If you are a nerd like I am, you may have noticed that parapets are often the first masonry feature on a Chicago building to deteriorate. This could be explained by the roofing membrane (waterproofing) that is often lapped up and over the parapet.
To give you an example, here is a picture of our original parapet from 2009.
Lapping the roofing membrane up and over the parapet may make sense in terms of waterproofing the roof. But it also creates a vapor barrier on the parapet side facing the roof. The parapet can now only dry into one direction – the side facing away from the roof. And this increased vapor pressure could be the cause for an accelerated parapet deterioration. Something I recently ran into head on with our front parapet.
If I could eliminate the vapor barrier, the parapet would dry in both directions. And that was my goal.
The solution was to install a dimple mat along the inside of the parapet, and then install the roofing membrane flashing up against the dimple mat. This way I created an air gap along the inside of the masonry wall – a vent strip.
All that was left was to cut the mat flush with the parapet, after we had the dimple mat attached to the parapet and the cant strips placed at the parapet base. We were now ready to install the roofing membranes, starting with the base.
We had emergency repairs done to the east and west parapet back in 2009. Back then I had the hunch that additional work may be needed once we began redoing the roof. That hunch became a prophecy.
Don’t get me wrong. The parapet repairs from 2009 were perfectly fine. The issue that I faced had to do with roof insulation.
We insulated the roof between the rafters. And I learned (the hard way) that we needed to continue with the roof insulation above the roof deck. The insulation above keeps the roof deck on the warm side so stays drier during the winter months.
Adding layers of insulation onto the roof deck shortens the height of our current parapet. To maintain the code required height, I needed to raise the parapet. I called our mason back and purchased a few pallets of additional salvaged common brick.
I mentioned a couple of posts back that working with common brick requires certain steps and a certain type of mortar to produce a lasting masonry system. And I have described the process and materials in a previous post (Mending more masonry + Bricks and mortar). I recommend that you look up that post if you plan a project that would use Chicago common brick.
One key aspect is to make sure the common brick is properly soaked in water prior to installation. This prevents the brick from pulling water out of the mortar. And that in turn provides the desired bond between the common brick and mortar.
It is also a good idea to keep wetting the brick during and sometime after the installation for the same reason. So I kept busy spraying it down. This can be a full time job during a sunny and hot day. The common brick dries out rather quickly. Cooler and overcast days are easier.
The cornice was repaired and re-attached to the masonry. It was time to call the mason back to finish the brick work on the front parapet.
The parapet repair behind the cornice was all done using common brick. From the cornice tie-in upwards, we switched to Roman face brick. The same brick that was used below on the front façade. Lucky for us, there is one company left in the Midwest (the Belden Brick Company), that still manufactures Roman face brick.
But we didn’t just use Roman face brick. To keep with the architecture of the facade below, we integrated graystone into the front parapet. This is the graystone that I salvaged a few years back from buildings that were torn down nearby.
The front parapet has a depth of three wythes. We rebuilt the wythe facing the street with graystone and Roman brick. The other two wythes behind it were invisible. Here we used regular common bricks again.
To render the common brick stable, we used header courses to tie the wythes together. To connect the street-facing wythe – the graystone and Roman brick – I used ties to connect the graystone pieces to the common brick behind.
Getting the cornice and front parapet repair out of the way was a major milestone. I could now focus on raising the parapets along the east and west sides in preparation for the re-roofing.
I covered in the previous post how we removed the old and crumbling parapet until we hit solid masonry. This post will cover the first stage of the parapet rebuilding.
I had to break-up the process into stages, because along the way, I had to repair the cornice that was attached to the masonry. I will cover that part in the next post.
We started the rebuilding from the solid masonry we had exposed, up to the level where the original cornice roof tied into the masonry. The new cornice roof, which we were about to install, will tie in at the same masonry course.
The parapet had a depth of three wythes. The cornice would only attach to the first wythe, which meant we could continue to raise the back two wythes.
Like most of the building, the core of the parapet used Chicago common brick. Working with common brick is a different process than working with modern brick products. It requires certain steps and a certain type of mortar to produce a lasting masonry system.
I have described the process and materials in a previous post (Mending more masonry + Bricks and mortar), and recommend that you look up that post if you plan a project that would use Chicago common brick.
Did I mention that the front parapet was badly crumbling? If you wonder why, the answer is easy: bulk water infiltration into the masonry.
The cornice roof (a copper sheet) was supposed to shed water away from the building. Not only did the cornice roof come apart at the seams, it had bent inwards, allowing water to pond right behind the edge. To “solve” that problem, a previous owner had punched small drain holes into the copper sheet, allowing ponding water to enter the cornice interior and the masonry behind.
Some of that masonry had deteriorated so badly that someone put a layer of cement parging across it to prevent it from falling off. That, however, further aggravated the problem, because the cement parging trapped moisture and prevented the masonry from drying out.
We went around and peeled back the roofing membrane which was lapped across the parapet. Underneath that, we found rows of mostly loose brick, if we were lucky. Behind the cement parging, we found brick crumbles.
There was hardly anything to salvage. We scooped up all the loose material and slowly worked our way down until we hit solid masonry. That meant in many cases going down to the bottom of the cornice.
From this point on, we could begin to rebuild the parapet in stages, and along the way, repair the cornice.
As usual, many thanks to our skilled friends Augusta and Rubani who helped us in this adventure.