Ninety Square Inches and Not One Mouse: Why Airtightness Is Not Exclusion

1. Introduction: somebody else has the number

This journal has complained many times that pest control has no measured standard for how well a building is sealed. The energy trade has one, it is enforced by code, and it is reported as a single figure.

1.1 Ninety square inches

Of aggregate hole, in a house that passes code and would be described as well built.¹

1.2 What this article argues

That the number is real, that it cannot be translated into a statement about pest entry, and that the reason is not a gap in the research but a difference in the mathematics. Sections 9 to 12 are the case.

2. What the test does

The method, briefly.

A calibrated fan is mounted in an exterior door frame, and it depressurizes the house, essentially pulling air out and measuring how much air leaks back in through cracks and gaps.⁸

The result is usually reported as air changes per hour at fifty pascals: the number of times all the air inside the home is exchanged with outside air at that test pressure.²

2.1 The calculation

Flow in cubic feet per minute, multiplied by sixty, divided by the building volume. One worked example gives a 10,000 cubic foot house at 167 CFM, which comes to 1 ACH50.⁴

2.2 Fifty pascals is not a real condition

One tester notes that testing a building at 50 pascals is subjecting the building to pressures it doesn't typically see, and that some of the leakage that is present at the elevated pressures will not leak under normal conditions.²

The estimated natural rate for a code-minimum house is given as about 0.2 air changes per hour, against 3 at test pressure.²

2.3 And one safety note worth recording

That all combustion appliances must be turned off during testing to prevent dangerous backdrafting.⁷

Depressurising a building can pull flue gases back down a chimney, which is a hazard created by the measurement itself and the kind of thing our occupational article found the pest trade less good at anticipating.

2.4 Which is a sensible design

An artificial pressure produces a repeatable measurement, and repeatability is what a code compliance test needs. Our detection articles have repeatedly wanted exactly this and not had it.

3. The standards

The numbers, which are refreshingly specific.

Codes require 3.0 ACH50 or less for most climate zones and 5.0 ACH50 for hot climates, with testing mandatory for new residential construction since 2015 under one model energy code,⁷ and code-required in residential construction since the 2012 edition of a model residential code.⁴

The high-performance standard requires 0.6 ACH50 or less, specified as airtightness: n50 ≤ 0.6 h⁻¹ at ±50 Pa, measured via a blower-door test.⁷⁶

3.1 And a retrofit tier

A retrofit may meet 1.0 ACH50 for the corresponding retrofit certification, with a declaration required if a project lands between 0.6 and 1.0.⁵

3.2 The protocols differ between regions

One source notes that the high-performance body uses a European standard to measure the air flow, and that while very similar to the American standard, the protocol is different.⁵

Which is worth flagging: two numbers from two protocols are not exactly comparable.

4. And the range in practice

What actual buildings return.

One tester reports: the best test result I've seen was .33ACH50; the worst was just over 15ACH50.²

4.1 A factor of forty-five

Between the tightest and leakiest buildings one practitioner has measured, which is a wide distribution for a property of the same class of object.²

4.2 Which is itself informative

A forty-five-fold spread means the property is highly variable and highly improvable, which is why it was worth writing a code requirement about. A quantity that clusters tightly does not need regulating.

Pest entry is plausibly just as variable between buildings and nobody has the distribution, which is our observation.

4.3 And the code bar is low

One contractor puts it plainly: meeting code is the minimum. It means your house won't fail inspection, but it doesn't mean your house is particularly tight.⁸

5. Equivalent leakage area

The transformation that makes the number intuitive, and that this article is about.

It represents the total area of all leaks combined into a single equivalent opening, offered to help visualize the cumulative effect of all air leaks.⁷

5.1 The illustrations given

That ELA of 50 square inches is equivalent to a 8″ × 6″ window open 24/7, 100 square inches to a 10″ × 10″ window always open, and 200 square inches to a 14″ × 14″ opening.⁷

5.2 The transformation is not free

Converting a flow measurement into an area requires assuming how air behaves passing through a notional hole, which means the figure carries an assumption the air change number does not.⁷

5.3 Which is a good explanatory device

And note what it is doing. It converts a distributed property into a single notional aperture, which is exactly the move §9 says cannot be made for the pest question.

