roofing calculator area

A roofing calculator area finder and with easy tips for making your own roofing estimates

a basic roof shapethe basic roof in plan
Roofing calculator area - Slightly unusual but this basic roof will illustrate the magic of the roof slope ratio.

They get a lot more complicated than the roof above, but I'll use it to illustrate a basic point.

If all the roof surfaces are all at the same slope as they are in most instances, then for purposes of finding the surface area of the roof,

you can forget about all the hips and valleys, the dormer windows and the Dutch gables. Just measure the rectangular areas on plan and multiply them by the slope ratio.

After reading the previous paragraph I'd be fairly certain that if you have not come across this before then you would be saying to yourself "that's bulls**t , it can't be so easy". Of course you didn't say that 'cos you've already had a peek at the sketches below.

the roof surfaces developed
Roofing calculator area - The roof surfaces developed into their true shapes.

The sketch above is what a cardboard model of the roof would look like if it was pressed flat onto a table, just holding together at the ridges.

I found out the lengths of the sloping sides by multiplying their plan lengths by the slop ratio. I used the same pitch as in the previous example, 12 : 12 or 45 degrees that gives a slope ratio of 1.41. Note that the edges that are horizontal, the eaves and the ridges remain the same length. The do not change, only the sloping ones change.

the same surfaces made  into compact rectangles
Roofing calculator - The same surfaces made into compact rectangles

Now here we get to the nitty gritty of it all. Still imagining that what you see is a cardboard model, then by cutting the triangular areas off and rotating them and repositioning them it is easy to see that what we have is just two ordinary rectangles.

So for purposes of estimating the roof cladding surface area, be it tiles shingles or corrugated iron, then calculate the square area of the two rectangular areas on the plan. Add them together and multiply...once only... by the slope ratio.

the total roof area

So here it is, once again with my cheap calculator and taking the same slope ratio from the previous page. "Easy as... eh?"

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    Please Note! The information on this site is offered as a guide only!  When we are talking about areas where building regulations or safety regulations could exist,the information here could be wrong for your area.  It could be out of date!  Regulations breed faster than rabbits!
    You must check your own local conditions.
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