In contrast to sheet roofing materials for the proper calculation of the quantity of asphalt shingles, it is sufficient to know the roof area, because on each package of roofing material indicates the number of square meters of overlapping area. Let us look at specific examples to determine the amount of asphalt material and its components. The instructions are relevant for all asphalt roofing manufacturers.
Components for asphalt shingles: purpose and calculation
Before starting to calculate the roof, we will understand the purpose of the shingle elements. Names and types of components may slightly different from metal shingle elements, but in general they have similar applications.
In asphalt roofs, metal strips are also used for roofing: wind, cornice (drip), adjoining strip. They have a slightly different shape, but are similar in purpose to metal roofs. Let’s look at the most common of them.
- The S1 apron is a ledge or drip. It is used for drainage of condensate from the waterproofing membrane surface.
- Apron S27 – the drip is installed directly on OSB board above the gutter.
- The apron S5 or wind strip is used for insulating the end part of the roof against precipitation and wind.
- Apron S4 is a wall-mounted corner slat or an adjacency strip. It is used at the joint between the roof and the vertical surface (wall or chimney).
- Apron S6 with a wall consignment note performs the same functions as S4. It differs in the installation of strips.
- Wall-mounted apron S7 is an overlap strip (like S5) with the possibility of installation in the wall.
The presented asphalt shingle elements have a standard length of 2 meters. To calculate the metal strips it is necessary to divide the total length on which this or that apron will be installed by 1.9 meters (useful length of each strip, taking into account the overlap).
Names and sizes of metal strips may slightly differ.
The most important element in the construction of a soft roof is the underlay carpet. It consists of bitumen and is an additional waterproofing of the roof in case the main roofing is damaged. Bituminous material is laid over the entire roof area on waterproof OSB slabs or waterproof plywood of at least 9 mm thickness. The underlay carpet is installed horizontally, from bottom to top with an overlap of 100-150 mm.
In case of a roof construction with inner slope corners, a special valley carpet is laid on these places. As well as lining it is delivered in the form of a roll, but the material itself is thicker and has various colour variations corresponding to a tone of asphalt shingles.
The underlay carpet is calculated basing on the roof area with a small margin (about 10%) for overlapping.
The above materials are the main components necessary for the construction of a roof made of asphalt shingles. Additional elements may be needed in case of complex roof forms.
Additional elements for asphalt shingles
The ventilated asphalt roof ridge is made of durable plastic, has a special hole for ventilation under the roof and foam inserts as a barrier against precipitation or insects.
An alternative to the ridge valve are roof aerators. There are different shapes, but the principle of operation is similar – ventilation of under-roofing space to prevent the formation of moisture and mold, and thus protect the wooden structure and OSB boards and the entire structure of the roofing system.
Aerators for flexible roof shingles
If the length of the slope is long (more than 10m), calculated from the top to the bottom point of the roof, it is necessary to install aerators. Otherwise, the under-roof ventilation will not work properly.
To prevent insects or birds from getting under the roof, mosquito nets must be installed throughout the eaves.
Ventilation tape
It can be made of aluminium or film (PVC ventilation tape). The element is fastened with ordinary wood screws. When installing flexible shingles, many people neglect this element despite its low cost, which can lead to unpleasant consequences later on.
Calculating snow holders for roofs
To prevent avalanche snowfall, we recommend installing snow stops. For flexible shingles, a special construction in the form of a small hook is used. Elements are installed in a chess order and fastened with wood screws in special holes on the plate.
For bituminous shingles it is necessary to install a system of snow retention at the time of installation of the roof, because part of the element is wound up under the shingle plate.
Snow retention system
To find out how many snow stops are needed in case of a soft roof we will use the following rule: on slopes with a slope of 30 – 40 degrees snow stops are installed in the lower part of the roof – 4 pcs. per 1 meter, and at a roof slope of 40 to 70 degrees – 6 pcs. per 1 meter.
Calculation of flexible shingles for double roofs
To calculate the quantity of the material for gable roofs, it is necessary to know the size of the roof slopes. For example, let us assume that each gable is a rectangle with sides a=10 m, b=6 m.
According to the formula S=ab we calculate the area of each gable. If the slopes are the same as in our example, we get the roof area S=2ab=210*6=120 square meters. Flexible shingles should be purchased with a small stock (about 5%), so the number of roofs for gable roof we get in the amount of 126 sq.m. We consider OSB or moisture resistant plywood for the same area. In case of underlay carpet we add another 10 square meters for the overlap.
