Tag Archives: moisture management

Vent strip installation

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.

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Front parapet demo

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.

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Bracing for the cornice issue

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.

Next step, taking down the crumbling parapet.

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Chiberia 2019 – ERV hibernation

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.

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Wet duct insulation!

Let’s stick with the ventilation subject for a moment, dear readers, because I need help with a hack. I hope that some of you can point me in the right direction. Here is the problem that needs solving:

The duct insulation in the flex ducts that connect to my ERV is getting wet every winter.

Why do I have the flex duct in the first place?

The purpose of the flex duct is to stop vibration transmission from the ERV to the rigid ducts.

Why does the duct get wet?

During the winter month the fresh air intake carries cold air and the exhaust duct from the ERV to the building exterior does the same. This cold air often cools down the duct below the dewpoint. That causes any moisture that is lingering in the flex duct or that gets past the duct sleeve to condense on the flex duct core. It is subsequently absorbed by the fiberglass insulation around the flex duct. Theoretically, this should not happen. The outer duct sleeve should prevent any air, and with it moisture, from getting to the flex duct core.

The weak points in this system are where the flex duct connects to the rigid duct, and even more so, were it connects to the ERV.

I use sturdy duct zip ties and even have the tool to zip them as tight as possible. But even with utmost diligence, it appears impossible to make these connections airtight.

An added complication is that the ERV needs occasional maintenance, which in some cases requires me to disconnect the flex ducts from the ERV. The zip tie system makes disconnecting and reconnecting fairly easy, but apparently fails to get it 100% airtight. I am also concerned that handling the duct during the maintenance operations may lead to breaches in the duct sleeve.

Solutions?

Is there a product out there that would be better than flex duct but still provide the vibration isolation? Or is there a better system for connecting and sealing the flex duct to the ERV?

Whatever a better and air tight solution may be, it must allow for easy disconnection and reconnection of the duct to the ERV.

Any suggestions? Who’s going first?

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