Air leakage, LEED, and Appendix G of ASHRAE 90.1

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The National Institute of Standards and Technology (NIST) did an
extensive study documenting a greater than 40% natural gas savings and a
greater than 25% electricity savings across the nation for building
energy consumption if buildings were uniformly constructed with air
barrier systems installed. They evaluated 116 existing buildings and
computer modeled several different building types. The purpose of their
study was to provide information to ASHRAE concerning whether it would
be desirable to add an air barrier requirement to ASHRAE 90.1.

As a result, I've always thought that Appendix G to ASHRAE 90.1 allows
you to change the air leakage rate off the default and onto a rate
corresponding to an air barrier installation, so that you could claim
LEED points for the corresponding energy savings. However, an architect
at a presentation I did said you could not do that under the LEED and
ASHRAE requirements. (I know the models will do it, because I've done
it on the TRANE model and obtained results that support the NIST

I see in Appendix G that: "G3.1.2.5. Ventilation. Minimum outdoor air
ventilation rates shall be the same for the proposed and baseline
building designs." However, I searched the document for "outdoor air
ventilation" and the phrase occurs only in the context of mechanical
systems that are designed to intentionally bring air into the building.
If this section is the basis for concluding that air leakage barriers
should be left out of the modeling, then I have trouble understanding

Appendix G says that all components of the building are to be modeled as
designed. That would preclude modeling as if an air barrier system did
not exist in the design. It says the baseline building model is to have
steel-framed above-grade walls, and it is silent about the design
building, but the User's Manual says that if the design building walls
are block or cast concrete, then "the mass is credited in the building
performance rating method." Likewise, if the walls are wood stud
instead of steel, then the Manual says credit is given for the superior
energy performance of wood frame versus steel frame. The User's Manual
states that it: "Offers information on the intent and application of
Standard 90.1." Given these examples in the Manual based on existing
thermal mass energy-saving data and wood-versus-steel stud energy data,
it is difficult to conclude that a wall that is constructed with
materials meeting the air leakage limits and installation requirements
of the Air Barrier Association of America and determined to produce
significant energy savings by the NIST study based on those same limits
and requirements should be modeled as if it leaked air like a building
without an air barrier.

Please let me know what you think, and if you know of any reason why it
is not proper to change the air leakage rate through the building
envelope in the design model to show the benefit of air barriers.


Paul Grahovac, LEED AP

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As I understand it the issue is that the 90.1 Standard does not establish a
base line condition for air leakage so no savings can be claimed. I
certainly agree that the savings are real and should be counted. I know
that the Appendix G committee has this issue on their extensive ?to do?

Marcus Sheffer

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I am sure there is just as much baseline for air leakage reduction
benefit as there is for the concrete walls and wooden studs that the
User's Manual says can be modeled and their energy savings captured for
inclusion in the overall modeling results.

I cannot accept that the USGBC and ASHRAE can arbitrarily say reduction
in air leakage will not be considered, but that increases in thermal
mass energy-savings from using concrete walls or energy benefits from
using wooden studs will be used to compute building energy performance.
This obviously rewards concrete block producers and wood stud suppliers
and penalizes air barrier suppliers.

I'm reminded of Lord Acton's famous observation: "Power corrupts, and
absolute power corrupts absolutely." Fortunately, even the power of
organizations like ASHRAE and USGBC are subject to some ultimate check.
Such organizations are prohibited by law from arbitrary practices that
favor one group over another. Below are excerpts from the leading
United States Supreme Court case on the subject.

Paul Grahovac, LEED AP

(1982), Supreme Court Justice Blackmun, writing for the majority:

"Furthermore, a standard setting organization like ASME can be rife with

opportunities for anti competitive activity. Many of ASME's officials

associated with members of the industries regulated by ASME's codes.

Although, undoubtedly, most serve ASME without concern for the interests

their corporate employers, some may well view their positions with ASME,

least in part, as an opportunity to benefit their employers. When the

influence of ASME's reputation is placed at their disposal, the less
altruistic of

ASME's agents have an opportunity to harm their employers' competitors

through manipulation of ASME's codes."

ID.., at 571, 102 S.Ct., at 1946.

