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Application

Inverted (Protected-Membrane) Roof

A flat concrete roof must carry the waterproofing, the insulation, the SANS 10400-XA thermal requirement and usually paver or maintenance traffic in one build-up. In an inverted (protected-membrane) roof the insulation is laid ABOVE the waterproofing under ballast, shielding the membrane from UV and thermal shock — but the insulation itself then sits permanently in the drainage plane and is wetted by every rainfall. That single fact governs the specification: the board must have proven long-term water absorption by immersion and diffusion, proven freeze-thaw resistance and proven creep behaviour under sustained ballast load, which is why the classical inverted-roof board is XPS, not EPS.

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What it must achieve

Performance targets

Roof/ceiling minimum TOTAL R-value
3.7 m²K/W
SANS 10400-XA:2021
Applies in ALL climatic zones. The Zone 5H (humid-coastal) 2.7 m²K/W concession is conditional on ROOF VENTILATION — a sealed concrete inverted/warm roof has none, so 3.7 is the target. Total R = deck + screed + insulation + surface resistances, not the insulation alone.
In-service U-value correction for rainwater cooling
Required — magnitude not quantified by Technopol
EN ISO 6946 / BS 6229 (inverted-roof correction)
In an inverted roof, rainwater runs BETWEEN the insulation and the membrane and carries heat away, so the built U-value is worse than the dry calculation. The designer must apply the drainage correction and add thickness. Technopol publishes no correction factor — do not assume the dry R-value is the delivered R-value.
Sustained design stress on the insulation
≤ compressive resistance @1% strain
ASTM D7180 (design) / ASTM D6817 (grade)
Ballast, pavers, pedestals and maintenance traffic are PERMANENT loads. Design to the @1% (elastic-limit) value — never to the @10% figure, which is the failure-region strength and will creep under sustained load.
Ballast hold-down against wind uplift and flotation
Project-specific — by the designer
SANS 10160-3 (wind actions)
EPS at 12–30 kg/m³ floats and is light enough to lift. The ballast layer is a structural element, not a finish, and must be checked for uplift and for flotation when the roof is flooded. Technopol publishes no ballast weight table.
The inverted roof build-up, layer by layer
The same build-up, in the order it goes together. Generated from the assembly data this page lists below, so the drawing and the words cannot disagree.
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Where it goes

The assembly

Section through the inverted roof assembly
  1. Ballast / paver wearing course (by others)
  2. Water-flow-reducing / separation layer (by others)
  3. Insulation boards…
  4. Waterproofing membrane (by others)
  5. Screed to falls / structural concrete deck
  6. Soffit / internal finish

Layers listed outside → inside. The section is drawn to show the ORDER of the layers and where the Technopol product sits in it; the band widths are not to scale.

What each layer is doing — 6 layers, full detail
  1. Ballast / paver wearing course (by others) — Washed round gravel, or pavers on pedestals. Structural duty: holds the insulation down against wind uplift and flotation and screens the EPS from UV. Depth and weight are designed to SANS 10160-3, not taken from a brochure.
  2. Water-flow-reducing / separation layer (by others) — Permeable geotextile or proprietary WFRL above the boards. Keeps ballast fines out of the joints and limits the rainwater volume reaching the membrane interface — the source of the U-value correction above.
  3. Insulation boards — Technopol EPS (bulk-insulation; geofoam grades where trafficked; 2d-shapes cut to falls) — CONDITIONAL LAYER. In a true inverted roof this board lives permanently in the drainage plane, where the insulation must be qualified for long-term immersion (EN 12087), diffusion (EN 12088), freeze-thaw and wet creep — a duty for which EPS is not specified. Use EPS here ONLY with a designer-accepted moisture and creep assessment — otherwise specify XPS for this layer, or move the insulation below the membrane (warm roof).
  4. Waterproofing membrane (by others) — Torch-on bitumen, single-ply or liquid, installed and flood-tested BEFORE the insulation. Where EPS contacts the membrane, the membrane and primer must be EPS-compatible — no hot bitumen direct to EPS, no solvent-based primers or adhesives (they dissolve polystyrene). A slip/separation sheet is the usual remedy.
  5. Screed to falls / structural concrete deck — Falls are set here. Technopol can hot-wire-cut tapered EPS (2d-shapes) as a lightweight alternative to a fall screed in the WARM-roof configuration, where the tapered board sits under the membrane and stays dry.
  6. Soffit / internal finish — A correctly built inverted roof needs no separate vapour-control layer — the membrane is the vapour barrier and sits on the warm side. In the warm-roof alternative the condensation risk moves and a VCL below the insulation must be assessed.
Which products, and why

The products that do this job

Product

Bulk Insulation Products

The insulation layer itself — rigid closed-cell fire-retardant EPS board (LiteCel/FRCel), grades 12–30 kg/m³, cut to size, thickness 5–600 mm. Grade is chosen from the sustained ballast/traffic stress, not from thickness alone.

