Ponding water is often seen as a threat to a flat roofing system. The roof Pitch or roof slope will affect the interior volume of a building, the drainage, the style, and the covering material of roof. The minimum roof pitch for shedding snow is around 30°, or a 6:12 or 7:12 slope, although this is not a definite, as the material of your roof, the direction of the snow and wind are some factors that can affect whether or not snow will slide, as roofs of as little as 10° have been reported to shed snow. Pitches between 8/12 and 10/12 (33° - 40°) are also considered walkable, but it is not advisable and, if you have to walk on these roofs, extreme caution should be taken. Find the inverse tangent of the pitch to find the angle in degrees. The smallest pitch of a roof is 0.5/12. rafter = √38.25 = 6.18 m, angle = arctan(pitch) = arctan(0.25) = 14°. We can divide roofs into the following categories: Generally, roof pitch is calculated from the same formula that describes a right triangle. Contents. To keep damage like leaks from occurring, water should not stand on a flat roof … Divide the first part of the ratio by 12 to work out the pitch. However, this could differ depending on your project. Roof pitch is simply the slope created by the rafter. M Hip Roof Framing M Gable Roof Framing M Skillion Roof Framing M Gambrel Roof Framing M Rafter Cutting M Rafter Cut Templates Full Scale M Soffit Drop Calculator M Bullnose Roof Sheeting Pitch to Angle Square Tail Fascia Cuts. The ‘fall’ is the measurement by which the gutter drops to allow water to drain towards the outlet downpipes. 1degree At approx 1 mt , 2 degree in 2 mt , 3degree in mt ect how do I measure or convert to mm? Some observers suggest it’s harder to replace a flat roof than a traditional pitched shingle roof because of the labor required to remove its layers (especially on older flat roofs). However, this is only possible in theory; it is very difficult to achieve in practice. However, this could differ depending on your project. a flat roof shouldn't be flat I know the name says flat roof but there usually around 5 degrees of fall or a ratio of fall of 40:2 don’t quote me on that ratio though I’d have to check with my carpenter. In snowy areas, your roof should be at least 10/12 (40°) to allow snow to shed, while the safest roof pitch in very windy areas is between 4/12 - 6/12 (18/5° - 26.5°). If asphalt shingles are to be installed on a low slope roof, special steps are required to avoid short roof life and roof … Fall Distance (General Industry) In general industry, any fall hazard 4’ or greater, requires protection. It encourages the deposition of dirt and leaves which can be unsightly, may obstruct outlets and /or become a slip hazard. Roofs any steeper than this are considered unwalkable, and special equipment or scaffolding is required. A 12/12 pitch roof has a pitch angle of 45°. You can enter this value either as a ratio x:12 or as an angle, whichever suits you better. Standard asphalt and composition shingles are the best for a 4/12 roof; rubber and wood shingles are unsuitable. When it comes to modern design roofing, two popular methods dominate: the flat roof and the A-frame. Slope is calculated by rise over run, thus a low-sloped roof is a roof where for every 12 units (inches, feet, or meters) measured horizontally (Run), the roof does not increase or decrease by more than 4 units vertically (Rise). … Flat roof with no permanent access and altitude not exceeding 100m, 0.75 kN/m² UDL & 0.9 kN point load Most areas exceeding 100m but not exceeding 200m, (excluding parts of Scotland, Pennines, North East England, refer to BS 6399-3), 1 kN/m² UDL & 0.9 kN point load The maths behind this number is that it is the square root of ((rise/run)2 + 1). Gradients from 1 in 40 to 1 in 110 will normally give adequate flow velocities. 4. Check your results with the Omni Roof Pitch Calculator. But it does depend upon the pitch and size of the roof … A low-slope roof is one that has a slope of less than 3-in-12. For water to flow on a flat roof, the minimum slope must only be greater than 1 0. Based on minimum permitted pitch, roofs may be categorised as flat or low (which includes roof decks), medium and steep pitch (see Table 2). Anything less than one-eighth of an inch may pool on the roof. How to calculate patio fall. (well there are a few more steps to add the roof covering and trim, but you can read about them below!) ROOF AREA TO BE CONSIDERED The design capacity for a roof drainage system depends on the quantity of water to be handled. Run length = 3250 mm Fall ratio = 1:40 Pipe fall = 3250 ÷ 40 Pipe fall = 81.25 mm. A completely flat roof is a poor design, as water and snow will collect on it, eventually leading to your roof collapsing in from the weight of it all. The previous diagram may be completed by adding a pipe gradient. Measure the run length - it is the horizontal distance between the roof ridge and the wall of the building. The pitch of a roof is its vertical 