“Thermal insulators are crucial to reduce the high energy demands and greenhouse emissions in the construction sector. However, the fabrication of insulating materials that are cost-effective, fire resistant, and environmental-friendly remains a major challenge. In this work, we present a room-temperature processing route to fabricate porous insulators using foams made from recyclable clays that can be locally resourced at very low costs.”

Read more: Minas, Clara, et al. “Foaming of Recyclable Clays into Energy-Efficient Low-Cost Thermal Insulators.” ACS Sustainable Chemistry & Engineering (2019).

Oula Lehtinen – CC BY-SA 3.0

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.

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.

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.

Wall Thickness

The most widely used estimate of the U-value (the measure of thermal conductivity) of a UK solid-wall property is 2.1 Wm−2 K−1. 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 1.3–1.4 Wm−2 K−1. There are two reasons for this large discrepancy.

First, standard solid brick wall U-values are based on an assumed wall thickness of 220 mm brick and approximately 12 mm of dense plaster. Modern bricks are 220 mm long and so this assumption would be logical for a modern brick wall. However, the thickness of 220 mm 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.

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 mm thickness, three-storey buildings require a minimum of 300 mm and four-storey buildings require walls of at least 400 mm. 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 mm of a single brick wall.

Air Cavities

Secondly, so-called ‘solid walls’ 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 5–10 mm.

Although some mortar will intrude into the space as snots from joints between stretchers, the practical constraints of bricklaying mean that this gap is often not filled with mortar. There is a high probability that solid-wall segments built with stretchers contain air gaps. If stretchers are assumed to comprise 50–80% of the wall surface, with air gaps of the order of ≈10 mm, then a straightforward calculation with identical assumptions regarding brick density etc. yields U-value estimates in the range of 1.65–1.8 W−1 m2 K.

‘Solid’ stone walls may also contain residual air cavities for similar reasons. Walls built with stone are often thicker overall than single-brick walls and often employ rubble-filled cores. It is almost certain that there are voids within these cores that would increase the thermal resistance of the element relative to that of a completely solid wall.

Consequences

Among the many implications for policy, discrepancy between real-world U-values and U-values assumed in energy modelling and standard UK building assessment protocols suggests that standard solid-wall U-values may be inappropriate for energy certification or for evaluating the investment economics of solid-wall insulation.

Reducing the represented U-value of solid walls in the stock from 2.1 to 1.3 Wm−2 K−1 reduces the estimated mean annual space heating demand by 16%, and causes approximately one-third of all solid-wall dwellings to change Energy Performance Certification (EPC) band.

Source:
Li, Francis GN, et al. “Solid-wall U-values: heat flux measurements compared with standard assumptions.” Building Research & Information 43.2 (2015): 238-252. http://www.tandfonline.com/doi/full/10.1080/09613218.2014.967977

“How do we go about designing buildings today for tomorrow’s weather? As the world warms and extreme weather becomes more common, sustainable architecture is likely to mean one major casualty: glass. For decades glass has been everywhere, even in so-called “modern” or “sustainable” architecture such as London’s Gherkin. However in energy terms glass is extremely inefficient – it does little but leak heat on cold winter nights and turn buildings into greenhouses on summer days.”

“For example, the U-value (a measure of how much heat is lost through a given thickness) of triple glazing is around 1.0. However a simple cavity brick wall with a little bit of insulation in it is 0.35 – that is, three times lower – whereas well-insulated wall will have a U-value of just 0.1. So each metre square of glass, even if it is triple glazed, loses ten times as much heat as a wall. Cutting back on glass would be an easy win. Windows need to be sized, not glorified, and sized for a purpose: the view, or to provide natural light or air. Windows also need to be shaded. Many would argue that we need to re-invent the window, or the building. We need to build buildings with windows, rather than buildings that are one big window.”

Read more: Climate change means we can’t keep living (and working) in glass houses. Via Lloyd Alter.

The Kume curtain is a simple and inexpensive home-made insulating curtain that can help save money, keep our homes cozier and be kinder to the environment.

The Kume is a roll-up curtain that is composed of four distinct layers.

• A front panel which acts as the first layer and seals the perimeter of the window opening when the curtain is closed
• A moisture barrier which prevents indoor humidity from reaching the window and condensing on the cold glass and window frame
• Wooden battens which maintain the fabric stretched out and thereby ensure that the curtain fits tightly against both sides of the window opening (the battens also create air pockets which further reduce heat losses through the curtain)
• A back panel which acts as the final layer of insulation and helps seal the perimeter of the window opening when the curtain is closed.

Why is a Kume curtain so effective at reducing heat loss?

• Still air is one of the best insulators found in nature, and the Kume curtain contains a lot of it. First, between the fibers of the thick polar fleece that is used to make the curtain, and second inside the thin spaces that are created between the front and back panels by the battens.
• When closed, the Kume curtain fits tightly against the top, bottom and sides of the window opening. By doing so it traps a layer of insulating air between the glass and the curtain, and prevents the cold air that forms against the glass from seeping into the room.
• A Kume curtain basically works just like a good down jacket on a cold winter day. The air that is trapped in the thick layer of down creates an effective insulating layer, and the tight fit of the jacket around your waist, neck and wrists keeps your body heat in, rather than letting it leak out into the cold environment.

See and read more (including construction plans) at Kume Insulating Curtains. Via BuilditSolar. Thanks to Frank Van Gieson.

“This is a simple technique for insulating windows with bubble wrap packing material. Bubble wrap is often used to insulate greenhouse windows in the winter, but it also seems to work fine for windows in the house. The view through the bubble wrapped window is fuzzy, so don’t use it on windows where you need a clear view. But, it does let plenty of light through.”

“The bubble wrap has a short payback in cold climates. About 2 months for single glazed windows, and half a heating season for double glazed windows. For an 7000 degree day climate (northern US), and single glazed windows, the bubble wrap increases the R value from about R1 to about R2. This cuts the heat loss from the window in half.” Read more.

“Growing interest in improving the energy efficiency of residential buildings inevitably raises questions about what to do with existing windows. Homeowners often assume that replacing older, leaky windows is the only way to save energy, an assumption actively promulgated and reinforced by companies selling replacement windows and by the availability of federal tax incentives for installing new, high performance windows.”

“The confusion is often compounded by a lack of easily accessible information on the range of window improvement options available and the ability of these options to provide meaningful energy savings.”

“This study examines multiple window improvement options, comparing the relative energy, carbon, and cost savings of various choices across multiple climate regions. Results of this analysis demonstrate that a number of existing window retrofit strategies come very close to the energy performance of high-performance replacement windows at a fraction of the cost.”

“Saving Windows, Saving Money: Evaluating the Energy Performance of Window Retrofit and Replacement“, Preservation Green Lab, 2012. Via Old House Web.