Understanding dampness - Revision history

Designing Buildings at 08:33, 6 November 2020

2020-11-06T08:33:20Z

← Older revision		Revision as of 08:33, 6 November 2020
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	* Wall insulation and moisture risk.		* Wall insulation and moisture risk.

−	[[Category:Conservation]] [[Category:Theory]]	+	[[Category:Conservation]] [[Category:DCN_Commentary]] [[Category:DCN_Guidance]] [[Category:Theory]]

Designing Buildings at 07:57, 16 June 2018

2018-06-16T07:57:22Z

← Older revision		Revision as of 07:57, 16 June 2018
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	=== Related articles on Designing Buildings Wiki ===		=== Related articles on Designing Buildings Wiki ===

		+	* Building damp-free cavity walls.
	* Cavity tray.		* Cavity tray.
	* Cold bridge.		* Cold bridge.

Designing Buildings at 10:44, 10 June 2018

2018-06-10T10:44:18Z

← Older revision		Revision as of 10:44, 10 June 2018
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	* Defects in stonework.		* Defects in stonework.
	* Dew point.		* Dew point.
		+	* Diagnosing the causes of dampness (GR 5 revised).
	* Draught proofing.		* Draught proofing.
	* Dry rot fungus.		* Dry rot fungus.
	* Efflorescence.		* Efflorescence.
	* Humidity.		* Humidity.
−	* Hygrothermal.
	* IHBC articles.		* IHBC articles.
	* Interstitial condensation.		* Interstitial condensation.
−	* Limecrete.
	* Penetrating damp.		* Penetrating damp.
−	* Retrofitting traditional buildings.
	* Rising damp in walls - diagnosis and treatment (DG 245).		* Rising damp in walls - diagnosis and treatment (DG 245).
	* Rising damp.		* Rising damp.
	* Spalling.		* Spalling.
−	* Structural waterproofing consultant.
−	* Tanking.
	* The Institute of Historic Building Conservation.		* The Institute of Historic Building Conservation.
	* Wall insulation and moisture risk.		* Wall insulation and moisture risk.

	[[Category:Conservation]] [[Category:Theory]]		[[Category:Conservation]] [[Category:Theory]]

Editor at 15:21, 20 April 2018

2018-04-20T15:21:49Z

← Older revision		Revision as of 15:21, 20 April 2018
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	* Defects in stonework.		* Defects in stonework.
	* Dew point.		* Dew point.
		+	* Draught proofing.
	* Dry rot fungus.		* Dry rot fungus.
	* Efflorescence.		* Efflorescence.

Editor at 13:48, 20 April 2018

2018-04-20T13:48:45Z

← Older revision		Revision as of 13:48, 20 April 2018
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	* Damp proof membrane.		* Damp proof membrane.
	* Damp-proof course.		* Damp-proof course.
		+	* Damp proofing.
	* Defects in brickwork		* Defects in brickwork
	* Defects in stonework.		* Defects in stonework.

Editor at 13:41, 15 March 2018

2018-03-15T13:41:54Z

← Older revision		Revision as of 13:41, 15 March 2018
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	* Spalling.		* Spalling.
	* Structural waterproofing consultant.		* Structural waterproofing consultant.
		+	* Tanking.
	* The Institute of Historic Building Conservation.		* The Institute of Historic Building Conservation.
	* Wall insulation and moisture risk.		* Wall insulation and moisture risk.

	[[Category:Conservation]] [[Category:Theory]]		[[Category:Conservation]] [[Category:Theory]]

Editor at 14:58, 5 March 2018

2018-03-05T14:58:32Z

← Older revision		Revision as of 14:58, 5 March 2018
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	* Rising damp.		* Rising damp.
	* Spalling.		* Spalling.
		+	* Structural waterproofing consultant.
	* The Institute of Historic Building Conservation.		* The Institute of Historic Building Conservation.
	* Wall insulation and moisture risk.		* Wall insulation and moisture risk.

	[[Category:Conservation]] [[Category:Theory]]		[[Category:Conservation]] [[Category:Theory]]

Editor at 11:12, 26 September 2017

2017-09-26T11:12:25Z

← Older revision		Revision as of 11:12, 26 September 2017
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	* Efflorescence.		* Efflorescence.
	* Humidity.		* Humidity.
		+	* Hygrothermal.
	* IHBC articles.		* IHBC articles.
	* Interstitial condensation.		* Interstitial condensation.

Designing Buildings at 08:33, 24 September 2017

2017-09-24T08:33:31Z

← Older revision		Revision as of 08:33, 24 September 2017
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	* Limecrete.		* Limecrete.
	* Penetrating damp.		* Penetrating damp.
		+	* Retrofitting traditional buildings.
	* Rising damp in walls - diagnosis and treatment (DG 245).		* Rising damp in walls - diagnosis and treatment (DG 245).
	* Rising damp.		* Rising damp.

