Timber Calculator for House and Sauna
About Timber Calculation
The Timber Calculator for House and Sauna determines the volume of wood needed for exterior walls, interior partitions and gables. The calculation accounts for the building layout, timber dimensions, number of courses and the characteristics of profiled joints. It also determines the wall area and the estimated length of sealing strip between courses.
Timber volume is calculated in cubic metres (m³) from the overall dimensions of the material. This helps estimate the amount of wood to purchase, taking into account the full timber height even when the effective height after assembly is smaller.
Guidelines and recommendations
Calculating wall and partition lengths
Exterior walls. The total length is calculated from the outside dimensions of a rectangular building. Length A and width B are entered in metres. The following formula applies to every layout:
Lext = 2 × (A + B)
For example, for a house measuring 8 × 7 m, the total length of the exterior walls is 30 m. The timber volume uses the full external perimeter without subtracting the overlapping portions at corners.
Interior partitions. Their total length depends on the selected layout. Twice the exterior wall thickness is subtracted from the internal span. For layouts with several partitions, the position and length of each section are taken into account.
The following relationships are used:
- Layout 1: no interior partitions.
- Layout 2: the partition length is
B - 2text. - Layout 3: offset AB is added to
B - 2text. - Layout 4:
A - 2text - tintis added toB - 2text. - Layout 5: two sections, each equal to offset AB, are added to
B - 2text. - Layout 6: two partitions, each measuring
B - 2text, are included.
Here text and tint denote the thicknesses of the exterior and interior walls in metres. The timber thicknesses entered in millimetres are divided by 1000 before lengths are calculated.
Number of courses and wall height
Overall and effective timber height. Overall height H1 is the full dimension of the product. Effective height H2 indicates how much one course increases the assembled wall height. With profiled timber, the effective height may be smaller because of interlocking grooves and tongues.
Number of courses. The specified wall height is divided by the effective height of one course. The result is always rounded up to the next whole number:
N = ⌈H / H2⌉
Here H is the specified wall height, H2 is the effective timber height, and N is the number of courses. Both heights are converted to the same units before calculation.
For example, a wall height of 3 m and an effective timber height of 140 mm require ⌈3000 / 140⌉ = 22 courses.
Height of full courses. This is calculated by multiplying the number of courses by the effective timber height:
Hfull = N × H2
In this example, 22 full courses have a height of 3.08 m. The specified height is exceeded by 80 mm. The upper course can be trimmed if necessary. The course count is calculated separately for exterior walls and partitions when the effective timber heights differ.
Calculating timber volume
Exterior wall volume. This is based on the total wall length, timber width, overall height and number of courses:
Vext = Lext × text × H1 × N
All linear dimensions in this formula are expressed in metres. The result is in m³. The same formula is used for partitions with their own lengths, timber widths, overall heights and numbers of courses.
For example, a house measuring 8 × 7 m with 3 m high walls and 200 × 150 mm timber with an effective height of 150 mm requires 20 courses. The calculated exterior wall volume is 30 × 0.2 × 0.15 × 20 = 18 m³.
Material quantity. Volume is calculated from the full cross-section of the timber in each course, including the uppermost one. No additional waste allowance is applied, so the calculation factor is 1.00. Openings and potential reuse of offcuts are not included in the geometric calculation.
Calculating timber for gables
Gable geometry. Each gable is assumed to be triangular. Its area is calculated from its base width and the height from the uppermost wall course to the ridge:
Sgable = Bgable × Hgable / 2
Here Bgable is the gable width in metres and Hgable is its height in metres. With several identical gables, the area is multiplied by their number.
Gable timber volume. This is calculated for individual horizontal courses. The number of courses is the gable height divided by the effective height of the exterior wall timber, rounded up. The length of each successive course decreases towards the top of the triangle.
The length of a course is calculated as follows:
Lj = Bgable × (1 - j × H2 / Hgable)
Here j is the course index, starting at 0 at the gable base. The length of each course is multiplied by the width and overall height of the exterior wall timber. The volumes of all courses are added together and multiplied by the number of gables.
