Airtightness FAQ

What is Airtightness?
Why is airtightness important?
Can a building be too airtight?
What is an Intelligent Membrane and why should I use INTELLO PLUS to achieve a continuous airtight seal as oppose to conventional vapour barriers or vapour checks?
Is airtightness testing mandatory?
What does an air permeability of a Q50 of less than 10m3/hr/m2 mean?
What are the most common air infiltration/leakage paths?
If I conceal the leak with an internal finish will this provide a reliable airtight seal?
When does testing take place?



What is Airtightness?

While the term 'Airtightness' often conjures up the image of a hermetically sealed space, the reality is that airtightness refers to the minimisation of draughts from outside to inside and as a result the expensive heated air leaving the living space through the external envelope of the building been replaced by cool external air. The key is to build tight and ventilate right. Whereas ventilation is designed into the building, a gap between a window frame and a wall is not. Effective ventilation is an essential part of a healthy living space, air leakage or a draught will lead to increased energy bills, discomfort, and may lead to potential mould growth and structural degradation within building components. To summarise, random holes/leaks are not designed into buildings. Ventilation is. An airtight house is a sustainable low energy house.

Why is airtightness important?

Air tightness plays a significant role in the energy efficiency of buildings. Because

a link has been established between carbon emissions and global warming

the production of energy emits carbon

the built environment contributes about 50% of carbon emissions in the European union

heated/conditioned air leaking from buildings requires the use of additional energy to maintain temperatures

It is generally accepted that approximately 30% of the heat loss which occurs through the building fabric is as a result of air leakage and uncontrolled ventilation.

By limiting the leakage of heated/conditioned air from buildings, it is possible to reduce energy consumption and costs. The government has made commitments to reduce carbon emissions through the European Energy Performance of Buildings Directive (EPBD) and the Kyoto Agreement. Part L is their method for addressing the conservation of fuel and power in buildings and as such places requirements on air tightness from July 1st this year.

Can a building be too airtight?

Airtightness can also be referred to as the air leakage rate of a building. While a completely airtight building with no leaks is desirable, the reality is that in practice it cannot be achieved on a building site. The aim is to minimise air leakages and to maximise controlled ventilation. Even in the lowest energy Passive House, there is a degree, be it very small of air leakage. The key is the 'Build Tight and Ventilate Right'.

What is an Intelligent Membrane and why should I use INTELLO PLUS to achieve a continuous airtight seal as oppose to conventional vapour barriers or vapour checks?

Pro clima INTELLO PLUS Intelligent membrane is airtight, and vapour permeable or vapour tight, depending on average air humidity within the construction. It allows water vapour dry out of a construction when humidity is high within structural elements, either due to seasonal change or unexpected moisture intrusion. When average air humidity is low within the building fabric (i.e. when the construction is dry), INTELLO PLUS resists the penetration of vapour into the construction, preventing interstitial condensation. In this way INTELLO PLUS prevents vapour driving into the construction in winter months, and if moisture ever manages to get into the construction and cannot dry out towards the outside in winter, it can dry towards the inside in summer months. This is something traditional vapour retarders/barriers/checks cannot do. This may lead to sweating occurring behind such membranes. In this way INTELLO PLUS not only provides a continuous airtight seal, but also protects constructions against the potential risks associated with condensation within the construction.

Is airtightness testing mandatory?

From July 1st 2008 new residential buildings need to demonstrate a minimum level of air permeability (Q50 < 10m3/h/m2) and this is done through an on-site blower door test. Testing is performed to the European Standard EN13829.This is not an onerous requirement in itself but the design air permeability for a particular building may be lower to achieve the overall carbon emission rate and an efficient Building Energy Rating (BER) for the building and/or client specification. We recommend that to achieve an efficient energy rating the air permeability or Q50 should be no more than 3 m3/h/m2 in accordance with ATTMA (Airtightness Testing and Measurement Association) best practice standards.

What does an air permeability of a Q50 of less than 10m3/hr/m2 mean?

