EXTERNAL THERMAL INSULATION MATERIALS

Calculate the cost of my external thermal insulation project

Enter the floor area of your house and the number of linear metres, deducting the area of your windows and doors: the calculator at Centrale ITE will generate a complete list of materials for your rendered EWI, with the exact quantities to order, from the starter rail to the bucket of render.

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2 Calculation of requirements

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PSE Grey ISOL France TH31 120 mm – External wall insulation board, R=3.85 Ref. ISOL120GRISTH31 12,36 € Including VAT

PSE Grey ISOL France TH31 140 mm – External wall insulation board, R=4.50 Ref. ISOL140TH31 14,50 € Including VAT

PSE Grey ISOL France TH31 160 mm – External wall insulation board, R=5.15 Ref. ISOL160TH31 16,94 € Including VAT

PSE Grey ISOL France TH31 180 mm – External wall insulation board, R=5.80 Ref. ISOL180TH31 19,72 € Including VAT

PSE Grey ISOL France TH31 50 mm – External wall insulation board, R=1.60 Ref. ISOL50TH31 5,65 € Including VAT

PSE Grey ISOL France TH32 100 mm – External wall insulation panel, R=3.10 Ref. ISOL100 10,01 € Including VAT

PSE Grey ISOL France TH32 120 mm – External wall insulation board, R=3.75 Ref. ISOL120 12,28 € Including VAT

PSE Grey ISOL France TH32 140 mm – External wall insulation board, R=4.35 Ref. ISOL140 14,32 € Including VAT

PSE Grey ISOL France TH32 160 mm – External wall insulation board, R=5.00 Ref. ISOL160 15,36 € Including VAT

PSE Grey ISOL France TH32 200 mm – External wall insulation board, R=6.25 Ref. ISOLGRIS200 20,46 € Including VAT

PSE Grey ISOL France TH32 260 mm – External wall insulation board, R=8.10 Ref. ISOL260 24,20 € Including VAT

PSE Grey ISOL France TH32 40 mm – External wall insulation board, R=1.25 Ref. ISOL40 4,58 € Including VAT

TH31 Grey EPS Panel, 200 mm, ISOL France – R=6.45 m².K/W Ref. ISOLGRIS200TH31 21,91 € Including VAT

TH31 40 mm Grey EPS Panel, ISOL France – R=1.60 m².K/W Ref. ISOL40TH31 4,73 € Including VAT

TH32 20 mm grey EPS panel, ISOL France – R=0.60 m².K/W Ref. ISOL20 3,07 € Including VAT

TH32 Grey EPS Panel, 220 mm, ISOL France – R=6.85 m².K/W Ref. ISOL220GRIS 30,59 € Including VAT

TH32 30 mm grey EPS panel, ISOL France – R=0.90 m².K/W Ref. ISOL30 3,12 € Including VAT

TH32 60 mm Grey EPS Panel, ISOL France – R=1.85 m².K/W Ref. ISOL60 7,54 € Including VAT

TH32 80 mm Grey EPS Panel, ISOL France – R=2.50 m².K/W Ref. ISOL80GRIS 9,17 € Including VAT

TH38 160 mm White EPS Panel, ISOL France – R=4.20 m².K/W Ref. ISOLBLANC160 14,74 € Including VAT

TH38 180 mm White EPS Panel, ISOL France – R=4.75 m².K/W Ref. ISOL180BLANC 17,10 € Including VAT

RE Coat+ 140 mm rock wool panel – External wall insulation, R=4.00 Ref. 140RECOAT 30,24 € Including VAT

RE Coat+ 160 mm rock wool panel – External wall insulation, R=4.55 Ref. 160RECOAT 34,56 € Including VAT

RE Coat+ 180 mm rock wool panel – External wall insulation, R=5.10 Ref. 180RECOAT 38,88 € Including VAT

RE Coat+ 200 mm rock wool panel – External wall insulation, R=5.70 Ref. 200RECOAT 43,19 € Including VAT

RE Coat+ 60 mm rock wool panel – External wall insulation, R=1.70 Ref. 060RECOAT 16,80 € Including VAT

RE Coat+ 80 mm rock wool panel – External wall insulation, R=2.25 Ref. 080RECOAT 17,28 € Including VAT

Thermolan N50F 20 mm rock wool panel – External wall insulation, R=0.50 Ref. 020N50F 7,69 € Including VAT

Thermolan N50F 30 mm rock wool panel – External wall insulation, R=0.75 Ref. 030N50F 9,76 € Including VAT

Thermolan N50F 40 mm rock wool panel – External wall insulation, R=1.00 Ref. 040N50F 13,01 € Including VAT

Thermolan N50F 50 mm rock wool panel – External wall insulation, R=1.30 Ref. 050N50F 16,26 € Including VAT

GUTEX Thermowall 40 mm window reveal panel – External wall insulation, R=0.975 Ref. FDB40 13,42 € Including VAT

GUTEX Thermowall-L wood fibre 180 mm – External wall insulation board, R=4.85 Ref. FDB180 39,68 € Including VAT

GUTEX Thermowall-L wood fibre 200 mm – External thermal insulation panel R=5.40 Ref. FDB200 44,10 € Including VAT

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What quantities should be allowed for per m² for EWI with render?

