Addition in existing buildup of log home (shear)

[josta]

We have a one-story with loft log home on a downslope lot with a wood frame buildup 12' high on the downside, and 2' high on the upside. The Owners would like to convert the buildup area into livable space with new windows.

County plan checker is saying not only do I have to check the buildup for lateral loads with the new openings but he also wants the existing upper floor checked as well, which could mean having to retrofit the existing log shear walls (somehow!).

One engineer said he would only check the buildup and another says to check the whole house. Your thoughts?

Thanks!

 

[jayrod12]

I'm assuming we are discussing seismic lateral and not just wind lateral?

If it were seismic I would likely be including the whole building, wind only and I would likely only check the infill.

You could have a structural separation between the two allowing the existing to stay as is and you only having to design the new. But that's generally too costly and requires funky detailing.

 

[msquared48]

Unless the structure was never permitted, I would just say to check the lateral on the lower story (you will have to generate the load using the upper story anyway), and check the log headers remaining to make sure they are adequate for gravity, considering any point loads from the framing above.

Yes, hold down retrofitting will be a bear unless you can show that the wall can span from end to end as a timber frame using only the remaining structure... Just a thought....

If this does not work, you could always go to an internal plywood shearwall. Not the best alternative, but it would give them another level.

Mike McCann, PE, SE (WA)