In American Society of Mechanical Engineers, the U.S. Supreme Court
affirmed a jury

verdict that awarded treble damages to the company that was injured by
certain members of the

trade organization that had manipulated the trade organization and its
role in the industry to set

standards designed to enrich those members' corporation and diminish the
ability of its

competitors to fairly compete in the marketplace. In deciding to hold
the trade organization

responsible for the actions of its members, the Court explained:

"It is true that imposing liability on ASME's agents themselves will
have some

deterrent effect, because they will know that if they violate antitrust
laws through

their participation in ASME, they risk the consequences of personal
civil liability.

But if, in addition, ASME is civilly liable for the antitrust violations
of its agents

acting with apparent authority, it is much more likely that similar

violation will not occur in the future. "Pressure will be brought on the

organization to see to it that its agents abide by the law." United
States v. A&P

Trucking Co., 358 U.S. 121, 126, 79 S.Ct. 203, 207, 3 L.Ed.2d 165
(1958). Only

ASME can take systematic steps to make improper conduct on the part of
all its

agents unlikely, and the possibility of civil liability will inevitably
be a powerful

incentive for ASME to take those steps. Thus, a rule that imposes
liability on the

standard setting organization- which is best situated to prevent
antitrust violations

through the abuse of its reputation-is most faithful to the
congressional intent that

the private right of action deters antitrust violations."

14:., at 572-573, 102 S.Ct., at 1946.

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Perhaps you should volunteer your time on the ASHRAE 90.1 committee.

Brenda V. Morawa, PE, QCxP, HPBDP, LEED AP

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My understanding is that one of the co-founders of the Air Barrier
Association of America is actively involved with the committee, and I
have an e-mail from him confirming that reduction in air leakage can be
modeled and the energy savings used in the award of LEED points.

However, given the contrary position I am hearing, I am beginning to
become concerned that some approach other than begging ASHRAE and USGBC
to be reasonable needs to be considered.

Paul Grahovac, LEED AP

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Perhaps you should volunteer YOUR time on the ASHRAE 90.1 committee.

Brenda V. Morawa, PE, QCxP, HPBDP, LEED AP

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First, I feel that the statement that EAC1 methodology "penalizes air barrier suppliers" and "rewards concrete block producers" is completely off-base. These are not either/or technologies. There are many other factors going into the selection of these items besides energy performance. If there is real energy and maintenance savings justification as an investment, then owners will consider it even without contributing to EAC1. LEED covers many things, but it isn't an exhaustive manual of sustainability. As well, the LEED process, although growing, still covers only a small fraction of new building projects, regarding Appendix G applicability. This is an energy modeling forum, so let's focus on the Appendix G part of the discussion.

Specifically for 90.1 energy performance, it isn't a matter of arbitrarily accepting one or the other - we as an energy modeling community have many years of experience and research involved in accurately modeling the heat transfer in envelope components. The capability of various modeling techniques have been demonstrated to be capable of relatively accurate modeling of the differences between thermal mass and insulation levels for many years, therefore these calculations are included in the standard as a path of calculating energy usage and savings between alternatives.

The modeling software are generally able to predict what would happen due to a given change in level of infiltration. The modeling improvements need to be made in the area of showing that the calculations are accurate in determining those levels, rather than using a specified reduction. Does the software available have the needed parameters to model a product such as yours? On a case-by-case basis you may be able to show that you know all of the needed parameters to make these calculations. I'm not sure if you could apply these to all projects, and all software packages though. For instance, do you feel that your product has different effectiveness than other brands? How would someone capture these differences in efficiency in eQuest or EnergyPlus? Would it be okay with the USGBC to propose a straight percentage reduction? What's the starting point for the base case? How much variability is there in the construction process?

Your input would be welcomed if you offer some expertise in these areas.

You mention a study that shows benefits in many cases for 116 buildings (and common sense would agree with this). Some focus should be on educating designers to use the strategy and contractors on proper installation, regardless of the "points" that are achieved, and under what conditions the strategy would be most effective.

Just my $0.02.

David Eldridge, PE

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I don't think any of us disagree that there are significant benefits to be
had by having tighter buildings.

Part of the issue is the lack of a documented base line here in the US. I'm
not aware of any (enforced or otherwise) baseline that is required and/or
published. Does anyone else have that data?

Additionally, projects are not required, at this point in time, to
demonstrate or document air leakage rates after construction. So that is
typically leaving us with two variables in a model that are based on the
modeler's best judgment. Understanding many things in the model are the
'modelers best judgment', at this point, we need more to go on.

My unofficial two cents.

The good thing about this is there's always room for improvement and there
are a good many, very well intentioned volunteers working on improving the

Brenda V. Morawa, PE, QCxP, HPBDP, LEED AP

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Dear Bldg-Sim community,

On the one hand, Lord Acton was right.

