Subversive De-Icicling

2 February 2019

Once again I was in a conference call, comparing the sizes of icicles in photos. We had designed a renovation of a one-story building in the Adirondacks to reduce the massive buildup of icicles on all the roof edges that had occurred every winter. Our proposed solution, which had been executed the previous summer, involved relocating the thermal plane from the attic floor to above the sloping roof – essentially “pushing the envelope” out to incorporate the leaky attic heating ducts into the conditioned building space and take the ineffective attic floor insulation and air permeable ceiling out of the equation. The large overhanging roof soffits were air sealed and stuffed with insulation. We even included air return registers at the peaks of the attics to prevent humidity buildup.

The scheme had its detractors, but I had felt confident that this would solve the client’s problem: The icicles. They had been so severe that they posed safety risks, and the ice dams caused water backup and leakage. The roof edges were being repeatedly damaged from workers hacking away at the ice. The side benefits that I had touted, which included reduced energy usage, more comfortable interior spaces, and lower carbon emissions – were all ancillary, and were not driving the project. The icicles had to go.

But the pictures, taken two days apart during single-digit temperatures, were incontrovertible: The icicles were still growing over the mechanical room. Our client was not happy, and I was baffled and frustrated. Buildings are complicated. Why did I ever think that we could make this work? Will I need to tell my partners that we might need to spend some money to fix this problem? Will this be the end of our Building Envelope Services?

Then the conference call took a turn. The people who actually worked in and maintained the building started to talk. Their stories painted a very different picture:
• The reduction of icicle buildup on the roof edges this year compared to previous years is “amazing.”
• No water is leaking inside the building.
• The small area where the icicles continue to build are in an inaccessible rear corner of the building, which is not causing a problem to anyone.
• The rooms at the ends of the building, which in previous years were so cold that people complained, are comfortable – even during the recent bitter cold snap.
• Heating oil usage is about ONE THIRD of what it was last year.

“Alleluia!” I said out loud in the call. The Owner’s Program Requirements had been met, and then some. Looks like the strategy, and the execution, worked the way we thought it would. But what about the area where the icicles continue to grow?

When it’s very cold, the furnaces run longer and more frequently. This pushes more hot air through the leaky, poorly insulated ducts in the attic, which are clustered over the mechanical room. The heat from these ducts, as well as from the uninsulated flues from old, inefficient furnaces, heat that attic to well above the anticipated interior temperature, which melts the snow on the roof. Sealing the ducts and improving their insulation, and insulating the hot flues – or better yet, replacing the old furnaces with more efficient condensing units – will mitigate this problem and further reduce building energy usage – if they want to.

So we’ll continue to take on de-icicling existing buildings, best we can, one challenging roller-coaster of a project at a time. We can usually improve, if not completely eliminate, icicle buildup, while accomplishing our secret agenda of dramatically reducing buildings’ carbon emissions. Until and unless carbon is given an economic value in the market, it’s is the way that we can make some headway in this epic battle to lower anthropogenic greenhouse gases.


Four Meta-Metaphors

28 February 2017

1 – Imagine that you came home from being out of town for a couple of weeks, opened your front door, and saw water dripping from the ceiling and everything in your home was sopping wet. You realized that a water pipe must have broken in the upstairs bathroom. What’s the first thing you do? The answer, of course, is SHUT OFF THE WATER.
We are pumping 90 million tons of CO2 into the atmosphere every day. It’s starting to cause us big problems that will likely be getting much bigger. What’s the first thing we should do? The answer, of course, is SHUT OFF THE GAS.
The first step in crisis management is that when you find yourself in a hole, STOP DIGGING.
2 – Suppose an oncologist diagnoses you with cancer and advises drastic and immediate intervention – surgery, chemotherapy and radiation. Would you get a second opinion? A third? How many doctors would you go to until you found one who dismissed your symptoms and told you there was nothing to worry about? 20 or more? And then – would you really believe them?
Some people embrace the beliefs of the small minority of climate scientists who don’t accept the basic tenets of anthropogenic climate change (ACC). There will never be complete consensus by all scientists – climate science is too complex to expect such a thing. But there is a very significant majority of opinion that it’s real, and it’s a problem. Who do you believe – the overwhelming majority or the very small (but vocal) minority?
3 – When it was in my 30s, I took out an term life insurance policy. I knew the odds of my dying in that one year were very small – less than 5% – but the potential consequences of my family suffering financially were something that I did not want to risk.
As a structural engineer I have designed hospitals for seismic events that have less than a 5% likelihood of occurring within the anticipated service life of the building – to avoid the potential of catastrophic consequences.
What do you think is the likelihood that all of the climate scientists that are concerned about ACC are in error? If less than 100%, do you not think it worth some precaution, given the potential for global catastrophic consequences?
4 – What if astronomers discovered that a large meteor was headed directly for Earth’s path, and that in a few years it would cause an unprecedented global calamity if nothing was done. What if engineers then devised a massive plan to divert the meteor and prevent its impact. The plan was determined to have a high probability of succeeding if development started immediately. Implementing it would take a refocusing of resources worldwide, but economic studies showed that there would be significant economic benefits – not only from the avoidance of an economic (and humanitarian) calamity, but from the subsidiary benefits of the necessary global economic cooperation and R&D needed to execute the plan. Would we accept the astronomers’ warning and commit to action, or would we refuse to believe them?
ACC is our meteor. We cannot tolerate leaders who deny the science, and delay or reverse action.

