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Purpose The purpose of this research is using materials to improve the thermal insulation, and reducing the cost. A large amount of energy is consumed by masonary due to cooling and heating. Adding material with certain percentages to the building materials is one of the ways to improve the thermal insulation, and these additives should keep as much as possible the mechanical properties of the building materials. Carbon additives are one of commonly used materials to masonry materials. In spite of the many advantages of using carbon fibers and carbon nano tubes (CNTs) to the cementitious materials, they are very expansive and their thermal conductivity is high. Design/methodology/approach In this research charcoal (which is a product of burning process) with very low thermal conductivity and cost in the form of micro particles will be used with mortar and compared with short carbon fibers and multiwall carbon nanotubes (MWCNTs) via thermal conductivity, density and compressive strength tests. This research includes also an effort to build a model of building to evaluate the thermal insulation of the materials used in the practical part. The main building design and performance simulation tool in this research is DesignBuilder. Findings Results showed that adding micro charcoal particles to mortar resulted in improving the thermal insulation and decrease the rate of reduction in the compressive strength compared to other additives, while adding short carbon fibers resulted in improving the thermal insulation and decrease the compressive strength. Adding MWCNT to the mortar had a negative effect on mechanical and physical properties, i.e. compressive strength, density and thermal insulation. Originality/value This paper uses DesignBuilder software to design a model of building made from the materials used in the practical part to predict and evaluate the thermal insulation.

Construction materials needs to be low energy consuming and mud construction system is less energy consuming and very successful in different weather conditions. Cob is an old earth building method passed down through the millennia, Cob is a sustainable earth building material with mud soil, coarse sand, straw and water are thoroughly combined and beaten together. This research aims to study the effect of some additives on physical properties (thermal conductivity and water content %) and mechanical property (compression strength) of Cob. These additives are: polymethyl methacrylate (PMMA) grains, hooked end steel fibers (HESF), wood as sawdust (SDW) and goat hair fibers (GHF), with 2 and 4 % by weight as the percentages of additives. Results shows that (PMMA) improves the insulation of Cob to maximum values compared to other additives in both 2 and 4 % followed by (SDW) and (GHF) respectively. All additive materials improve the compressive strength of Cob but with different extents depending on the water content. (GHF) is the best material to improve the compressive strength of Cob followed by (HESF) and (PMMA) respectively while adding (SDW) will lead to reverse effect i.e. decreasing the compressive strength.