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Airtightness measurements in Passive Houses

Instructions for carrying out measurements

Airtightness measurements in Passive House buildings are to be carried out uniformly worldwide according to ISO 9972, method 1. The deviations (these are not of a fundamental nature), clarifications and additions to the standard in relation to Passive Houses are described here.
The calculation of the reference volume for passive houses is to be carried out according to the procedure listed below which is not part of the ISO 9972. The resulting volume is to be used for the determination of the n50-value.
For the calculation and documentation, it can be helpful to use the “room data”, which is included as an additional tool in PHPP Version 10.

1. Comparison of designations

The superseded standards EN 13829 and the current ISO 9972 use different designations in some places. For a better overview, the most important ones are compared here:

2. Calculation of volumes

The air volume Vn50 used for calculating the Vn50 value inside the heated building envelope should be determined and comprehensibly documented separately for each room. In doing so, the base area of the room should be multiplied by the average clear height of the room. Overall assumptions for determining the internal volume of the enclosed space (gross volume) by means of a reduction factor are not permissible.Room by room
The base area to be used for this calculation differs from the treated floor area which is normally used. The air volume Vn50 is not the same as the “enclosed volume”, nor is it the same as the volume of air in a heated zone as used in the PHPP sheet “Annual Heating Demand” (overall room height 2.5 m). For this reason, the calculated volume Vn50 from the test report must also be transferred into the PHPP.
not TFA,
not VV
instead, Vn50
Irrespective of the degree of completion of the building, the dimensions used should always be those of the finished building (e.g. where there is no screed). Air volumes above suspended ceilings do NOT count towards the total air volume. This is regardless of whether the ceiling already exists, is tightly connected with the wall, or has different types of holes (“acoustic ceiling”). The reduction of the volume by layers of plaster does not have to be taken into account.Final dimensions only
A full and comprehensible room-by-room calculation of the volume must be provided for each airtightness measurement. Auxiliary calculations may also be necessary; these must also be provided. For example, in the case of inclined roofs, the air volume is determined by means of triangular or prism calculations. A proportional factor such as those used in the table below (Figure 1) can be taken into account.Documentation
Figure 1: Example of documentation for room by room volume calculation.

The total air volume within the thermal envelope will thus be taken into account. Special features are shown in Figure 2 for more detailed explanation.

Figure 2: Guidelines for calculating the air volume inside the airtight layer of a building. The red dashed line all around represents the air tight layer.

Visible rafters, beams, plasterboard encasings, wall-mounted installations (if these do not have the same height as the room) and the like are not taken into account; in the calculation they are not deducted for simplification. They are thus treated as if they did not exist (= air space).Rafters, beams wall-mounted installations.
The volume of window reveals (see Figure 3) is not taken into account either (measured only up to the inner wall surface). The same applies in the case of doors and openings.
These stipulations are for the purpose of simplification. Any deviations occurring as a result are usually small.
Window reveals
Figure 3: The volume of window reveals is not taken into account in the volume calculation

The volume of a stairwell is part of the air volume and is fully taken into account. The volume of the stairs themselves (building component) is not taken into account, therefore it is not deducted. The base area of the stairwell can thus be multiplied with the clear height of the storey.
No deduction of the stairwell volume
The volume of elevator shafts and any other kind of shafts inside the thermal envelope are part of the air volume and is fully taken into account. The volume of the elevator cabin, pipes etc. themselves (building component) is not taken into account, therefore it is not deducted. The base area of the shaft can thus be multiplied with the clear height of the storey Elevator and shafts count to the air volumes

An overview of the distinctions between the VL value from the PHPP and the Vn50 value for the blower door measurement can be found here.

3.Time of measurement

Airtightness of the finished building is relevant, therefore it is obvious that the measurement should be carried out after completion of the building; however, by this time, all installations, screed, cladding etc. will have been completed already. It will not be possible to access many important connections and penetrations of the airtight layer in a non-destructive manner. Remaining leaks in the airtight layer can no longer be remedied, which would not be practical.
For this reason, carrying out measurement preferably directly after completion of the airtight layer (e.g. window installation, airtightness sheeting in the roof etc.) will be more effective. In this way, leaks in the airtight layer can be localised directly and essential corrections can be carried out. At the time of the measurement, building components of the building envelope (e.g. entrance door) may be missing only in exceptional cases; in such cases, these must be sealed up temporarily. All seals and preparations must be mentioned in the test report in an understandable way.Measurement directly after completion of the airtight layer
After the measurement, the construction manager in charge must ensure that damage to the airtight layer is not caused during subsequent construction work. Should there be cause for concern about this due to various reasons, then another measurement should be carried out.
In most cases however, one airtightness measurement is sufficient.
Second measurement?

