{"id":3849,"date":"2018-02-21T00:52:06","date_gmt":"2018-02-20T23:52:06","guid":{"rendered":"http:\/\/www.notechmagazine.com\/?p=3849"},"modified":"2018-03-06T00:36:18","modified_gmt":"2018-03-05T23:36:18","slug":"thermal-insulation-of-solid-walls-underestimated","status":"publish","type":"post","link":"https:\/\/www.notechmagazine.com\/2018\/02\/thermal-insulation-of-solid-walls-underestimated.html","title":{"rendered":"Thermal Insulation of Solid-Walls is Underestimated"},"content":{"rendered":"
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Oula Lehtinen – CC BY-SA 3.0<\/p><\/div>\n

Approximately 5.7 million solid-walled houses exist in England, comprising 25% of the housing stock. Most were built between 1750 and 1914. Research shows that their energy efficiency has been underestimated for decades.<\/p>\n

The English Housing Survey (EHS) defines solid-wall construction as a building where external load-bearing walls are made of brick, block, stone or flint with no cavity. In England, the shift to the use of solid-wall brick construction began during the great rebuilding from mid-16th century.<\/p>\n

For the present English housing stock, the overwhelming fraction of solid-walled dwellings, constructed mostly of brick, derives from the expansion of population from the mid-18th century to the beginning of the First World War. Solid walls continued to be the most common construction for the domestic sector until the British housing boom of the 1920s and 1930s.<\/p>\n

Wall Thickness<\/h3>\n

The most widely used estimate of the U-value (the measure of thermal conductivity) of a UK solid-wall property is 2.1\u2005Wm\u22122\u2005K\u22121<\/em>. However, there is growing evidence that solid-wall U-values are much lower than previously assumed. Several studies in recent years have found that the mean or median U-values measured for solid-walled construction were around 1.3\u20131.4\u2005Wm\u22122\u2005K\u22121.\u00a0There are two reasons for this large discrepancy.<\/p>\n

First, standard solid brick wall U-values are based on an assumed wall thickness of 220\u2005mm brick and approximately 12\u2005mm of dense plaster. Modern bricks are 220\u2005mm long and so this assumption would be logical for a modern brick wall. However, the thickness of 220\u2009mm was used as a conservative estimate to capture variation in brick production. Following the Great Fire of London in 1666 brick properties over two stories were required to be constructed with walls that were more than one brick thick.<\/p>\n

The required thickness of load-bearing masonry walls in England therefore increases with the height of the building. While two-storey buildings can be built with walls of just over 200\u2005mm thickness, three-storey buildings require a minimum of 300\u2005mm and four-storey buildings require walls of at least 400\u2005mm. Consequently, it is obvious that the mean thickness of solid walls in the UK housing stock is likely to be greater than the nominal 220\u2005mm of a single brick wall.<\/p>\n

Air Cavities<\/h3>\n

Secondly, so-called \u2018solid walls\u2019 are in fact often not completely solid. Brick walls can be built up in a variety of different patterns, but are typically constructed with a mixture of brick types, with some going straight through the full depth of the wall, known as headers, and some laid side by side, known as stretchers (see image above). In order to allow walls to be constructed with a regular type of mortar bond, the total width of two adjacent stretchers is less than the length of a header by the width of a mortar joint, which is typically 5\u201310\u2005mm.<\/p>\n