Your walls almost certainly do not need insulation. Your roof does.

If you own a normal South African brick house, the energy regulations already regard your walls as compliant, exactly as they are, with nothing added. Anyone selling you wall insulation on an energy-compliance argument is misleading you.

Your roof is a different story. The requirement there is 3.7 m²K/W in every climate zone in the country, most houses do not come close, and the numbers a lot of people are still designing to were withdrawn.

We manufacture insulation. We would rather tell you where it is wasted than sell it to you there.

1. The rule nobody tells homeowners

Under SANS 10400-XA, a wall is deemed-to-satisfy — that is, compliant with no calculation and no added insulation — if it is either:

• a double-skin (cavity) masonry wall, or
• a plastered single leaf of 140 mm or more.

That is the overwhelming majority of South African houses.

No added insulation is required for compliance. Not a millimetre. The regulation looked at a brick wall, decided it was good enough, and moved on.

So if a salesman tells you your brick walls need insulation "for SANS compliance", he is either mistaken or he is not being straight with you. There are real reasons to insulate a masonry wall — we come to the honest one in section 4 — but compliance is not one of them, and it is the reason most often given.

The exception, and it is not a narrow one at all

A wall with a surface density lighter than 270 kg/m² — light steel frame, timber frame, drywall, a sandwich-panel wall — is not deemed-to-satisfy, and the bar it must clear is a serious one:

(SANS 10400-XA:2021, Chapter 3.)

That is roughly three times the resistance of an insulated cavity-brick wall, and you will not reach it with a token layer. If you are building in light steel or timber, thermal performance is a binding constraint on your wall, not an afterthought.

And there is a requirement almost nobody quotes. The same clause states that a walling construction with any metal sheet, metal studs, metal tracks or metal battens fixed to each other shall have a thermal break. Not "should". Shall.

A steel stud is a thermal bridge running from the inside face to the outside face of your wall. Filling the bay between the studs does not fix it, because the heat simply goes round the insulation and through the steel. The only thing that fixes it is a continuous layer the stud cannot cross — which is what a thermal break is, and what continuous external insulation does.

We modelled exactly this. See Steel doesn't punish insulation — it punishes insulation it can short-circuit, where a 2-D finite-element study of six South African wall assemblies found that steel studs quietly take back 38% of a mineral-wool-filled bay's resistance — and that adding a continuous external EPS layer halves the penalty to 18%.

2. The roof is where the law actually bites — and where nobody is looking

SANS 10400-XA:2021 requires a total roof/ceiling R-value of 3.7 m²K/W, in every climate zone. The only relief is Zone 5H (the humid sub-tropical coast — Durban, East London), which keeps 2.7 provided the roof is ventilated.

If you learned the old zone-by-zone numbers — 3.2 for zone 2, 2.7 for zone 3, and so on — those are superseded. They came from XA:2011. People are still designing to them. Do not.

Note also what "total" means: the whole assembly, including the internal and external surface resistances and the roof void — not the insulation board on its own. Never size a board straight off a headline R-value; you will get it wrong in one direction or the other.

3. What 3.7 actually costs — from our own price list

Assume the ceiling surface resistance, the external resistance and the roof void together contribute about 0.34 m²K/W. That leaves the insulation to find 3.36, which at λ = 0.038 W/m·K means about 128 mm of EPS.

Our EPS flat sheeting, 1 May 2026, supply only, ex VAT, ex delivery, ex installation:

An awkward fact we are not going to hide. The target needs 128 mm. Our sheet sizes go 125 mm, then jump to 150 mm. So 125 mm lands just short of compliance (3.63 against 3.7), and 150 mm clears it but overshoots — costing 20% more for R-value you were not asked for. No stock EPS thickness lands neatly on the South African target. Ask us for a cut thickness if you want to land on it exactly.

And the comparison an honest supplier makes

The standard South African ceiling blanket is 135 mm glasswool. At λ ≈ 0.040 that gives a total of 3.71 m²K/W — which is the XA target, almost exactly. That is not a coincidence: the industry default is calibrated to the regulation.

For a flat ceiling in an ordinary house, a mineral-wool or glass-wool blanket is normally the cheaper route to 3.7 than EPS board. We will say so plainly, and we supply mineral wool too, so we are not losing the argument by telling you.

EPS earns its place where the blanket cannot go:

• where the board must be rigid — you can walk on a service platform, you cannot walk on a blanket;
• where moisture is in play — wet mineral wool loses most of its thermal value and does not recover it when it dries; closed-cell EPS does not care;
• where the board is the finished ceiling — a PolyCool or SuperCool panel is insulation and ceiling in one, which is a different sum entirely and usually a better one;
• in a cathedral or exposed-soffit ceiling, where there is no void to lay a blanket into.

Choose on the job. If a supplier only ever recommends the product he happens to make, weigh his advice accordingly.

4. The one honest reason to insulate a masonry wall — and it is not compliance

It is where you put it.

A brick wall is heavy, and heavy things store heat. That thermal mass is either working for you or against you, and the insulation decides which.

• Insulation on the OUTSIDE of the brick puts the mass inside the thermal envelope. The wall becomes a flywheel: it absorbs heat through the day and gives it back at night, and the internal temperature stops swinging. The house holds its warmth overnight instead of dumping it into the garden by 3 a.m.
• Insulation on the INSIDE leaves the mass outside the envelope. You get a light, fast box that heats quickly and cools just as quickly — which is what you want in a room used for two hours a day, and exactly what you do not want in a home.

This is a comfort argument, not a regulatory one, and it is the real case for an external insulation system. It is worth making honestly. It is not worth dressing up as compliance, which it is not.

5. Compliance is not comfort

Here is the thing the regulations cannot tell you.

South Africans live in cold houses and have decided this is normal. We do not heat; we put on a jersey. That has a consequence for every insulation payback calculation you will ever be shown: if you were not spending much on heating in the first place, insulation cannot save you much. A payback figure borrowed from a European or American brochure does not survive contact with a South African house, and we are not going to quote you one.

The honest residential case for insulation in this country is usually not the electricity bill. It is:

• being able to use your house in winter without a heater running in every room;
• condensation and mould — a cold internal surface is where water condenses, and a warm one is where it does not. This is a health problem long before it is an energy problem, and in our lower-income housing stock it is a serious one;
• the ceiling, in summer. A South African roof space reaches 50–60 °C on a January afternoon. What separates that from your bedroom is the one thing this whole article is about.

You can tick every box in SANS 10400-XA and still live in an uncomfortable house. You can also insulate a roof properly, ignore the walls entirely, and transform the place.

Do the roof. Leave the walls alone unless you have a reason that is not compliance.

6. What we cannot prove

We hold no thermal-conductivity (λ) test for any of our products. Every R-value in this article rests on λ = 0.038 W/m·K, which is the value tabulated for the EPS class — declared, not measured on our material. We are commissioning the test.

Until it is done, treat our R-values as declared values. And treat everybody else's the same way, unless they can hand you the report.

Sources

SANS 10400-XA:2021 · Technopol EPS flat sheeting price list, 1 May 2026 (supply only, ex VAT).

Prices ex VAT, ex delivery, ex installation, current at 1 May 2026.