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This question comes up quite a bit, particularly in affordable housing. Using a blower door to depressurize a rowhome means that air is being pulled not just from the outside, but also from adjacent units through the common or party walls of the home. And while the air that leaks into one home from another may be conditioned (heated or cooled) and not a real issue from an energy-efficiency perspective, there may very well be indoor air quality concerns related to combustion safety, radon, smoking, etc.
Five approaches
In 1987, the Canadian R-2000 program evaluated 5 different ways of blower door testing units within a 6-unit rowhome building in British Columbia (“Methods for Airtightness Testing of Multi-unit R-2000 Housing;” Sheltair Scientific Ltd, 1987; this report is not readily available on the Web).
Detached-Unit (DU) Method: Shared surfaces are treated as part of the exterior shell of the row home being tested. Ideally, windows and doors of the adjacent units are open. This method involves one blower door.
Pressure Equalization (PE) Method: Depressurize adjacent units at the same time and to the same values. That means 3 blower doors and permission of neighbors to set up. This method cancels out air flow between adjacent units and yields just the air leakage of true exterior surfaces.
Pressure Drop (PD) Method: Depressurize the test home with a blower door while also measuring pressure differences in adjacent units to estimate the air flow associated with adjacent units. This requires just one blower door, three pressure gauges (manometers), limited access to adjacent units, and does involve some assumptions and additional calculations.
Whole Building (WB) Method: Treat the multi-unit building as a single detached unit and assign air leakage proportionally based on total exterior surfaces. This approach does not really work for long strings of rowhomes that don’t really have common spaces.
Single Point (SP) Method: This method is a variation of the Pressure Equalization Method, except that rather than testing at a range of pressures, testing of the unit and adjacent units is just at one pressure, presumably 50 Pascals (Pa). This method does save some time compared to the PE method, but if you are going to set up 3 blower doors and gain access to the adjacent units, might as well take full advantage and run the PE method.
Which approach works best?
Without a doubt, the approach that works the best is the Pressure Equalization Method. It provides detailed information on exterior air leakage alone, and, by changing the pressures of adjacent units, provides information on shared-surface leakage. This method is, however, the most difficult to accomplish because it involves three blower door setups and access to both adjacent units.
David White of Right Environments used the Pressure Equalization Method on a recent Passive House rowhome project, the Park Slope Townhouse. “The Passive House Institute approved testing the airtightness of the home using this method,” says White. “And we did vary the pressures between units to learn more about leakage between the units.” When I asked David how they succeeded in gaining access to the neighbors’ homes, he replied, “We pretty much just asked politely.”
This method might be the best, but it simply is not reasonable for weatherization or affordable housing programs.
Which approach is the most practical?
The most practical method is clearly the detached-unit method, particularly if you luck out and test while neighbors happen to have windows open! While you won’t be able to get quantitative information on air leakage originating from common walls relative to exterior surfaces, you can use a smoke stick (or a Wizard stick – see photo at bottom of page) to identify air leakage along the common walls.
When I asked Elliott Seibert of Every Day Green about blower door testing of rowhomes, here is what he had to say: “For practical reasons we use the detached-unit method. In our experience testing both new construction and gut-rehab row homes, attached units can perform tightly if the extra effort is made to air seal the common walls. For instance, exposed brick walls can result in a lot of infiltration in gut-rehabs if not repointed. Yes, this testing method marginally overestimates outdoor leakage. But when the test shows serious leakage, it almost always means big problems in the exterior envelope because that’s where the holes get cut. The method is not perfect for estimating precise energy usage, but it is still useful as a metric of relative leakiness and for identifying major leakage failures.”
NOTE: Rowhomes are just one particular type or configuration of multi-family building; there are lots of others. If you are interested in a comparison of approaches to blower door testing other configurations of multi-family buildings, take a look at this 1999 Master’s Thesis by Sebastiano DePani..
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8 Comments
rediculous... crazy talk bro
Better to just test a unit and fix air leaks we know are the usual. This blog post sounds like a real waste.
I could be wrong.
