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Air Gap Method: Air-Gaps in Building Construction to avoid Dampness & Mould
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , 55 p.
Keyword [en]
humidity, air gaps, water damage, convection, building, construction
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:kth:diva-102873ISBN: 978-91-7501-485-2 (print)OAI: oai:DiVA.org:kth-102873DiVA: diva2:557172
Public defence
2012-10-12, B 1, Brinellvägen 23, KTH, Stockholm, 13:00 (Swedish)
Opponent
Supervisors
Note

QC 20120928

Available from: 2012-09-28 Created: 2012-09-27 Last updated: 2012-09-28Bibliographically approved
List of papers
1. Air gaps in building construction avoiding dampness and mould
Open this publication in new window or tab >>Air gaps in building construction avoiding dampness and mould
2008 (English)In: Structural Survey, ISSN 0263-080X, Vol. 26, no 3, 242-255 p.Article in journal (Refereed) Published
Abstract [en]

Purpose - Water damage is a severe problem in modern construction, causing economic loss and health implications. The patented Air Gap Method, which is a slight modification of the common infill wall construction, provides means to build houses in a more robust way, minimizing the negative effects of water damage. This full-scale study of the method aims to show how walls and floors may be built to create ventilation within the construction, with air gaps equipped with heating cables. The general hypothesis is that the patented Air Gap Method drains and evaporates dampness after water damage. The purpose of this study is to show how the method is built and how the method deals with water damage, such as a flooding, and with mould growth. Design/methodology/approach - The Air Gap Method is based on a common timber-framed construction and is completed by the provision of inlets, air gaps, slits, and outlets. The power for the convective airflow is given by an electrical heating cable. The study was carried out as a full-scale experiment using a 24m2 large apartment build by this method. This apartment was flooded with 120 litres of domestic wastewater and the drying period was compared when heating cables were switched on or not. Mould growth was also investigated. Findings - The method dries out a flooded floor in nine days when two heating cables were switched on, in 13 days with one heating cable and 21 days when the heating cables were off. The method prevents all mould growth provided that the indoor RH is lower than 65 per cent. Practical implications - The method provides means to build houses in a more robust way, minimizing the negative effects of water damage. Originality/value - The issue of ventilated construction is rarely investigated in scientific research.

Keyword
Building conservation; Buildings; Heating and ventilation services; Humidity; Water
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-9487 (URN)10.1108/02630800810887126 (DOI)2-s2.0-47949099064 (Scopus ID)
Note

QC 20100622

Available from: 2008-11-07 Created: 2008-11-07 Last updated: 2012-09-28Bibliographically approved
2. Air gap method: measurements of airflow inside air gaps of walls
Open this publication in new window or tab >>Air gap method: measurements of airflow inside air gaps of walls
2008 (English)In: Structural Survey, ISSN 0263-080X, Vol. 26, no 4, 343-363 p.Article in journal (Refereed) Published
Abstract [en]

Purpose - Water damage is a severe problem in modern construction, causing economic loss and health implications. By using the patented Air Gap Method inside building constructions, harmful water in the construction can be dried out. The method drains and ventilates air gaps inside walls and floors with an airflow driven by thermal buoyancy caused by a heating cable in vertical air gaps. This paper aims to investigate this method and measurements of airflow inside air gaps of walls. Design/methodology/approach - This study investigates the measured correlation between the power of the heating cable, the difference of temperature inside and outside the air gap, and the airflow. Data are collected by experimentation with a full-scale constructed wall. Findings - The study finds that airflow increases with raised temperature difference between the air gap and room and with raised power of the heating cable. The measured airflow reaches values up to 140 m3/metre wall and day for one cable. A small increase in temperature, between 0.2 and 0.3 oC inside the vertical air gap results in an air flow of approximately 60 m3/metre wall and day. The air change rate per hour for the air inside the wall construction varies between 15 times for a 6 W/m cable and 37 times for a 16 W/m cable. Practical implications - The method provides the means to build houses in a more robust way, minimising the negative effects of water damage. This investigation provides an understanding of how temperature and ventilation are related in this method of construction. Originality/value - The issue of ventilated construction is rarely investigated in scientific research.

Keyword
Air diffusion; Buildings; Humidity; Temperature measurement; Water
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-9488 (URN)10.1108/02630800810906584 (DOI)2-s2.0-51849151932 (Scopus ID)
Note

QC 20100622

Available from: 2008-11-07 Created: 2008-11-07 Last updated: 2012-09-28Bibliographically approved
3. Air Gap Method: drying of a concrete slab on ground construction
Open this publication in new window or tab >>Air Gap Method: drying of a concrete slab on ground construction
2010 (English)In: Structural Survey, ISSN 0263-080X, E-ISSN 1758-6844, Vol. 28, no 4, 281-299 p.Article in journal (Refereed) Published
Abstract [en]

Purpose – The purpose of this paper is to report on a study which has been carried out on a timber floor construction above a ground-supported concrete slab, which was used in small detached houses built in Sweden during the period 1960-1990. This method of building has turned out to be a risky construction nowadays, but there are 800,000 houses built this way in Sweden.