6. The experiment

A builder who did the obvious thing and published it.

Testing a house of more than 1500 square feet of living area and a volume of around 14,800 cubic feet at rough framing, he recorded .55 ACH50, 140 CFM, giving a leakage area equal to approximately 15 square inches.¹

6.1 Then he started drilling

Wanting to know how many holes of a specific size it would take to get the home to the code minimum 3 air changes per hour at 50 pascals, he began drilling 2.5 inch holes in one of the yet to be cut out window openings.¹

6.2 The target

To achieve the code result there must be less than 740 cubic feet per minute of air flow moving past the blower door fan, against the 140 he started with.¹

7. Ninety square inches

The conclusion he drew.

That 3 ACH50 or 90 square inches of leakage area for a 1500+ square foot home is considered tight.¹

7.1 Six times the leakage of the house he tested

Fifteen square inches at 0.55, ninety at the code minimum.¹

7.2 And his own target

One ACH50 or less, at an investment he puts at well under 1% the total construction budget.¹

8. Which sounds like a pest problem

The obvious reading, which we want to state before dismantling it.

A mouse requires an aperture of roughly six millimetres, which is under a twentieth of a square inch in area. Ninety square inches of equivalent leakage sounds like room for a great many mice.

8.1 And the illustrations encourage it

An equivalent leakage area of a hundred square inches is offered as a ten inch by ten inch window always open,⁷ which is a vivid image and an aperture any rodent in this province would use.

The image is doing exactly what it was designed to do, which is make a diffuse quantity feel concrete. It happens to make it feel concrete in a way that is wrong for this question.

8.2 That inference is wrong

And understanding why is more useful than the number itself.

9. Why it is not

The first and most important reason.

Equivalent leakage area is an aggregate. Ninety square inches distributed across a building is not ninety square inches of hole; it is the flow-equivalent of every crack, seam, penetration and gap added together.⁷

9.1 Most of it is far too small for anything

A hairline gap along a hundred feet of baseboard, a millimetre wide, contributes real area to the sum and admits nothing.

9.2 And the sum is indifferent to distribution

Ninety square inches as one opening and ninety square inches as nine hundred hairline cracks produce, to a first approximation, the same test result. They produce entirely different pest outcomes.

That is the argument and §10 states it formally.

10. A sum and a maximum

The formal version, which we offer as ours.

Air leakage is a sum. Every aperture contributes in proportion to its area, and the total is what the fan measures.

Animal entry is a maximum. What determines whether a mouse gets in is the smallest dimension of the largest continuous path, and every other aperture in the building is irrelevant to that question.

10.1 An illustration

Two buildings. The first has one hundred apertures of one square inch each. The second has one aperture of one square inch and nine hundred and ninety-nine hairline cracks totalling ninety-nine.

Both come to a hundred square inches. The first offers a hundred ways in and the second offers one, and no blower door result distinguishes them.

10.2 These are different functions of the same geometry

Given a complete description of every opening in a building you could compute both. Given only one of the two results you can compute neither the other nor any bound on it.

10.3 Which is why no conversion exists

Not because nobody has worked it out. Because a sum does not determine a maximum and a maximum does not determine a sum.

10.4 And it runs in both directions

A house at 0.6 ACH50 can admit mice through one oversized service penetration. A house at 15 ACH50, leaking through a thousand shrinkage cracks in old lath and plaster, may have no single aperture an animal can use.

11. The consequences of that

Three, and they are practical.

Passing a blower door test is not evidence of exclusion. It is evidence about total flow.⁷

Failing one is not evidence of a pest entry. Leaky can mean diffusely leaky.

And an airtightness figure cannot be quoted as a pest control credential, which we would expect somebody to try eventually.

12. The second reason: paths

A further disanalogy.

Air passing through an envelope needs a pressure difference and a route of any shape. It will travel through a fibrous insulation batt, along a stud cavity, around a corner and out through a crack, losing pressure as it goes but arriving.

12.1 An animal needs a traversable path

Continuous, of adequate dimension along its whole length, and connecting a place the animal can reach to a place it wants to be.

