How do I calculate the sq ft of a cottage roof when I only know the perimiter lengths.?

Question

I have a cottage (or pyramid) roof. I don't know what the rise or height is (and it's a two storey house). I only know the outside dimension (all sides are 20' ...800 sq ft house). I want to estimate the cost of the steel/aluminum sheets so I have enough money saved.

Answer 1

Sorry you need one more piece of information. Either the slope of the roof or the rise or the length of a pitch. can't do it without.

Answer 2

There was an old forestry tool that was useful in measuring the height of a tree, that might work for you... here is a link to a site, showing how to make the tool, and what measurements it needs to match, when you make it.
http://www.cnr.berkeley.edu/departments/espm/extension/TREESTK.HTM

Now, once you have the tool, pace off 100 feet, and measure your roof from peak to a line running from eave to eave... any straight edge held cross wise to the measuring tool will help. Using the chart supplied, you can calculate that measurement.

Now, using Pythagorus's theorum, you can calculate the actual 'slope'... Asquared +Bsquared = Csquared.
A= the number you come up with on the tool.
B= the length from the eave to the center of the roof.
C= the roof slope, or 'hypotenuse' of the triangle formed by the base (B) and the right angle side (A)

http://people.bath.ac.uk/ma2hlk/pythagorus_thm.html

For example... if the measurement from the tool = 6ft, and the measurement from the eave to the center of the roof = 10ft, then the 'slope', or hypotenuse would = about 11.6 ft

:) this means doing a little math, but is something you can use with materials on hand to measure it. :)

I seem to remember there was a way to measure the shadow of a stick and compare that to the measurement of the shadow of a tree (or house, for that matter) that worked on the same principle... but that method meant you had to actually pace off the shadow, and the shadow had to lie on ground that was level to the source of the shadow... the measuring stick shown on the Berkely link, is much handier.

Have Fun

Answer 3

If the roof is a 12/12 pitch (45deg) you'd have 2 15'x20' sections (if there's no dormers) that's the largest it would beunless you have a roof steeper than the usual extreme

Answer 4

if you can climb up to the eaves, (where the gutter is) i assume you have a ladder. measure the amount showing of one tile/slate. count how many course of tiles you have and multiply it by that measurement.
a rough guide :-
1 small plain tiles normally have 4" showing so multiply course by 4"
2 24"X12" slates normally have 10.5" showing
3 20"X10" slates normally have 8.5" showing.
you obviously have an old roof so examples above should be adequate. hope this helps.