Insulating the whole building box

by Tania Wannenburg

When specifying insulation, it is important to consider the whole building envelope and select insulation types fit for each application.

The impact of insulation on a building’s internal comfort, and subsequently its energy efficiency, can be significant. While the thickness and quality of the specified product plays a major role, the installation is also influenced by factors such as climate, building orientation and overall maintenance. Regulations such as SANS 10400 XA have been put in place in order to ensure sufficient insulation for buildings in its entirety, top to bottom.

Mark Russell from Isoboard explains: “The aim of the SANS 10400XA standard is to get the building itself to use as little energy as possible for lighting, water heating and HVAC, or at least be less than or equal to the mandatory maximum usage targets for that type of building occupation classification. In other words, to have an energy-efficient building. Insulation influences the comfort of individuals, which in turn influences how we use HVAC systems.”

Deemed-to-satisfied confusion
Russell points out that the deemed-to-satisfy regulations of SANS 10400XA specify three alternate methods of achieving compliance. One of these is the prescriptive thickness tables, another is rational design and the last is maximum energy demand and usage as per tables for specified buildings.

“It has become convention to refer to the thickness tables as deemed-to-satisfy, but this is only one way in which the requirements of XA are deemed to be met. This can cause confusion, as the thickness tables produced by the Thermal Insulation Association of Southern Africa (TIASA) for instance, refer to a residential house of a certain size and type of roof and ceiling, and calculate the R-values and subsequent thicknesses required based on that example. Different buildings will have different solutions. It is the R-value which must be achieved, not the thickness of any particular type of insulation,” he clarifies.

When considering insulation, it is the roof and ceiling that first come to mind, and rightly so, since insulating these areas has the greatest potential to reduce the heat load on South African buildings.

Insulating on the outside of roofs
A fairly novel way of insulating building roofs in South Africa is inverted roofing, an upside down roofing method which sees the insulation installed over the waterproofing layer instead of underneath it as in more traditional methods of roofing.

In an article by world leading building science centre, BRE, it is explained that inverted roofs are designed with insulation boards loose-laid on top of the waterproofing membrane and then weighted down with paving slabs or gravel ballast. Rain percolates through the ballast, between the insulation boards until it reaches the membrane, and then drains away through rainwater outlets.

“The great benefit of inverted roofs is that the insulation protects the membrane from extremes of weather, such as frost, UV exposure and the expansion and contraction that comes about from summer or winter temperature cycles,” the BRE article reads. In South Africa, temperatures can vary greatly over 24 hours.

While inverted roofing is also done on pitched roofs, according to Russell, it is easily applied to flat concrete roofs with gentle drainage slopes when the insulation needs to be secured by some sort of ballast. “It is a very elegant and simple solution,” he says. “As long as the roof is properly planned to accommodate the mass of ballast, and designed with correct drainage of water, installing under supervision is very simple.”

Russell also points out that inverted roof insulation facilitates many new uses for flat roof systems. “As space becomes more valuable, people turn to green roof systems, rooftop urban farming, aquaponics, roof entertainment areas, parking space on roofs and helicopter access,” he states.

“Not yet as popular locally as it could be, this method is becoming more so as designers and customers apply their minds to energy-efficiency solutions, passive building principles and lifetime cost analysis.”

Don’t forget the walls
In light of the current energy challenges in South Africa and people looking to ways of improving building efficiencies in homes and offices, Quinton Peters, ETICS product manager at Weber Saint-Gobain, highlights that insulating walls has become important, but is still often overlooked.

“While we don’t have extreme weather conditions, we have extreme ranges of temperature in the same day. And when looking at SANS 204, the required R-values set out according to climatic regions for walls, floors and roofs are quite high,” he states.

“Most buildings in South Africa are built out of brick. For existing buildings, where insulation has not been built into the walls, an alternative way of insulating them is to add insulation boards to the outside.”

Quinton points out that external thermal insulation composite systems (ETICS) had been around for a long time, and were originally designed to repair and clad old facades. These systems can be clad onto bricks, block work or lightweight steel frame structures to improve the thermal performance thereof.

This way of retrofitting using exterior insulation facade systems (EIFS), according to Russell, is very popular internationally to bring existing building stock up to current regulatory standards for energy efficiency, particularly for lightweight frame buildings.

“In steel-framed buildings, if the roof is well insulated but not the walls, heat will flow in through the walls and become trapped under the roof insulation,” he explains. “Wall insulation can play a big part in limiting heat flows in a building, and as such is frequently considered as part of a rational design energy usage solution as this will invariably be a cheaper solution than prescriptive compliance. Rational designs allow greater freedom of design expression, while keeping projects affordable. For instance, introducing wall insulation can eliminate costly glazing solutions,” Russell adds.

Considering installed performance
When putting in insulation, one should consider its performance over the life of the building. Russell notes that it is important to allow for deterioration in the performance of the insulation over time due to water absorption and the substitution of the original blowing agent with air, particularly for concealed applications such as inverted roofs or cavity walls. According to him, buildings will not achieve or sustain their energy usage design objective if an appropriate design value that can be sustained for the life of the building is not considered and anticipated.

“All insulation is subject to degradation and there is always a fall-off in thermal performance over time, depending on the type of insulation and application,” Russell says. “Moisture, dust, gas migration, compression, weathering and oxidization all play a role, as would physical factors such as an installation that is disturbed so as not to form a continuous barrier to heat flow. It is essential that specifiers obtain true aged and wet values for thermal conductivity from suppliers.”

Choose apt materials
In addition, it is important to determine whether a certain type of insulation is fit for the intended installation in keeping with the building’s design and the conditions under which it would be expected to perform. Different compositions, thermal resistance and compatibility with other building materials such as solvents, paints, adhesives and other fastening materials also play a part and should be considered.

Rigid insulation boards, for example, can be made from either thermoplastic or thermoset materials. According to Building Science Corporation’s Guide to Insulating Sheathing, thermoplastics are based on linear or slightly branched (non-cross linked) polymers. These foams will soften and melt at elevated temperatures, while thermoset plastics are based on cross linked polymers, which allow them to be used for higher temperature applications.

In the end it is not about certain thicknesses or specific products, it is about creating optimum thermal comfort in buildings using the methods and materials suited to the building type, climatic region and application method followed.

Full thanks and acknowledgement are given to Isoboard, Weber Saint-Gobain, BRE and the Building Science Corporation for the information given to write this article.

In this article:
–    What deems to satisfy the standard? Three ways of complying.
–    It is important to insulate the whole building, not just the roof.
–    The thermal performance of insulation is affected by many factors once installed.
–    To achieve optimum performance over the life of the building, these external elements, as well as degradation, need to be taken into account.

–    Inverted roofing insulation is a fairly new method holding many benefits.
–    Many new uses for roof systems are gaining popularity.

–    Retrofitting with ETICS is a simple way to insulate existing buildings.
–    Insulating cavity walls in new builds.

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