On the other hand, my own experience as a member of an ANSI TAG (Technical
Advisory Group) was that the checks and balances normally work acceptably.
My TAG had a couple dozen members, of which about 6 represented equipment
manufacturers (I was one of those). Each of us equipment folk were very
familiar with each other's competitive advantages and were attentive to
proposals which may have favored one or another of us. The end result was
essentially fair for all, although one who will remain nameless couldn't be
faulted for effort to bias the standard!

Any human effort will be flawed to some extent!

USGBC (and ASHRAE) seem to be interested in gradual improvement, so I hope
that infiltration will be one of their targets in the future. That said,
infiltration is subject to so many details of proper installation that any
modeling effort is unlikely (unable?) to represent it well.

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

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Dear Paul, et al

I have to agree with Paul's comments on this one.

We can and have to take account of infiltration reductions within our UK
building regulations calculations and indeed in certain circumstances they
can be the difference between different grades for the buildings when
thermal mass and other passive design techniques or super efficient HVAC
systems have been taken into account.

At the design stage you "choose" an infiltration rate that the design team
is willing to take the risk on achieving and if not you can use a default
infiltration rate which equates to a reasonably well built modern building
(this obviously gets reviewed and reduced a little over time to increase the
requirements). The key to it being that in order for the builder to obtain
the building regulations and occupation certificates, the actual measured
air infiltration rates have to be put into the design simulation model post
build to ensure that what the design team has said will be achieved, is
actually achieved. In fact it is possibly at the moment one of the most
successful parts of our regulations.

This has 2 main benefits, it means that contractors have to think about the
quality of their build and good detailing from the start and subsequently if
they allow a poor building to be built that exceeds the minimum standards or
their chosen design value, they have to go and identify the air leakage
paths and bring the building up to that standard before they can get an
occupation certificate.

When you consider that our default air leakage rate is 10m3/hr and we see
many large commercial warehousing projects (a good example where composite
panels are often used for air tight seals) that have leakage rates of less
than 2m3/hr.m2 it is possible to see that large benefits might be possible
in some instances. On a large warehouse with perhaps background heating for
the operatives, this reduction in infiltration can result in very large
reductions in energy use/carbon emissions for heating, etc.

I am slightly surprised that a USGBC/ASHRAE baseline rate doesn't exist to
allow benefits to be taken into account, especially when it is possible to
use the test results to enforce improvements to be made, in a way it acts as
both carrot and stick.


Dr Paul Carey

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In my experience modeling of infiltration has nothing to do with actual infiltration in a constructed building. How much infiltration results in an actual building is 99.9% construction and 0.1% design and specification. A well design building to minimize infiltration, with poor attention to details during construction and sloppy workmanship can end up having more infiltration than an average design with a good construction team.

I have looked in many plenums only to see daylight and cold-wintery air flowing into the building, even on LEED projects.

These issues make it very difficult to justify infiltration savings in an energy model.

Jon Evans, PE, LEED AP

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We are attempting to replicate the UK model for some school projects we are
working on. We established a goal of <0.4 cfm/sf @0.3?wc (good practice
under the UK system) and will require post-construction testing.

A good compendium of links on the subject can be found at - If anyone knows of other
studies/resources it would be great to see them.

So some data exists on building performance in this arena and hopefully the
Appendix G folks can come up with a reasonable baseline so we can encourage
more diligent construction practice toward this end.

Marcus Sheffer, Chair EA TAG


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The Air Infiltration and Ventilation Centre (AIVC - has published a number of documents regarding infiltration and
ventilation rates in buildings, though perhaps the most useful I have found
is the:

"Ventilation Modelling Data Guide", Orme & Leksmono, 2002, ISBN 2 9600355 2
6 - This guide book GU5 according to the website, comes from an update to
the old technical document "Numerical Data for Air Infiltration and Natural
Ventilation Calculations" which I have used for a number of years when
carrying out advanced modelling of infiltration. I don't have the update,
but the original book I have is still useful with infiltration rates given
for a variety of materials and constructions that may well be a good
starting point for compiling a baseline.

The BRE have published a few things about infiltration and certainly
post-construction testing, as have BSRIA.

Post-Construction testing is the key to this working as Jon Evans rightly
pointed out. It isn't much good assuming something then getting it built
poorly. This is a way of pulling up the performance of contractors and has
a way of sifting out the cowboys to some extent.