Editor at 14:26, 2 August 2017

2017-08-02T14:26:10Z

← Older revision		Revision as of 14:26, 2 August 2017
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	Vapour permeability is often used to describe a host of moisture movement mechanisms. Some materials allow moisture movement and some do not: vapour permeability is the ability of building fabric to allow water vapour to diffuse through it. Water molecules are relatively light and in any given volume of air, gaseous water will rise naturally. When trapped in building fabric, diffusion acts outwards and upwards, and will find its way around areas where vapour barriers have been formed.		Vapour permeability is often used to describe a host of moisture movement mechanisms. Some materials allow moisture movement and some do not: vapour permeability is the ability of building fabric to allow water vapour to diffuse through it. Water molecules are relatively light and in any given volume of air, gaseous water will rise naturally. When trapped in building fabric, diffusion acts outwards and upwards, and will find its way around areas where vapour barriers have been formed.

−	Traditional buildings were designed so that moisture could move. It is when this moisture movement is restricted or stopped that one finds concentrations of moisture in other areas. Many buildings have been compromised in this way through ‘improvements’ such as the replacement of timber floors with concrete, retrofitted damp-proof courses, and the installation of impermeable, solid wall insulation, to name but a few. Moisture affects the thermal performance of building fabric. In bringing these two issues together, we call it hygrothermal performance. Critically, damp building fabric is a much better conductor of heat than dry building fabric. This increase in heat loss is cited in BS 7913: 2013 as being at least 30 per cent, and some claim it to be even greater. Therefore, managing moisture so that building fabric remains comparatively dry will save energy. Mould growth and condensation are often noted in vacant properties where heating has been turned off. Lack of heat results in many episodes of condensation as the temperature of fabric drops below dew point temperature. Constant heating at around 15°C, combined with ventilation, will reduce this risk, particularly during winter months.	+	Traditional buildings were designed so that moisture could move. It is when this moisture movement is restricted or stopped that one finds concentrations of moisture in other areas. Many buildings have been compromised in this way through ‘improvements’ such as the replacement of timber floors with concrete, retrofitted damp-proof courses, and the installation of impermeable, solid wall insulation, to name but a few. Moisture affects the thermal performance of building fabric. In bringing these two issues together, we call it hygrothermal performance. Critically, damp building fabric is a much better conductor of heat than dry building fabric.
		+
		+	This increase in heat loss is cited in BS 7913: 2013 as being at least 30 per cent, and some claim it to be even greater. Therefore, managing moisture so that building fabric remains comparatively dry will save energy. Mould growth and condensation are often noted in vacant properties where heating has been turned off. Lack of heat results in many episodes of condensation as the temperature of fabric drops below dew point temperature. Constant heating at around 15°C, combined with ventilation, will reduce this risk, particularly during winter months.

	In understanding dampness prior to retrofitting proposals, one has to understand how moisture movement has already been compromised, and then work out how different retrofit proposals will further effect the movement of moisture. Reinstating the original moisture movement characteristics would seem the ideal option, but often this is either impossible or cost-prohibitive.		In understanding dampness prior to retrofitting proposals, one has to understand how moisture movement has already been compromised, and then work out how different retrofit proposals will further effect the movement of moisture. Reinstating the original moisture movement characteristics would seem the ideal option, but often this is either impossible or cost-prohibitive.
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	Analysing moisture content in timber is relatively easy using the common electric twin-pinned moisture meter. One must be aware that readings could indicate dampness in dry timber if it has been treated with chemicals. This is a distinct possibility in roof spaces. Some timber may, however, be concealed, and an experienced building pathologist may be able to determine the moisture content of adjoining building fabric and make predictions based on other factors. Micro-drilling can also be used to determine the strength of timber. This, often used where joists are bearing into walls, can indicate whether such concealed timber is rotten.		Analysing moisture content in timber is relatively easy using the common electric twin-pinned moisture meter. One must be aware that readings could indicate dampness in dry timber if it has been treated with chemicals. This is a distinct possibility in roof spaces. Some timber may, however, be concealed, and an experienced building pathologist may be able to determine the moisture content of adjoining building fabric and make predictions based on other factors. Micro-drilling can also be used to determine the strength of timber. This, often used where joists are bearing into walls, can indicate whether such concealed timber is rotten.

