repairing masonry parapets on 80 yr old building

[archeng59]

I am working on a renovation/restoration project. the building is 80 years old with clay brick/clay tile parapets that are damaged and need to be repaired/replaced. Most of the damage is on the back side of the parapets at the roof flashing level. The parapets are approximately 6 ft tall above the roof deck and lean outward. a masonry specialist recommends removing and replacing the masonry with CMU and brick veneer, with most of the veneer consisting of repaired existing brick. not sure about using the CMU but will explore shrinkage/expansion differences between the CMU and clay masonry. that aside, I need to reinforce the parapets. the reinforcing needs to extend far enough below the roof deck for adequate rebar embedment. wondering if there is a good source (historic renovation website, etc.) regarding how to handle the interface between base of CMU (if used) and the top of the remaining structural clay tile.

 

[jjeng2]

If applicable to project, consider bracing the parapet back to the roof. Hilti cont. L at top or at more than one level and brace back to roof framing.

 

[JAE]

Yes, I would agree.. you will have lots of difficulty putting back a pure - 6' tall parapet and meeting today's code requirements for wind and/or seismic. In addition, the clay tile below is probably unreinforced so, as you have asked, there is a great difficulty in turning the tile wall below into a wall capable of resisting the bending from the parapet above.

I would see if some type of diagonal strut system could be installed behind the parapets.

Alternatively, you could see what your roof structural system is comprised of and transfer the lateral moment from the parapet into the roof, bypassing the wall below.

If you are putting back the old brick, be sure to have the existing mortar analyzed to allow the new mortar to be of similar properties...specifically the amount of lime content should be higher with older buildings. A mortar with too high of a stiffness will fail the brick.

 

[jjeng2]

Also, if you are going to brace you should repoint both front and back and fix any cracks, etc. Make sure that the lateral connection at the roof level is good and fix if reqd. As a side note, sometimes when parapets bulge outward it will rip the flashing or roofing on the back of the parapet...water in, freeze thaw and/or rot, and your connection at the roof becomes compromised.

 

[jjeng2]

If you are looking at reinforcing, consider using post installed CFRP or similar. Would be tough to analyze with a combo clay tile/brick wall but would be easiest practical solution as the parapet could remain in place. I have a similar rehab in progress that I am constantly thinking about. I have mine pretty much worked out but ideas keep popping into my head.

 

[archeng59]

thanks for the suggestions. using braces was my first thought but was rejected by the architects because they didn't want to have to flash around them. Now that we've discussed it more, they like the bracing better than the amount of wall that needs to be removed to properly reinforce the parapets. Now my problem is trying to determine the existing roof framing. The interior ceiling finishes are considered historic and no one wants to damage them to allow me access to the roof framing. wish my x-ray vision was working.

 

[JAE]

Can't you core down from above? Have a contractor slowly remove layers of roofing, sheathing, whatever, with you present. You would then have at least some idea of what's in there.

 

[jjeng2]

You are going to damage the roof and need to repair it in order to build bracing. Get an idea of what youd like to do and demo small portions of roof where you think you will be working anyway.

 

[archeng59]

JAE and jj, those things have been discussed. The roofing will need to be replaced as there is visible water damage to some areas of the ceilings, mostly in the corners where the roof drains are located. The architects are concerned that the interior finishes that are not water-damaged will be damaged when the roof is removed/replaced/repaired. I expect that a good portion of the deck is damaged/corroded in the areas where the water damaged ceiling finishes are located. As of today, I've prepared a preliminary parapet bracing design. The contractor is evaluating it for cost and trying to determine where we can begin some moderate demo of either the roofing or ceilings to determine the roof framing. A wrinkle is that the architect wants the contractor to guarantee repairing any damaged historic finishes. The contractor is refusing. interesting dilemmas.