Remodel of 1922 Wood Home

[digrazi]

A client would like to add a two story addition to an existing two story wood framed home that was built in 1922. The addition will add approximately 25% to the length of the building in the longer direction. Is there a "best practices" approach for the lateral analysis of the new portion? Should we add some mass and loads from the old building into the loads on the new portion? Should the new portion be stiffened beyond what is needed for itself to accomodate possible lateral loads from the old building? Is it ok to assume that the existing building is adequate laterally and design the new portion so as to add no new loads to the old building?

Is there any good reference material that deals with this situation?

 

[SperlingPE]

If you connect to the existing, you will need to investigate what lateral capacity there is and design accordingly (possibly strengthen the existing structure). If you do not rely on the existing structure for stability, the new structure will have to stand on its own. Where ever you connect to the existing, more than likely you are taking capacity away from the exisiting (by removing plaster, sheathing, bracing, etc.) YOu will need to account for this loss.

 

[whyun]

I will assume the new two story addition is a lateral expansion and not vertical.

To avoid having to analyse the "combined" structure, you can construct the new building adjacent to the existing with a lateral separation joint. There will be no load added to the existing building (vertical and lateral); only price you pay is having a "double wall".

 

[digrazi]

Yes. The addition is only lateral. No new vertical loads are being added to the old building. I think I would prefer to make the addition stand alone as I am sure the client does not want to modify the existing building. Nor do I really...sounds like a much larger "can of worms". I think the added wall and foundation for a stand alone adjacent structure would be more cost effective for me and the owner than analyzing and retrofitting the entire old building. So the only material connecting the two portions will be essentially finish materials? That makes sense to me.