Building Services

1. Building Services By Dr David Johnston – licensed under the Creative Commons Attribution – Non-Commercial – Share Alike License http://creativecommons.org/licenses/by-nc-sa/2.5/

2. ENVIRONMENTAL SCIENCE & SERVICES - LEVEL 1 Ventilation Dr. David Johnston

3. Objectives By the end of this lecture you should be able to: • Define what is meant by the term ‘ventilation’. • Understand why buildings require ventilation. • Define air leakage and understand how it occurs. • Be able to identify common air leakage paths in buildings. • Understand what is meant by the term ‘airtightness’. • Be aware of different methods of ventilating buildings and their associated advantages.

4. Structure This lecture is structured as follows: • Introduction. • Air leakage and airtightness. • Examples of airtight buildings. • Natural ventilation. • Mechanical ventilation.

5. Introduction

6. The purpose of ventilation Ventilation is simply defined as the process of changing air in an enclosed space. In order to maintain optimum air quality in buildings, a proportion of the air contained within any enclosed space should be continuously removed and replaced with fresh outside air. All buildings require ventilation for: • Human respiration. • The health and comfort of the occupants. • The control of condensation and humidity. • Fuel burning appliances. • The dilution and disposal of pollutants. Ventilation can also be used to control thermal comfort. If the incoming ‘fresh’ air is contaminated by pollutants, then measures have to be taken to remove them.

7. Types of ventilation Buildings are ventilated via a combination of: • Purpose-provided ventilation – This is the controllable air exchange between the inside and outside of a building by means of a range of natural and/or mechanical devices. • Infiltration – Thisis the uncontrollable air exchange between the inside and outside of a building through a wide range of air leakage paths in the building structure. Methods of achieving sufficient purpose-provided ventilation are contained within the Building Regulations 2000 Approved Document Part F 2006 edition (ODPM, 2006a). Ventilation requirements for UK dwellings are typically: • Recommended - between 0.5 and 1.0 ac/h. • Minimum - between 0.3 to 0.5 ac/h. Infiltration can be reduced by reducing the air leakage from the building

8. Air leakage and airtightness

9. Air leakage Air leakage is defined as the uncontrolled exchange of air both into (infiltration) and out of (exfiltration) a building through cracks, gaps and other unintentional openings in the building envelope. It is driven by the same physical processes that drive natural ventilation, namely: • Wind effect. • Stack effect. Wind effectStack effect The rate of air leakage is dependent upon: • The air permeability of the construction. • The wind speed and direction. • The temperature difference between the inside and outside of the building, as well as within the building.

10. Airtightness Airtightness is the measurement criteria used to evaluate the air leakage of a building. The airtightness of a building determines the uncontrolled background ventilation or leakage rate of a building which, together with purpose-provided ventilation, makes up the total ventilation rate for the building. Total Ventilation Rate=Uncontrolled Background Ventilation + Purpose Provided Ventilation Traditionally, airtightness was expressed in air changes per hour (ac/h or h-1). However, nowadays air permeability (m3/(h.m2) is more commonly used as it takes into consideration the effects of shape and size. The more airtight a building, the lower the air permeability. In the UK, airtightness is measured at an artificially induced pressure of 50Pa (n50).

11. Measurement of airtightness The airtightness of a building envelope can be measured using • Fan pressurisation (blower door) technique. • Tracer gas technique. Fan pressurisation is the simplest, quickest and most widely used technique in the UK and involves the use of: • Portable variable speed fan. • Adjustable door frame and panel. • Fan speed controller. • Pressure and flow gauge. Pressurisation tests are the basis for guidelines and legislation in a number of countries.

12. Measurement of airtightness A series of multiple fans or trailer mounted fans are used for pressure testing largedomestic and non-domestic buildings.

13. Leakage identification The most widely used technique for identifying the main areas of air leakage within a domestic building is smoke detection.This technique involves either pressurising or depressurising the building, and then locating the areas of air leakage using a manual or electronically operatedhand-held smoke puffer. . In most instances, detection is undertaken from inside the dwelling under pressurisation, as it is much easier to identify where the smoke leaks out of the habitable space. Important point about smoke detection is, that in most cases, it is only possible to identify the point where the smoke leaks out of the habitable space, and not the path that the smoke takes from the inside to the outside of the building.

