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Thermal Insulating Properties of Historic Masonry Buildings

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When undertaking the renovation of an historic masonry building, there are two major issues that must be dealt with early in the design phase – what to do about thermal insulation and old windows (I’ll deal with windows on another day). If the building was built before the 1950’s, it is likely that the building was not designed to take advantage of our current HVAC technology, so don’t expect to put in a simple set of ducts and a furnace and move in. As I have been learning more about renovating masonry structures, I have realized it’s much more complicated than that.

The first source of information for any historic project is to consult the Secretary of Interior’s Standards for the Treatment of Historic Properties and the preservation briefs. The standards represent the consensus opinion of historic preservationists and will serve as a guideline for most phases of the project. Some of the requirements may sound expensive or unnecessary, but I strongly suggest following them. If anyone chooses to disregard this advice, please consider doing a lot of research into alternate options before making a final decision.

Keeping heat in your building requires a thermal envelope. When it comes to thermal insulation, brick is a disaster. Don’t let anyone lie to you, this material is a horrible insulator. Sometimes you will read about the benefits of high mass, a mass factor (or M factor), adjusted insulation value, or similar theories. Some of these claims are true under specific conditions, but not in a cold climate. The important thing to understand is that the R value of historic masonry is not high, thus heat and cold will transfer readily through the walls. Masonry walls are typically rated about R = 0.15/in, so a 16″ thick wall has an R = 2.5. Minimum standards for a new building in the midwest are approximately R = 16. This means a modern building has a wall that transmits heat 8x less than a typical historic masonry wall.

This assumes that the R = 2.5 value is accurate, while in reality it may have an actual R = 1.5 or less, there is just so much uncertainty that it is wise to be conservative in your calculations. Basically, the old brick wall is going to need some help in the form of additional insulation. It is possible to add insulation on the exterior or interior, with the interior being much more common because who wants to cover up the facade of an historic building? At this point, we must introduce the next complication: moisture.

Insulating a brick wall by just throwing up some fiberglass batts or foam board puts the brick wall in a bad situation. The wall is the same temperature as the exterior weather, but is exposed to interior air. This will cause condensation on the interior surface, just like the water that puddles around a cold glass during a humid summer day. A typical building has an interior Relative Humidity level of 30% or so. This is a lot of moisture (a lot!), and moisture/water can easily destroy an historic building. If the walls are cold and exposed to the humid interior air, the wall will generate a nearly unlimited amount of water over the life of the building.

Wet insulation has an R value of nil, and wet wood stud walls is a recipe for mold growth. Attempts have been made to reduce the exposure of walls by way of vapor barriers, but this usually just seals in the moisture. Trying to reduce the problem by incorporating vents usually defeats the purpose of insulating in the first place.

As of right now, there is no easy, cheap way to insulate. Large, expensive renovations should consult a specialist when dealing with this scenario, because conventional construction methods will not work. Smaller scale projects should probably base their solution on proven methods, and luckily we now have some great examples. So here are the success stories:

The best one I have seen yet is a renovation done for Harvard University, the Blackstone Office building by Bruner Cott (certified LEED Platinum).

Another source of information is the renovation of the Portland Armory building. This was renovated for the new home of a theater, and they faced many of the same issues as a typical masonry project as well as some special ones because of the large interior spaces. Also certified LEED Platinum.

Finally, the renovation of the Lofts St. James in Montreal. As with this project, any successful strategy involves finding a way to control heat flow, moisture flow, and air flow. Every project is unique, especially when dealing with existing buildings, but there are always ways to get across the finish line.

Midwest Earthquake

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Everyone by now has probably already heard of the earthquake that took place on Friday. See USGS data for information on our little friend. It was centered about 150 miles away from Indianapolis, but still quite powerful when it arrived. The attached map from USGS shows the event intensity and peak ground motion.

This earthquake did a lot of good things from my perspective, and didn’t really cause any harm to properties or people. Those are the kind of earthquakes that save lives, in my opinion.

First, it brings earthquake and emergency preparedness back to the forefront of media attention, and that is always good. Next, it reminds building owners that they have an obligation to build and maintain safe structures. But most importantly (from my point of view), harmless earthquakes give structural engineers a great opportunity.

I think going through an earthquake can give just about any engineer a better understanding of how the ground moves. Looking at seismic data for historic events, it just doesn’t affect you the same way as experiencing an actual event. What I learned was this – the ground (and building by extension) does indeed move. I can imagine that a bad earthquake would be truly terrifying. I also learned that earthquakes make noise. It was a low rumbling noise, not loud at all. I also learned that nothing I had experienced in my life so far resembled what happened, but I have to say the Modified Mercalli Intensity measurements are pretty accurate if you need a comparison. See Wikipedia Intensity article for a good explanation.

Now for a little science lesson… Earthquake magnitude is measured by the “Richter Scale” typically. This represents the energy released during an event, and is related to the waveform of movement radiating from the epicenter. It is a mathematical measurement, and completely free from objective interference by people. A 5.2 magnitude earthquake somewhere else in the world releases the same amount of energy as the one in Illinois did. One note about the Richter scale is that is a logarithmic measurement. Thus, a 6.2 EQ would indicate of release of 32 times more energy than the 5.2, while a 7.2 EQ would be 1000 times more energy. In other words, if you thought the 5.2 was scary you ain’t seen nothing yet. See Wikipedia Richter Scale article for more info.

Now, the effect of the earthquake has a lot to do with the specific area it occurs in. Here in the midwest, we have a wonderful rock layer that transfers and amplifies the waveform quite easily. So it’s not surprising that people all over the Eastern US felt this. The Modified Mercalli intensity scale includes the actions of the soil and rock, so it’s more useful for discussion when talking about structural engineering. We experienced a III-IV level intensity here in Indianapolis. Which is pretty amazing considering how far away the epicenter was. If a large earthquake were to hit the New Madrid fault in Northeast Arkansas, like many geologists say could happen, it is likely that many places in the Eastern US will be affected. It may not happen for 2500 years, it may happen tomorrow.

Back to the post at hand – This EQ gives structural engineers an opportunity to discuss seismic events with clients, business owners, and the public. It is essential that they understand the real dangers of earthquakes in the Midwest. We should not misrepresent the danger or try to scare people, but do let them know that they have choices when it comes to EQ design. Any building can be made more robust. Masonry parapets can be secured against toppling, gas and water pipelines can installed with flexible connections, and hospitals and important bridges can be designed such that only an atomic bomb will close them down. It’s a lot of work, it’s expensive, and construction proceeds slowly. However, they say the best time to patch a roof is when the sun is shining.