Universal formula for determining the number of packs of soft bituminous roofing for a simple roof structure: ” roof*1,05 / “packing.
Approximate calculation of bituminous mastic – 5 liters for 60-70 square meters of the roof. For our area we get about 10 liters.
Now let’s proceed with the calculation of components and accessories. Depending on the manufacturer skate-roof tiles are available in different lengths of overlap, but most manufacturers have one package covers 12 running meters of skate and 20 meters of eaves. For our sizes, the length of the eaves is 20 meters (10 meters on each side), ie 1 package. Plus one more pack for the skate, which length is 10 linear meters (10 meters on each side). In total, we get a package of “skate / curtain rod” in the amount of 2 pieces.
Note that for laminated (two- or three-layer shingles) there is no need to purchase eaves tiles, because the lower rectangular layer of the roof already performs its function.
We consider a ventilated roof ridge by the formula: length of the ridge / length of the ventilated ridge. That is 10 m divided by the length of the vent. ridge (each manufacturer has different sizes). For such a gable roof, the ridge fans will be sufficient. If the roof has more area, you need to add additional aerators – one aerator for about 40 square meters.
Metal strips have a standard length of 2 meters. We calculate the number of wind (gable) strips S5 by the formula: 24/1.9 = 13 pcs., where 24 – the total length, where the wind aprons will be installed (6m x 4), and 1.9m – the useful length of each bar, taking into account the overlap.
The ledge (S1 and S27) shall be calculated in the same way. 20/1.9 = 11 pcs. In this variant there are no connections between the roof and the wall or chimney, but the calculation would be done according to the same formula.
Aluminum mosquito net or PVC film is mounted in the eaves, so their length will be equal to 20 meters in our case.
The procedure for calculating roof nails is as follows: 0.5 kg per 10 square meters of roofing (or 4 pcs. per sheet). For the presented sizes about 6 – 7 kg.
We will summarize the calculation in the table:
Flexible shingles 126 m²
OSB or plywood 126 m²
Lining carpet 136 m²
Bituminous mastic 10
Skate and curtain tile 2 op.
Ventilated ridge 10 m
Wind bar S5 (2 m) 13 pcs.
Curtain rod S1 (2 m) 11 pcs.
Drip S27 (2 m) 11 pcs.
Mosquito net 20 m
Roof nails 7 kg
Example of soft roof calculation for a four-piece hip roof
The calculation of the number of flexible shingles is done in the same way. The first thing we know is the roof area and by adding 5-7% we get the amount of soft roofing. We also calculate OSB and lining carpet.
The roof consists of two trapezes and two triangles.
The area of the trapezium is calculated by the formula:
S = (a+b)H/2 = (3+12)5/2 = 37.5 sq. m.
The triangle’s area is equal:
S = dH/2 = 104/2 = 20 sq.m.
Adding up all the areas, we get the roof area of 115 sq.m. For the roof we will take about 123 sq.m. with a small reserve, and for the underlay carpet – 135 sq.m.
There will be more ridge and curtain elements due to the presence of not only the upper ridge, but also the side ribs. In the lower part of the whole perimeter also laid “ridge / curtain rod” except for the laminated roof. We will get that for covering the ridge it will take a length of 4s + a = 35 meters (3 packs), and for the eaves 2b + 2*d = 44 meters (3 packs). Vent. ridge is calculated only on the upper (horizontal) part of the rib. For proper ventilation of air under the roof we add 6 aerators: 2 on trapezoidal slopes and one on triangular ones.
The second difference from the gable shape is the absence of wind bars, but we add the number of eaves aprons throughout the roof perimeter: 44/1,9 = 24 pcs.
We also need a little more mastic and nails to seal the ridge tiles and fix them. Otherwise, the calculations for the soft roof are no different from those described above. We will also conclude with a table showing the required number of flexible shingles and accessories.
Flexible shingles 123 m²
OSB or plywood 123 m²
Lining carpet 135 m²
Bituminous mastic 13 l.
Skate and curtain tile 6 op.
Ventilated horse 3 m.
Roof aerator 6 pcs.
Curtain rod S1 (2 m) 24 pcs.
Drip S27 (2 m) 24 pcs.
Mosquito net 20 m.
Roof nails 10 kg
Important: Measure the roof as accurately as possible!
We hope this article was useful and answered the questions of how to calculate the most flexible roof tiles without the help of online calculators.Note that the process of determining the amount of bituminous roofing should always be done by yourself, as special resources mainly offer an approximate result, not taking into account additional accessories and stock of material.