Percentage Flat Roof Calculation Help Needed

[Clive35]

Hi

Can anyone out there help me please.

I’m trying to calculate the percentage of flat roof on a house for insurance purposes as they need to know what percentage flat roof it has.

The main roof is a pitched tiled one but has a flat roof dormer projecting from it at both front and back.
In addition to that there is a flat roof extension on the ground floor.

I’ve had a go at trying calculate it but I’m uncertain if my maths is correct, please see the attachment.

Thanks to anyone who can help

Clive

 

[The Highlander]

Hi

Can anyone out there help me please.

I’m trying to calculate the percentage of flat roof on a house for insurance purposes as they need to know what percentage flat roof it has.

The main roof is a pitched tiled one but has a flat roof dormer projecting from it at both front and back.
In addition to that there is a flat roof extension on the ground floor.

I’ve had a go at trying calculate it but I’m uncertain if my maths is correct, please see the attachment.

Thanks to anyone who can help

Clive
View attachment 37776

Looks OK to me.

You do have some rounding errors but they only affect your final answer if it is rounded to more than 3 decimal places.

For example: you have quoted it as 38.1767% when it is actually 38.1770% to 4 d.p. (but both of those would round to 38.177% )

(And you should use a lower case 'm' for metres, so: m² not M²; but that's not a major problem.)

Hope that helps.

 

[The Highlander]

@Clive35

I noticed your rounding errors when I was checking your results on my little calculator.

When carrying out calculations like these you should only round when you get to a final answer.

If you are not comfortable (or don't know how to) storing intermediate answers in your calculator's memory then a spreadsheet is a useful way around that problem.

I plugged your numbers into an MS Excel™ spreadsheet and got the results shown below.

I added a second (copied) 'Sheet' with the numbers displayed to 10 decimal places (just to show you that they are stored inside the program to a much higher accuracy). If you look down at the bottom left-hand corner of the spreadsheet you will see the Sheet Tabs that allow you to switch between sheets.

​

I have attached the spreadsheet for you to have a look at (if you have MS Office™; if not it can be opened online and by most other spreadsheet apps too).

NB: This forum isn't set up to attach anything other than pictures or text files so I have changed the name of the file from "Flat Roof.xlsx" to "Flat Roof.txt" (so I can attach it) and you will need to change it back to "Flat Roof.xlsx" (after you Save it) for it to 'work'. That's if you want to get it, ofc.

Here are the the calculations that the spreadsheet produced (to both 4 & 10 d.p.)

 

[Clive35]

Hello Highlander

First of all, thank you for taking the time to reply its much appreciated.

Yes, I’ve messed up by using a capital M for metres as you rightly pointed out.

As far as rounding up is concerned, I have to admit I haven’t been too fussy about it as I think insurance companies probably wont even work the percentage out to any decimal places ie they will more than likely work to the nearest whole figure, but I understand what you are saying.

My main concern was if I’d worked the percentage out correctly, I didn’t want to put 38 or 39% on the insurance documents only to find out if I did have to make a claim they’d tell me the percentage was incorrect.

Thanks again

Clive