With this method, the timber volume can exceed the geometric volume of the triangle because full-height course blanks are counted. For example, for two gables 7 m wide and 2 m high, using 200 × 150 mm timber with an effective height of 150 mm, the geometric volume is 2.8 m³, while the calculated timber volume is approximately 3.014 m³.
Total wall area and material volume
Wall area. This is calculated by multiplying the combined length of exterior walls and partitions by the specified building height. If gables are included, their geometric area is added:
S = (Lext + Lint) × H + Sgable
The area is calculated for one face of each wall, without doubling the surface. Unlike the volume of timber to purchase, the area uses the specified wall height rather than the height of the complete set of courses.
Total timber volume. This is the sum of the volumes of exterior walls, partitions and gables. If a component is absent, its volume is zero. The result is expressed in m³ and rounded to 0.001 m³.
Calculating sealing strip between courses
Exterior wall sealing strip. Its length is based on the number of horizontal joints between courses. A wall with N courses has N - 1 joints between courses. The total length is calculated as:
Lseal = Lext × (N - 1)
For example, exterior walls with a perimeter of 30 m and 20 courses require approximately 30 × 19 = 570 m of sealing strip.
Partition sealing strip. This is calculated in the same way, using the combined length of the partitions and their own number of courses.
Gable sealing strip. The total length of all gable courses is also included, including the joint between the lowest gable course and the wall below it.
The calculation assumes one sealing strip along each horizontal joint. If exterior walls and partitions use timber of different widths, sealing strip lengths are shown separately for each group. If the widths are identical, a combined result is shown.
Whether sealing is needed, the required strip width and the number of parallel strips depend on the timber profile and assembly method. Some profiled timber systems do not require an additional sealing strip between courses.
Practical guidelines and European standards
Timber dimensions. Cross-sections of 150 × 150 mm, 200 × 150 mm and 200 × 200 mm are commonly used in timber house construction. For profiled timber, the overall and effective heights must be distinguished. Actual dimensions should be taken from the manufacturer's technical documentation.
European standards. EN 1995-1-1, "Eurocode 5: Design of timber structures - Part 1-1: General - Common rules and rules for buildings", applies to timber structures. EN 14081-1, "Timber structures - Strength graded structural timber with rectangular cross section - Part 1: General requirements", specifies requirements for strength-graded structural timber. EN 14080, "Timber structures - Glued laminated timber and glued solid timber - Requirements", applies to glued laminated timber.
These standards set requirements for timber structures and materials. The timber volume calculation itself is based on the geometric dimensions of the building and products. No universal normative timber consumption factor is applied.
FAQs
Why can the calculated timber volume exceed the geometric wall volume?
The purchasing calculation uses the full overall height of each timber piece, while the number of courses is based on its effective height. In addition, the course count is rounded up to a whole number. As a result, the volume of timber to purchase can exceed the geometric volume of the finished wall.
How should the difference between overall and effective timber height be taken into account?
Overall height is the full product dimension used to calculate the timber volume. Effective height is the actual increase in wall height after one course is installed. These values often differ for profiled timber, so the dimensions provided by the manufacturer should be used when calculating timber quantities.
Why does the height of full courses not always match the specified wall height?
The calculator rounds the number of courses up because an additional course may be needed to reach the specified height. For example, with an effective height of 150 mm, a 3.1 m wall requires 21 courses with a combined height of 3.15 m. The difference is 50 mm and can be removed by trimming the upper course.
Why is the timber volume for gables larger than the volume of the triangular walls?
Gables are assembled from horizontal timber courses that become shorter towards the top. The calculator counts the volume of each such blank using its full cross-section, rather than only the geometric volume of the triangle. This gives a more suitable material estimate for constructing gables.
Is sealing strip always required between courses?
No. The need for sealing depends on the joint design. It is normally used with ordinary sawn timber, while some profiled timber systems have joints that need no additional sealing. The calculator estimates the length of one strip along the horizontal joints between courses.