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Product

Geofoam Lightweight Fill

Where the roof carries pavers, planters or maintenance traffic, the higher-density geofoam grades (EPS20/24/30) provide the @1% design compressive resistance the lighter grades cannot (per-grade @1% safe-working loads 15/17/45/70/100 kPa for EPS12/15/20/24/30).

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Product

2D Shapes & Sheets

Hot-wire-cut tapered / cut-to-falls boards and upstand fillets — used to form falls without a heavy screed in the WARM-roof build-up (insulation under the membrane, dry).

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The numbers

Performance data

Every test report and certificate behind these figures is held by Technopol and is available on request.

9 figures, full data
PropertyValueStandard
Thermal conductivity λ @10 °C (EPS grade ladder, dry)0.033–0.045 W/m·KTechnopol per-grade datasheet (@10 °C)
Example dry thermal resistance — 100 mm of grade 20DV at λ 0.035≈2.9 m²·K/WR = thickness ÷ λ
Compressive resistance @1% strain — the DESIGN limit under sustained ballast15–100 (EPS12/15/20/24/30 = 15/17/45/70/100) kPaASTM D7180
Compressive strength @10% strain (NOT a design load — failure region)60–200 kPaASTM D6817
Water absorption (indicative only — NOT an inverted-roof qualification)< 4 %Manufacturer datasheet value
Service temperature80 long-term / 100 short-term °CSupplier datasheet
Reaction-to-fire class (FR-grade EPS board)B-s1,d0SANS 53501-1 (Euroclass; SBI + ignitability)
Fire-resistance rating (REI / minutes) of the EPS boardNone — reaction-to-fire class only; all EPS is combustible (fire-retardant treated)SANS 10177-2
Quality management system (company credential)ISO 9001:2015 certified — EPS blocks, sheets, cornice, insulated ceilings, adhesives, roof solutionsISO 9001:2015 (EQCSA, SANAS C22)
Size it

SANS 10400-XA compliance checker

Enter the deck, screed, insulation λ and thickness to test the build-up against the 3.7 m²K/W roof/ceiling total-R requirement. The checker computes the DRY resistance only — apply the inverted-roof rainwater U-value correction (EN ISO 6946 / BS 6229) on top and add thickness. To choose between EPS, PIR and Stone Wool for a wet or fire-sensitive layer, use ../../technical/core-comparison/.

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On site

Installation

The full installation sequence — 9 steps
  1. Confirm the configuration FIRST. If the insulation will sit permanently above the waterproofing in the drainage plane, obtain the designer's written acceptance of EPS in wet service — or specify XPS for that layer, or move the insulation below the membrane (warm roof) and use Technopol EPS there.
  2. Verify the deck: falls laid to the outlets, membrane installed, flood-tested and signed off BEFORE any insulation is placed. In an inverted roof the membrane is unreachable afterwards.
  3. Check EPS compatibility at every interface. No hot bitumen direct to EPS, no solvent-based primers, adhesives or sealants — they dissolve polystyrene. Use a slip/separation sheet or an EPS-safe solvent-free product.
  4. Select the board GRADE from the sustained stress (ballast + pavers + pedestals + maintenance traffic), keeping the design stress at or below the @1% strain resistance. Do not select on thickness alone.
  5. Loose-lay the boards on the membrane, break-jointed and tight, with no adhesive and no mechanical fixings through the membrane. Cut around outlets and upstands with a hot wire or fine-tooth blade.
  6. Lay the water-flow-reducing / separation layer over the boards, lapped, and dress it up at perimeters and outlets.
  7. Place the ballast to the designer's depth and weight IMMEDIATELY — EPS must never be left UV-exposed or unweighted overnight. Ballast is a structural hold-down against wind uplift and flotation, not a finish.
  8. Keep EPS clear of flues, hot pipes, plant discharge and any surface running above 80 °C, and away from hot-works; maintain the designer's separation distances.
  9. Record the grade, thickness, board layout and ballast depth as-built — the insulation is buried and cannot be inspected later.
The limits

Where not to use this

A material specified for the wrong job fails you, then us.