12.2 And it has a behavioural component

The animal has to find the path. A traversable opening in the middle of an unclimbable wall is geometrically adequate and functionally irrelevant to a species that does not climb.

Which adds a third condition to §12.1 and means the assessment is species-specific in a way an airtightness figure never is.

12.3 Which is a much stronger requirement

Most of a building's air leakage routes are not traversable by anything. They are tortuous, narrow, obstructed or interrupted.

That distinction is ours and it compounds §10: not only is the metric the wrong function, most of what it counts is not a candidate for entry at all.

13. And the third: which barrier

The layer being tested is not the layer that keeps animals out.

The blower door measures the air barrier, which in modern construction is a specified continuous plane, sealed at every penetration, and frequently located inboard of the insulation and the cladding.

13.1 The pest barrier is the outer surface

Cladding, soffit, flashing, screening and the ground junction, which is where an animal actually arrives.

13.2 So an animal can be inside the assembly and outside the air barrier

In the rainscreen cavity, the soffit, the rim joist or the attic, all of which are outside the tested plane in many buildings and all of which our wildlife and rodent articles identify as harbourage.

A perfect blower door result says nothing about that space, and that observation is ours.

13.3 And the gap between the planes is habitat

A rainscreen cavity is a ventilated space by design, warm relative to outdoors, sheltered, and lined with insulation. Our articles on overwintering insects and on rodent harbourage describe exactly that combination as attractive.

So modern construction creates a conditioned space outside the air barrier and then tests the air barrier, which is our observation and not a criticism of either practice.

13.4 Which is not a criticism of the test

It is measuring what it is designed to measure. The error would be in reading it as something else.

14. What each trade is actually measuring

Collecting it.

The energy test produces one number for a whole envelope. A pest inspection produces a list of specific locations, each assessed for aperture and accessibility.

14.1 One is a score and one is a survey

A score can be compared between buildings and cannot tell you where anything is. A survey tells you where things are and cannot be compared between buildings.

14.2 Which is why this journal's complaint was misdirected

We have repeatedly wanted a measured exclusion standard. What the building science comparison shows is that a single-figure standard for exclusion may not be possible, because the quantity that matters is a property of individual apertures rather than of the envelope.

That is a correction to our own position and §23 is what we would want instead.

15. Where the two do align

Because the argument above is about inference rather than about the underlying work.

The physical operations overlap almost entirely. Sealing a rim joist, closing a service penetration, fitting a door sweep and repairing a soffit all improve both numbers, and both trades recommend all four.

15.1 The materials differ

An air sealing detail can be done in foam, tape or sealant, none of which resists gnawing. Our exclusion articles describe the hardware cloth, sheet metal and mortar that do.

15.2 And the sequencing conflicts too

The airtightness test is performed when construction is almost complete, all finishes have been applied, and all services have been run into and out of the airtight layer.⁵

Which is the point at which most exclusion details are already buried. A rodent-resistant treatment of a pipe penetration has to happen when the penetration is made, not when somebody discovers it failed.

15.3 Which is a real and specific conflict

A building sealed to an excellent airtightness figure entirely in expanding foam is airtight and not excluded, because the material meets one requirement and not the other.

That is our observation and it is the most directly useful thing in this article.

16. The ordering coincidence

Why the two trades nonetheless tend to agree in practice.

Both start with the largest openings, because that is where the return is. An energy retrofit seals the biggest leaks first for flow, and a pest exclusion closes the biggest apertures first for access.

16.1 So the first hours of work coincide

And diverge afterwards, when the energy work moves to the diffuse remainder and the pest work moves to the small number of remaining traversable gaps.

16.2 And a warning follows

An energy retrofit that stops after the large openings leaves the diffuse leakage and closes most of the pest apertures. One that continues to the diffuse remainder gains energy performance and nothing further on exclusion.

So the pest benefit of air sealing saturates early, which is our inference and the opposite of how the energy benefit behaves.

16.3 Which explains a common observation

That houses which have had energy retrofits often do have fewer rodent problems. The mechanism is that the first tranche of work was the same work, not that the airtightness caused it.

