How the material you choose changes the estimate: EPS and mineral wool

What really changes, and what does not

The geometry does not change. The same wall is the same 218.38 m² whether you fix EPS or mineral wool to it, so neither the reserve nor the opening deductions move.

In the calculator the insulation type is literally a label: it is carried into the assumptions and into the share link, but it changes no computed number. That is not an omission but the only honest option — the differences between two products are a property of the specific article and the system it belongs to, not of the category.

That is why every consumption field in the tool ships empty. No assumed pack coverage, no kilograms of adhesive per square metre, no dowels per square metre — all of it is read off the pack or the system's data sheet. The numbers in this article exist only to show how sensitive each item is, and not one of them is attributed to EPS or to wool.

The pack is the biggest difference in piece count

Pack coverage depends on both the product and the board thickness: the same material in a 5 cm pack covers far more square metres than in a 15 cm one, because boards are packed by volume. So copy the coverage for exactly the thickness you are buying.

The range is wide. On 218.38 m² with a 5% reserve the figure to cover is 229.3 m², and that is 115 packs if one covers 2 m², or 39 if it covers 6 m². The piece count therefore says nothing about the amount of material — two orders with completely different pack counts can bring almost the same number of square metres.

The last column shows exactly that: the purchased area runs from 229.5 to 234 m², a spread of under five square metres, while the pack count varies almost fourfold. Compare products by square metres, not by how many pieces end up on the order.

In pieces, the reserve behaves backwards

The same 5% reserve costs 7 packs when one covers 1.5 m² and only 2 when it covers 6 m². It looks as though the reserve is “more expensive” with small packs, but it is the other way round: small packs round more precisely, so less is left over.

The purchased area confirms it. With a 1.5 m² pack you end up with 11.12 m² to spare, and with a 6 m² pack 15.62 m² — even though the second order is only 39 pieces.

The practical conclusion: set the reserve by how much cutting and breakage you actually expect, not by how many packs it adds. The 5% is an editable planning starting point, not a norm and not a prescribed quantity.

Dowels are counted on the net area

Dowels are the one item the tool counts on the net area, without the reserve. The reason is simple: a dowel fastens the wall that exists, while the reserve is spare board for cuts — and an offcut does not acquire its own anchors.

On this wall that is a visible difference. At six per square metre the answer is 1,311 dowels on the net 218.38 m². Apply the same density to the 229.3 m² with the reserve and you get 1,376 — sixty-five more than the wall calls for.

How many go per square metre is not written here but in the system's data sheet, and it depends on the height of the building, the substrate and the board. The table below only shows how quickly that number grows.

Adhesive goes on the area with the reserve

Adhesive, primer and render are consumed across the whole surface you actually cover, so across the 229.3 m² with the reserve. The bags are then rounded up, because you cannot buy half a bag.

Consumption per square metre differs by system and substrate, and we do not invent that number. The table below shows a range with a 25 kg bag, only to make the sensitivity visible: one kilogram per square metre is worth about nine bags.

The same arithmetic applies to the primer and the render — you enter the consumption from the pack and the pack size, and the tool returns kilograms and a pack count. For fixings, corner beads and small sundries the tool gives no estimate, because those are counted per metre of opening and edge, not per square metre of wall.

How to calculate exterior wall area with gables →

What we deliberately do not estimate

Mesh overlap is not counted as a separate item. The roll is lapped at every joint, but the lap width depends on the system and the set-out, so instead of an invented factor the tool says the reserve covers it.

Mesh does not turn into pieces the way people expect anyway. On 229.3 m² a 50 m² roll gives 5 rolls and a 55 m² roll also 5 — the bigger roll saves nothing here, because the count rounds up. At 25 m² per roll it is 10 rolls.

And there are no prices. Prices differ by market, by merchant and by quantity, and we publish no price data — the price fields in the tool exist so you can enter your own quote, not so you can receive our estimate.

Check your own numbers

Open the calculator, enter your area or your house measurements, then open the material groups and copy the numbers from the pack you have chosen. Leave a group empty and that line is simply not shown, while the rest of the calculation still stands.

The quickest way to compare two products: enter the area once, then change only the pack coverage and the consumption twice. The difference you get is the real difference between those two articles, not between two categories of material.

Open the calculator with this article's area →