The other place that you might find useful information would be the
International Journal of Ventilation, where the editorial board reads like a
who's who of ventilation research -


Dr Paul Carey

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1. Recent posts to this listserv show that air leakage reduction is
successfully modeled in the UK.

2. "The LEED point system drives designers to reduce the HVAC
system down to the optimal level." US Green Building Council LEED
training, May 27, 2004, Dallas, Texas.

3. Melding the data from across the US, air barriers would reduce
building natural gas consumption by greater than 40% and electrical
consumption by greater than 25%. National Institute of Standards and
Technology, "Investigation of the Impact of Commercial Building Envelope
Airtightness on HVAC Energy Use, NISTIR 7238.

4. Air barriers, if modeled under LEED, would reduce HVAC
construction costs.

5. "There are barriers to implementation of radiant systems in
North America. One is that engineering fees are based on a percentage of
the mechanical and electrical construction budget. The lower the cost of
these systems, the lower the engineer's fee." Geoff McDonell, P.E.,
senior mechanical engineer in the Burnaby, British Columbia, office of
Earth Tech's Global Facilities and Infrastructure division.

6. ASHRAE engineers have a financial incentive not to allow air
leakage reduction to enter into LEED point calculations.

7. A change proposal to allow modeling of air leakage reduction has
been pending with the ASHRAE 90.1 simulation group for five months
without any action - and without any hope of action in the future.

Paul Grahovac, LEED AP

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I am a member of the ASHRAE Standard 90.1 Energy Cost Budget Committee
which is responsible for the modeling rules in Appendix G. As far as I
know there have not been any continuous maintenance proposals submitted
to our committee to change the way building leakage is modeled. If there
were such a proposal, the ANSI rules that Standard 90.1 operates under
would require some sort of action (I do not know what the time frame for
that is). There has been a proposal to 90.1 Chapter 5 (Building
Envelope) to require a continuous air barrier which has been out for
several rounds of public review. If that proposal ever gets approved,
Appendix G may need to make changes in the rules for modeling air

There is currently nothing in Appendix G that would prohibit someone
from using an exceptional calculation to gain credit for reductions in
building leakage. It would simply be up to the user to demonstrate that
they are doing something in excess of standard practice, and that their
calculations are accurate. Remember that LEED CIR rulings are totally
separate from ASHRAE and under LEED, credit may not be allowed.

On a final note, there is not one member of the ECB subcommittee that
makes his living as a consulting engineer designing HVAC systems, so we
have no financial incentive to ignore a proposal affecting the modeling
of infiltration as you are insinuating in item number 6.

Michael Rosenberg

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Where did you get your information regarding number 6 and 7?

Sam Mason

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Sam Mason

6 derives from 1 -5.

7 is from the person who submitted the change proposal.

Paul Grahovac, LEED AP

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Air leakage reduction of the entire envelope has been brought up on a number
of occasions to the ASHRAE 90.1 committee and to various LEED staff/groups
by a number of people, including me.

I believe that the problem is far more fundamental than having a standard
and being able to model changes accurately and more encompassing than
perhaps the focus of these postings. I personally have never seen one
building, including LEED certified, that when even grossly inspected meets
requirements for air leakage/infiltration let alone a tighter goal. I am
sure some exist but 10 buildings in the country will not get us there. It
would be interesting to see ASHRAE measure their new and improved
headquarters air leakage without undertaking a project to tighten it up

The problem is virtually no buildings are built or most certainly none are
remodeled with the inspections and testing necessary to the envelope and
mechanical systems to meet current requirements. Most designs do not seem
to comprehensively manage air and vapor and certainly do not require proof.

At the very least there should be a requirement of provable inspection and
spot barrier testing and a requirement that every building must have the
envelope commissioned prior to issuing an occupancy permit. This would
drive huge energy savings, carbon reduction, money savings, and reward
material manufacturers and contractors who make it right and build it right.
Owners can not know what they do not know so they have no awareness of the
impacts. We have actually been involved in projects where a new roof system
is installed that is tight and better insulated and people notice an
increase in the breezes at exterior walls as what used to go out the top now
goes more out the sides.

You can get LEED certified (pick a level) and an occupancy permit with
virtually every gasket in your windows/curtain walls leaking air/vapor/even
running water (not performing) with finger size gaps at plenum joints, and,
no air/vapor barrier connection between a buildings? fa?ade and roof systems
but not with a 2 foot square single pane window, crazy.