That reading is ours and we found no study of it.

17. What a blower door test can tell a pest inspector

Constructively, because there is real information here.

Where the air is coming from. A depressurised building with a smoke pencil or an infrared camera reveals leak locations, and any leak location is a candidate aperture worth measuring.

That the envelope has a plane at all. A very poor result on a newer building suggests the air barrier was never made continuous, which usually means penetrations were left unsealed.

And a shared vocabulary with the builder. A pest contractor who can discuss ACH50 is talking to the trade that will actually do the sealing.

17.1 And one thing it would settle

Whether an aperture a pest inspector found is actually connected to the outside. A gap that shows no air movement under fifty pascals of depressurisation is probably not a route through the envelope.

Which is a genuinely useful test of traversability per §12, available with equipment somebody else already owns. That application is ours and we have not seen it proposed.

17.2 The first of those is the substantive one

Because the depressurisation is doing the searching. It turns a diffuse inspection problem into a directed one, which is what our detection articles repeatedly say is missing.

18. And what it cannot

Stated once more because it is the point.

The number itself carries no information about pest entry, in either direction, and no arithmetic recovers it.

18.1 Which is worth saying because somebody will try

An airtightness figure is attractive precisely because it is a number in a field that has none, and a number will get used for whatever it appears to be about.

Our articles on allergen action levels and on trap catch interpretation both describe figures being carried beyond what produced them, and this one is positioned to go the same way.

19. The unit argument

A methodological dispute inside building science that this journal has opinions about.

One tester writes: air leakage happens through surfaces, yet we are testing and reporting the findings as a volume calculation, and notes that many testing professionals and building scientists prefer the information shown as flow per square foot of surface area.²

Another states it more bluntly: whatever your air tightness goal, ACH50 isn't the best unit to measure it, giving 3 ACH50 as about 0.25 cfm50 per square foot of envelope.³

19.1 A third figure exists too

The estimated natural infiltration rate, which one tester describes as calculated by his software and can be unreliable.²

So the trade has a measured number, a preferred alternative normalisation, and a derived estimate of the quantity anybody actually cares about, with the last being the least trustworthy.

19.2 The complaint is that the normalisation is wrong

Dividing by volume makes a compact building look worse and a sprawling one look better than the envelope quality justifies, because leakage is a surface phenomenon being divided by a volume quantity.²

19.3 And the preferred unit is not winning

One tester concedes that most of us are familiar with ACH50; it will take time to get comfortable with the alternative.²

20. Which this journal recognises

Because we have written the same complaint about a different number.

Our article on allergen thresholds found action levels expressed in units two sources converted differently. Our article on trap catch found counts reported without the effort that produced them.

20.1 The general form

A measurement is a quantity divided by something, and the denominator is where the arguments are. A number quoted without its normalisation is not interpretable.

20.2 And building science is ahead of us here

Its practitioners are arguing publicly about the right denominator for a standard that is already enforced by code. Pest control has neither the standard nor the argument.

21. The moisture consequence

A second-order effect that matters to three earlier articles.

One builder notes that less air leaks, especially during the winter months, will limit the moisture moving through the building shell finding a surface to condense on.¹

21.1 Winter is when it matters

Because warm indoor air carries much more water vapour than cold outdoor air, and the stack effect drives it outward through the upper envelope, where it meets a cold surface and gives the water up.¹

21.2 Which is straightforwardly good for the timber

Our wood decay article established that fungal activity in timber is governed by a moisture content threshold, and our grain article found the same relationship in a different substrate.

Air sealing reduces the moisture arriving in the assembly, which moves the wood away from the threshold.

21.3 And bad for the air inside

Because moisture generated indoors, by occupants, cooking and washing, now has less route out. An airtight house with no ventilation accumulates humidity.

21.4 Which is the dust mite condition

Our article on dust mites found that those animals require approximately sixty-five per cent relative humidity to maintain water balance, and that Winnipeg households humidify in winter, raising both mite numbers and allergen production per mite.

Airtightness without ventilation pushes indoor humidity in the same direction, and that connection is ours.

22. Why the standard mandates ventilation

And the building science people knew this first.

