Building Infiltration

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I'm involved with a project that is considering pursuing LEED certification. It is a remodel/renovation of an existing office building.

The existing office building has quite a bit of infiltration. As part of the renovation process, the exterior walls are being sprayed with a foam insulation that will significantly reduce this infiltration. Someone has asked the question, if we can take credit for this reduction in infiltration. In other words, they want to model the Appendix G baseline building with the old infiltration rate and model the proposed building with the new infiltration rate. This will show a good amount of energy cost savings.

Is this acceptable? I'm having a difficult time finding any reference to infiltration rates within Appendix G.


Mark Prince

Mark Prince's picture
Joined: 2011-10-02
Reputation: 0

There aren't any. There are a few standards that have infiltration
baselines. I believe the HERS (Home Energy Rating System) uses an
infiltration baseline of about 0.35-0.4 ACH, and there are some other
standards out there. Of course, some people will argue that the building
should be positively pressurized so that there will be no infiltration. I
don't know of anyone that has gotten credit for LEED EA C1 for infiltration,
but in my opinion, this is a huge Appendix G oversight. My suggestion is to
apply for a CIR and suggest an infiltration baseline. If the building is
100% renovation, the baseline could be established using a blower door test
on the original building, or you could come up with another reasonable,
established baseline.


No Username provide's picture
Joined: 2011-09-30
Reputation: 200

While I agree that there is oversight in not giving credit to reduce infiltration, I do not feel like LEED credit should be given if there isn't an established baseline. Say, for example, the building infiltration was exceptionally poor. Improving the building to even average infiltration performance may have a large effect on the energy model, and LEED points would be given for a building that may or may not deserve it. While improving the infiltration issue saves energy for the owner, there is no guarantee that the building does not perform poorly. Maybe there should be a LEED "most improved" award which uses existing conditions as the baseline.

Todd Lagus, EIT

Todd Lagus's picture
Joined: 2011-09-30
Reputation: 0

Here's my take on it. The baseline building envelope on a renovation is
supposed to be modeled in the pre-renovated condition. This would include
wall and window thermal properties (U, SHGC, etc.) as well as infiltration
estimates. The proposed design would incorporate all changes and
improvements to the envelope and be modeled as such. It should be noted
however that Section 5.4.3 of 90.1-2004 contains mandatory provisions for
air leakage so the proposed design must at least meet the mandatory

It is unrealistic to assume a positive pressurization strategy eliminates
infiltration. Keep in mind infiltration occurs due to the vapor pressure and
air pressure differences across the envelope. During unoccupied periods fans
usually do not run so a positive pressurization strategy will not work if
fans are off. During the evenings and weekends the vapor pressure will
equalize from inside to outside bringing in any vapor in this air. Blower
door tests are not practical for most commercial buildings due to the large
volume of air movement required to create a pressure differential. Central
AHU supply and exhaust fans could be used with DDC controls to measure air
leakage provided flow measuring instrumentation was installed.


Craig J. Gann, P.E.

Craig Gann's picture
Joined: 2011-10-01
Reputation: 1

My understanding is that if you are doing LEED EBOM certification, the
energy credits are based on actual utility bills post-retrofit via the
Energy Star Portfolio Manager tool. Modeling is still useful to show
the benefit of the infiltration reduction, but I don't believe you need
to follow Appendix G for LEED EBOM. Is there some other LEED program
for existing buildings that does use Appendix G?


Doug Maddox's picture
Joined: 2011-09-30
Reputation: 0

In addition to what Craig says below the very idea that it is okay to blow
energy out of the building or suck in unconditioned air at a high, variable,
uncontrolled rates due to high leakage through the envelope in both
directions dependent upon pressure differentials is certainly not very
'green' or energy saving at the least and we feel contributes to much higher
energy use than necessary and we know it contributes to higher maintenance
costs and lowered useful life of building envelope components. Because it
is not easy, is not something that HVAC manufacturers/companies/ ASHRAE can
contend with, and requires knowledgeable on site inspection during
construction/remodel/repair it does not get the attention it deserves. My
belief is that it is a significant contributor to why modeling software does
not match up well with reality.

