the contractors I would consider working with (too small a job), even the more sketchy contractors aren't jumping at my job.  I am confident I can handle the physical aspects (along with some able-bodied buddies), but there seems to be some voodoo math, that I cannot yet figure out.

Any help (or warnings) would be appreciated.  Thanks, Finger

[lakemom]

Are the 2 10' walls where the trusses would rest?  If so they are load bearing and the 14' wall is not.  However I do believe you should have some reinforcing along that wall as the existing stringer/joist was not sized to support the weight of an additional story.  I'm thinking what is needed along that wall is at least one jack in the center of the garage as well as an additional strength on the joist (either an entirely new one there or making a "sandwich" with additional 2X's.  Can you get a contractor/architect/engineer out as a consultant to draw you up some specs for what you want to do?  I know my son in law does this kind of stuff on the side (has an architecture degree but not licensed yet and does design work) for a reasonable fee.

[Finger]

Thanks for the reply.  Yes, the two 10' walls would be the load bearing walls, the north face 10'er would be right over the existing wall, it should be good to go (this would replicate the rest of the house that is 2x4 walls 16" oc over 2x10 rim board/floor joist).

 The other 10'er that is supporting the other half of the truss is the south face and it is over nothing, i.e. directly below is the open garage space.  The closest thing to support is the 2x10 floor joist, that runs the width of the garage.  I roughly figure the load to be somewhere between 600-900 pounds per lineal foot, way over what the 2x10 would support on a 10' span, even, I think (but honestly don't know how to read the span tables) if I structurally built it up with one or two more 2x10s.

I don't mind paying someone to verify and calculate loads but none of the reputable folks here will take it on, a lot more value for them to design full houses and huge remodels.

I think I just need to find some engineering text books at the library for an undergraduate structural engineering class and hunker down to do some learning.

[Exflyboy]

This is all standard framing stuff from the sounds of it.

If your codes work the same as they do in Oregon this is what you'll have to do..

1) The gable end (if this is where you garage door opening is) is NOT a structural wall.. In other words you make the gable end truss the same as all the others.. i.e it will support the weight of the roof over the full span.. The garage door just fills in the space underneath the end truss.

2) the truss company will have a certified Structural engineer (PE license) on hand that will stamp the truss company drawings and roof load calculations.. So you don't need to hire any professionals to calculate this.

3) You will have to do your own drawings.. Pretty simple, showing the wall construction and submitting the truss company roof load drawings and calcs.

4) any windows will need headers.. the size of the headers is all standard.. Home Depot used to sell a book on house framing that will tell you all you need to know.

5) Go down to the planning dept and get the free leaflets that will show you all you need to know.. We doubled the size of our house using pretty much just these leaflets.

6) Use the standard span tables for the floor joists.. if they need to be reinforced ask the supplier of the composite I beams what size you need to meet code.. Warning, go over kill here.. basic code will give you a very spongy floor.. for example I bought I beams that met code on 2 ft centers.. but installed them on 16" centers for a very solid floor.

As long as you can prove the foundation is sufficient (just compare with the leaflets from the planning dept) you';; be good to go as long as you can do the simple drawings.

You'll need a permit for the structure, the electrical and the mechanical extensions.

[Greg]

Regardless of what you use as a beam to span the 12' and support the wall above, I would recommend posting the beam end point loads to the foundation through the first floor walls.  This means opening the interior, adding 4x material that is tight at the top and bottom, and closing it back up.

A 12' span is not that far and a 4x10 (or whatever floor depth you have) glu-lam beam would be easy to do.

For a sleeping room, you would be better to make the walls 2x6 for better insulation.  Also, you'll need an egress window (emergency exit) for fire code.

Sounds like fun!

[Finger]

I looked into the glulam route, just need to calculate (for the inspector) that it can support the ~790 #/lf load of the addition.

I plan on opening up the walls to add support for the beam.  I was going to use three 2x4s nailed into a H formation and then secured to the bottom and top plates of the existing wall.  The beam will not be resting over an existing 2x4 stud since the existing ceiling 2x10s are resting on the existing studs.

The room will have a few windows and likely a door that exits onto a small deck on the flat roof that I am not building over.

thanks for the help, Ed

[Greg]

(3) 2x4's in an H pattern is not good enough, use a 4x4 instead.

Lots of info online for span tables, pick a brand available at your local lumber yard.  For example:
http://www.aitc-glulam.org/capacity.asp

[Finger]

Thank you for the advice, I will go with the single 4x4. 

The link looks good too.  Half the battle is just finding the info.

Thanks,
Ed

[Greg]

At my go-to lumberyard, the sales team has all of that info at their fingertips and sometimes at the tip of their tongue.  Often it's just a matter of knowing who to ask.  If you sketch up (or Sketchup®) your plans, they would be able to fill in details like dimensions of beams etc. to satisfy permit officials.  They can also provide an overall lumber package quote which is helpful for seeing the big picture costs.