Design/methodology/approach – By using the patented Air Gap Method inside building constructions, harmful water can be dried out. The method ventilates air gaps inside walls and floors with an air flow driven by thermal buoyancy caused by a heating cable in the vertical air gaps. The drying out process has been studied both by measuring the moisture level in the slab and also by measuring the humidity transport and comparing this with air flow measurements.

Findings – The paper shows that the Air Gap Method manages to dry out water from both the slab and the overlaying wooden construction. The study shows also that the relative humidity (RH) levels in the air space below the floor are reduced in a significant way, thus minimizing mould growth. It is also shown that a thin layer of concrete upon floor beams prevents mould to grow even in a humid situation.

Research limitations/implications – The research reported in this paper is only concerned with timber-framed small detached houses. Similar studies of apartment buildings are ongoing.

Practical implications – The Air Gap Method can thus be useful in the context of renovating a water damaged house of this type built during this 30-year period. The method provides a possibility of drying out such damage without a separate drying period. The inhabitants could therefore be able to use a renovated water-damaged kitchen six/eight weeks earlier compared to ordinary building methods.

Originality/value – The paper is useful because it provides better understanding of the mechanism of RH inside a building construction and how this parameter could be lowered. The paper is also useful in the context of renovating water-damaged small detached houses built by the risky method of construction used in the last decades of the twentieth century.

Place, publisher, year, edition, pages
Emerald Group Publishing Limited, 2010
Keyword
concrete slabs, construction materials, Drying, Property, Structural timber, Sweden
National Category
Natural Sciences
Identifiers
urn:nbn:se:kth:diva-102866 (URN)10.1108/02630801011070984 (DOI)2-s2.0-77956554861 (Scopus ID)
Note

QC 20120927

Available from: 2012-09-27 Created: 2012-09-27 Last updated: 2017-12-07Bibliographically approved
4. Air Gap Method: Dependence of water removal on RH in room and height of floor air gap
Open this publication in new window or tab >>Air Gap Method: Dependence of water removal on RH in room and height of floor air gap
2012 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 56, 1-7 p.Article in journal (Refereed) Published
Abstract [en]

This study is performed in combined floor and wall constructions with air gaps within and with a heating cable in the vertical air gap. All surfaces of the air gap are covered with polystyrene plastic to avoid leakage into the construction. Wet gypsum boards that are weighed at start and end of experiment are used to measure the dry out process.Three different heights of the floor air gap, 25 mm, 15 mm and 5 mm are investigated. The influences of the RH in the surrounding room and of the wetness of the gypsum boards are also investigated.It is shown that the height of the floor air gap has a great impact on the rate of drying. The optimal height is less than 25 mm and somewhere between 15 and 5 mm.

Place, publisher, year, edition, pages
Elsevier, 2012
Keyword
Ventilated cavity, Air gap, Heating cable, Water damage, Air flow, Relative humidity
National Category
Natural Sciences
Identifiers
urn:nbn:se:kth:diva-102867 (URN)10.1016/j.buildenv.2012.02.014 (DOI)000305315700001 ()2-s2.0-84858804457 (Scopus ID)
Note

QC 20120927

Available from: 2012-09-27 Created: 2012-09-27 Last updated: 2017-12-07Bibliographically approved
5. The drying out capacity of a ventilated internal cavity with a heating cable, analytical model and empirical verification
Open this publication in new window or tab >>The drying out capacity of a ventilated internal cavity with a heating cable, analytical model and empirical verification
2012 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 52, 171-176 p.Article in journal (Refereed) Published
Abstract [en]

This study is concerned with the use of interior air channels in walls for the drying out of surplus water in floor constructions. The floor is to be dried out by the means of an air gap, while a heating cable at the bottom of an adjacent wall channel provides a driving force for the flow. The model of this study can be used to quantify the drying out capacity of such a construction, given the geometrical configuration and the effect of the cable. By posing heat and mass balance equations for a star network equivalent to the delta network of the actual physical problem the temperature and moisture profiles for the floor channel are obtained. The wetted surface of the floor is assumed to be saturated, while the saturated moisture content varies with temperature along the surface. The temperature and moisture distributions along the air gap and the drying out capacity are obtained as a function of the flow rate. The physical problem of the wall channel is posed in terms of the governing equations of conservation. The Boussinesq approximation is used to restrict the variation in density to that of the gravitational force. The buoyancy generated by the cable is related to the frictional forces of the channel walls, providing a relationship between the flow rate and the effect of the cable. The analytical results are compared with laboratory measurements and show good agreement for a number of different heights of the air gap in the floor.

Keyword
Ventilated cavity, Air gap, Heating cable, Buoyancy, Moisture profile, Temperature profile
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-92988 (URN)10.1016/j.buildenv.2011.12.012 (DOI)000301319200016 ()2-s2.0-84856091911 (Scopus ID)
Note
QC 20120411Available from: 2012-04-11 Created: 2012-04-10 Last updated: 2017-12-07Bibliographically approved

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