−	In examining the moisture content of other materials, such as masonry, an electric capacitance meter may help, but only in the hands of the very experienced building pathologist. So-called dampness readings may not be highlighting dampness at all and can be very misleading. Only in experienced hands should the use of such equipment be contemplated. Note, however, that British Standards state that chemical methods should be used to determine dampness, and this involves the extraction of building fabric. This can be through the ‘gravimetric’ method, described in BRE Digest Rising damp in walls - diagnosis and treatment (DG 245), which involves testing the samples in a laboratory. Alternatively, the samples can be tested on site using a carbide meter, often known as the ‘speedy meter’.	+	In examining the moisture content of other materials, such as masonry, an electric capacitance meter may help, but only in the hands of the very experienced building pathologist. So-called dampness readings may not be highlighting dampness at all and can be very misleading. Only in experienced hands should the use of such equipment be contemplated.
		+
		+	Note, however, that British Standards state that chemical methods should be used to determine dampness, and this involves the extraction of building fabric. This can be through the ‘gravimetric’ method, described in BRE Digest Rising damp in walls - diagnosis and treatment (DG 245), which involves testing the samples in a laboratory. Alternatively, the samples can be tested on site using a carbide meter, often known as the ‘speedy meter’.

	Some typical dampness problems occur when external ground levels are too high. This inhibits the movement of moisture from the building fabric via the external face, and so develops a greater tendency for it to move internally in greater quantities.		Some typical dampness problems occur when external ground levels are too high. This inhibits the movement of moisture from the building fabric via the external face, and so develops a greater tendency for it to move internally in greater quantities.
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	Replacing timber floors with concrete incorporating a polythene damp-proof membrane removes any possibility for moisture to move through the floor. This will tend to move it towards the perimeter of the floor and into the walls. Here there will be a tendency for increased moisture within the walls. Combine this with heightened external ground levels and the situation will be even worse. The answer for many has been to install a retrofitted damp-proof course, which deals with the symptoms but not necessarily the true cause. Dealing with the cause could mean installing a limecrete floor.		Replacing timber floors with concrete incorporating a polythene damp-proof membrane removes any possibility for moisture to move through the floor. This will tend to move it towards the perimeter of the floor and into the walls. Here there will be a tendency for increased moisture within the walls. Combine this with heightened external ground levels and the situation will be even worse. The answer for many has been to install a retrofitted damp-proof course, which deals with the symptoms but not necessarily the true cause. Dealing with the cause could mean installing a limecrete floor.

−	When moisture penetrates the external face of a wall through any of the moisture movement mechanisms, it should have the opportunity to move out from the wall via the external face. Unfortunately, many older buildings with masonry walls have a core which is not fully mortared but merely has a rubble fill. With the advent of penetrations being formed for building services, the vibration in cutting holes through the walls can result in the settling of the rubble and the creation of hollow areas or voids. Any moisture penetrating the face of the walls can trickle down within the core and come out at a lower level, sometimes quite a distance from where the moisture originally entered the wall. Over time the situation may get worse, as the continuing flow of moisture could increase the number and size of hollow areas when any mortar which is present is washed away.	+	When moisture penetrates the external face of a wall through any of the moisture movement mechanisms, it should have the opportunity to move out from the wall via the external face. Unfortunately, many older buildings with masonry walls have a core which is not fully mortared but merely has a rubble fill. With the advent of penetrations being formed for building services, the vibration in cutting holes through the walls can result in the settling of the rubble and the creation of hollow areas or voids.
		+
		+	Any moisture penetrating the face of the walls can trickle down within the core and come out at a lower level, sometimes quite a distance from where the moisture originally entered the wall. Over time the situation may get worse, as the continuing flow of moisture could increase the number and size of hollow areas when any mortar which is present is washed away.

	The answer is not to just deal with the external face of the wall, as this means that moisture entering the wall may find any external access points blocked, thereby increasing the tendency for increased moisture internally, but to fill the voids with mortar or grout. However, the above view is not universally shared. There are many situations where voids can encourage the evaporation and diffusion of moisture, and act as insulation to keep the dew point down and prevent condensation. The lesson here is that all situations are different and proper analysis by a competent building pathologist is essential.		The answer is not to just deal with the external face of the wall, as this means that moisture entering the wall may find any external access points blocked, thereby increasing the tendency for increased moisture internally, but to fill the voids with mortar or grout. However, the above view is not universally shared. There are many situations where voids can encourage the evaporation and diffusion of moisture, and act as insulation to keep the dew point down and prevent condensation. The lesson here is that all situations are different and proper analysis by a competent building pathologist is essential.
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	* IHBC articles.		* IHBC articles.
	* Interstitial condensation.		* Interstitial condensation.
		+	* Limecrete.
	* Penetrating damp.		* Penetrating damp.
	* Rising damp in walls - diagnosis and treatment (DG 245).		* Rising damp in walls - diagnosis and treatment (DG 245).