'rise' over its horizontal 'span'. You can also use this roof slope calculator to recalculate the roof pitch from degrees to percents. In general, the minimum slope for a flat roof … (b) Provision of a fall, not less than 1:80, on the flat roof or external ground sloping away from the adjoining internal/usable floor area. The roof joists can be fixed spanning directly between wall plates. Some building codes start at a quarter of an inch per foot. In considering the roof area, it must be remembered that rain does not necessarily fall vertically andI that maximum A 4/12 slope is enough to accommodate water runoff, but is not suitable for regions that are affected by heavy snowfall. Description. The best roof pitch depends on the style of roof you are going for. Snow type. A common choice for flat roofing material is EPDM rubber, as it is highly durable, waterproof, and can be made from recycled materials. This is necessary for allowing water to run off of the EPDM membrane surface and towards an appropriate drainage system.But this slope doesn’t need to be extremely steep, and when covering a large property, the angle of the flat roof … It can be assessed in two ways - either as the angle the rafter makes with the horizontal or the proportion between the rise and the run of the roof. A ratio is the most common way of expressing roof pitch or roof slope, but degrees are also possible. Please do not take risks on roofs, as the fall can be fatal. The quantity of water in turn depends on the roof area, slope, and rainfall intensity. This applies to general roof areas along with any internal gutters. Flat and low pitch roofs and decks For low pitch roofs and decks (less than 3°), the only cladding option is a membrane roofing system. A flat roof is the smallest ratio of the pitch (though flat roofs certainly do have a subtle pitch), while the A-frame varies in degree of pitch. It is a requirement of Building Regulation Part H that adequate provision is made for rainwater to be carried from the roof of the building. According to the International Building Code, the typical built-up flat roof that uses tar or asphalt goes by the guideline that for every foot (12 inches) of a flat roof, a minimum of … The slope of the roof … This translates into a fall of just under 2.5" on an 8 foot roof. The slope of your roof is vital as a moisture barrier, among other things, and having a roof that is too flat can potentially cause your shed to cave in. Slope measurements are determined by dividing the vertical rise in inches for every horizontal twelve-inch length. We need to find the total slope or fall in mm , or cm , the floor run is 7 mt long I have put my iPhone down on the floor in 7 areas starting from left to right and it give me. Through robust test and assessment schemes, the BBA give approval of construction products. Roof Pitch Use recommended minimum roof pitches as specified by roof sheet supplier. They are: the angle of inclination, percentage, per mille and it can also be expressed as a ratio. This minimum must be maintained over the entire roof, and throughout the life of the building. Some Bauder waterproofing systems are BBA approved for use with zero falls but back falls are not acceptable and should be corrected. Contemporary houses often have ‘flat roofs’ which shouldn't be completely flat but should be around 1:40. Roof pitch is the measurement of roof steepness. Let's assume it is equal to 6 m. Measure the rise of your roof. Make sure you use the same units in both the run and the rise calculators. In this example, that means that the patio should fall 1 … This could be the edge of the roof or any openings on the roof surface such as skylights and hatches. If your roof slope is above 3/12 (so called steep-slope), you can install either asphalt shingles, or a metal roof, or one of the exotic roof types: Slate, Tile, Wood, etc. BS EN 12056-3 and the Building Regulations Approved Document Part H contain relevant design information to enable rainfall calculations to be undertaken and give design principles for gutters and downpipes. Roofs with extensive ponding require increased maintenance input. Tapered insulation systems are a lightweight, convenient and cost effective alternative method of providing falls to the roof and can be used with our reinforced bitumen membrane (RBM) and synthetic single ply roof systems. You can find this information on the shingle packaging. A low-sloped roof is defined as a slope equal or less than a ratio of 4 to 12. There is no standard, universal roof pitch. The angle is not significant enough to prevent water from pooling on the surface. There are guidelines laid down that designers can follow to design the roof with a drainage fall (gradient) of 1:40. (1/4" per 1'). … Roof pitch refers to the slope which the rafter creates. Metal roof panels should be installed on roof slopes according to … Enjoy having one less thing to worry about. Check the roof space for obstructions and ease of movement. Low-slope & steep-slope terms describe roof slope, the slant of a roof. Snow cover thickness. If the rise is 6 inches for every 12 inches of run, then the roof slope is “6 in 12.” The … The roof pitching is essentially how steep the roof is going to be – they are either going to be “flat” or “pitched.” In this instance, we want to take a look at how this can be changed and improved with the help of a roof … Run length = 3250 mm Fall ratio = 1:40 Pipe fall = 3250 ÷ 40 Pipe fall = 81.25 mm. However, you can only use this pitch with built-up roofing or specialized synthetic roofing. The above formula may be rearranged for Fall if the gradient is known: FALL = GRADIENT X DISTANCE For example, calculate the fall in a 50 metre section of foul water pipework if the gradient … In the event of damage, the interior may suffer greater water ingress. Our Technical Department can design bespoke insulation schemes for individual projects and provide advice on roof fall design. will not allow you to move freely. If the gradient is steeper than 1 in 40, the liquid may run faster than the solids in the sloping foul water pipe thus leaving the solids stranded, which could then block the pipe. Drainage needs to be provided via internal rainwater outlets and downpipes or via external guttering systems or hoppers. A roof with a 6″ rise for every 12″ run has a 6″ per foot, or 6 in 12 pitch. The value displayed as the rise will be your x. rafter² = rise² + run² = 1.5² + 6² = 2.25 + 36 = 38.25 Note: The ratio is determined to be "1 in n" which is different to the mathematical "1:n". Internal gutters linking internal outlet positions should be at least 500mm wide. for asphalt shingles. I'm building a flat roof (3.6m x 3m) and I've purchased some treated timber firring strips which go from 100mm to 0 along the length. The minimum roof pitch eligible for a solar roof installation is 3:12 (or 14 degrees). Having … A 4/12 is a roof slope that rises by 4 inches for every 12 inches across. For flat roof drainage, where you place your drains, scuppers and the final material of the roofing is more important. Slope is calculated by rise over run, thus a low-sloped roof is a roof where for every 12 units (inches, feet, or meters) measured horizontally (Run), the roof does not increase or decrease by more than 4 units vertically (Rise). The Formula is as follows …… degree of slope X 1.746 cm X 1 Metre of run equals rise in centimetres (or negative FALL) e… Please call us on 0845 271 8800 or use our contact form to get in touch. The way pitch, also known as roof slope, is measured is rise over run. I always recommend at least a minimum pitch of 1 in 40. Flat and low pitch roofs and decks But I would like to know how it is calculated so I don't exceed the 5 degree slope. If you … This puts the Tesla solar roof at a disadvantage considering solar panels can work on all roof types. Download a range of our brochures to help support you in designing flat roofs, green and blue roofs, and photovoltaic solutions for your flat roofing projects. localised screed or additional rainwater outlet. According to BS 6229 & BS 8217, flat roofs should be designed with minimum falls of 1:40 to ensure a finished fall of 1:80 can be achieved, allowing for any inaccuracies in the construction. pitch. Fall Distance (Construction) A low-sloped roof is defined as a slope equal or less than a ratio of 4 to 12. Low slope roofs are from 0 to 3 / 12 in pitch. Posts These span tables are designed for a minimum post size of 50 x 50 x 2.5mm up to a maximum height of 3.0m. I seem to recall a builder telling me there needed to be a 20mm drop for every metre of roof length. You have more than enough slope for your roof, however you will likely need some sort of membrane roofing since it is very low slope. I will then add ply, vapour barrier, insulation, OSB3, then roof covering. It can also be written down as 25% or 14°. Vertical clearances of less than 1 m (39 in.) However, in many U.S. cities with older housing stock — think Federal Hill in Baltimore or Alexandria, Virginia‘s Old Town — the roofs are often flat or have very low slopes.. Flat roofs make replacing a roof a challenge. Water ponding on membrane roofs should be avoided because: Although all Bauder systems are capable of withstanding ponding water for long periods of time, their ultimate life expectancy will undoubtedly be affected. To convert from degrees to the American ratio: A roof pitch multiplier, also known as a roof pitch factor, is a number that, when multiplied by the area covered by a sloped roof, gives the actual area of the roof. Often, you express roof pitch as the ratio between the rise and the run in the form of x:12. Most modern residential homes have relatively steep pitches. A-frame roofs are popularly seen in most residential homes structures built in the 20th century. I will then add ply, vapour barrier, insulation, OSB3, then roof … Despite the name, all flat roofs need to be slightly angled in some direction. Roof pitch varies