Although we had the solar posts installed, we were not moving ahead with the solar array right away. There were a few other items that we needed to address first, namely the drainage layer and the insulated roof pavers, which will be the subject of the next posts.
I have designed and engineered enough green roofs to understand that materials on top of a roofing system should be separated by an appropriate drainage layer. In our case, we opted for a 1/4 inch dimple mat, with a geotextile on top. It is the very same material we used for the vent strip installation.
The 1/4 inch mat gave us enough flow rate to effectively drain precipitation off the roof and prevent the forthcoming insulated pavers from sitting in water. The geotextile that is attached to the top of the dimples helps to keep debris out of the 1/4 gap to maintain the needed flow rate.
The material selection came naturally: While scouting our regional reuse stores, I came across several rolls of the dimple mat, which must have been surplus from another project. I was short a couple of rolls, but was able to purchase those new to have enough square footage for our roof.
The mat came in rolls measuring 4 feet by 50 feet and should be installed perpendicular to the roof slope, starting at the bottom of the roof, similar to the base sheet and torch down membrane. For logistical reasons, we started laying down the mat at the top, but made sure that all the overlaps were pointing downstream.
We very carefully swept the roof first to make sure there was no debris under the drainage mat. While rolling it out, we cut small openings into the mat to fit it over the solar posts. We also made sure to weigh it down with pavers to prevent it from blowing off.
Along the parapet, we extended the drainage mat over the cant strips, similar to the base sheet and torch down installation. We can always cut the drainage mat back later, if needed, but we can’t add to it.
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.
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.
Our house came with a beautiful cornice that was attached to and supported by the parapet behind it. It was constructed out of copper, but the bottom section had been painted, unfortunately.
It has terrified me for years. This was because upon closer inspection, the top of the cornice was in dire need of repair and we had water infiltration issues, which led the supporting parapet to crumble. And no matter who I asked, I never got a straight answer on how it actually was constructed, supported or attached to the building. It remained shrouded in mystery, leaving me to procrastinate.
With the looming solar array installation, there was no avoiding this any longer. I opened up the top copper sheet to get a visual on the inside and the attachment mechanism – or lack thereof. And the more I started digging the more terrifying it got.
The “support mechanism” was rotting pine boards, which were rotting either in the masonry or the opposite end. And the supporting masonry had deteriorated into loosely stacked bricks.
The crumbling masonry had to be removed and rebuilt. The bottom of the cornice was salvageable, but the top sheet had to be entirely replaced to prevent any further water infiltration into the masonry behind. Mind you, the job of the cornice is to shed water away from the building façade. Along with all this we needed a new support mechanism.
To save and reuse the bottom section of the cornice, I had to brace it before I could remove and repair any of the masonry or top copper sheet. The last thing I wanted was for it to fall off the building.
I managed to score a stack of reclaimed two by fours at The Rebuilding Exchange, which I used to rig up a solid bracing system.
Two aspects of our mechanical system fell victim to the Siberian express that ran over us during the last week of January. One of them was the Energy Recovery Ventilator (ERV).
The ERV typically operates down to 10 degrees Fahrenheit (-12 degrees Celsius). Below that, the enthalpy wheel freezes up, and a temperature sensor in the ERV shuts the unit off. That meant that we were without mechanical ventilation for three days.
That’s not too much of a problem, as we could crack open a window or two to get fresh air into the building. The down side was the big energy penalty when opening the windows.
I can report that it didn’t get stuffy despite the presence of two human beings and two dogs, and that humidity levels stayed under control as was evident by the minimal condensation at the bottom of the windows during the early morning hours.
Our ERV is an earlier model of the RecoupAerator 200DX. With the current model, temperatures below 10 degrees Fahrenheit (-12 degrees Celsius) should not be an issue as the unit comes with a pre-heating element.
The element is built into the fresh air intake and is tied to a temperature sensor which pulses it on and off as needed to maintain the incoming air at 12 degrees Fahrenheit (-11 degrees Celsius) to prevent the enthalpy wheel from freeze up. This allows the unit to operate at outdoor temperatures below 10 degrees Fahrenheit (-12 degrees Celsius). And if combined with a solar PV array, it can even operate at a low carbon footprint.