Sobre arquitectura

1_{Leeds Sustainability Institute, Leeds Beckett University, Leeds, United Kingdom.}

2 _{Cardiff School of Art and Design, Cardiff Metropolitan University, Cardiff, United Kingdom}

3 _{School of Architecture, Design and Environment. Plymouth University. Plymouth, Devon, United Kingdom}

Keywords: fire, compartmentation, house building, infiltration, smoke spread, thermal performance

ABSTRACT

The Government’s National Productivity Plan has set an ambitious target to build in excess of one million new homes in England by 2020. Homes that can be delivered to regulated quality standards are an essential part of the Plan. However, if the mass scale housing follows a similar process to those currently employed faults may be embedded within the fabric presenting future risks. Observations of current practice have revealed that many new buildings are inherently leaky, built with defects that result in underperforming building envelopes. A review of photographic evidence and supporting literature has revealed that where buildings have high levels of permeability, the integrity of the building envelope is compromised to a degree that could impact on its safe operation. The gaps, which are a result of ineffective interfaces and penetrations, allow air movement. The uncontrolled movement of air, through infiltration and exfiltration, deep into what may be termed the ‘micro-structure’ of the fabric has an impact on the thermal performance. More importantly, the air movement, within and between buildings also presents a hazard, increasing the risks associated with the movement of smoke and fire. The paper exposes the potential risks of infiltration and exfiltration and identifies common paths. The knowledge and skills required to avoid unwanted air movement within the structure, between internal and external faces, needs to be embedded into construction practice.

52

INTRODUCTION

Generalising about the building stock can be problematic, as buildings vary in design, size, characteristics and components; however, the causes of infiltration arise from some commonly occurring interface problems (Gorse 2016; Littlewood et al 2017). Interface problems and the quality of fit between building components is a topic that has long caused concern (CIRIA 1983). In the past, particularly between the 80s and 90s, such issues were often discussed under the term ‘buildability’, and particularly emphasised the difficulties arising from design and assembly problems. When components didn’t fit together with ease, it was suggested to be a result of poor detailed design, which also had the potential to compromise efficiency, increase costs and also impact on safety (Illingworth, 2008). The concern with regard to a lack of coordination between design and contracting professionals to achieve safe workable solutions, has in part, led to the Construction (Design and Management) Regulations (CDM) 2007 and 2015 (Statutory Instruments 2007, 2015). While this legislative effort encouraged cooperation in design and construction practice the problems of building assembly persist. It is clear that the practice of construction has potential for further improvement ensuring that buildings are constructed with greater concern for their integrity, safe operation and sustainability.

The CDM regulations have focussed on safer construction and maintenance, sometimes with less consideration for the deficient construction assemblies that persist and result in performance gaps. Other regulated processes have also failed to support and deliver the expected standards. Building Control Bodies, are required to help ensure that all relevant building work accords with standards and guidance (DCLG 2014). When design and construction issues manifest building control officers are required to act independently and apply relevant standards (DCLG 2014). Recently, building control professionals were requested to be more vigilant and have an increased awareness of the performance gaps (Bowden 2016). This awareness campaign relates to thermal performance, but problems of function and fit, which affect thermal performance, can also impact on airtightness and moisture control (Gorse 2016; Littlewood and Smallwood 2016). The simple observable issues at the heart of this problem are often discussed but not clearly exposed.

A common issue is that voids occur where the interface between two components doesn’t fit together properly. If these voids interconnect they can allow air into and through the building fabric, potentially bypassing any insulation; i.e. creating a thermal bypass (Stafford et al 2012a; 2012b; 2014; Hubbard 2011; Johnston et al 2009; Littlewood et al 2011; Littlewood 2013). Research on infiltration in dwellings has shown there is considerable variation in air tightness (Hubbard 2011; Johnston et al