A true inverted roof where the EPS sits permanently in standing or freely draining water, or is subject to freeze-thaw (high-altitude interior, Zones 1 and 6 in winter)
An inverted-roof board must be qualified for long-term water absorption by immersion (EN 12087) and by diffusion (EN 12088), for freeze-thaw and for wet creep. Technopol EPS is not specified for that duty: wet EPS loses thermal performance and gains weight, so the delivered R-value cannot be relied on.
→ Specify XPS (EN 13164) for the inverted insulation layer, OR flip to a WARM-roof build-up — insulation above the deck but BELOW the waterproofing, dry for life — where Technopol EPS (bulk-insulation, tapered 2d-shapes) is fully appropriate.
Roofs carrying vehicles, sustained plant loads, planters or paver pedestals designed against the @10% compressive figure
The @10% strength (60–200 kPa) is the failure region, not a design load. Sustained stress above the @1% elastic limit (15–100 kPa by grade) causes creep — the boards consolidate, the falls flatten and water ponds over the membrane.
→ Move up the geofoam grade ladder (EPS24/EPS30) with the sustained stress checked against the @1% value, or use an engineer-designed load-spreading slab or pedestal system.
Anywhere near flues, hot pipework, roof-plant discharge, hot-works or a surface above 80 °C
EPS softens above ~80 °C long-term (100 °C short-term) and ALL EPS is combustible — FR grades are fire-retardant treated, not non-combustible.
→ Stone Wool (non-combustible) in the hot or fire-separation zone, with the designer's separation distances maintained.
Any interface with hot bitumen, solvent-based primers, solvent adhesives or plasticised PVC single-ply in direct contact
Solvents and migrating plasticisers attack polystyrene — the board dissolves or shrinks at the contact face, silently and invisibly under ballast.
→ EPS-compatible torch-on over a slip sheet, an EPS-safe solvent-free adhesive, or a separation fleece between the membrane and the boards.
A roof where a rated fire-resistance (REI, minutes) is required of the deck, or where non-combustible insulation is mandated (boundary/firebreak conditions, escape routes below)
Plain EPS board carries NO fire-resistance rating. The only fire claim applying to the board is reaction-to-fire B-s1,d0 (IT 23-08-00009, 60 mm FRCel 20DV) — a reaction-to-fire class is not a fire-resistance rating. A plain EPS-core panel failed its SANS 10177-2 test (FTC 16-162); PIR failed too (FTC 21-163).
→ Stone Wool insulation, or a concrete/composite deck assembly designed and tested for the required REI.
EPS left exposed to sunlight or weather during construction, and green/blue roofs with root penetration
EPS embrittles and yellows under UV, and no root-resistance test exists on file.
→ Ballast the boards immediately on placement; for green roofs use a tested root barrier over an XPS insulation layer.
Where it has been used

Project references

2D Shapes & Sheets

Riverstone Mall, Meyerton

Meyerton · Retail

Geofoam Lightweight Fill

Sun International Times Square

Menlyn, Pretoria · Casino / hotel

Geofoam Lightweight Fill

South African Reserve Bank (SARB)

Institutional / banking

Geofoam Lightweight Fill

Liberty Life Style Centre

Commercial

Geofoam Lightweight Fill

Lesotho Highlands Water Project, Phase II

Lesotho · Civil / water infrastructure

Geofoam Lightweight Fill

Steyn City

Steyn City, Johannesburg · Mixed-use development

All 54 project references →

Questions

Specifier FAQ

Can I use Technopol EPS as the insulation in a true inverted (protected-membrane) roof?
Only with the designer's explicit acceptance. The classical inverted-roof board is XPS, because the insulation lives permanently in the drainage plane and must be qualified for long-term immersion (EN 12087), diffusion (EN 12088) and freeze-thaw. Technopol EPS is not specified for that duty. The clean, defensible use of Technopol EPS on a flat concrete roof is the WARM-roof configuration — insulation above the deck, below the waterproofing, dry for life.
What R-value must this roof achieve?
A total roof/ceiling R of 3.7 m²K/W in every climatic zone under SANS 10400-XA:2021. The Zone 5H humid-coastal 2.7 m²K/W concession requires roof ventilation, which a sealed concrete flat roof does not have — so 3.7 applies. In an inverted build-up you must also apply the EN ISO 6946 / BS 6229 rainwater-cooling U-value correction, which makes the delivered performance worse than the dry calculation; Technopol publishes no correction factor, so the designer adds the thickness.
What thickness of EPS gets me there?
R = thickness ÷ λ. At λ = 0.035 W/m·K (grade 20DV), 100 mm gives roughly 2.9 m²K/W dry, before the deck, screed and surface resistances are added and before any wetting correction. λ is grade-dependent (0.033–0.045) and is a declared datasheet figure — confirm the grade against the specification and run the build-up through the XA checker.
Is the EPS board fire-rated?
It carries a reaction-to-fire classification of B-s1,d0 to SANS 53501-1 (report IT 23-08-00009, valid to Aug 2028), established on a 60 mm FRCel 20DV sheet. That describes how the material contributes to a fire; it is NOT a fire-resistance (REI, minutes) rating. No plain EPS board has a fire-resistance rating, and all EPS is combustible even in fire-retardant grades.
Doesn't Technopol's Agrément certificate cover this roof?
No. Agrément SA 2020/609 covers the LiteCore Building System as a NON-LOAD-BEARING WALL only. There is no Agrément certificate for bulk EPS board, geofoam, LiteSpan, LiteClad or any roof application. The company-level credential is the ISO 9001:2015 quality management system.
Can I cite the LiteSpan panel's B-s1,d0 report for the loose board?
No. IT 24-06-00029 classifies the 150 mm LiteSpan sandwich PANEL (Chromadek + EPS core), not loose EPS board. The board's own claim is IT 23-08-00009. Cite the report that matches the product actually installed.

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