14. Leakage identification Infrared thermal imaging using an infrared camera can also be used to identify the main areas of air leakage within the building fabric. It can provide additional information which is not always possible to recognize purely by smoke detection. However, this technique is considerably more complex and problematic than smoke detection. Limitations as to when and where it can be used as a detection technique often prohibit its use. Also, without appropriate skills and knowledge of the construction, it is possible to misinterpret the images obtained.

15. Main air leakage paths The main air leakage paths in UK dwellings are illustrated below: Important to realise that air leakage can occur both directly and indirectly. 1. Gaps at ceiling-to-wall joint at the eaves 2. Gaps around windows 3. Leaky windows 4. Leaky doors 5. Leaks at threshold 6. Open chimneys 7. Leaks around flue penetration of ceiling 8. Gaps in and around suspended timber floors 9. Open fire/stove 10. Gaps around skirting board and floor 11. Gaps around internal partition/ceiling junction 12. Gaps in and around electrical fittings 13. Gaps around loft hatch 14. Gaps around soil stack 15. Gaps around ceiling light fittings 16. Vents penetration roof/ceiling 17-21. Gaps around waste pipe and flue penetrations 22. Gaps around wall-to-floor join

16. Direct air leakage points These are points in the building envelope where air leakage occurs directly through the primary air barrier from inside the insulated envelope to outside or vice versa. Common direct air leakage points include: • Around trickle ventilators and through poorly closing trickle ventilators. • Around and through the loft hatch. • Around poorly fitting windows and doors. • Through gaps at bay windows and around sliding mechanism of patio doors. • At thresholds. • Around services at the point where they penetrate through the primary air barrier.

17. Indirect air leakage points These are points in the building envelope where air leakage occurs indirectly through the primary air barrier via a series of interconnected voids from inside the insulated envelope to outside or vice versa. Common indirect air leakage points include: • On external and party walls at the ground floor/external wall junction. • Under kitchen & utility room units. • Around staircases. • Into intermediate floor voids and at intermediate floor perimeters. • Into service voids (e.g. behind bath panels). • At service penetrations where they penetrate the dry-ling and/or internal finish.

18. Quantifying air leakage In UK dwellings, experience indicates that the majority of air leakage tends to occur indirectly rather than through easily identifiable directgaps and cracks in the building envelope. Work undertaken in the late 1990’s by the BRE suggested that the vast majority of component air leakage could not be attributed to a single component. Instead, it could be attributed to the numerous “hidden paths”, through cracks and gaps that exist throughout the building. Component air leakage in dwellings [After: Stephen, 2000] These “hidden” air leakage paths are often complicated, making it very difficult, if not impossible, to trace and seal effectively. Therefore, it is much more effective to design and construct airtight dwellings in the first instance, rather than try to carry out post construction tightening (most commonly taking the form of secondary sealing) once the dwelling is built.

19. Airtightness and ventilation The level of airtightness achieved within a building will have an important influence on the overall ventilation rates that will be achieved and the type of ventilation strategy that should be adopted. However, irrespective of the ventilation strategy adopted, the aim of good ventilation design should always be to minimiseuncontrolled infiltration by making the building envelope as airtight as possible, and then ventilate the building appropriately by providing sufficient purpose-provided ventilation. In other words: ‘build tight, ventilate right’

20. Thermal bypassing and airtightness Thermal bypassing is complex and is often confused with airtightness. A thermal bypass occurs where air is allowed to move through, around and between the insulation, in effect bypassing the benefit of the insulation. Therefore, it is possible to have a very airtight dwelling but still have thermal bypassing resulting in lower thermal performance. The important issues in relation to thermal bypassing are: Location of the primary air barrier. • The location of the thermal insulation and its relationship with the air barrier. • If there is separation of the thermal insulation from the air barrier, then a thermal bypass can exist. Position of the insulation. There are no air gaps between the thermal insulation and the primary air barrier. By constructing a building with a high level of airtightness and ensuring that the air barrier is kept in contact with the thermal insulation layer, thermal bypassing can be effectively eliminated from the structure.

21. Airtightness and the Building Regulations Airtightness in England and Wales is currently addressed in Approved Document Part L1A 2006 (ADL1A 2006). ADL1A 2006 requires that the building fabric should be constructed to a reasonable quality of construction so that the air permeability is within reasonable limits (ODPM, 2006b). A reasonable limit for the design air permeability is given as 10 m3/(h.m2) @ 50Pa. In the majority of cases, compliance with the regulation will require some degree of compulsory pressure testing. Details of the pressuretesting regime associated with each method of compliance are detailed within ADL1A 2006. A more onerous testing regime is required if accredited construction details have not been adopted. Compliance with ADL1A 2006 also requires that the pressure tests are undertaken in accordance with the procedure set out in the Air Tightness Testing and Measurement Association Technical Standard 1 (ATTMA, 2007). Compulsory pressure testing (and re-testing, if required) will be performed at the house builder’s expense.