depending on culture, climate, style, and available materials. These will be placed directly on the joists. Intuitively, this is the number of inches of snow on your roof … In the plans the maximum roof slope is 5 degrees. The Gradient Calculator is another online tool … 12.2 DESIGN AND CONSTRUCTION OF FLAT ROOF The proper design of falls in a flat roof is an essential consideration in the overall drainage of the roof. A roof of pitch 7/12 (30°) is manageable, but caution should be taken. So how do I calculate the fall across the 5.5m. However, most often a ratio of "pitch" (also fraction) is slang used for the (more useful) 'slope' (of rise over 'run') of just one side (half the span) of a dual pitched roof… Find the tangent of the angle, tan(angle). Falls on a roof can be achieved by adjusting the height of the supporting beams or purlins, by using tapered supports, or by the addition of firring pieces before the deck is laid. For example, a pitch 1:12 means that per every twelve yards of building length the rise will be equal to one yard. Some online information indicates flat roofs are less that 1.5 degrees slope and other info says less than 10 degrees. Water pon- ... plan ratio and permeability. Download our standard CAD detail drawings for all of our waterproofing systems (to be used for conceptual purposes only). Roof pitch, or slope, is a measure of vertical rise to horizontal run expressed in inches per foot. Due to this, there are other factors that are taken into account when working out the ideal slope for a flat roof. This could mean flat roofs … However, an ideal roof drop per foot should be at least one-eighth to one-quarter of an inch per foot. A pitch over 9:12 is considered a steep-slope roof, between 2:12 and 4:12 is a low-slope roof, and less than 2:12 is a flat roof. Water pon- ... plan ratio and permeability. So, if your roof rises 4 inches for every 12 inches of horizontal length, then the pitch of your roof is expressed as 4:12. These will be placed directly on the joists. A gradient may be defined as fall … Thermal design - insulation and condensation, Refurbishment roofs - assessing requirements, Refurbishment roofs - improving drainage falls, Refurbishment roofs - improving thermal properties. There are a lot of factors that will affect how much getting your roof pitched will cost - design, style, accessibility, cost of labour etc. We will explain to you how to determine the roof pitch step by step. Filed Under: Fall Protection, OSHA Tagged With: fall prevention, fall protection, fall protection flat roof, fall safety, low sloped roof work, OSHA, OSHA flat roof. A flat roof is the smallest ratio of the pitch (though flat roofs certainly do have a subtle pitch), while the A-frame varies in degree of pitch. It is a simple and cost-effective method to use for certain commercial construction buildings like warehouses. Roof pitch. To convert between American roofing ratios and pitch degrees, follow these steps: A roof pitch of 6/12 (26.5°) or less is considered easily walkable, and no extra precautions are required. * Boarding to be fastened on top of flat roof joists with a depth to width ratio greater than 4 The allowable clear spans have been calculated in accordance with BS 5268-2:2002 Structural use … Roof pitch. Assessments Anything less than one-eighth of an inch may pool on the roof. Commonly used roof slopes are flat roofs, low slope, and steep slope. All roof claddings have a minimum permitted pitch – either the minimum recommended by the manufacturer, or as set out in E2/AS1 (see Table 1). They have the same deck requirements as shingles. minimum fall and the benefit of additional fall. Most roofs have a pitch in the 4:12 to 9:12 range. Roof pitch is often expressed as a ratio between rise and run in the form of x:12. Some info says that a skillion roof (which normally would have significant slope and I would call a pitched roof) is a form of flat roof. Flat roof systems are a bit of an outlier. The industrial age brought about economical building methods and the prevalence of flat roof construction. However, minimum slope for a flat roof by building code here is 2%. Minimum slope It is essential that the minimum fall of roof is maintained to ensure that water drains away. These are only estimates though, talk to your neighbours to see what roofing costs in your area. There are profiled metal roof cladding systems specifically designed for low-slope application. It is a requirement of Building Regulation Part H that adequate provision is made for rainwater to be carried from the roof of the building. BBA certification is widely known throughout the construction industry as a symbol of quality and reassurance. In the case of a cast in-situ concrete slab, falls are normally provided by use of a screed. Pipe Rise / Fall Hand Online Calculator. Description. Let's say it is equal to 1.5 m. Calculate the rafter length, substituting these values into the following formula: Calculate the roof pitch as the proportion