Facade calculator

How the facade area is calculated

perimeter = 2 × (length + width) · gross walls = perimeter × wall height · gable = width × height ÷ 2 (times the number of gables) · net facade = gross walls + gables − openings

A facade is not floor area and not the sum of the rooms — it is the shell of the house. The perimeter comes first, multiplied by the wall height to give the gross wall area. The gables, those triangles of wall under a pitched roof, are added to that, and only then are the windows and doors deducted.

The order matters. A gable is a triangle: width times height divided by two, and that result is multiplied by the number of gables — a typical house with a pitched roof has two, one on each gable wall. If the roof is flat, or the facade does not run over the gables, leave the fields empty.

Openings are entered as width × height × quantity rows, exactly as in the area calculator. Window reveals are not added separately — they do consume material, but the reserve covers them, and their area depends on the insulation thickness and the depth of the opening. If the openings turn out to be as large as the whole facade or larger, the calculator says so instead of offering zero as an answer.

The reserve: what it is for and why you can change it

The 5% reserve is a starting value and a planning habit, not a prescribed quantity. It covers cutting boards around openings and corners, breakage in handling, and the mesh overlap, which is deliberately not calculated separately.

The overlap is real — mesh is lapped at every joint and around openings — but how much it comes to depends on the system, the roll width and how the wall is set out. Had we built in an overlap factor, we would be handing you a number you could not check against any product label. So the reserve covers it, and every calculation says so.

Every quantity except the dowels is calculated on the area with reserve, because the reserve really is bought. Dowels are the exception: they are counted on the net facade area, because a dowel fastens the wall that exists while the reserve is spare board for cutting. Our laminate calculator applies the same rule to underlay.

Take the consumption figures off your own label

No consumption field has a default value, and that is deliberate. Pack coverage, adhesive in kg/m², the area of a roll of mesh, dowels per m², primer and render consumption — all of it differs from manufacturer to manufacturer and from system to system. There is no figure we could publish with a source, so we would rather not invent one.

Insulation type and thickness change no number in this calculator. They ride along as a note on your calculation and travel with the link when you share it. The reason is simple: a pack of 5 cm boards covers far more square metres than a pack of the same volume in 15 cm, so you have to read the coverage off the pack for your own thickness.

Prices are your own local ones too. The calculator multiplies the quantities by your prices, adds up materials, labour and scaffolding, and divides the total by the net facade area to give the cost per square metre — the net area, not the one with reserve, so the figure matches what you actually cover.

Example: a 10 × 8 m house with two gables

The house is 10 × 8 m with 6 m walls and two gables 8 m wide and 2 m high. There are eight 1.2 × 1.2 m windows and one 1.0 × 2.1 m door.

The perimeter is 2 × (10 + 8) = 36 m, so the gross walls are 36 × 6 = 216 m². The gables add (8 × 2 ÷ 2) × 2 = 16 m². The openings come to 8 × 1.44 + 2.1 = 13.62 m². The net facade is 216 + 16 − 13.62 = 218.38 m², and with a 5% reserve the calculation runs on 229.299 m².

If your own packs each cover 3 m², that is 77 packs of insulation. Adhesive at 5 kg/m² comes to 1,146.5 kg, or 46 bags of 25 kg. Mesh on 50 m² rolls means 5 rolls. Dowels at 6 per m² are counted on the net 218.38 m², which is 1,311 pieces — not 1,376, which is what you would get by counting them on the reserve as well.

At 12 per pack, 15 per bag, 60 per roll and 0.35 per dowel, the materials come to 2,372.85, or 10.87 per m² of facade. Once you know the area, you can estimate the facade paint in the paint calculator.