Practitioners in the profession of engineering affirm and value reliable data and use it to advance the human enterprise. We develop engineering solutions to problems based on scientific advancements that improve our understanding of the physical world. Accordingly, taking action to address the effect that human activities have on climate stability is in our wheelhouse.

I would make the case for engineers to acknowledge and act on anthropogenic climate disruption with some simple points:

  1. The global average air and ocean temperature at the Earth’s surface is increasing. This is a trend since the 1970’s and there has been a significant spike in the past couple of years. Reference data from NASA, NOAA, or any of the other international data sets.
  2. Since warm air holds more water, there is now about 4% more moisture in the atmosphere than there was about 40 years ago. This has caused an increase in the global intensity and frequency of large storms and flooding events. At the same time, severe droughts have increased, mainly because warmer temperatures evaporate more moisture from land surfaces.
  3. The amount of C02 in the atmosphere has increased by 30% since the 1800’s. It had previously held fairly steady for millennia. Even more dramatic spikes in methane, nitrous oxide, and other gases have also occurred within this short timeframe. EPA has good data.
  4. A significant majority of climate scientists agree on the cause-and-effect relationship between human emissions of CO2 and other greenhouse gases and climate disruption.
  5. Climate disruption will become worse in future years. However, the changes will be less severe if we reduce greenhouse gas emissions. The sooner we act, the better the outcome.
  6. The engineering of systems such as buildings, energy and water distribution, transportation, and other infrastructure systems has tremendous potential in reducing emissions. The first step is to quantify the impact, or footprint, of these systems, and then develop alternatives that reduce or eliminate the greenhouse gas emissions. We have better credible information, tools, and ideas than ever before to help us make these changes.

Thank you for reading this far. I do hope that you are not reading it simply to identify things to attack, with references to papers that are not in the mainstream of scientific thought on this. Climate change is a complex science – I wouldn’t put it upon the scientific community to uniformly “consent” – the advancement of science simply doesn’t work that way. I am not a climate scientist. I am an engineer.

I see this period of time as a critical turning point, for humans and the engineering profession in particular. The world needs us to be the best engineers that we can be, in the largest sense of the word.

Many of our clients had been using the “Prescriptive R-Value” method of compliance for reroofing projects. This is the simplest of the compliance paths, but also the most conservative. With the adoption of the new 2016 New York State Energy Code on 3 October, it may be time to consider an alternative – namely, the Prescriptive U-Factor, since the new code changed the required prescriptive R-value of above-deck insulation in Climate Zones 5 and 6 from 20 to 30 – a 50% increase. The prescriptive U-factor method requirements, as well as the thresholds for COMcheck and REScheck, have changed similarly, but require less insulation for tapered insulation systems. Here’s why.
The R-value of insulation, which most everyone is familiar with, has a straightforward but subtly complex relationship with its inverted counterpart, the U-factor. Simply put, U=1/R and R=1/U. This means that while an assembly’s R-value increases linearly with insulation thickness, the corresponding U-factor decreases asymptotically. Many design professionals are not clear what the implications of this are, regarding variable or tapered insulation thicknesses. Are you?
What this means is that R-values cannot be averaged by area. In order to determine an effective R-value for varying amounts of insulation, you can invert the R-values to arrive at U-factors for each area, obtain an area-weighted average U-factor, then invert the result. See below.
In the world of roof insulation, tapered thicknesses to create positive pitches to drains are common. This makes the calculation rather complex, as shown below.
So how does a conscientious design professional determine the adequacy of a tapered insulation roof assembly to meet code? In order to come up with the effective U-factor for each roof area, either the natural log formula or charts for various roof insulation configurations can be used. These both require nothing more than the maximum and minimum R-values of the tapered insulation. We have simplified and summarized the analysis to present some common code-compliant configurations for both polyisocyanurate and rock wool insulation.
The above figures illustrate the different amounts of insulation required for the different energy code compliance paths: the prescriptive minimum R-value method, which mandates a minimum amount of insulation at all areas of roof, and the prescriptive U-factor method, as well as the envelope component tradeoff method, which both allow an averaging of the U-factors to compare to the maximum prescribed value. For the latter two methods, thicker areas of insulation can offset the thinner areas, such as around drains. COMcheck and REScheck both use the envelope component tradeoff method – you need to understand how to properly determine the effective average insulation values in order to correctly use these programs.
Another major difference between the R-value and U-factor methods is the ability to include the thermal resistance of the other, non-insulation components of an assembly, including the interior and exterior air films, in the calculations to determine an area’s U-factor. For opaque walls this can be significant, but less so for roof calculations – since the thermal requirements are so high, the contribution of the insulation is a much larger percentage of the overall thermal resistance of an assembly.
The fourth compliance path, total building performance, requires the use of energy modeling to show a reduction in the energy cost of a building compared to a base building. Using this method, tradeoffs between envelope and mechanical system performance can offset each other. However, with this method the baseline against which the proposed building must be compared must be modeled with an envelope performance meeting the prescriptive requirements, so this is not an easy way to reduce required insulation amounts.
Finally, with the prescriptive U-factor, envelope trade-off, and performance compliance paths, any thermal bridging conditions present must be taken into account by including an area of roof with a higher U-value in the calculations. This includes any grillage penetrations, roof edge angles, and clerestory wall support details. Consult a structural engineer with an understanding of how to quantify the thermal losses of thermal bridging details for advice.