The high-performance standard's requirements include, alongside the airtightness figure, efficient mechanical ventilation with heat recovery (typically ≥75% sensible efficiency).⁶

22.1 The two requirements are one requirement

You cannot make a building that tight without supplying the air exchange mechanically, and the standard pairs them rather than leaving it to the builder.⁶

22.2 Which is the correct structure

A performance requirement that creates a foreseeable problem, issued together with the measure that addresses it. Our articles on unintended consequences of control measures would have had less to write about if more standards were built this way.

22.3 And it is the pest-relevant part

The humidity our dust mite article describes is managed by the ventilation requirement rather than by the airtightness one. A retrofit that seals a building without adding ventilation gets the airtightness and not the correction.

23. What a measured exclusion standard would need

Since §14.2 concedes that a single figure will not do.

A maximum permitted aperture. Stated as a dimension rather than an area, since §10 establishes the minimum dimension is what matters.

Applied to traversable paths only. Which requires defining traversable, and that is where the work is.

With a location schedule. Ground junction, service penetrations, soffit, roof junctions, doors, vents, and whatever else the building presents.

And a material specification. Because §15.1 shows that closing an aperture in an unsuitable material does not close it.

23.1 And a verification method

Which §17.1 suggests already exists in somebody else's toolkit: depressurise the building and check whether the apertures on the schedule move air.

23.2 That is an inspection protocol rather than a score

Which is less satisfying than a number and is what the physics allows.

23.3 And parts of it exist

Aperture dimensions for common commensal species are published in extension material and our exclusion articles cite them. What does not exist is a protocol that assembles them into a verifiable standard somebody could be held to.

24. Our own position

The disclosure.

We sell exclusion work and we cannot measure it. Section 23 describes the standard we would want to be held to and it does not exist, which means our exclusion work is assessed the way everything else in this trade is, by whether the problem comes back.

24.1 And we would fail our own proposed standard today

Because we do not measure apertures. We find them, close them and describe them in words, which is the ordinary practice of the trade and is not what §23 specifies.

24.2 What we can do in the meantime

Document the apertures we found, their dimensions, what we closed them with and what we did not close, which turns an unverifiable service into a record somebody can check against the building.

That is not a standard. It is the nearest thing available to one.

25. The Manitoba position

Two local notes.

Airtightness matters more here than almost anywhere. A large winter temperature differential drives both the energy penalty and the stack effect, and our overwintering articles describe insects exploiting the same warm air leaving the building at the top.

And the humidity trap in §21.3 is a prairie problem. Cold dry winters, heated airtight houses and household humidification, which our dust mite article identified and could not find local data for.

25.1 And one specific local hazard

Frost heave and seasonal soil movement open and close gaps at the ground junction annually, which means an exclusion detail verified in August may not be intact in April.

A blower door test taken once at construction says nothing about that either, and the seasonally-varying aperture is a problem neither trade appears to have a method for.

25.2 What we could not find

Any study relating measured airtightness to pest entry, in any jurisdiction, and any Manitoba data on either the airtightness distribution of the housing stock or the prevalence of rodent entry.

26. Limitations and open questions

Every source is a builder, a tester, a manufacturer or a commercial site. This is practitioner literature rather than research, and each reference is flagged individually.¹²⁷⁸

The ninety square inch figure is one builder's calculation. For one house, at one volume, published on his own site.¹

And equivalent leakage area depends on assumptions. Converting a flow measurement into a notional hole requires a discharge coefficient and a reference pressure, neither of which our sources state.⁷

The central argument is analytical and untested. We found no study measuring both airtightness and pest entry in the same buildings, which is what would confirm or refute it.

The aperture dimensions in §8 are from memory of the extension literature rather than from a source read in this search, and we have used them only illustratively.

Sections 1.2, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 20, 21.3, 22.2, 23, 24 and 25 are our reasoning. The sum-against-maximum argument, the traversable path requirement, the barrier-location point, the material conflict, the ordering coincidence, the correction to our own earlier complaint and the proposed standard are ours rather than sourced positions.