2009; 2011; Stephen 1998; 2000) raising the question of the fabric’s integrity. In addition to heat losses there are four further problems associated with air moving through the structure, via the bypasses. Firstly it introduces the problem of transporting aerosols containing liquids and solids, fungal spores, carbon, bacteria, pollen and other particulates. Secondly the flow of moisture, generated from internal sources can be transported into colder areas of the structure, which can result in interstitial condensation and mould growth. Thirdly gaps through separating elements will have a detrimental effect on their acoustic performance. Finally, and what is possibly of greater concern, is that unexpected air movement, which may assist fires, by allowing gases and vapours requisite for combustion through parts of the structure that are considered to be separated (Gorse

53

Table 1: Notable impact of uncontrolled movement of air within and through the building fabric Impact of uncontrolled movement of air through the building fabric

1. Thermal bypass Air circulating through the structure carries heat energy.

2. Transportation of aerosols Aerosols containing liquids and solids, fungal spores, carbon, bacteria, pollen and other particulates can be transported into the buildings micro fabric (creating problems for the future).

3. Transportation of moisture Flow of moisture, generated from internal sources can be transported into colder areas of the structure, which can result in interstitial condensation and mould growth. 4. Transportation of air borne sound Gaps in separating elements will have a detrimental effect on their acoustic performance.

5. Increased risk of combustion, spread of fire and smoke

Unexpected air movement, which may assist fires, by allowing gases and vapours requisite for combustion through parts of the structure that are considered to be separated.

The breach of fire resistant compartments and passage of air into concealed spaces was observed by Littlewood and Smallwood (2015; 2016) when conducting in-construction testing (iCT). The gaps in construction and ineffective edge seals may also allow the passage of smoke, should a fire occur. Shipp et al (2016) reported on analysis of building fires occurring between 2003 and 2013 and found that 32% had issues of fire spread due to defects in construction details, such as missing or inadequate fire stopping at junctions of compartment walls and also inadequate cavity barriers; and the main problems occurring in concealed spaces within buildings.

This paper investigates and discusses the implications of unplanned infiltration on fire safety on the 1 million homes planned under the National Productivity Plan (HM Treasury 2015).

Construction Integrity and Insulation

While there is an element of uncertainty with factors that impact on the performance of buildings, defects such as infiltration rates are measurable via blower door tests. The tests on small samples of buildings have shown relatively large variability, even where the building contractors and developers know air tightness tests are being undertaken. In Johnston et al’s (2011) report, the performance of properties varied from 4.0 to 16.5 m3_/(hm2_{) @ 50Pa. Earlier work by Stephen (1998; 2000)}

considering larger samples reported much greater variance, from 2.0 to 30 m3_/(hm2_{) @ 50Pa.} The work of Johnston et al (2011) shows components not butting up and fitting together properly with air being allowed to move through the structure. Variation in material properties, defects that occur through packing and handling, workmanship issues, crushing and damage of materials, or poor fitting as a result of measurement errors all impact on the final performance (Aissani et al 2016; Domingues-Munoz et al 2010; Gorse et al 2015; Huang and Zhang 2014). Defects can also result from

54

‘design issues’, often at the interface between components or structure changes; ‘during

construction’, due to poor workmanship or inadequate quality processes; or as a result of

‘operational life’, including aging, settlement, shrinkage and expansion (through temperature,

moisture and chemical attack) or as a result of impact damage (Aissani et al 2016; Littlewood 2013; Littlewood et al 2016). All of these issues are thrown into a field of defects that impact on performance. Where defects are recognisable during the construction phase they should be identified and corrected to ensure the risk associated with the impact and consequence of the defect is minimised.

Build Quality

High energy and airtightness performance targets can be met, the buildings that meet the relevant standards in whole-house heat loss studies confirms this (Stafford et al 2012a; 2012b). While the work identifies defects in properties, the same body of research from which these observations have been made have also identified examples of good practice. The work reported by Johnston et al

(2014; 2015) distinguishes between those buildings that have achieved high, expected, standards of fabric and energy performance and those which present a performance gap.

Buildings that meet their design standard show limited evidence of unintended bypass, air leakage and thermal bridging. It is evident that buildings that offer effective thermal barriers resist air movement and provide more consistent and reliable fabric behaviour; however those that allow heat and air movement also have implications for fire and smoke safety. The research indicates that there is a considerable discrepancy between design intentions and as-built performance, which are seldom accounted for by margin of error alone (Gorse et al 2016a; 2016b; Littlewood & Smallwood 2015).