A Q50 of less than 10m3/hr/m2 refers to an air permeability of less than 10m3 of air per hour per m2 of the external envelope of a building when the building is exposed to a pressure differential by depressurisation and or pressurisation of 50 Pa. This literally means that when we exclude ventilation and design openings, and exert a pressure difference of 50Pa on the external envelope of the building 10m3 of air per hour passes through every square meter of the external envelope...by no means airtight! A pressure differential of 50 Pa can be equated to approximately a wind speed of 20 miles per hour on every side of the building envelope at once, by no means an extreme pressure. An example: If the leakage flow measured is 2000M3Hr and the envelope area is 100M2 then the air permeability is calculated as 2000/100 = 20M3Hr/M2 and would therefore not be compliant. If the leakage areas should subsequently be identified during testing (with infrared scanning, smoke pencils or with ones hand to feel the leak) and remedied and the then the reduced leakage flow is measured at 900M3Hr and again the envelope area is 100M2 then the air permeability is calculated as 900/100 = 9 M3Hr/M2. Now the dwelling will be compliant.

What are the most common air infiltration/leakage paths?

In essence achieving an air tight building should not be too difficult. Identifying potential air paths is fairly straightforward and addressing them is often not complicated or may be already dealt with by measures to achieve acoustic or fire requirements. Areas to focus on: 1. Where elements of the air barrier meet eg wall to floor, wall to structural ceiling (suspended ceilings are permeable), cladding to roofing, eaves details, etc. In more complex constructions it may be helpful to identify the air barrier-which must be continuous (i.e. INTELLO PLUS). Typically the air barrier will be external or party walls, ceilings and floors plus elements bordering 'unconditioned areas' (e.g. plant rooms, garages and cold roof spaces). Sometimes detailing around partition walls and floors may also present an air path into cavities or voids that link to an external space. Extensions can create particular difficulties where contractors are trying to seal against the external face of an existing building as well as running services and allowing access between the new and old areas. 2. Where components meet e.g. block work joints, joints between beam and block flooring, where cladding systems overlap or meet blockwork. 3. Where penetrations interrupt the air barrier/INTELLO PLUS:

Doors and windows - ensure door and window fitters produce a good seal between the building and the product (ensuring air cannot escape outside or into the cavity) - In this area pro clima Contega FC or TESCON PROFIL maybe used depending on the method of construction..

Loft hatches - some hatches may distort; and few hatches have been tested and certified for airtightness. One hatch which has received certification for airtightness is WELLHOEFER. (See details in our products section)

Piping - especially soil piping, sealing where pipes enter boxing and/or where they exit eg into unconditioned loft spaces. These can be sealed using pro clima service grummets.

Electrical fittings - We recommend including a service void where possible or to minimise services on the external envelope. Down-lighters in ceilings can present a problem. This can be sealed using the Optime Downlight Protector System (See our products section)

Overlaps, penetrations and connections to building components of the INTELLO PLUS Intelligent membrane or a vapour check. This can be sealed using proprietary pro clima airtightness tapes, glues and grummets.

If I conceal the leak with an internal finish will this provide a reliable airtight seal?

An 'out of sight, out of mind' mentality, may lead to many unforeseen leaks in the external envelope. The following areas should be noted when building for airtightness:

Above suspended ceilings

Below raised floors

Behind bath panels and shower trays

Behind skirting boards

Service penetrations in the Hot Press

At its most basic, the objective is to create a continuous air barrier between:

Inside (warm space) and outside (cold space)

Conditioned and unconditioned spaces i.e. apply the same principles to barriers between heated and unheated areas e.g. plant rooms, stair wells

Adjacent units e.g. flats or attached houses are tested individually so, as far as the test is concerned, air leakage into neighbouring units is still leakage.

Achieving a high level of airtightness requires the communication and coordination between:

The Architect

The Builder - namely the construction manager and/or the site manager

The subcontractors - notably those that are responsible for creating the air barrier eg plasterers, timber frame erectors and those that may penetrate it eg plumbers and electricians, insulation installers

When does testing take place?

When the building is completed, typically everything has been finished. Before the building is completed it is good practice to carry out a pre-emptive quality assessment of the airtightness layer prior to the final surface finish been applied by using a blower door fan or the pro clima WINCON airtightness quality control unit (see products section). In this way leakages are identified as early as possible and can me 'made good', relatively cheaply and very effectively.