The Clay Brick Association of South Africa (ClayBrick.org) has been closely involved with the development of walling requirements for SANS 204: Energy Efficiency in Buildings, as well as SANS 10400XA: Energy Usage in Buildings, and also sponsored essential research that tabulated the thermal requirements for the CR Product values, as incorporated in Table 3 of SANS 204. These tables and the CR methodology link Thermal Capacity (C-value) and Thermal Resistance (R-value) into a combined performance requirement for walling.
Designers and builders provide comfortable and energy efficient structures in part by achieving the required level of thermal resistance and thermal capacity in the walls of buildings. This is achieved without compromising structural integrity and without making structures unnecessarily expensive. ClayBrick.org has initiated this survey of solutions and options available, and an analysis of the efficacy thereof, in order to guide designers and the industry as to how to best to achieve these objectives.
Members of the Thermal Insulation Association of South Africa were contacted and requested to provide information specific to their masonry insulation solutions.typically of low compressive strength.
Materials comprising of reflective or low emissivity surfaces are able to minimise radiant heat transfer, if orientated correctly in relation to adjacent air-spaces. Some insulation products are combinations of these reflective insulation materials and resistive insulation.
The cavity between structural wall leaves provides the ideal space and protection for thermal insulation, be it reflective insulation in the form of foil layers adjacent to air-spaces, or resistive insulation of sufficient thickness.
Insulation can also be fixed to internal or external wall leaves. External insulation systems are more effective for temperature management than internal systems as the benefits of the high thermal mass of the walls is then available and can actively absorb or give up heat to the internal occupied space.
The fixing of internal insulation materials to walling is often between wooden studs and noggings, to which a panelling of timber or plasterboard is fixed as protection. This method of fixing walling insulation is not recommended for moderate climates such as those that prevail in South Africa, as the benefit of heat exchanges between the masonry and the internal air is lost. Such systems would need to have a level of thermal insulation commensurate with a low mass wall in order to compensate for the effective absence of thermal mass.
Low density block materials can be considered as in part thermal insulation materials, and may be manufactured from aerated autoclaved cement, perlite or vermiculite blocks, foamed glass, calcium silicate or low density wood fibre (with cement or polymer binder) and may be laid against or bonded to an external masonry wall leaf.
External rigid fibre and foam insulations are applied to older structures as retrofit systems with external rendering and rain-proof coatings.
The thermal efficiency of coating systems may contain phase change materials which are able to absorb a portion of transferring heat as they change into a liquid phase. Coatings which are smooth and white in colour may also temporarily delay radiant heat transfer into high mass elements. Heat adsorbing and reflective paints are not covered in this document as the mechanism by which this material works is not by thermal insulation mechanisms.
Accordingly the various masonry insulation solutions are categorised as:
- Full cavity,
- Partial cavity,
- External cladding and rendering,
- Internal systems, which may be split into lightweight block and wall-liner solutions.
Regulations and Standards
In terms of the National Building Regulations walls are required to be capable of safely supporting or sustaining any loads which are likely to be applicable, adequately resisting water penetration, and to have combustion and fire resistance appropriate to their positioning.
The application of the National Building Regulations, SANS 10400 Part K, sets out the deemed-to- satisfy for these requirements, SANS 10400 Part T the Fire aspects, and SANS 2001 CM2; 2006 details good practice in masonry wall design and construction
Environmental Performance Requirements
The requirements of SANS 10400X pertain to the Environmental Sustainability, and Part XA; Energy Usage in buildings. The requirements for the overall efficacy of the building in entirety, is set out in Section 4.2 which details energy consumption and demand performance levels.
In Section 4.2.2 it is stipulated that the R-values derived from SANS204 for a building shell may be used to comply with the regulations, however the building envelope's minimum requirements are set out in Section
4.4 and External Walls are covered by Section 4.4.3. In this section the deemed-to-satisfy requirements for masonry walls are set out and a minimum performance of R-Value (thermal resistance) of 0.35m2/WK is prescribed, subject to the allowance for single-skin masonry greater than 140mm thickness being deemed to satisfy.
Masonry Thermal Insulation Aspects
The structural and fire requirements of masonry wall insulation are generally met by virtue of the design and use of clay bricks and mortar of appropriate strength and durability. The positioning of thermal insulation in the structure is thereafter designed to provide compliance to the Energy Usage requirements.
The requirement of 2.5 wall ties per square meter for cavity walls of less that 75mm, and 5 wall ties per square meter for cavities up to 100mm (the maximum) is clear, and the provision and requirements for cavity wall construction methods are well documented in the SANS 2001 standards and in definitive literature.
For cavity insulation, the presence of the masonry walling provides the necessary fire protection to the thermal insulation. In the case of internal and external wall insulation, the protection of combustible insulation materials will require protection as classified in terms of SANS 428 and performance indicated by SANS 10177;2006 Part 2 - Fire Resistance.
There are no South African regulatory or standards aspects dictated for damp and moisture management in insulated walls, or the positioning of vapour barriers. However good practice is to follow international methods and those set out in insurance industry standards, such as The Loss Prevention Council, as highlighted in the column titled 'Requirements for Efficacy & Compliance' below.
In this paper the various methods of insulating masonry walls are reviewed, with the range of solutions from the many technologies detailed. The design R-values and insulation thicknesses have been selected by applying ISO6946; Building Components and Building Elements - Thermal Resistance and Thermal Transmittance - calculation method, and thermal conductivity co-efficient results as published by the various suppliers, in order to meet the requirements of the South African National Building Regulations and Standards.
Recommendations for Long Term Performance
Thermal bridging via wall ties and brick force will undermine the theoretical values obtained with traditional Thermal Resistance calculations. Allowance for these highly conductive elements should be built into calculations. Estimation methods to be applied that account for these conductive elements are provided for in ISO6946, and via the ASHRAE Zone Method.
If the designer does not build in protection of these systems via moisture barriers, these moisture effects should be allowed for in the Thermal Resistance calculation, particularly in damp climates, in accordance with ISO10456; Building materials and products – Hygrothermal properties – Tabulated design values and procedures for determining declared and design values.
ClayBrick.org has tested a number of insulated masonry systems to ASTM C1363; Thermal Resistance using the Hot Box method and the correlation to calculated Thermal Resistance is good, provided allowance is made for the highly conductive wall reinforcing.
The quality of workmanship will need to be taken into account by building professionals. Discontinuities and gaps of a few millimetres between sheets of insulation can cause significant loss (20-50%) of thermal performance; hence the supervision of workmanship is an aspect which can add to the installed material's performance. It should be clearly stated in drawings and specifications as to where and how thermal insulation is positioned and fixed in masonry walls. Consideration should also be given to discontinuities between insulation systems in between the roofs and walls, and in between walls and floors/perimeter insulation. It is in these areas that heat leaks will take place.
Thermal insulation systems available for use with masonry walling are many and varied. Specifiers should therefore familiarise themselves with the relative advantages and disadvantages of these possible solutions.
The information provided in this document is intended to serve as an information resource. ClayBrick.org is neither able to warrant the suitability of the details and performance of any building material in a particular environment and does not accept any claims arising from this information. The responsibility for the correct specification and installation of masonry insulation materials and systems remains that of the building contractor and professional.