Fire Safety

Variations in thermal performance can often be an indication of non-compliant build standards, with buildings also failing to properly address acoustic and fire standards (Littlewood & Smallwood 2015). Littlewood’s research following the iCT methodology, when conducting air permeability tests combined with whole dwelling smoke tests (used for air tightness compliance), found that air leakage paths resulting from breaks in the insulation and penetrations in the fabric that connected to neighbouring properties, allowed the passage of smoke from one property to the next, into concealed spaces, roof spaces and into areas designated as means of escape. The passage of smoke occurred generally in minutes and thus questions the ability for these properties to achieve the minimum smoke/fire resistance of between 30 and 60 minutes. The properties tested included two- storey houses, and multi-storey apartment buildings. The paths that breach fire barriers, compromise the basis of compartmentation which is used to ensure sufficient time for evacuation, in the event of a fire, is maintained.

Part L of the Building Regulations (HM Government 2016) stipulates that when cavity barriers are used for edge sealing purposes, then the seal must be effective at restricting air flow between the party wall cavity and the external wall cavity. The Building Control Alliance (2011) describes how an edge seal is to be judged as being effective in a qualitative manner, stipulating the various ways in which an insulation material can practically fill and effectively seal the cavity. The guidance calls for the insulation seal to be impermeable to the passage of air and moisture, seal both leaves of a wall, have continuous runs, be in line with the thermal envelope and be flexible to accommodate

55

construction undulations. As an additional note they describe that any unintended gaps in the insulation due to imperfections are deemed acceptable providing that any gaps don’t create an uninterrupted path between wall junctions, elements and components. While such descriptions are useful, however, it is of some concern that there are no current standard test to quantitatively demonstrate the effectiveness of edge sealing using a cavity barrier. Research undertaken by Gorse

et al (2015), which exposed the different degrees of effectiveness of cavity barriers, has explored a number of options for observing and testing the effectiveness of cavity barriers. The use of tests and inspection procedures would prove useful when engaging designers, building control bodies and warranty providers, who would benefit from assurance that barriers and the fabric are effective.

Assuring the Quality of New Housing

With the scale of the UK National Productivity programme proposed, it is important that the homes produced remain robust, affordable, allow safe operation (provide safe means of escape in the event of a fire – min 30 to 60 minutes) and sustain their economic value and performance over time. However, for buildings to sustain their economic value they need to be considered free from defects, especially those defects that may be detrimental to the safe operation of the property.

While the economic value of a property is linked to location, style and size, the sustained value of a building is also linked to the product’s ability to function safely. The performance and condition of the property are linked, by survey and assessment, to its value, and the case law evidence has set a precedent on the impact of defects and the resulting value (for example, see Gilbert 2015). A defect that could render a building unsafe would be considered a major defect. During resale, in most cases, major defects need to be addressed or the price reduced (Gilbert 2015). Hidden defects are also likely to pose a financial and safety risk (Ship et al 2016; Littlewood et al 2017). Those defects that remain hidden and could not be reasonably discovered at the time of handover or during initial inspection will be classed as latent defects and thus, the responsibility for rectifying the defect, would exceed the normal defects liability period. The liability period under the Act, in most instances, would commence at the point of the defects discovery (Latent Damages Act 1986; Elias 1990). Contractors and developers can’t rely on the protection of the defects liability period where their defects are covered up (eg where the defects are hidden from sight or not obvious through normal practice). Where defects have implications on the building operation, health and safety of occupants and value of the building, it would be prudent to avoid or rectify defects early in the design and construction process. Where such issues are known about but not adequately addressed by designer, inspectors or advisors issues of professional negligence may also be considered. The impact of the defects and the risk they pose to the safe operation of the building could result in significant remediation work and would carry associated costs. The work reported here focuses on the recognition and removal of known defects rather than the legal and financial consequences, although the direct links that can be made to such consequences are worthy of note. The focus in this research is on the recognition of defects, to alert built environment professionals to the defects that can be observed and thus provide a remedy so that financial and legal risks can be avoided.

56