Roofing calculators.Pitched and flat roofs, tiles, slates, battens, membranes, lead, gutters and pricing.

Roof geometry

Roof geometryRoof pitch from rise and run (degrees, percentage, 1 in n)

p = \arctan \frac{R}{G}

Roof geometryCommon rafter length from span and pitch, with ridge board and overhang

G = \frac{1000 S}{2} - \frac{t}{2}

Roof geometryHip or valley rafter length and pitch (equal pitches, square corner)

H = G \sqrt{2}

Roof geometryRoof slope area from plan area and pitch

k = \frac{1}{\cos p}

Roof geometryDuo-pitch (gable) roof: area, eaves, verge and gable triangle

L_{s} = \frac{S}{2 \cos p}

Roof geometryHipped roof (rectangular, equal pitches): area, ridge, hips and eaves

R = \frac{W}{2} \tan p

Roof geometryGable-fronted dormer: cheeks, front, dormer roof and main roof displaced

d = \frac{h}{\tan p}

Coverage

CoverageSingle-lap (interlocking) tiles per m² and battens per m² from gauge

g = L_{t} - h

CoverageSlates and plain tiles (double lap): gauge, number per m² and battens

g = \frac{L_{s} - h}{2}

CoverageNumber of tiles or slates for a roof, including waste

N_{n} = A n

Battens and underlay

Battens and underlayBatten set-out: equal gauge, courses and batten length

n = ⌈ \frac{D}{g_{m}} ⌉

Battens and underlayUnderlay rolls with horizontal laps

n = ⌈ \frac{1000 S_{l} - h}{1000 W - h} ⌉

Fittings and fixings

Fittings and fixingsRidge and hip tiles from lengths

N_{r} = ⌈ \frac{1000 L_{r}}{e} ⌉

Fittings and fixingsNails and clips for tiles and slates (to the fixing specification)

N_{n} = ⌈ ((N - N_{p}) n_{f} + N_{p} n_{p}) (1 + \frac{w}{100}) ⌉

Loads

LoadsRoof covering weight (dead load) in kg/m² and kN/m²

w_{c} = n m + B m_{b} + m_{u}

Falls and firrings

Falls and firringsFlat roof fall: drop over a run at a chosen ratio

h = \frac{1000 L}{G}

Falls and firringsCheck the fall of an existing flat roof

G = \frac{1000 L}{h}

Falls and firringsFirring sizes, stock timber and number of firrings

d_{1} = d_{0} + \frac{1000 L}{G}

Single ply and liquid

Single ply and liquidEPDM membrane sheet size with upstands and edge turn-downs

L_{s} = L + \frac{a_{1} + a_{2}}{1000}

Single ply and liquidEPDM deck adhesive and contact adhesive quantities

L_{d} = \frac{A}{c_{D}}

Single ply and liquidGRP fibreglass roof: resin, mat, topcoat and catalyst

k = 1 + \frac{w}{100}

Felt

FeltReinforced bitumen membrane (felt) rolls with laps

C_{e} = (W_{r} - \frac{s_{l}}{1000}) (L_{r} - \frac{e_{l}}{1000})

Leadwork

LeadworkLead sheet weight from thickness (BS EN 12588 codes)

q = t ρ

LeadworkLead flat roof or gutter bays: drips and rolls from LSA maximum sizes

n_{d} = ⌈ \frac{1000 L_{f}}{D_{m}} ⌉

LeadworkLead flashing pieces, lead length and weight

n = ⌈ \frac{R - l_{p} / 1000}{L_{m} - l_{p} / 1000} ⌉

Rainwater

RainwaterEffective roof area draining to a gutter (Approved Document H)

A_{p} = L_{g} D

RainwaterGutter flow and number of outlets or downpipes

Q = A_{e} i

RainwaterFascia and soffit board lengths and soffit area

L_{w} = P_{f} (1 + \frac{w}{100})

Insulation

InsulationWarm deck flat roof U-value and insulation thickness

R_{t} = R_{s i} + \frac{d_{i}}{1000 λ_{i}} + \frac{d_{d}}{1000 λ_{d}} + R_{o} + R_{s e}

Pricing and business

Pricing and businessRoofing job price: m² rate, materials markup and VAT

Net = A r + M (1 + \frac{m_{k}}{100}) + E

Pricing and businessLabour time from roof area and daily output

days = \frac{A}{P k} + X

Pricing and businessBusiness mileage at HMRC simplified rates

M = 2 d k_{v}

Pricing and businessCIS deduction on a subcontractor invoice

B_{n} = G - V_{t} - M_{t}

Roofing calculators.Pitched and flat roofs, tiles, slates, battens, membranes, lead, gutters and pricing.

Roof geometry

Coverage

Battens and underlay

Fittings and fixings

Loads

Falls and firrings

Single ply and liquid

Felt

Leadwork

Rainwater

Insulation

Pricing and business

Roofing calculators

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