12X18 addition with a catch!

[Nelsn]

Hi folks, I have been reading past post and can't find anything on what I am up to so thought u could help.
I am building a 12x18 addition 90 deg. from end of two story w 12/12pitch, upper floor is basically the attic with short side walls and dormers. The existing home is 26' wide with the add-on being 18' wide. My problem is we want to move the exterior wall 4' back into the main house, this would put the load under upper side walls with 4' of 2x10 ceiling joist extending into new rm. could I attach new ceiling joist to end of existing joist and rafters and go with it? Also intend to pour foundation beam under new load bearing wall. Hope this makes sense.

[homebild]

"Hope this makes sense."

Sorry, but it doesn't.

Could you show some floor plans?

[bighammer]

you can download free google sketch up and draw us a rough floor plan of what your proposing. If you can think it and draw it, we can help you build it.

[Richard A Hetzel]

What you're saying is that you want to cantilever the existing floor joists 4 feet and then attach the load from the new floor joists to them.

In simple English, the answer is NO.

[Nelsn]

Thanks all, can I add an attachment like u would in an email? If so how? Richard, you have the idea, it is a basic 90 addition which will make the home L shaped with the difference being moving the exterior load bearing wall the addition comes off of back into the house 4'. The existing joist and rafters would be cut flush with the original ext wall like u would on a normal addition. The new joist and rafters would be 90 degrees to the existing like a normal addition. How about a beam instead of the first ceiling joist?

[Nelsn]

hope pic comes through. Beam where dotted line is even with bottom of joist?

[Richard A Hetzel]

How many stories is the house? Why cut the existing floor joists? Seems to me the joists in the addition should run the same way as the existing floor joists, and bear on the same foundation. The floor joists and the ceiling and roof framing do not necessarily have to run in the same direction.

Yes, you'll need a considerable header (beam) where the wall is removed, probably multiple fairly deep LVL's, depending on what's above. Have someone qualified design it for you; it's not a matter for guesswork.

I don't see any need to mess with the existing foundation at all.

[Nelsn]

Have decided to run joist in line with existing, less span, more structural support and lot less weight than large beam spaning 18'. The house is two story with the second story being the Attic, with knee walls, roof and collar forming rooms. Pitch is 12 12. When I remove exterior wall the cantilever will only be about 3.5' from new load bearing wall. If I scab 2x10s onto existing joist with the ends resting on new wall, bolt joist/rafter ends to addition joist and add knee wall up to existing rafters to transfer load, should be fine. Also while pouring concrete (this used to be a garage) add a footing under new wall to handle load transfer. Have talked to a couple builders who agree but if anyone has a concern please let me know! Thanks

[Nelsn]

Here is a drawing of connection to addition

[Richard A Hetzel]

If the house has one story and an attic, it's not two-story.

Why not just put a header where the wall is removed and connect the joists to the header? Yes, you have to deal with a header, but you don't have to change the foundation.

[Nelsn]

Thanks Richard, the floor will be repaired anyway, that is why I wanted to add a footing while we were at it. But....if I did use a header, I could just run the joist in same direction and not worry about all the extra weight of the joist on the header. Sounds like a plan.

[mjpliv]

I noticed in your drawing that the "knee" walls in the original attic space are not notched into the roof rafters. While this is normal and accepted construction, it means that the "knee" walls are not designed to support the rafters. Putting a load bearing wall under a non-load bearing wall does not make it bearing. Also, I wouldn't feel comfortable with a single bolt hole through a scabbed together floor joist replacing the bearing capacity of the original bearing wall in addition to restraining the end of the rafter from the "out push" forces inhierent with this roof structure.

It keeps coming back to Richard's suggestion (and mine too!) that a beam be designed to replace the bearing wall with the ceiling/roof diaphram of the new structure used to counteract the rafter out push. The beam can be designed to drop below the ceiling or as a flush beam with the rafters/ceiling joists carried by proper hangers.

[Nelsn]

Thanks for the reply mjpliv.as I said last post I've decided to take your and Richards advice and go with a beam. On the knee wall, you also have another one further in that forms the br wall. That would make 2 support walls plus the collar plus the new bearing wall plus the 'truss effect' inherent in a gable plus a header plus bolts through rafter/joist connections. The new joist will run parallel to the header making framing easier, header doesn't have to be that massive because of the above mentioned additional supports. Most of the builders I called said they would just sister the joist over the new wall and go on. I just don't like future problems. Nelsn

[mjpliv]

Good luck with the project and I hope you are able to follow up with some pictures later so we can see how it turned out!

[Richard A Hetzel]

The header has to be "massive" enough to take all the loads on it. All that other stuff (truss effect, etc.) has no structural value, and will not relieve any load from the header.

Figure out the entire load on the header and design it for that. Don't expect any "help" from anything else.

[Nelsn]

Richard, the joist, 2x10s 16oc extend only 3.5', with a new footing and support wall(s) it is not necessary to install a beam that will weigh more than the weight being transferred, this could actually cause a sag in the finished ceiling over a period of time. Also the beam would do nothing to stop a spreading of the rafters, that won't happen after securing the rafter/joist connections. I will be calling an engineer that gave me the specs on a hidden beam in our home before starting, just to make sure. mjpliv, thanks and we will post some pics. Nelsn

[Richard A Hetzel]

If the beam (header) is at the same location as the existing wall, and it supports the existing joists plus the new joists, why will it not stop a spreading of the rafters?

If the beam (header) is correctly designed, why could it cause a "sag" in the finished celing over a period of time?

Who is giving you structural advice? Neither of those two assertions make any sense at all. I feel you are needlessly complicating a very simple problem.

[mjpliv]

Richard is correct. If the existing floor joists are connected to the tails of the rafters then there is no need to design in any lateral restraint for the beam. the only design forces would be straight down, either on top of the beam or hung on the side using hangers. You can specify any deflection for the beam and I would suggest requesting at least L/480 live load design criteria which would work out to less than 1/2" in the center of the beam.

[Nelsn]

Job Code: EP0209056

Engineering Project:
I reviewed your addition
framing design. Your solution (1) will work
with one modification. If you extend the new
addition ceiling joist to under the upper
attic/room wall, the forces will counter
act/balance over the new wall. This should
work well. If you have any questions please
freel free to call.

Note; Solution 1 is the detail drawing of rafter/joist/bearing wall connections. No beam added. As I have said, thin garage floor will have to be repaired in any case. Nelsnn

[Richard A Hetzel]

But you STILL have to build a new foundation wall below the new wall...

[Nelsn]

You are right Richard, but then I do not have to worry about the two major load bearing points that would be created with a load bearing beam holding the weight of all the joist on the addition and the weight of the existing rafters/roof/beam. I think the engineer would call for piers at these points had we gone that way. By the time we go with drilled piers, hangers, concrete, rebar, labor etc. having the concrete guys install a beam under the new wall where the floor will be removed anyway comes out ahead. I was going to go with the beam until further thought of the weight added to a 40 year old foundation came into play. Will post pics as we go.

[carlsguide]

You guys are good. That's all I wanted to say. I'm impressed.