Adding a 5th Floor

[shobroco]

I've got an owner who wants to put a 5th floor on a 115 year old 4 storey masonry load-bearing wall (4 wythes of brick) building. It has wood-framed floors & flat roof. He has a prospective tenant who wants to run a rooftop restaurant, mostly glass-enclosed. The building is only 28' wide, but 150' long. I think I can drop a steel structure on top of the walls consisting of basically a pre-eng frame with floor beam/tie at the column base that will carry joists between the frames. If the frames are close together (15-16') & the baseplates big enough, the brick can carry the gravity loads and there is minimal lateral load on the masonry. The brick walls extend 2' above the wood roof joists so the roof can remain in place. I have not done any calcs yet, it has all come up very quickly. Am I crazy?

 

[shobroco]

Dik:The exterior architect has lots of experience with historic masonry & he's working on several aspects of the envelope; I've dealt with it a fair bit as well. There has never been a vapour barrier in this building & there won't be now, however we are looking at interior surface treatments. We are working with a masonry restoration company that has been a leader in this field for several decades.

MM: There is 0 distance between the buildings; in fact they have a common wall in one area. There is a sign painted on the former exterior of the neighbouring building that was uncovered when the plaster was removed.

 

[dik]

Just a caution... new buildings due to their use have a lot more vapour... that should be addressed...

Dik

 

[jdgengineer]

I have never done epoxy in the beam pockets but that is an interesting thought. I wouldn't be surprised if it hasn't been tested. Although unrelated I know when installing a wood Shearwall to an existing wood diaphragm I think there have been some installations that use wood glue to establish the diaphragm connection rather than trying to use an -a34 clip or similar with small screws to the underside of the diaphragm. Not really similar but kinda on the same line.

Also for some ideas I'd recommend checking out FEMA 547 it's a good reference for retrofitting existing buildings.

 

[bookowski]

I think a lot of this will depend on your local code.

I am in NYC and we do this type of thing all the time. The code here is extremely forgiving with alterations to existing buildings including adding stories and increasing load while not forcing you to upgrade. Whether or not that is good practice is a separate issue but it is done very frequently.

As for cast iron columns - you can find a lot of literature that will give you the original design strength equations (look at a book called 'Historical Building Construction', it has a lot of good references). I would not trust those at all though. If you follow the history of those equations you will find that the design capacity was successively reduced as we learned more about cast iron columns until eventually we stopped using them. One of the biggest problems is the connections. They are truly close to a pin, they basically just stack the columns and add some very wimpy connection plates. I would not increase the load at all on existing cast iron, it is unpredictable. You should span outer brick wall to wall, and add posts/reinforce as required at those areas.

 

[JacksPanic]

all i can say is good luck.
whenever an alteration is done to a building here, we have to bring it up to code requirements (seismic).

 

[paddingtongreen]

The last one that I did like this had a listed exterior and high ceilings. It was also completely empty. We found that by progressively gutting and replacing the interior structure on a different grid, we could squeeze an extra floor in the same height with just a slightly raised glass mansard (almost hidden behind the existing parapet from a ground view), the mansard being only two or three feet high at the top of the wall. We would have needed major strengthening of the existing structure to make code.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[shobroco]

Thanks to everyone for the input. I just spent 2 days with a metal building systems company at their annual meeting & one of their guys did this 25 years ago on an 11 storey building of the same age (not a full 12th floor addition, just a section). I have told the owner that we might be able to do it but I have a lot of issues to work through. I have the MBS company doing a design for the full structural package of the addition, floor included. I am specifying where they can load the walls; they will give me reactions, & I have to go from there. I'll post a thread in a while when I know where it's going.

 

[dik]

This may not fly with a dedicated building, specially the facade... Depending on the building and the approvals required this could take months/years...

Dik

 

[shobroco]

Dik: The pretty pictures are currntly under review by the heritage board; they are not opposed to the first impressions, but it's a long way from approved. They issued a permit & gave the owner some slack on the facades and the work he had already started only because they know the team presenting the proposal (myself, the architect, & the masonry company) but that's only going to go so far with the rest of it. The bigger issue will likely be the building itself & whether or not it can handle it.