What insulating a broiler house is actually worth

Three findings, and two of them cost us money.

The first board does almost all the work. Going from a bare roof to 35 mm of ceiling captures about 86% of all the heat you will ever save. Everything after that is fighting over the last 14% — and we will show you the arithmetic, using our own price list.

We will not quote you a payback. Not because we cannot, but because the two numbers that decide it are yours: what you burn, and what you pay for it. We give you the kilowatt-hours. You put the rand on them.

And an American R-value is not a South African R-value. They differ by a factor of 5.678, and that mistake is being made in this market every week.

1. The unit trap

Almost every good article on poultry housing is American, and their R-values are in different units.

The US extension services recommend a broiler-house ceiling of R-21, minimum R-12 (Mississippi State, Kentucky). Those are imperial — hr·ft²·°F/Btu. 1 m²K/W = 5.678 of them.

Note in passing that SANS 10400-XA asks 3.7 m²K/W of a roof/ceiling. The same number, arrived at independently by a US farm-economics guide and a South African building regulation. It is simply what the physics costs.

If an insulation R-value looks impressively large, divide it by 5.678 and see if it still does.

2. What our own ceiling boards actually deliver

PolyCool and SuperCool are EPS boards with a facing — vinyl on PolyCool, uPVC on SuperCool — made from 15D fire-retarded EPS. Prices below are from our published price list of 1 May 2026, supply only, excluding VAT, delivery and installation.

λ = 0.038 W/m·K. That is a declared value, not a measured one — see section 6, where we are honest about this.

(R total = board + internal and external surface resistances + a ventilated roof void.)

An honest gap: to reach the US R-21 target (3.70 m²K/W) you need about 129 mm of EPS. Our price list stops at 100 mm, which reaches 2.93. We are not going to pretend otherwise. Whether you should chase 3.70 at all is the next section.

3. The first board does almost all the work

A bare steel roof with no ceiling has a U-value of roughly 6.0 W/m²K. Here is what each thickness takes off it:

Read the last column. The thinnest board is the most efficient purchase, by a wide margin, and every millimetre after it buys less.

Put sharply: going from 75 mm to 100 mm costs 22% more and buys 1.8% more heat saving.

That is because the first 35 mm already collapses the U-value from 6.0 to 0.82 — about 86% of every watt you will ever save. The rest is a fight over the remainder.

So why do the Americans say R-21? Because they have long, hard winters and far more heating hours than we do. The colder and longer your heating season, the further up that table it pays to climb. On the Highveld the economic optimum is probably thinner than the American advice, and in a warm region thinner still. Do the sum for your own site — the next section shows you how.

Where thicker genuinely does earn its money: if your real problem is summer heat stress, not winter heating — which in much of South Africa it is — this table is the wrong one to read from. Heat rejection, condensation control and damping the daily swing all reward a thicker board, and none of them appear in a winter-gas calculation.

4. The sum, without pretending to know your fuel

Different farms burn different things — gas, coal, biomass, electricity — at different prices, with different burner efficiencies. So we will not produce a rand figure. We will produce the heat, which is physics, and you will put the price on it.

Heat saved (kWh/yr) = ΔU × ceiling area × ΔT × heating hours ÷ 1000

Worked, for a 1500 m² house with a 75 mm PolyCool ceiling (ΔU = 5.56 W/m²K):

Now convert with your own fuel:

Against: 1500 m² × R193.59 = R290 385 supply only. Add VAT, delivery, and installation — the price list is a supply rate, and installation is a separate quote you must get.

The sanity check that protects you from every supplier, including us

Insulation cannot save more energy than you actually burn. Take your fuel invoices for a winter cycle. That is the entire prize. If a saving is quoted to you that exceeds your fuel bill, the arithmetic is impossible and you can stop listening.

5. When this does not pay

• An open-sided house. There is no thermal envelope to insulate. A ceiling still buys you shade and radiant heat rejection, which is real — but it is not a fuel-saving argument and must not be sold as one.
• A leaky house. Insulating a shed with gaps around every door and inlet is a jersey worn with the windows open. Seal first — it is cheaper than insulating, and every extension guide that has studied this puts it first (The Poultry Site).
• You cannot insulate past the ventilation. A broiler house must ventilate to remove moisture — that is welfare, not preference — and that air carries heat straight out. As houses get tighter and better insulated, "winter ventilation ... will contribute a higher proportion of the heat loss" (Maryland Extension). There is a floor under your heating bill and insulation cannot get below it.
• A mild site with a short brooding window. The saving scales with ΔT and with hours. Both may be too small.

6. What we cannot prove, and will not claim

We make EPS. Two things we will not pretend about.

We hold no thermal-conductivity (λ) test for any of our products. The 0.038 W/m·K used throughout this article is the value tabulated for the EPS class — declared, not measured on our material. We are commissioning the test. Until it is done, treat every R-value we publish as a declared value — and treat every competitor's the same way, unless they can hand you the report.

The claim that insulation improves FCR is weakly evidenced. Vendors quote dramatic feed-conversion gains. We could not find a controlled study isolating insulation from everything else that changed at the same time. The mechanism is sound — a bird held closer to its thermoneutral zone spends less feed staying warm — but we will not put a number on it that we cannot defend. The energy saving is real, calculable, and yours to verify against your own invoices. Treat any FCR benefit as an unpriced bonus.

Sources

Mississippi State Extension · University of Kentucky · University of Maryland Extension · The Poultry Site · Technopol price list, 1 May 2026 (supply only, ex VAT).

Prices ex VAT, ex delivery, ex installation, current at 1 May 2026. Every assumption above is one you should replace with your own — that is the entire point of the article.