27. Conclusion

Building science has what this journal keeps asking for: a repeatable envelope measurement, enforced by code, reported as one number, with thresholds at 3.0 air changes per hour at fifty pascals for most climate zones and 0.6 for the high-performance standard.⁷ It can even be expressed as a single notional hole, and a builder testing a fifteen-hundred-square-foot house reports that the code-compliant version amounts to about ninety square inches of equivalent leakage area.¹

None of it transfers. Air leakage is a sum over every aperture in the envelope, weighted by area, and animal entry is a maximum over the minimum dimensions of continuous traversable paths. A sum does not determine a maximum and a maximum does not determine a sum, so ninety square inches distributed as nine hundred hairline cracks and ninety square inches as one opening give the same test result and entirely different outcomes. The tested plane is usually the air barrier, which sits inboard of the cladding, soffit and rim joist where animals actually arrive. And a building sealed to an excellent figure entirely in expanding foam is airtight and not excluded, because the material satisfies one requirement and not the other.

The honest consequence is a correction to something we have said repeatedly. We have wanted a measured exclusion standard and assumed the absence was negligence. What the comparison suggests is that a single-figure standard may not be available for this property, because the quantity that matters belongs to individual apertures rather than to the envelope. What is available is an inspection protocol with a maximum permitted dimension, a location schedule and a material specification, which is less satisfying than a score and is what the physics allows. Until somebody writes it, we document what we found, what we closed it with, and what we did not.