The NIST study and others show that new buildings at the time the studies
were done did not meet code let alone some stricter goal.

It is not that the materials and construction processes do not exist. It is
that to do it right costs more, so it can be done, but not without the
proper inspections and testing.

Andy Hoover

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I agree with Jon's comments about specification of products as being a small
portion of how much infiltration a building will have, not only do
construction practices play a role but also wind profiles on the building,
whether the mechanical systems are controlling building pressure, whether
the building is tall enough to have a stack effect, building shape etc.
Even in performing a winter load calculation and a summer load calculation
we usually change the infiltration rates slightly because average winter
wind speeds are greater than summer wind speeds.

If infiltration is going to be accounted for as a savings in energy
modeling, I would think that building leakage testing (similar to duct
leakage testing) and envelope commissioning would need to become more
prominent in our business. ASHRAE has funded some studies on infiltration
but the data I have seen has been for residential construction.

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Robert Gengelbach, PE, LEEDR AP

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Construction practices for each unique location/building combination should
take into account the items Robert mentions presuming appropriate design.
Wind profiles, building pressure control, stack effect, building shape and
so on should all be accounted for in design and then appropriate practices
should be followed.

Without appropriate inspections during construction, building leakage
testing, and envelope commissioning 'savings' may be shown in energy
modeling but never achieved in the real world. My opinion is that this is a
contributor to why energy calculations do not match up to reality now.


Andy Hoover

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Miss Brenda:

My suggestion is that LEED immediately start to require a goal for air
leakage and testing of that goal after construction along with requiring
building envelope commissioning. The current waste of energy and carbon
impact is immense not just in energy operating costs but in dramatically
shortened useful life of building envelope components and entire facades and
roofs. Most building envelope components reach the end of their useful life
at 40 to 60 percent of the time they should last. This is one of the
largest contributors to lack of sustainability in the world. The
significant factors in this are poor/improper installation and lack of
maintenance. Based upon our rough observations, most NEW buildings are at
double to triple the 'by code' air leakage rate because there is no
inspection, testing, and building envelope commissioning.

Those who say the technology does not exist to do the inspecting and testing
are not truthful. It can be done today. It is not free but the return is
huge. Certainly there should be the same requirements in code, but a good
start is you folks, Energy Star and the new ASHRAE rating system.

This is an opportunity for USGBC to LEED T, pun intended J, the way.

Wow, that 2 cents felt good.


Andy Hoover

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If I were the USGBC and I were to give credit for air tightening/air
leakage I would simply state in the modeling rules, if you are going to
take credit you need to do whole building testing or for a large
building major sections that are representative of the work.

Likewise if I were submitting to the USGBC I would state that in the
rationale. To do whole building testing, while doable is still a new
industry and the USGBC should be working towards bringing whole building
testing into the mainstream.

Leonard Sciarra

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Additionally, there is not one member of the envelope sub-committee that
make their living as a Mechanical Engineer. SSPC 90.1 works very hard
to provide full balance to their discussions. That said, you know we
are all working very hard (lots of hard work here) on an enforceable
continuous air barrier addenda.

Thanks for all your interest, as always it is a pleasure engage in
discussions regarding building science.

Leonard Sciarra

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I take it one step further than Leonard with LEED and think ASHRAE should be

You should not be able to get any LEED certification without meeting a
minimum provable level of air/vapor/moisture tightness and every building
should be required to undergo whole building commissioning with appropriate
testing to prove it.

Regarding ASHRAE, it should be a requirement that whole building
commissioning of air/vapor/moisture tightness occurs with submitted results
so that the requirement ends up in code. Not only will this provide the
mechanism to show if buildings are meeting code requirements for
infiltration (the vast majority exceed the accepted/mandated standard) but
also will let owners compare and see how effective, therefore money saving
and what human comfort level, their structures provide compared to others.
It would be wise for ASHRAE to include provable inspection requirements so
that issues are identified as work occurs and dealt with, the whole building
commissioning/testing will only tell that you do or do not have a problem
and sometimes where the problem might be/is but not always.

Lots of assemblies and components are very specified but little
inspection/testing of them once built is required let alone the entire
building envelope, which is what really counts. So we know the assembly is
good IF it is built properly and the building envelope is good IF every
assembly is built properly and IF every assembly is integrated properly into
the whole but we do not have any requirement to show/prove it such as
inspect, commission, and/or test/measure - crazy in my opinion.

Andy Hoover

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