of rise and run: Finally, you can find the roof pitch in the form of x:12. So, if your roof rises 4 inches for every 12 inches of horizontal length, then the pitch of your roof is expressed as 4:12. Thus, the pitch is the ratio of the rise in inches to a 12-inch run and is often expressed using a semicolon, for example, 6:12. But now, flat roofs often are constructed with fewer layers because of improved waterproofing technology. Related Regulations + Add to My Handbook; FALL PROTECTION. Flat roofs are hard to replace. Based on minimum permitted pitch, roofs may be categorised as flat or low (which includes roof decks), medium and steep pitch (see Table 2). The table below shows standard roof … In order to ensure a finished surface with zero fall, a design fall of 1:80 should be used and a detailed structural analysis should account for construction tolerances, settlement and for deflection under load. You can enter this value either as a ratio x:12 or as an angle, whichever suits you better. Just in case you are trying to fathom out some markings on a plan somewhere…. MEMBRANE ROOFING … You can use the following equations to find the length of the rafter and the slope: If you want to find the roof pitch in the form of x:12, simply calculate the pitch and substitute 12 for the run length. If you choose another material, such as metal or wood, the range is $7.35 - $10.73 per sq.ft. A-frame roofs … Ice may be a slip or wind hazard during the winter months. The fall of the roof may be created in the structure itself by laying the supporting beams, or joists at a slope (giving a sloping soffit) or by installing tapered beams with horizontal soffits. Even if a roof is very small, it is recommended there are at least two drainage points in case one becomes blocked. Some of the factors include: Since they vary in quality as well as method of installation, the choice preferred for a flat roof will ultimately have an effect on the final slope of the flat roof. In the event that the above measures cannot be … A roof that rises 4 inches for every 1 foot or 12 inches of run is said to have a “4 in 12” slope. This roof pitch calculator is a handy tool that will help you quickly assess what is the pitch of your roof of what length of rafters you need for your construction works. Flat roof span tables allow for a maximum roof pitch of 5º. There are a lot of factors that will affect how much getting your roof pitched will cost - design, style, accessibility, cost of labour etc. You can divide roofs into these categories: Flat roofs which aren’t perfectly flat require a small slope to allow for water runoff. A gradient of 1 in 80 is converted to a number instead of a ratio - 1 / 80 = 0.0125 Fall = 0.0125 x 50 Fall = 0.625 metres or 625mm. The way pitch, also known as roof slope, is measured is rise over run. In the USA, the range of standard pitches is anywhere between 4/12 and 9/12. Sika Sarnafil Watchmead Welwyn Garden City AL7 1BQ 01707 394 444 1. Check out 5 similar roofing calculators . A ratio is the most common way of expressing roof pitch or roof slope… For a Gothic style, the rafters must equal the span (60°), while an Elizabethan style requires the rafters to be longer than the span. Intuitively, this is the number of inches of snow on your roof in the place where the cover is the thickest. There are 4 different ways of that are used to specify the slope. Where areas are found by a site level survey to have negative falls, i.e. This would mean the roof fall is 110mm. A gradient of 1 in 80 is suitable for commencing calculations for pipe schemes. Particular attention should be paid to the controlled disposal of rainwater from green roofs, designed to support planting, and blue roofs, which are designed to attenuate the drainage of stormwater from the roof. Run length = 25 metres Fall ratio = 1:80 Pipe fall = 25 ÷ 80 Pipe fall = 0.3125 m. Example Calculation 1. In the USA, you can expect to pay between $3.19 - $4.43 per sq.ft. Commercial roofs call for a particular kind of roof anchor. If you a looking for a sleek, modern style, a (not entirely) flat roof with a pitch of 1:40 should be used. It increases the dead load and may cause progressive deflection of the deck. If you have a flat roof shed or porch, you’ll need to be sure it has adequate pitch or you could find yourself having to conduct frequent roof repairs due to poor drainage. Generally, such roofs … If your roof is pitched, enter the length and width of the flat area covered by the roof. Is an area of your flat roof sunken in and holding water? In Italy, with its more temperate climate, the range of angles is 16 - 25. You can shingle a 3/12 pitch roof, but special application measures should be taken to prevent leakages at some point down the line. The pitch of a roof is its vertical 'rise' over its horizontal 'span'. FALL = GRADIENT X DISTANCE. Pipe Rise / Fall … Except as otherwise provided in paragraph (b) of this section, each employee engaged in roofing activities on low-slope