forces to existing building for new patio cover

[radiocontrolhead]

I've been searching for this with no luck.

I have a new patio cover addition where the open end will be designed as cantilever columns (lateral checked). however, when it comes to the interface of the new patio cover and existing building (attached via a ledger connection) how do you typically account for the forces to the existing exterior wall in plane?

I'm designing for an R of 1.5 for the cantilever column system but trying to check existing conditions for that level of force requires a significant retrofit of exterior wall. There has to be a more reasonable way. I cannot find a code provision that addresses this situation but can it be reasonable to assume that the exterior wall is checked for the R it was designed with a new tributary area (including patio cover)?

 

[LockeBT]

Code-wise, I think that falls under the combination of different SFRS in the same direction. The most stringent system (one with the lower R) will govern the design. Sauce: ASCE 7-16 Section 12.2.3.

I honestly do not know how this is typically done. Before even having your problem mine starts at using "Timber Frames" system. They're not even allowed in SDC E or F (I'm CA so pretty much everything is in these 2 SDCs) yet I see them everywhere and I'm not sure how they get approved or designed. I am guessing you are using Ordinary Steel Cantilever Column? If you are using wood columns then I'm guessing you are not in SDC E or F?

Technically the right way of doing it is what you mentioned. Which ends up with a much costlier project due to the shearwall retrofit. Heck you might end up finding out not only your shearwall isn't working with the additional shear force, now your holddowns/anchorage might not work either. The clients will give you a giant "WTF!?".

I worked as a building plan checker for 1 1/2 year and I have always let this go even though I tend to discuss my decision with the design engineer first (they are ultimately the EOR). Most of them share your sentiment. So if you factor down the shear force proportional with the R of your shearwall I would approve it. It's my engineering judgement lol. Cover patio failure due to lateral loading is uncommon and residential constructions have a lot of redundancy anyway.