I recently asked a group of about 20 structural engineers in Pittsburgh if they thought that structural engineers should have any obligation to address energy code requirements. Less than half of them responded affirmatively. We then explored the topic a bit – which was apparently the first time that many of them had considered such a notion.

  • Is compliance with Energy Codes any less important than compliance with other codes, such as the Building Code? Of course SE’s consider the structural portions of the IBC – Chapters 16, 17, and the others – of paramount importance to their work in providing assurance of structural safety and reliability. How can energy efficiency be considered in the same category of importance? Well, the truth is – noncompliance with any part of the applicable codes just as illegal as any other. Code requirements are code requirements.
  • For those SE’s who feel that the design and detailing of building envelopes is a separate task for others to address – how many SE’s show a vapor barrier under their slabs on grade? The purpose of this material – frequently included by rote in our details – is to mitigate vapor drive through the building envelope. It has absolutely nothing to do with the structural performance of the slab. In this way, structural engineers have been incorporating fairly sophisticated building science principles into our designs for years. The inescapable fact is that buildings are integrated systems, and structural components can have major effects on nonstructural system performance – especially envelopes.
  • Some structural engineers show foundation insulation (where the climate zones warrant it) and some do not. The problem develops when the insulation integrates with – or even interrupts – the structural foundation and perimeter slab edge detail. Building envelope professionals now realize that proper detailing of the insulation conditions at slab edges and continuity of insulation with minimal thermal breaks can greatly affect the amount of energy loss through the envelope – and can be an essential aspect of compliance with energy code requirements.
  • A serious problem developed with steel shelf angle and roof edge angle details while we were not paying attention. The prevalence of continuous wall insulation has obliged us to design these elements with thick horizontal projecting legs to span across the insulation. Ironically, these conditions represent tremendous building energy loss due to thermal steel bridging. There are alternatives to these thick, continuous conductive plates through the insulated envelope that should be illegal in my opinion, and in some places actually are.
  • Many other structural conditions at building perimeters warrant consideration of thermal transfer effects, including balconies, canopies, lintels, steel-framed roof overhangs, and CFMF conditions. These represent opportunities to actively engage with architects, owners, and other members of the design team to address these conditions, which can lead to very positive results.

As a Professional Engineer, I feel it is important to have a high level of control in what I design and what gets built under my stamp. If structural details need to be modified to improve the energy performance of the envelope of a building, it should be done by the Structural Engineer of Record – whether the purpose is to assist with code compliance, or to better coordinate with the architectural design, or because we know that proper attention to our structural details can improve the energy performance of our buildings.

These eight tenets form the basis of my perspective as a structural engineer in 2015.