Wait a minute... I do have a friend that is addicted to having a perfect lawn whatever that is...
To AJ
Are you serious?
Please stop.
Great post Peter.
AJ's dissatisfaction with this article
Hi AJ - Sorry to disappoint you. When I started to research this topic, I learned three things that I thought would be of interest:
1. Someone had looked at 5 different ways to assess air tightness in rowhomes and as much as 23 years ago.
2. Windows and doors open in the adjacent units gives better results for the detached-unit method; it makes the common walls perform more like exterior walls.
3. For different situations, building performance specialists are actively using different methods.
I am glad if you already knew these three things that I did not but also discouraged that you are not more tolerant of those of us who did not know and/or find these things interesting and maybe even useful.
Best - Peter
I'm with Brett
I agree with Brett. Really informative article. Looking at the list of 5, I guess I've used both the SP and DU method. The DU method just doesn't feel right, but sometimes neighbors aren't so friendly. Have to do more research on the PE method specifically with reference to the range of pressures. Good stuff!
Over thinking, over doing, over blogging, is a waste
First of all... radon... in your situation and in even in all homes... is not the boogy man it is made out to be. And... spending huge efforts to decide how to really really really test a row house perfectly is insane. Yes... if you are planning to land on the moon... then you better get serious.
Here's how to test row houses. Test and repair them one after the other with the same men improving and duplicating as they go their work. Definitely has to be done only if the follow up work is to be done. Total waste to just do for the knowledge.
And once yaa go thru some of them... the AFFORDABLE FIXES WILL BE APPARENT.
The key to all of the work including the fancy study is ... AFFORDABILITY.
No sense doing the study or the test if no affordable sealing is going to be done that would save the proper amount of $$$$ and actually mitigate some really bad air.
A little radon or a little smoke from between units IS NOT YOUR LOW HANGING FRUIT. Most of us old farts lived thru thousands of hours of exposure to second hand smoke so thick you couldn't see the other side of a restaurant. How much less exposure could the worst non blower door assisted adjoining wall let into another unit? And today smokers don't even smoke in their own homes!!!!
But if your lively hood depends on valueless .................. go for it.
The more I think about this study the more ridiculous I think it is.
Very happy to agree to disagree
:)
And even my added posts... are a waste. OVER POSTING... LOL
Response to AJBuilder
AJ,
If you want to do work without accurate blower-door testing -- fine.
But don't ridicule those who care about technical issues and want to learn how to make accurate measurements.
Accurate measurements are sometimes necessary -- even if you don't care to make them.
I'm not a biologist, and I have no interest in collecting mushroom spores. But I feel no need to visit mycological Web sites just to make fun of those discussing spore collection.
Martin you didn't read my post very well
I am for simple blower door testing followed up with sealing work being done that makes economic sense.
I am not for over analyzing row houses. Crazy. Radon has never been proven to be harmful in homes. And the biggest over inflated statement is second hand smoke issues! Totally ridiculous!
I like some posts and some blogs and state so. And I state when I have issues. What...you want everyone to be a patsy??? Not my nature. And... When someone stands up and lets you have it.... you may just learn something from it once in awhile... not always... but...
I stand by my comments till some thoughts make sense as to them being off base.
Simple blower door testing and sealing is all that any row house needs and forget the second hand smoke yap.
Working in the trench.
I don't think it is possible to consistently get accurate accurate air leakage measurements on row homes. In the real world trench that AJ works and that I used to train in, conditions on one side or the other are almost never ideal for accurate testing.
The old research that was done by GRASP in Philly on attic insulation and attic air sealing techniques and basement BUP treatments was much more useful than research on air leakage testing.
The intelectuals all can imagine how testing could be done perfectly in theory and all nod their heads as the procedures are discussed. The folks in the trenches that have to fix things on a day in day out basis just shake their heads especially after they spent the day working and the house has the same leakage rate at the end of the day as it had at the beginning because the neighbors came home and opened the windows.
Air leakage testing on row homes is useful. It gives the work crew a way to find leaks to fix and it gives technocrats something to discuss.
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