4. Carrying out the measurement

Method 1
In the PHPP the state of building use during normal operation is relevant for the energy balance of a building, therefore the airtightness measurements in Passive House buildings must be carried out according to Method 1. Normally there is no difference between Method 1 (in use) and Method 2 (building envelope test) in the case of Passive Houses. As a rule, the only intended openings are the outdoor air and exhaust air openings of the ventilation system which must be sealed for the measurement. In a Passive House building, openings which are sealed according to Method 2 should generally be implemented so that these can be closed (e.g. smoke extraction in elevator shafts). What matters is the exact and comprehensible documentation of each temporarily sealing measure that is carried out for the measurement.
Building as used
Sealing the ventilation system
Controlled ventilation in residential buildings should be operated continuously during the heating period for reasons of hygiene. Because a balanced ventilation system does not constitute a source of leaks, it is temporarily closed off for the measurement (e.g. by taping over or using a sealing balloon). In doing so, the outdoor air and exhaust air sides should be sealed if possible, in order to avoid measuring the leakages of the duct network and the ventilation unit as well.
Residential buildings: sealing the ventilation system
In non-residential Passive House buildings (schools, kindergartens etc.), ventilation systems are often not operated during the night or at the weekend (intermittent operation). In such cases, ventilation systems must have tightly shutting flaps at the outdoor air and exhaust air ends to prevent the building from losing additional heat due to thermal lift and strong winds while the ventilation system is not running. For certified units, leaks within the ventilation unit itself are already taken into account in the device test, i.e. the heat recovery efficiency.

In buildings with intermittent operation, the existing sealing flaps must be closed during the airtightness measurement, but they must not be taped over in addition.

Fans for mechanical summer ventilation that are present in a building may not be taped over either.
Non-residential buildings: closed flaps only
Further sealing
No further openings (keyholes, leaks in windows, cat flaps etc.) in the building envelope may be sealed off for the measurement. Features that are problematic in terms of airtightness, such as an open fireplace or a room-sealed boiler etc., cannot be used/operated in a Passive House as a rule.\\
No further sealing
The only exceptions may be temporarily taping over openings for missing building components, as described above, which affect the airtightness (e.g. missing door sill, missing odour trap in the waste water pipe). Again, an exact record should be kept about such sealing.Exception: Missing building components
The aim is to obtain realistic results reflecting the building’s airtightness in use, rather than to create an “artificially” improved situation.Building as used
Negative AND excess pressure measurement
Unlike in the ISO 9972 standards, both negative pressure AND excess pressure are generally required when measuring the airtightness in Passive Houses. In this way, the reliability of the measurement results is significantly improved, with a minimum of extra effort. Finally, the airtightness parameter of the building is determined as an average value from the negative and excess pressure results.
Measurement with negative and excess pressure

5. Special features of large buildings (qE50-value)

In large buildings it is necessary to calculate the airtightness value with reference to the envelope area (qE50-value) in addition. The n50-value alone is no longer significant on account of the more favourable A/V ratio (surface area to volume ratio).
In the case of large buildings it is therefore recommended that the exterior surface of the building should also be ascertained. This is also determined according to ISO 9972.
Exterior surface
Buildings with an air volume Vn50 ≥ 1500m³ are defined as large buildings.≥ 1500m³
For such large buildings, as a result both values, i.e. the n50-value and the qE50-value, will then need to be indicated in the measurement report.n50 and qE50 values required
Instructions regarding the procedure for calculating the envelope area according to ISO 9972:
The envelope area is the total area of all floors, walls and ceilings enclosing the volume under consideration, including all walls and floors that are below ground level. Interior dimensions from the inner edge are used; the facing areas of intersecting interior walls are not deducted. See Figure 4.
In deviation from ISO 9972, the envelope area used in the PHPP can also be used for simplification. The exterior dimensions used in the PHPP only lead to negligible differences.
Figure 4: Interior dimensions from inner edge for calculating the envelope area (according to ISO 9972).

In terraced houses, the partition walls of the building also count as the envelope area; in apartments in multi-storey buildings this also applies to all floors, walls and ceilings adjoining neighbouring apartments. These areas must only be taken into account if each accommodation unit is measured separately.Terraced houses and multi-storey buildings
Recommended target value for the qE50 requirement
An n50-value smaller than or equal to 0.6 h-1 has been set as a limit value for the certification of Passive House buildings (see certification criteria on

The requirements for the envelope area of smaller buildings can be used as a reference for the target value for larger buildings (≥ 1500 m³), resulting in a target value of:

qE50 ≤ 0.6 m³/(h m²)

Numerous measurements in large and very large buildings have shown that this target value (or even lower values) can be achieved with an appropriate airtightness concept. Higher requirements may apply for special types of buildings (e.g. swimming pool).
Target value qE50
Note: In smaller buildings, more meticulous airtightness measures may be necessary in order to meet the n50 < 0.6 h-1 requirement. Compliance with the qE50 criterion alone is thus not sufficient.The qE50-value alone is not enough

See also

planning/airtight_construction/airtightness_measurements_in_passive_houses.txt · Last modified: 2021/08/24 11:11 by nsukhija