22. Airtightness and the Building Regulations In a recent consultation document on ADL1A 2006, it is proposed that an air permeability target is introduced for those dwellings that are not tested (CLG, 2009). In such cases, the assessed air permeability of the non-tested dwellings is the average air permeability obtained from other tested dwellings of the same type increased by 2 m3/(h.m2) @ 50Pa. This takes into account the likely variability of air leakage that would be achieved by on- site testing.

23. Airtightness and energy performance Airtightness can have a significant impact on the energy use and CO2 emissions attributable to buildings. In the UK, any exchange of air from the inside to the outside is likely to result in: • A significant reduction in the thermal resistance of the thermal insulation, due to thermal bypassing, leading to increases in realised fabric U-values. • An increase in the building’s ventilation and fabric heat losses, resulting in an increase in space heating requirement. • Increased energy usage and higher carbon emissons. Impact of poor airtightness on a dwelling.

24. Airtightness and energy performance It is also important to realise that as the fabric performance of new dwellings improves, the proportion of total heat losses attributable to ventilation is likely to increase, unless air leakage is addressed. For instance, in reasonably well insulated but relatively leaky dwellings (those built to Part L 2006 with an air permeability of 10m3/(h.m2)), ventilation heat losses can account for up to one third of the dwellings’ total heat loss. Comparison of ventilation and fabric heat losses for a ‘notional’ (80m2) semi-detached house

25. Airtightness of new UK dwellings Recent measurements undertaken on a sample of 750 dwellings,of various construction types and forms, the majority of which were built to conform to ADL1 A 2006 showed: Mean air permeability of new UK dwellings [Source: BSL, 2009] • A very wide range of airtightness within the sample – 0.75 to 24 m3/(h.m2) @ 50Pa, with a mean of 6.13 m3/(h.m2) @ 50Pa. Sample of 750 dwellings Mean of 6.13 m3/(h.m2) @ 50Pa Dwellings built to Part L 2002 Sample of 99 dwellings Mean of 9.2m3/(h.m2) @ 50Pa Existing stock Sample of 384 dwellings Mean of 11.5m3/(h.m2) @ 50Pa

26. Airtightness of new UK dwellings In terms of construction type: [Source: BSL, 2009] Sample of 750 dwellings

27. Airtightness of new UK dwellings In terms of building form: [Source: BSL, 2009] Sample of 534 dwellings

28. Airtightness of new UK dwellings In terms of main construction type and building form: [Source: BSL, 2009] Sample of 534 dwellings Timber frame Masonry

29. Zone of Current UK Practice (~ 3 – 15ach @ 50Pa) Kronsberg P assive House Estate, Hannover, Germany 32 Dwellings (Feist, Peper & Gorg, 2001) Stamford Brook, Altrincham, UK 44 dwellings (Miles Shenton, Wingfield & Bell, 2007) Dwellings built to Part L 2002 Dwellings built to Part L 2006 750 dwellings 99 dwellings (BSL, 2009) (Grigg, 2004) Probability Existing UK stock (pre - 1995) 4 71 dwellings (Stephen, 2000 & 2004) 0 5 10 15 20 25 Mean air change rate (ach @ 50Pa) Airtightness of new UK dwellings incontext 0.29 - 4.3 6.1 10.6 12.6

30. Factors influencing airtightness A number of factors are known to influence the airtightness of dwellings. These include: • Age of the dwelling. • Construction type • Location and continuity of the primary air barrier. • Number of storeys. • Size and complexity. • Seasonal variation. • Longevity. • Sequencing of construction processes. • Site supervision and workmanship. • Quality of construction. • Communication.

31. Size and complexity Other things being equal, the larger and more complex the floor plan and the more complex the construction techniques used, the greater the number of junctions between the elements of the thermal envelope. This increases the potential for air leakage. This does not mean that complexity should be avoided. Instead, designers and constructors need to understand the airtightness problems that may be introduced by adopting complex detailing and devise appropriate and robust solutions.

