• Creation Date: Friday, 14 June 2019

Insulation is a subject that everyone knows about but few know how to apply the many products properly and in many cases, diminish the effect of the insulation and thus waste money.

There are 5 main areas in a normal home where insulating materials need to be applied.

Under the ground floor slab, in the walls, in the roof space, around hot water pipes and then with the glass in windows and doors.

When one considers insulating a home, most of what I mentioned is mandatory and your architect should be including all of it in the design of your home. There is a minimum standard set out in the SANS 10400 X and XA building codes which requires specification or calculation by a “competent” person which is usually your architect or designer.

I want to touch on each area briefly so that when you see what your builder is doing or perhaps not doing, you have some understanding as to what is going on. What I have written may change in some cases depending on the design and layout of the building.

Foundations and floor slab.

Your architect should have specified at least a 25mm sheet of polystyrene or polyurethane along the inside vertical inside edge of your foundation walls between the top of the foundation and the underside of the floor slab before the space under the floor slab is filled in and compacted. Secondly, there should be a layer of damp proof plastic over the whole floor area of the floor and then 25mm thick sheets of polystyrene should be laid edge to edge before the floor slab is cast. Any drainage or electrical conduits that are required to be placed under the floor should be placed before the damp proof plastic is laid.

This will ensure that the floor is properly insulated against heat loss or cold penetration through the floor and add to the comfort of your home. This is of particular importance if underfloor hearing is to be installed.


This is a new one to some but it is required that external 280mm brick cavity walls now have a 25mm sheet of polystyrene or polyurethane fixed to the outside edge of the inside brick skin of the entire wall. Fixing is usually done using wire ties. The insulating sheets are cut to 1m width along the length of the sheet to allow for the wire ties to be placed at the required 1 tie per square metre in the wall.

There are a number of alternative wall building methods and products that need to be treated differently to meet the energy efficiency requirements which I can chat about at another time.

Your roof.

The insulation requirement varies depending on the climate zone that your building is located in. Your architect will be able to determine the design requirement for your local area.
There are however a few common mistakes that are made by builders that render the insulation that they are placing, largely ineffective.

The biggest one is that when placing foil insulation just under the roof sheets or tiles, the builder places the roof sheets directly against the foil insulation. There needs to be a 25mm air gap between the foil and the roof covering to make it effective. This is achieved by cutting a 50x50 batten in half lengthways and fixing it over the purlin on which the foil has been fixed and this gives you the required 25mm gap.

The second is that while your architect may specify a particular thickness or brand name wool type blanket to be placed over the ceiling, a lesser thickness product is sometimes installed by the builder which is difficult to spot and not what you paid for. The ventilation of the roof space is also something which will greatly increase the management of heat in that roof space and increase your comfort levels.

Your hot water pipes and geyser. It is also mandatory to fit a heat blanket to your geyser and to insulate the hot water pipes in your home. Insulating the hot water pipework requires that larger slots need to be provided to fit the pipes with the insulation or the hot water pipes can be installed in the space of the wall cavity or built into the walls at the start.

Your glass windows and doors.

This is the one area where making a design choice will have the biggest financial impact. The bigger the windows or doors become, the more expensive the glass becomes. Large eaves overhangs, verandahs and shading or clever design, however, will go a long way to minimize the effect of the sun on the glass and thus affect the type and the cost of the glazing. The orientation of your home and the design of the glazing is part of what your architect is required to do and so it would be prudent to discuss this aspect of the design and the layout of your home with them early on in the design phase.

Investing your hard earned money wisely when you are building your house will only benefit you in the long term and having proper well-designed insulation will be a good investment.

Article by Les Abbott