  1. Anthropogenic Climate Change (ACC) – that is, the changing of the planet’s climate due human emissions of Global Warming Potential (GWP) gases into the atmosphere – is real and is occurring now.
  2. The short-term effects of ACC are presently happening, in the form of warming air and oceanic temperatures, increased intensity and frequency of storms and drought events, geographic shifts in plant and animal species concentrations, and reduction of polar and glacial ice. The long-term consequences of ACC are not clear, but may include catastrophic conditions.
  3. Mitigation of the most severe potential effects is possible, if enough action is taken. Effective action needs to be taken on several levels: Personal, Political, and Professional.
  4. Individuals need to take personal action to reduce their contribution to GWP gas emissions. Most important actions include reducing fossil fuel usage in home heating, cooling, and electrical usage, product awareness (including food), and fuel usage for travel.
  5. Political action needs to be taken to restrict high GWP gas emissions activities, especially for energy production, transportation, and manufacture of materials with high GWP gas emissions. Emissions of GWP gases in the form of carbon dioxide equivalent (CO2-e) by weight, must be appropriately factored into the costs of goods and services.
  6. Every professional must consider how their profession can facilitate the mitigation of CO2-e gas emissions, either by technological advances or implementation, education, or facilitating the transition to economic and social systems where CO2-e mitigation is the norm.
  7. Engineers must acknowledge their role as leaders in creating, maintaining, and advancing the various systems that society has become dependent upon, and incorporate an understanding of the need to reduce GWP gas emissions into every aspect of their work.
  8. Structural engineers must develop and implement strategies to reduce GWP gas emissions from the manufacture and construction of the structures they design, and acknowledge the role that a building structure can play in the ongoing heating and cooling operations of conditioned buildings.

Comments and suggestions are welcome!

Here is a radical, yet very doable, concept to greatly reduce the CO2 emitted from the construction of slabs-on-grade for most buildings, compared to conventional construction:

• Screed the slab ½” low, do not trowel finish it, and apply a self-leveling underlayment topping.
• Reduce the slab concrete’s design strength to, say, 100 psi. *
• Further reduce the Portland cement in the slab using fly ash and slag.
• Use a superplasticizer to achieve a 0.42 W/C ratio (including the weight of the fly ash and slag in C).
• Reduce the thickness of the slab from what is typically needed to minimize warping, since the less-strong concrete will have much less potential to warp.

* – The underlayment topping distributes point loads, so that the slab can be much less strong. If the base concrete is 100 psi, that’s still 14,400 psf, or over 200 times the required strength. A floor design load of 100 psf = less than 1 psi, yet we typically use (at least) 3000 psi concrete.

For example, say a 10,000 square foot, 5″ thick concrete slab-on-grade is specified at 3000 psf at 28 days. A standard mix design would have, perhaps, 400 lbs. of Portland cement per yard. This would be about 425 lbs. of CO2 per yard, with the majority of that emitted into the atmosphere during the manufacturing of the Portland cement.

Total lbs. of CO2 = 10,000 sf x 5/12 ft thick / 27 cf/cy x 425 lbs./cy = 65,600 lbs.

Yes, that’s nearly 33 TONS of CO2 for every 10,000 sf of slab, or 6.6 lbs for every square foot.

If we use a 3½” thick, low-strength, low-cement concrete, with 50 lbs. Portland cement (say 100. lbs CO2 per yard) and fly ash and slag with superplasticizers for a 0.42 W/C ratio, screeded level but not finished, and a ½” thick self-leveling underlayment topping of, say, 400 lbs CO2 per yard:

Slab CO2 = 10,000 sf x 3.5/12 ft thick / 27 cf/cy x 100 lbs./cy = 10,800 lbs.
Topping CO2 = 10,000 sf x 0.5/12 ft thick / 27 cf/cy x 400 lbs./cy = 6,200 lbs.
Total lbs. of CO2 = 17,000 lbs.

That’s 48,600 less lbs. of CO2, or a reduction of 74%.

Note that the CO2 emissions of the concrete and underlayment are estimated, for this exercise.

Other benefits:

• No need for a trowel finish on the concrete slab
• Slab finishes can be applied sooner, due to reduced levels of water vapor emissions
• Reduced potential for cracking and warping
• Cost neutral: Less expensive concrete, less slab placement labor offsets underlayment cost

To be clear: I’ve never seen such a slab. Concrete suppliers are reluctant to use low-strength concrete in a finished application, and contractors and engineers are reluctant to perform such “experiments.” But I can see no reason why this won’t work. The fact that such ideas, which could dramatically change the CO2 landscape of building construction, are not even being considered is testament to the fact that at this time in the U.S., the market value of reducing CO2 in building construction systems is zero – or less.

Two brand-new references provide much-needed veracity to this approach:

Palmer, William D., Jr. “Fast, Flat, Moisture-Free, Concrete Construction Magazine October 2014

National Ready-Mixed Concrete Association (NRMCA), NRMCA Member Industry-Wide EPD for Ready Mixed Concrete, October 2014