Roofings Calculator guides
The calculators give you a number. These guides explain where the inputs come from, which assumptions matter, and how to tell a good estimate from a bad one.
Gutters & ventilation
Attic insulation R-values by climate zone, and how much to add
Most attics already have some insulation. Measure it, convert it to R-value, and the zone map tells you how much more to add.
Attic ventilation: the 1:150 rule and balancing intake and exhaust
An attic needs air moving from the eaves to the ridge. The code gives the amount; the balance between intake and exhaust decides whether it works.
Downspouts: how many, where, and how far from the foundation
A gutter is only as good as the place its water ends up. Here is how to place downspouts so the water leaves the house and stays away.
Gutter sizing by roof area and rainfall
Gutters are sized for the worst few minutes of a storm on one face of the roof. Three numbers decide it, and one of them is local.
Shingles & materials
Bundles per square and the waste nobody budgets for
The bundle count is easy; the waste is where orders come up short. Here is where every percent of waste goes and how to set it for your roof.
Drip edge, step flashing and valleys: the pieces that stop leaks
Roofs rarely leak through shingles; they leak at edges, walls and valleys. Here is each flashing, what it does and how much of it a roof needs.
Ice and water shield: where the code wants it and how much
One sentence of code decides how much membrane a roof needs, and the pitch decides how it reads on the deck. Here is the sentence and the arithmetic.
Roofing nails: count, length and nailing patterns
Most shingle blow-offs are nailing failures. The count is arithmetic; the placement and the depth are what hold a roof down.
Underlayment: felt vs synthetic, coverage and overlaps
The layer under the shingles is the roof's second line of defence. Choosing it is easy; counting it right means counting the laps.
Metal, tile & flat
Cedar shakes and shingles: exposure, bundles and lifespan
A bundle of cedar does not cover a fixed area: it covers more at a longer exposure. The Bureau's rule makes the count simple once that is clear.
Flat roof membranes: EPDM, TPO and PVC quantities
A flat roof is a membrane, a slope to the drains and as few seams as possible. Here is how to count each one.
Metal roof panel maths: coverage width, laps and cut lists
Metal panels are counted along the eave and sized up the slope. Get coverage width and panel length right, and the rest of the order follows.
Standing seam vs exposed fastener: quantities, cost and life
Both are metal roofs; they are built, priced and maintained differently. The difference shows up in the screws.
Tile and slate: pieces per square, weight and what the structure must carry
Tile and slate last a lifetime and weigh three to five times as much as asphalt. Here is the count, the load and when the framing needs a second look.
Measuring & pitch
How to measure a roof from the ground (no ladder needed)
Everything a roofing order needs can be measured standing on the lawn. Here is the method, the one calculation that matters, and the checks that catch the usual mistakes.
Rafter maths: run, rise, line length and the birdsmouth
A rafter is two right triangles and a notch. Once the triangles are clear, every cut follows, and the only judgement left is structural.
Roof pitch explained: ratios, degrees and the pitch factor
Pitch is written four ways and used in almost every roofing calculation. One right triangle explains all of it.
Why your roof is bigger than your house
A 2,000 square foot house rarely has a 2,000 square foot roof. Three things make the difference, and each one is easy to measure.
Planning & safety
How long roofs last, by material
Every roofing material has a typical life, and every roof has a climate, an attic and an installer that move it. Here are the ranges and what to do with them.
Is your roof solar-ready? Area, pitch, setbacks and panels
Solar panels last 25 years or more. Before they go up, the roof under them needs to last as long, have room after the setbacks and face the right way.
Ladders and roof safety: the 4:1 rule and when not to go up
Falls from roofs and ladders are among the leading causes of construction deaths. Most of the rules that prevent them are simple; the first one is knowing when not to climb.
Repair or replace: the signs, the maths and the timing
A leak does not always mean a new roof, and a dry ceiling does not mean the roof is fine. Age, signs and a simple sum decide it.
Cost & hiring
How to read a roofing estimate and compare two
Two roofing quotes for the same house can differ by thousands and both be honest. Lining them up item by item shows why.
Tear-off: layers, weight, dumpster size and disposal cost
Tear-off is the messy line on a roofing quote. It is also the easiest to estimate, because roofing debris is all about weight.
What roofers charge per square, by material and region
Roofers price in squares, and a quote is a stack of per-square figures. Here are the published ranges, where they come from, and what moves a price within them.