32. Sequencing of construction processes Sequencing can have an important impact on the airtightness of a dwelling., as the build sequence adopted can often make it difficult to gain access to and maintain continuity of the primary air barrier. • Approach 1 - Top floor ceiling installed prior to the installation of the metal stud partitioning. • Approach 2 - Metal studwork partitioning installed first. Timber head plate then installed over the top of the head channel in metal partitioning in an attempt to reduce air movement through this channel.

33. Construction observations Plasterboard dry lining Experience suggests that it is extremely difficult, if not impossible, to achieve a completely airtight seal around the edges of plasterboard dry lining on external and separating walls and all openings when using adhesive dabs.

34. Construction observations Built-in joists Achieving an airtight seal is difficult with built-in joists. Excess mortar around built-in joists and gaps at perpends. Offset joist running parallel with the wall.

35. Construction observations Window sills There is potential for air movement under window sills. Window sill at various stages of construction.

36. Construction observations Service penetrations Service penetrations are often left unsealed and are then hidden behind boxing or panels.

37. Improving airtightness High levels of airtightness (low air permeabilities) are only likely to be achieved by understanding and adopting a number of basic principles throughout the design, procurement and construction of the building.. These principles relate to the following: • Design stage. • Sequencing of construction processes. • Site supervision and workmanship. • Quality control. • Communication.

38. Improving airtightness Design stage Defining a continuous and robust primary air barrier at the design stage by: • Identifying a line through the building that will act as the main barrier to air leakage. This is known as the dwelling’s ‘primary air barrier’. • Ensure that the primary air barrier is continuous around the thermal envelope and, where possible, in contact with the thermal insulation layer. This will not only minimise air leakage but also the possibility of thermal bypassing. • Check the continuity of the primary air barrier by undertaking a ‘pen-on-section’ test. This involves using a line to mark the location of the primary air barrier on a set of General Arrangement drawings. The line should be continuous and separate the heated (conditioned) spaces from the unheated (unconditioned) spaces. Red line indicates location of the primary air barrier and yellow shading the position of the insulation.

39. Improving airtightness Design stage (continued) • From the ‘pen-on-section’ test, identify areas where additional detailing will be required and identify those trades that are responsible for the design and construction of the air barrier. • Produce large scale drawings (1:5) of any areas of complexity or changes in plane identified by the ‘pen-on-section’ test and identify how continuity of the primary air barrier will be maintained at these areas. • Minimise the number of service penetrations through the primary air barrier. Consider the adoption of service zones or voids that may group services together. • Try and make the primary air barrier as simple as possible. Try and avoid or at least minimise changes of plane and complex detailing. • Consider the impact that materials with different tolerances may have on the primary air barrier. Ensure that any issues are resolved at the design stage prior to commencing construction. • Ensure that the primary air barrier is robust, impermeable and durable. • Do not rely on secondary sealing, for example using sealant to seal the junction between intermediate floors and the skirting board, to provide part of the primary air barrier.

40. Improving airtightness Sequencing Give explicit consideration to sequencing during design, procurement and construction by: • Attempting to install the primary air barrier over as large an area as possible in one single operation. For example, installation of the top floor ceiling prior to the erection of the internal partitions minimises the number of junctions and penetrations through the ceiling. • Ensuring that the primary air barrier can be completed, inspected, tested and repaired prior to any part of it being covered up by other materials or finishes. For example, where a parging coat forms the primary wall air barrier, it should be applied to walls before any subsequent trades commence. • Sleeve and seal service penetrations through the primary air barrier during installation wherever possible, to avoid the need to break out subsequent new construction. • Ensure that the method of sealing service penetrations through the primary air barrier is robust enough to enable later fitting-out work to take place without compromising the installed seal. For example, electricity cables that penetrate the primary air barrier should be fitted with an appropriate seal that allows for the cables to be manipulated during and after the installation of the terminal fitting without detriment to the seal.

41. Improving airtightness Site supervision and workmanship Ensure that there are high standards of site supervision and workmanship on-site by: • Providing airtightness training as an integral part of site induction. Both generic and trade-specific airtightness training should be provided to all operatives on-site. Training should explain why airtightness is important, how it is being tested, what quality control processes are in place and what happens when things go wrong. • Ensuring that operatives know what they are required to achieve and what constitutes an acceptable standard. The definition and visibility of the air barrier is crucial.