Furthermore, someone please take me to any existing 10 (heck 5) story or
taller building that does not desperately try to suck in air low and spew
it out high and any low rise with meaningfully controlled building envelope
conditioned air management. It is almost impossible to find complete vapor
barriers where they need to be at wall/roof interfaces let alone the rest of

We have seen these same issues in LEED certified, yes certified, new
buildings as the reward is low for actual building envelope air and moisture
penetration control (versus showing a design and calculation that shows it
is low) and no one is interested in inspecting and making sure the work is
done to meet LEED, heck even base code, requirements because so far there is
zero penalty (LEED, code, GBI, or anyone else). The energy savings for
existing buildings can be significant and the lowered repair and maintenance
costs for the building envelope are significant if air and moisture
penetration are controlled but the emphasis is certainly not there most of
the time.

My feeling is that we absolutely should reward with LEED points, attaboys,
smiles, pats on the back, tax credits, and everything else we can things
done to existing buildings that increase the useful life of components,
lower environmental impact, lower maintenance requirements and costs, and
decrease energy usage. I thought that is what the goals were, ACTUAL
lowered environmental impact in all ways and lowered costs. Building
envelope infiltration gets only lip service and design but there are no
inspection standards and accountability to prove the work is done

Andy Hoover

Andy hoover's picture
Joined: 2011-10-02
Reputation: 0

Andy, you're right on! Doug is also spot on re: LEED EBOM. EBOM actually
measures results, something LEED-NC cannot do because it's models aren't
built yet.

Infiltration calcs have always been a thorn in the side of anyone
calculating heating / cooling loads since they're so dependent on actual
construction practice (not to mention the effects of aging, settling, etc.)
In theory, a savvy building owner will continue to pay attention to energy
use over the life of the building and observe rising energy use that's
well-correlated to infiltration -- then fix it.

That's a rare owner, I know!

James V. Dirkes II, P.E., LEED AP

James V. Dirkes II  P.E.'s picture
Joined: 2011-10-02
Reputation: 0

ASHRAE Proposed Standard 189.1P Standard for the Design of
High-Performance Green Buildings Except Low-Rise Residential Buildings
contains air barrier requirements in Normative Appendix B, attached. The
public comment period of this draft ended last April, but I found a copy

Air leakage testing is one of three options for compliance. The other
two are using pre-approved materials or assemblies.


William Bishop, EIT, LEED(r) AP

Bishop, Bill's picture
Joined: 2011-09-30
Reputation: 0

Good Afternoon Mark et al:

I agree with Karen that the infiltration modeling requirements of baseline and proposed are very poorly defined in App G or ECB, and there's no real data in 90.1 section 5.4.3. A few years back I saw a study on average commercial construction infiltration rates and the general result was ACHs of 0.3 to 0.4. ASHRAE Fundamentals 05 Ch27.23, discusses commercial building infiltration and lists test results with a range from 0.1 to 1 ACH. I typically use the same infiltration rate between baseline and proposed when modeling for LEED, UNLESS I have defendable information in the Construction Documents to corroborate a different rate. For example I had a project whose specs called for blower door testing to prove that overall infiltration did not exceed 0.2 ACH and for the basline I modeled 0.4 ACH, in that job my proposed showed energy improvement via infiltration management as I was able to defend the descrepancy between proposed and basline.

Unless you can defend the difference between the two models I would recommend modeling the same rates. A blower door test on the original existing building compared to one done on the finished renovations would give you all the defense you need. One performed just on the new building if it proves the actual rate to be much less then the 0.4 ACH average, in my opinion would probably be defendable enough.

Good Luck,

Joshua W. Talbert P.E., LEED-AP

vt_powskier's picture
Joined: 2011-09-30
Reputation: 1

Hey folks:

Yes, we have seen that ASHRAE and ASTM have/are promulgating various
standards (and indeed some have existed for quite some time) and so on but a
real problem is that there are no test or inspection (by far the more
"doable") requirements for completed assemblies/buildings. When you combine
this with the fact that much of the work is impossible/very difficult to
view once a structure is completed and that attention to detail is
absolutely required for proper construction it is easy to see why most
buildings built do not meet their design "requirements".

How many here have ever seen one of their buildings inspected at various
points as they are constructed for building envelope component, let alone
total system proper construction and effectiveness??? Nice mock ups but....

It is one reason why at least many (I feel most) LEED and other "green"
buildings do not meet their design "requirements" for
infiltration/exfiltration/moisture transport/energy usage and so on.

We believe that there needs to be an inspection/sign-off certification for
the building envelope components and as a whole, and not from local code
enforcement. The payback in energy usage, environmental impact, and
structure life/cost effectiveness all will be significant. Most certainly
comfort will also be improved.


Andy Hoover

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Joined: 2011-10-02
Reputation: 0