For 1 m² of polystyrene EWI under render, allow for approximately 1.5 panels, 8 kg of mortar, 7 wall plugs, 1.1 m² of mesh, 0.14 l of primer and 2.5 kg of finishing render.

Quantities of materials per m² of rendered EWI

Product	EPS	Rock wool	Source
1200×600 panels	1.39 + offcuts	1.39 + offcuts	Manufacturer’s size
Adhesive mortar	4 kg	4 kg	Data sheet A 96
Reinforced base coat	4 kg	6.3 kg	Fassatherm Technical Advice
Anchors	≈ 7	≈ 7	ETA 17/0450, DTA
Glass fibre mesh	1.1 m²	1.1 m²	Overlap 10 cm
FX 526 primer	0.14 l	0.14 l	FX 526 data sheet
1.5 mm render	2.55 kg	2.55 kg	RX 561 data sheet

Rock wool requires a thicker base coat, as its fibrous surface absorbs more mortar and the Technical Approval stipulates two coats. Wood fibre follows its own system: 8 fixings per m² and a lime-based undercoat suitable for a breathable insulation material.

How do you measure your façade before carrying out the calculations?

Measure the length of each wall to be insulated along the façade to obtain the linear metres, multiply by the height up to the eaves, add the gables, then count your windows and doors.

A laser tape measure will do. Add up the lengths of the relevant façades: this is also the length of the starting rail. For a gable, measure the width and the height from the apex to the eaves; its area is half the product of these two measurements. Enter the area including openings: the calculator automatically deducts 1.5 m² per window and 1.9 m² per door. Count a bay window as two windows; a garage door as three doors.

What thickness of insulation should I choose to achieve an R-value of 3.7?

To achieve a thermal resistance (R-value) of 3.7 m².K/W, you need 120 mm of graphite-enhanced EPS TH32 (R 3.75), 140 mm of white TH38 EPS (R 3.70) or 140 mm of Re Coat+ rock wool (R 4.00).R 3.7 is the threshold commonly required for financial assistance for external wall renovation in France.

The calculator displays the ACERMI-certified R-value for the selected thickness and alerts you if it is lower than this. To compare insulation materials based on other criteria (fire resistance, acoustic performance, summer comfort), see our guide ‘How to choose your external insulation’.

What accessories should you make sure to include in your EWI order?

The most commonly overlooked items are starter rails, corner brackets, drip mouldings for lintels, shutter hinge spacers and protective fittings for joinery.The starter rail, selected to match the thickness of the insulation, protects the bottom of the system.

Fabric-reinforced PVC corner beads reinforce each external corner and each opening frame. The drip profile prevents water running down the lintels. The high-density EPS hinge blocks allow the shutters to rest without creating a thermal bridge. The calculator adds these components automatically. For installation details, read the steps for external wall insulation and which fixings to use for which substrates.

Whether you’re a homeowner or a trade professional: what should you do with your list?

Whether you’re a private customer or a trade professional, you can add the entire list to your basket at trade prices Centrale ITE.

Centrale ITE is the platform specialising in the sale of external thermal insulation (ETI) materials, created by Sun Distribution, a distributor of insulation products since 2012. Our advisers will review the lists generated by the calculator free of charge, check the compatibility of the products with your substrate and adjust the anchoring requirements according to the wind exposure in your region, whether in France, Belgium or Switzerland.

Frequently asked questions about calculating the cost of an EWI project

How many bags of adhesive are needed for 100 m² of EWI?

For 100 m² of polystyrene EWI, allow for approximately 800 kg of A 96 mortar, i.e. 32 to 34 25 kg bags: 4 kg/m² for bonding and 4 kg/m² for the reinforced base coat. For rock wool, allow for around 42 bags instead.

How many wall plugs per square metre are required for external thermal insulation?

As a general rule, allow for 5 wall plugs per 1200×600 mm panel, or approximately 7 per m². This number increases at the edges of the façade and in areas highly exposed to wind. A pull-out test on your substrate will help you determine the final layout for the wall plugs.

What allowance for off-cuts should be made for insulation boards?

Allow 5 per cent for a rectangular façade with few openings, and 8 to 10 per cent for an irregular façade with gables, numerous windows or recesses. Offcuts of EPS are often used to insulate window reveals and small areas.

What length of wall plug should you choose depending on the thickness of the insulation?

The anchor must pass through the insulation and the adhesive, then anchor into the load-bearing wall. Allow for the thickness of the insulation plus approximately 50 mm: a 200 mm LFM 10 is suitable for 140 mm of EPS on concrete blocks. On existing thick render, add its thickness.

Is the calculator suitable for rock wool and wood fibre?

Yes. It adapts the panel size, the thickness of the base coat, the number of fixings and the undercoat to each type of insulation material. Gutex wood fibre insulation uses a 1200×400 format and a lime-based undercoat, which are compatible with its breathable properties.

Are the calculated quantities guaranteed?

These figures are indicative and are based on the consumption rates stated in the products’ technical data sheets and Technical Approvals. Actual consumption may vary depending on the flatness of the wall, exposure to wind and the installer’s expertise. An advisor at Centrale ITE can review your order list before you place your order.