42. Improving airtightness Quality control Testing, monitoring, and feedback are essential to any quality control process. Specific ways in which process can be improved include: • Formally describing the quality control process and clearly setting out the different roles and responsibilities with the lines of reporting, recording, investigation and action established and applied consistently. • At key stages of the construction, check the integrity of the primary air barrier and undertake airtightness measurements before the construction progresses to a stage where it becomes impossible to efficiently undertake remedial action. • Maintain a photographic record of observations made during the construction process. This not only allows a more precise retrospective analysis in the event of future investigations, but also provides useful material for training and improving the awareness among site staff of the impact of their actions. • As far as possible, construction specifications should ensure standardisation of detailing to enable site teams to become familiar with the materials, components and tolerancing needs. Where modifications are required these should be undertaken in a controlled way accompanied by effective detailed documentation.

43. Improving airtightness Communication Communication of detailed design information and feedback on airtightness performance is crucial if high standards of airtightness are to be achieved. Effective communication requires: • Design information to be provided to all subcontractors and trades that may have an impact on the integrity of the primary air barrier, through an appropriate mixture of documentation and detailed briefings. The design information should include procedural specifications as well as drawings depicting the final form. In particular, all drawings and specifications should define the primary air barrier and detail drawings should show how the air barrier is to be maintained at junctions and penetrations. • Any modifications or deviations from the design made on site (including ad-hoc design alterations, product substitutions and procedural changes) should be fed back to the designers to be included in the final “as-built” detailed drawings. These amended details will need to be reassessed where necessary – particularly where there may be implications for the air barrier integrity, thermal performance or condensation risk.

44. Improving airtightness There are a number of benefits to be gained from improving the airtightness of a particular building. These are: • Energy and CO2 emission savings. • Improved thermal comfort. • Reduced risk of deterioration. However, care should be taken to ensure that the recommended ventilation rates can still be achieved! The aim should be to: ‘build tight - ventilate right’ That is, to minimise uncontrolled (and, usually, unwanted) infiltration by making the building envelope airtight while providing the required ventilation with ‘fresh’ air in a controlled manner. It should be emphasised that a building cannot be too tight - but it can be under-ventilated!

45. Examples of airtight buildings

46. Examples - UK The Denby Dale Passivhaus [Source: Green Building Store, 2010] • A 3 bedroom detached property designed to PassivHaus standards. • Wet plastered dense concrete block and natural stone masonry cavity external walls. • Considerable attention was given to airtightness during the design and construction. • Probably the tightest masonry cavity dwelling recorded in the UK, with an air permeability of 0.41 m3/(h.m2) @ 50Pa (0.38 ac/h).

47. Examples - UK Field Trial at Stamford Brook, Cheshire • A development of over 700 dwellings, designed to an energy efficiency standard some 10% to 15% in advance of the 2006 building regulations for England and Wales. • Masonry cavity construction. • Application of a thin (2-4mm) plaster-based parging coat to the interior surfaces of the dwellings external walls, prior to the installation of the plasterboard dry-lining. • Designed to have an air permeability target of 5m3/h.m2 @ 50Pa. • Workforce trained and briefed about the purpose and principles of the air barrier. • High level of supervision and workmanship on-site. • Of 44 dwellings tested, air permeability ranged from 1.8 to 9.7 m3/(h.m2) @ 50Pa, with a mean of 4.5mh-1 @ 50Pa.

48. Examples - UK The Hockerton Housing Project, Southwell, Nottinghamshire • The UK’s first earth-sheltered, self-sufficient ecological housing development. • Construction: • Masonry cavity and reinforced concrete rear and side walls. • All of the internal walls are wet plastered. • Considerable attention was given to airtightness during the design and construction. • Air permeability of between 0.95 to 1.23 m3/(h.m2) @ 50Pa (1.09 to 1.40 ac/h).

49. Examples - UK Stenness, Orkney Islands [Source: Olivier, 1994] • 2 pairs of semi-detached single-storey dwellings. • Timber-frame construction. • Workforce was briefed about the purpose and principles of the airtightness measures both before and during installation. • One of the tightest houses recorded in the UK when originally tested, with an air leakage rate of 1 ac/h @ 50 Pa.

50. Examples - UK Boundary Close, York • A development of eight 2½ storey 2 bedroom developments with a sleeping deck, designed to near PassivHaus standards. • Composite timber-frame joist panel. • Designed to have an air permeability target of 1 m3/(h.m2) @ 50Pa. • Dwellings had a well thought through, properly designed and properly executed primary air barrier. • Mean air permeability of 1.58 and 1.94 m3/(h.m2) @ 50Pa.