Restoration of the Army built heritage. Flat roofs rehabilita- tion and technology of Army buildings Bruno João Fernandes Poça Military Engineering Integrated Masters Supervisor: Dr. Jorge Manuel Caliço Lopes de Brito Co-Supervisor: Dr. Inês dos Santos Flores Barbosa Colen October 2015
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Flat roofs rehabilitation and technology of Army buildings · Flat roofs rehabilitation and technology of Army buildings Dissertation for the Integrated Masters in Military Engineering
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Restoration of the Army built heritage. Flat roofs rehabilita-tion and technology of Army buildings
Bruno João Fernandes Poça
Military Engineering Integrated Masters Supervisor: Dr. Jorge Manuel Caliço Lopes de Brito Co-Supervisor: Dr. Inês dos Santos Flores Barbosa Colen
October 2015
Flat roofs rehabilitation and technology of Army buildings
Dissertation for the Integrated Masters in Military Engineering 1
1. Introduction
A roof consists of a set of load-bearing and protective elements that intend to protect the interior of
buildings from meteorological phenomena such as rain, heat, cold, wind and snow, sheltering the
building's structure and ensuring high standards of living conditions [1].
In Portugal, according to data from the National Institute of Statistics (INE) the ratio of flat roofs to
pitched roofs has been steadily increasing and between 2006 and 2011 the use of mixed and flat roofs
represented 12.5% of those used in Portugal. Therefore, and given the increased importance of these
structures, it is necessary to create a system that supports the repair of anomalous situations in roofs
operation [2].
As flat roofs are practically horizontal, special care is needed when choosing and positioning materi-
als, as well as when evaluating the behaviour of the assembly in situ. When anomalies that can affect
the correct operation of a roof occur, diagnosis techniques are used to locate the origin of the anomaly
so as to be able to evaluate the most adequate intervention technique and repair the structure.
2. Technology
A flat roof is considered to be one in which its materials are positioned horizontally or close to it. In reali-
ty, according to the General Regulation for Urban Building (RGEU) the roof must have a minimum slope
of 1%. In the specific case of social housing, the Technical Recommendations for Social Housing
(RTHS) state that the minimum slope should be 2%. The upper limit of the slope for a roof to be consid-
ered flat is around 8%. This value changes depending on the country and existing legislation [3, 4].
The flat roof essentially consists of the following elements: a load-bearing structure, a shaping layer,
thermal insulation, a waterproofing layer and a protective layer. It may also include a smoothing layer,
a vapour barrier and a separation layer.
2.1. Functional requirements The functional requirements apply not only to the roof as a whole but also to its individual components.
Generally, flat roofs comply with the general directives of the European Union for Technical Approval
(UEAtc) and fall under the following quality categories: safety requirements, housing requirements,
durability, construction and functionality requirements.
The requirements for the waterproofing materials are part of the following categories: safety require-
ments, conservation, maintenance, repair and use requirements [6-11].
2.2. Roof classification The main aspects to be considered, according to the authors [3, 5], when designing and executing flat
roofs can be classified as:
accessibility;
waterproofing layer;
the type of coating used in the waterproofing layer;
the positioning of the thermal insulation relative to the waterproofing;
the slope;
the load-bearing structure.
Flat roofs rehabilitation and technology of Army buildings
Dissertation for the Integrated Masters in Military Engineering 2
2.2.1. Classification of the accessibility
Taking into account the type of use, flat roofs can be classified as accessible, non-accessible or spe-
cial [3, 5]. Non-accessible roofs are those thawhoset access is restricted to maintenance or repair
whilst accessible roofs allow people to circulate and remain on them. Accessible roofs may not only be
accessed to people but also to vehicles, like in car parks. Examples of special roofs are industrial
roofs, green roofs, etc.
2.2.2. Classification of the waterproofing layer
The purpose of the waterproofing layer is to protect other elements from ultraviolet radiation as well as
surface wear. Heavy protection, as well as satisfying these requirements also has enough weight to
ensure that other elements are not dragged by the wind.
The type of protection applied to the waterproofing layer (or the absence thereof) comprises three
categories: roofs with no protection, light protection, and heavy protection [3, 5].
