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Article-Lsitburek.jpg

©2014 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 56, no. 9, September 2014.

By Joseph W. Lstiburek, Ph.D., P.Eng., Fellow ASHRAE

About the Author
Joseph W. Lstiburek, Ph.D., P.Eng., is a principal of Building Science Corporation in Westford, Mass. Visit www.buildingscience.com.

How do you insulate uninsulated masonry buildings on the inside? Carefully. There I go again with the obvious. It is trickier to do it on the inside. But it is often less expensive than insulating them on the outside. True, you give up space, but nothing comes without some type of trade-off. The big concern is not to screw up the durability or to create moisture problems where none have existed prior to “improving” the enclosure by insulating it.

In cold climates, reducing heat flow has been linked to freeze-thaw damage in some buildings. We looked at this earlier (“Thick as a Brick,” ASHRAE Journal, May 2010). The take-away is that if rainwater is not concentrated on the façade, even crappy brick assemblies work. But how do you deal with the concentration part? And what if you can’t deal with the concentration part and have crappy brick?

Then, if you get past the concentration of rainwater part on the exterior, how do you stay out of trouble on the interior when you insulate? What type of insulation works? Well, they all work, sort of. It depends.

We need to start somewhere and one place to start is to ask where the building is. Is it in a cold enough climate that freeze-thaw is a risk? And does it get wet enough when it is cold enough? Ottawa sucks. Edmonton, not so much. Edmonton is colder than Ottawa, but much drier. Hard to screw up in Edmonton. Easy to screw up in Ottawa. Kinda indicative of the Canadian political system. In the U.S., New York is much more forgiving than Boston. Note that we are talking freeze-thaw here, not sociology.

Hygrothermal regions are a big deal, as is precipitation (Figure 1 and Figure 2). Here comes a “Joe Rule.” You only worry about freeze-thaw in cold climates (or colder) that have moderate (or higher) amounts of precipitation. Cold climates are defined more precisely as IECC Climate Zone 5 or higher, if you are a Yank. In Canada a cold climate is everywhere except Vancouver. Note that Boston is in IECC Climate Zone 5, but New York City is not. You can get away with stuff in NYC that you cannot in Boston.

So let’s say you are in a place that you should worry about freeze-thaw? Now what? OK, now we look at concentration of rainwater. This takes judgment and experience. Relax. We can do this. Old architects really got it right. We just need to remind the youngsters. One of my favorite all-time buildings is at my alma mater, the University of Toronto. Look at all the drip edges—at roof edges, at window openings, between floors. Notice that they are working. How can you tell? No stains. Look at this building carefully because it is an example of “what is good.”

 

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Figures 1 and 2

Lstiburek_F1-and-F2.jpg