Wall Insulation Calculator
About Wall Insulation Calculation
The Wall Insulation Calculator calculates the insulation area, required material volume and estimated cost. It takes into account wall dimensions, window and door openings, triangular gables, insulation thickness and a waste allowance. The results help estimate insulation material requirements for exterior façades and interior walls.
Guidelines and recommendations
Calculating wall area
Main wall area. This is calculated by multiplying the total length of the walls to be insulated by their height. Dimensions entered in centimetres are converted to metres by dividing by 100. The resulting area is expressed in m2.
Swall = L × H
Here L is the total wall length in metres and H is the wall height in metres. If wall heights vary, an average height is used. For an accurate result, the average should be weighted by the length of each wall section.
Subtracting window and door openings
Opening area. For each window or door type, the area of one opening is calculated by multiplying its width by its height. This is then multiplied by the number of identical openings. Openings of different sizes are calculated separately and their areas are added together.
Sopen = Σ (a × b × n)
Here a and b are the opening width and height in metres, and n is the number of identical openings. The symbol Σ means that the areas of all included window and door types are added together. Openings are subtracted only when this option is enabled.
Calculating gable area
Triangular gables. The area of one gable is half the product of its base width and the height from the base to the apex. Where there are several identical gables, the result is multiplied by their number.
Sgable = (a × h / 2) × n
Here a is the gable base width in metres, h is its triangular height in metres and n is the number of gables. The formula assumes a triangular gable. Its calculated area is added to the total wall area.
Net insulation area
Net geometric area. The total area of included windows and doors is subtracted from the rectangular wall area, after which the gable area is added. If the result is negative, the calculator uses zero.
Snet = max(0, Swall - Sopen + Sgable)
When opening deductions are disabled, their area is treated as zero. Similarly, gables are excluded from the calculation when their option is disabled.
Waste allowance for insulation
Waste factor. The calculated area is increased by the selected percentage to allow for cutting, offcuts and possible damaged material. The default allowance is 10%, corresponding to a factor of 1.10. For simple surfaces, 5% is often allowed, while façades with many openings or complex shapes may require 10-15%.
Sreq = Snet × (1 + r / 100)
Here r is the waste allowance in percent. For example, a net area of 100 m2 with a 10% allowance gives a calculated requirement of 110 m2. The allowance increases the quantity of material to purchase, not the actual wall area.
Insulation volume and cost
Insulation volume. The area including the waste allowance is multiplied by the insulation layer thickness. Thickness entered in millimetres is converted to metres by dividing by 1000.
V = Sreq × (t / 1000)
Here V is insulation volume in m3 and t is layer thickness in millimetres. For example, an area of 110 m2 including waste and a thickness of 100 mm require 11 m3 of insulation.
Insulation thickness. Wall insulation boards are commonly available in thicknesses of 50, 100, 150 or 200 mm. The actual thickness is chosen according to the wall material, climate and required thermal performance. For the same area, doubling the thickness doubles the material volume.
Insulation cost. If cost calculation is enabled, the required volume including waste is multiplied by the price per cubic metre.
C = V × P
Here C is total cost and P is the price per 1 m3. The result is expressed in the same currency as the entered price. The calculation uses material volume without rounding to whole packs.
European standards
European standards relevant to insulation products include EN 13162, "Thermal insulation products for buildings. Factory made mineral wool (MW) products. Specification", EN 13163, "Thermal insulation products for buildings. Factory made expanded polystyrene (EPS) products. Specification", and EN 13164, "Thermal insulation products for buildings. Factory made extruded polystyrene foam (XPS) products. Specification".
These standards set requirements for the properties of the respective insulation products. Material quantities are calculated from geometric dimensions and the selected waste allowance. The waste percentage is not a prescribed factor from these standards.
FAQs
How do I calculate insulation for walls of different heights?
If wall heights vary, use a length-weighted average height. To find it, divide the combined area of all rectangular wall sections by their total length. This gives a more accurate insulation quantity than a simple arithmetic average of the heights.
Should all windows and doors be deducted?
Deducting openings reduces the calculated insulation requirement, especially on walls with extensive glazing. However, insulating window and door reveals requires extra material. Reveal areas are not automatically included in the geometric calculation.
Why is the insulation area including waste greater than the wall area?
The net area represents the surface to be insulated, while the area including waste represents the estimated material requirement. With a 10% allowance, every 10 m2 of wall surface requires an additional 1 m2 of material. This helps cover losses when cutting insulation boards.
How does insulation thickness affect the required quantity?
For a fixed wall area, insulation volume increases in direct proportion to thickness. For example, insulating 100 m2 with a 50 mm layer requires 5 m3 without waste, whereas a 100 mm layer requires 10 m3. Use the actual thickness of the selected boards to estimate material requirements correctly.
How do I calculate wall insulation with gables?
The area of triangular gables is added to the main wall area before the waste allowance is applied. Each gable is calculated from its base width and height to the apex. If the gables contain windows, their areas can be included in the total opening deductions.