2.2.3. Classification of the types of waterproofing layers
Waterproofing layers can be classified as traditional or non-traditional [3]. Traditional waterproofing is
the one most currently used and well known in construction. Non-traditional waterproofing, on the oth-
er hand, is more recent and its performance on site is not as well known.
2.2.4. Classification of the positioning of the thermal insulation layer
The positioning of the thermal layer relative to the waterproofing layer can be classified as traditional
or inverted [3].
The traditional system has its thermal insulation underneath the waterproofing layer. The waterproof-
ing layer of this system suffers greater wear given that it is exposed to:
differential temperature variations (both daily and seasonal);
mechanical damage, especially during the construction process;
degradation due to ultraviolet radiation;
degradation caused by humidity present on the lower part of the waterproofing layer.
In an inverted roof, the thermal insulation layer is located above the waterproofing layer, and it there-
fore protects the waterproofing layer from the above external factors, leading to greater durability.
Figure 1 illustrates a temperature profile for each element of a traditional and an inverted roof. The
waterproofing layer of the traditional roof is subject to considerably higher temperature than that of
the inverted roof. Depending on the thickness of the thermal insulation, exposure to solar radiation,
the season and the type of roof protection, the waterproofing layer of the inverted roof can have up to
50% lower temperatures than when compared to the traditional roof.
Figure 1 - Temperature profiles of a traditional roof and an inverted roof (www.building.dow.com)
Traditional Inverted
Flat roofs rehabilitation and technology of Army buildings
Dissertation for the Integrated Masters in Military Engineering 3
2.2.5. Classification of the resistant structure
The classification of the roof and its structure is based on how much it deforms, and can be consid-
ered flexible or rigid depending on how significant the deformation perpendicular to the roof is. Rigid
structures can be further categorised as joint-free or discontinuous (in situations where they are exe-
cuted using joints).
2.3. Materials The most currently used waterproofing membranes used in flat roof are bituminous polymers, thermo-
plastic and elastomeric [12]. Polymer resins are also used not only in waterproofing but also for system
repairs. Table 1 summarises the classification of waterproofing materials.
Table 1- Classification of the waterproofing system [3, 13]
A-G4 Creasing/bulging A-S4 Inadequate lap joints’ design
A-G5 Cracking A-S5 Inadequate gutter’s design
A-G6 Puncture A-S6 Defects in fastenings
A-G7 Absence/inadequate layer’s positioning A-S7 Defects in copings
A-G8 Debris accumulation A-S8 Defects in tail-ends
A-G9 Inadequate slope/ponding
A-G10 Biological growth
A-G11 Corrosion
A-G12 Moisture stains of condensation/infiltration
4. Rehabilitation
The rehabilitation process of this type of anomalies can be done either integrally or partially. Integral
repair consists in removing all the affected elements, including the lateral ones. However, in cases where
the anomaly in the waterproofing system is localised, the repair can also be localised. In these cases,
the intervention and repair technique used are generally identical to those used if the anomaly is general.
Another intervention solution to ensure the waterproofing of a flat roof is to apply a new con-
structive system without removing the existing layers. The choice of these alternatives, according to [15,
16], depends on various factors, the most important of which are:
the age of the existing waterproofing system;
the condition of the system and the roof's layers;
compatibility of the materials to be in contact with each other;
roof accessibility.
4.1. Classification of the rehabilitation techniques With the objective of re-establishing all of the functional requirements of the flat roof, Table 3 lists the
rehabilitation techniques used.
Flat roofs rehabilitation and technology of Army buildings
Dissertation for the Integrated Masters in Military Engineering 5
Table 3 - Classification of the rehabilitation techniques
Rehabilitation technique
General
R.1 Cleaning of the exterior coating of the flat roof
R.2 Application/repair/substitution of the waterproofing system
R.3 Application/repair/substitution of the thermal insulation
R.4 Application/repair/substitution of the separation layer
R.5 Application/repair/substitution of the vapour barrier
R.6 Application/substitution of the shaping layer
R.7 Creation of circulation routes
Singularities
R.8 Application/repair/substitution of expansion joints
R.9 Repair of joints and associated protective elements
R.10 Application/repair/substitution of the drainage system
R.11 Application/repair/substitution of fastening elements
The rehabilitation techniques presented in Table 3 can be classified as curative repair techniques
(RC), preventive repair techniques (RP) and/or as maintenance work (M). The definition of each type