References

1. Building science, a visual for blower door testing. Builder's technical blog post. Practitioner source publishing his own testing, cited as attributed material. Used for the account of testing a code minimum house at rough framing stage with a result of 0.55 ACH50 and 140 CFM, giving a leakage area of approximately 15 square inches; for the house description of more than 1500 square feet of living area and a volume of around 14,800 cubic feet; for the statement that achieving the code required result of 3 air changes per hour at 50 pascals requires less than 740 cubic feet per minute of air flow past the fan; for the described experiment of drilling 2.5 inch holes in an uncut window opening to determine how many would be needed to reach the code minimum; for the stated takeaway that 3 ACH50, or 90 square inches of leakage area for a house over 1500 square feet, is considered tight, with the author's own goal being 1 ACH50 or less at an investment well under one per cent of the construction budget; and for the durability argument that fewer air leaks, especially during winter months, will limit the moisture moving through the building shell and finding a surface to condense on. https://www.northernbuilt.pro/building-science-a-visual-for-blower-door-testing/
2. Using a blower-door test and interpreting the results, building trade magazine article. Practitioner source, cited as attributed material. Used for the explanation that the ACH50 number indicates how many times all the air inside a home is exchanged with outside air at the test pressure of 50 pascals; for the statement that code requires new houses be under 3 or 5 ACH50 depending on location, and that the author regards homes over 5 as candidates for improvement; for the reported range of results, the best seen being 0.33 ACH50 and the worst just over 15; for the methodological complaint that air leakage happens through surfaces yet is tested and reported as a volume calculation, with many testing professionals and building scientists preferring flow per square foot of surface area, and the concession that most practitioners are familiar with ACH50 and will take time to become comfortable with the alternative; for the worked conversion of a test result into flow per square foot of surface area; and for the account that testing at 50 pascals subjects a building to pressures it does not typically see, that some leakage present at elevated pressure will not leak under normal conditions, and that a home at the code minimum of 3 ACH50 will have a rough natural air-leakage rate of about 0.2 air changes per hour, exchanging its volume roughly five times per day. https://www.finehomebuilding.com/project-guides/insulation/using-a-blower-door-test-and-interpreting-the-results
3. How much air leakage in your home is too much? Building performance publication article. Practitioner source, cited as attributed material. Used for the statement that the high-performance program takes houses about as far as airtightness can go and that its threshold is 0.6 ACH50; for the reported test of a net-zero house at less than 200 cfm50 of air leakage, about 0.5 ACH50; for the identification of 3 ACH50 as a more achievable target required by a named model energy code for most climate zones; for the position that whatever the airtightness goal, ACH50 is not the best unit to measure it; and for the conversion of 3 ACH50 to about 0.25 cfm50 per square foot of envelope, or 25 cfm50 per hundred square feet. https://www.greenbuildingadvisor.com/article/how-much-air-leakage-in-your-home-is-too-much
4. What is a blower door test? Window manufacturer's professional resources article. Commercial source, cited as attributed material. Used for the description of air changes per hour at 50 pascals as the most common way to show leakage, requiring the volume of the structure; for the worked example of a house 25 feet by 40 feet by 10 feet with a volume of 10,000 cubic feet producing 167 CFM, and the calculation of flow multiplied by 60 minutes divided by volume giving approximately 1 ACH50; for the note that 1 ACH50 passes code but does not meet the high-performance certification requirement of 0.6 ACH50 or less; and for the statement that blower door testing has been code-required in residential construction since the 2012 edition of a named model residential code, with requirements found in its energy efficiency chapter and based on climate zone, subject to local adoption and amendment. https://www.andersenwindows.com/for-professionals/pro-views/what-is-a-blower-door-test
5. Blower door protocol for passive house certification, high-performance building supplier resource page. Commercial source, cited as attributed material. Used for the statement that a retrofit may meet 1.0 ACH50 for the corresponding retrofit certification, and that if a test can be brought below 1.0 but not below 0.6 a declaration should be submitted with certification; for the note that the certifying institute uses a named European standard to measure air flow, which while very similar to the named American standard follows a different protocol; for the definition of the internal volume used as deliberately heated, cooled or mechanically ventilated space within the building subject to measurement, generally excluding attic, basement and attached structures; and for the guidance that a simple one point depressurisation test during construction while the airtight layer is accessible gives a clear indication of leakage, while the final test should be done when construction is almost entirely complete with all finishes applied and all services run into and out of the airtight layer. https://475.supply/blogs/design-construction-resources/blowerdoor-protocol-for-verification-of-0-6ach50-for-passive-house-certification
6. Passive house, general reference compilation entry. Tertiary source, flagged accordingly. Used for the summary of the standard's key quantitative performance criteria, including an annual space heating demand limit or peak heat load limit calculated with the standard's planning package using local climate data; for the airtightness requirement stated as n50 no greater than 0.6 per hour at plus or minus 50 pascals, measured via a blower-door test; and for the requirement of efficient mechanical ventilation with heat recovery, typically at or above 75 per cent sensible efficiency. https://en.wikipedia.org/wiki/Passive_house
7. Blower door test complete guide to building air leakage testing, commercially operated information site. Commercial source, cited as attributed material. Used for the statement that building codes require 3.0 ACH50 or less for most climate zones while high-performance standards require 0.6 ACH50 or less; for the note that blower door testing has been mandatory for new residential construction since 2015 under a named model energy code, with requirements of 3.0 ACH50 for most climate zones and 5.0 for hot climates, and that for new construction testing is required after substantial completion but before final inspection; for the definition of equivalent leakage area as representing the total area of all leaks combined into a single equivalent opening, offered to help visualise the cumulative effect of all air leaks; for the illustrations that an equivalent leakage area of 50 square inches corresponds to an eight by six inch window open continuously, 100 square inches to a ten by ten inch window always open, and 200 square inches to a fourteen by fourteen inch opening; for the approximate conversion of 4.0 ACH50 to about 0.2 natural air changes per hour; and for the safety note that all combustion appliances must be turned off during testing to prevent backdrafting. https://solartechonline.com/blog/blower-door-test-guide/
8. Blower door test results, what the ACH50 number actually means. General contractor's blog post. Commercial source, cited as attributed material. Used for the description of the test method, in which a calibrated fan mounted in an exterior door frame depressurises the house, pulling air out and measuring how much leaks back in through cracks and gaps; for the reported experience of results as tight as 1.5 ACH50 across the firm's custom homes; for the position that meeting code is the minimum, meaning a house will not fail inspection but is not particularly tight; and for the observation that a tighter envelope means fewer drafts, since cold spots near windows and exterior walls are almost always caused by air leakage rather than insulation failure, and better humidity control, since uncontrolled infiltration brings moisture into the building envelope. https://southeasterngc.com/blogs/blower-door-test-ach50-explained