roofs, with unprotected sides and edges 6 feet (1.8 m) or more above lower levels shall be protected from falling by guardrail systems, safety net systems, personal fall … Previous Post: « Small … Fix your roof deck and you are done! This gives you the pitch of the roof. Run length = 25 metres Fall ratio = 1:80 Pipe fall = 25 ÷ 80 Pipe fall = 0.3125 m. Example Calculation 1. Some kind of protective, waterproof membrane should be put down underneath the shingles, as well as using shingles that are recommended by the manufacturer for that slope. will hold water, remedial action should be taken, e.g. A 30° roof pitch is roughly the same as a 7/12 roof pitch. If the gradient is less than 1 in 110, then the pipe could still block if the solids slow down and become stranded. Firrings It is normal practice for the joists of a flat roof … Many plumbers guidelines recommend a ratio of around 1:500 (which is roughly 20mm for every 5m of guttering). I'm building a flat roof (3.6m x 3m) and I've purchased some treated timber firring strips which go from 100mm to 0 along the length. Some sources consider low slope to include 3 / 12 pitch roofs. Roof Drainage Calculators Our online tools have been designed with simplicity in mind removing the need for any prior specialist industry knowledge. Minimum slope It is essential that the minimum fall of roof is maintained to ensure that water drains away. A roof that is nearly flat or slightly pitched is called a flat roof or low slope roof – No roof should be dead flat because it must have at least a slight slope to drain. While a flat roof appears to be level, a minimum slope is required to allow water to drain off. However, most often a ratio of "pitch" (also fraction) is slang used for the (more useful) 'slope' (of rise over 'run') of just one side (half the span) of a dual pitched roof. If your roof is pitched, enter the length and width of the flat area covered by the roof. Bauder Ltd, 70 Landseer Road, Ipswich, IP3 0DH T: + 44 (0)1473 257671, Bauder Ltd, O'Duffy Centre, Cross Lane, Carrickmacross, Co Monaghan T: +353 (0)42 9692 333. Roof pitch multipliers are extremely useful in estimating the amount of material required to fit your new sloped roof, as conventional mathematics will leave you short! In the UK, the typical house has a pitch between 40° - 50° - although 45° should be avoided. Falls create flow paths to direct the drainage of rain-water away from the roof to suitable discharge points. Metal roofs will have the highest wind blow-off resistance, and are best suited for ice dams prevention – especially if your roof slope is below 6/12! The slope of the roof is another factor. The tools guide the user step by step allowing fast and simple roof drainage design whilst ensuring full compliance with BS EN12056-3 … Multiply the pitch by 12 to find the x in the ratio x/12. Calculating the patio fall is a case of dividing the fall by the run. According to BS 6229 & BS 8217, flat roofs should be designed with minimum falls of 1:40 to ensure a finished fall … Flat roofs also tend to be cheaper and require less maintenance than traditional roofing, making them a perfect addition to your home. Unfortunately for homeowners with flat roofs, the Tesla Solar Roof will not be an option for you and your home. The minimum pitch for a roof is 1/4:12, which translates to 1/4 inch rise to 12 inches of run. Attics or roofs without a working space are covered later in this chapter, in Section 5.4, Cramped attics, cathedral ceilings and flat roofs. In the UK, you price of getting a roof fitting is £72-£75 per square metre. The pitch of your roof is 3:12. When it comes to modern design roofing, two popular methods dominate: the flat roof and the A-frame. When utilising Bauder outlets, we can offer drainage calculations based on outlet type, size, fall and location of roof to determine the number of outlets required. In this example, that means that the patio should fall 1 unit for every 80 units of distance. To prevent ponding caused by lap build-ups around rainwater outlets, these should be recessed or fitted in sumps, where practical. Roofs of steeper pitches will likely retain less snow, so, if you live in snow-prone regions, a steeper pitch is highly desired. Snow cover thickness. This minimum must be maintained over the entire roof, and throughout the life of the building. minimum fall and the benefit of additional fall. For example, calculate the fall in a 50 metre section of foul water pipe work if the gradient is to be 1 in 80. Unlike the construction code, there are no exemptions to this rule. This forms an angle of 18.5° between the horizontal section and the roof, and creates a gentle incline that is seen as a midpoint between a low-pitch and medium-pitch roof. Notes to the table above. Built-up roofs should be installed on roof slopes 0.25:12 or greater (2015 IRC R905.9.1), except for coal-tar built-up roofs that have a minimum roof slope of one-eighth unit vertical in 12 units horizontal (1% slope).