How do I figure Sq ft in a ceiling

ozarkgem · February 25, 2015, 04:43:26 AM

A guy wants to put Cedar in his outdoor Cabana or Pavilion, not sure what you call it. It is 24x24' with 4/12 pitch and hip roof all the way around. So how do I get the sq ft for the ceiling?

beenthere · February 25, 2015, 05:15:55 AM

If no overhang is to be figured in and the area to be covered is the underside of the roof, then the length to the peak would be about 12.65' for each of the four roof sections that meet at a peak. Then each of the four would have an area of ½(12.65 x 24) = 152 ft². Multiply by 4 to get 608 ft².

Unless I'm missing something.
Not sure what you mean by "ceiling" but assume paneling against a raised raised roof.

LeeB · February 25, 2015, 05:54:20 AM

Yep, same numbers I got.

ozarkgem · February 25, 2015, 07:26:55 AM

it is up against the roof. I guess not really a ceiling. It would be vaulted underneath. Could you explain your figuring for me. I am horrible at math.

scshaw · February 25, 2015, 07:44:53 AM

4/12 is 4 up 12 over. So you have 4 triangles leaning towards a center...all pitched 4/12. Area of a triangle is 1/2 X Height x Base. The base of all your triangles are 24 feet...just need to figure out the height. A 4/12 is 18.5*, so you use another triangle to get this dimension...knowing the angle is 18.5* and the base length is 12 ft (to center of room) you can use CAH....Cos (18.5*) =12/H -> H=12.65.

4x0.5x12.65x24=607.2 ft^2

LeeB · February 25, 2015, 10:04:09 AM

I'm not that fancy. I used A squared plus B squared equal C squared.

Den-Den · February 25, 2015, 11:33:14 AM

Be sure to allow for lots of waste on this job!

JIM GORMLEY · February 25, 2015, 12:47:22 PM

I usually add 10% of the total square footage for waste.

Brian_Weekley · February 25, 2015, 02:19:04 PM

Trigonometry and geometry. Doesn't get any better than that! 8)

GAB · February 25, 2015, 03:01:19 PM

Quote from: JIM GORMLEY on February 25, 2015, 12:47:22 PM
I usually add 10% of the total square footage for waste.

With all the triangles involved I do not think 10% is enough.
Gerald

JIM GORMLEY · February 25, 2015, 03:28:14 PM

If you square each triangle off, and figure out sf that way, your waste is already included.

For example, when I figure sf on the gable end of a house for siding, I just figure the side of the house as 1 big square no gable and that allows for your waste. Been doing it that way for 25 years . And I'm usually pretty close, never short or over by a lot

JIM GORMLEY · February 25, 2015, 03:31:08 PM

Stupid phone,lol

ozarkgem · February 25, 2015, 07:43:40 PM

Quote from: scshaw on February 25, 2015, 07:44:53 AM
4/12 is 4 up 12 over. So you have 4 triangles leaning towards a center...all pitched 4/12. Area of a triangle is 1/2 X Height x Base. The base of all your triangles are 24 feet...just need to figure out the height. A 4/12 is 18.5*, so you use another triangle to get this dimension...knowing the angle is 18.5* and the base length is 12 ft (to center of room) you can use CAH....Cos (18.5*) =12/H -> H=12.65.

4x0.5x12.65x24=607.2 ft^2

Next time this comes up I will call you. too complex for me.

beenthere · February 25, 2015, 08:30:52 PM

ozark
You have the square footage for the ceiling. You don't need to understand the method of calculating.
What you may need to decide is how much of the cedar you will need to saw to cover that area.

As mentioned, if it is a T&G panel, like 6" wide or whatever, you will lose a bit more than twice that width in the length of every strip as you go up.

Shout out if there is a part that is confusing.Someone can surely help. Maybe some drawings will help.

ozarkgem · February 26, 2015, 05:45:09 AM

That is what I like about this forum. No matter what kind of a problem you have somebody has an answer. My brain is simply not wired for math. History, geography and sphelling I am much better at. Math problems I will just post here.

LeeB · February 26, 2015, 06:52:51 AM

Or you could just use a handy calculator such as this one. I love google almost as much as this place.

http://final-analysis.com/calculators/roof_area.htm#hipgable

ozarkgem · February 26, 2015, 07:09:29 AM

Handy little calculator. It doesn't show what I am doing though. But I will keep it for other jobs. Thank you for sending the link.

LeeB · February 26, 2015, 08:26:48 AM

I must not understand fully what you are doing then. What I think you are doing is basically putting a roof on he underside. Is that not what you are doing?

drobertson · February 26, 2015, 09:52:28 AM

Thanks for that calc, link Lee, pretty handy, saved that one for sure,

beenthere · February 26, 2015, 10:53:28 AM

Quote from: LeeB on February 26, 2015, 08:26:48 AM
I must not understand fully what you are doing then. What I think you are doing is basically putting a roof on he underside. Is that not what you are doing?

+1

Remle · February 26, 2015, 07:16:47 PM

Quote from: LeeB on February 26, 2015, 08:26:48 AM
I must not understand fully what you are doing then. What I think you are doing is basically putting a roof on he underside. Is that not what you are doing?

The link does not show calculations for the Pyramid Style Hip Roof, which he is describing.

LeeB · February 26, 2015, 09:22:43 PM

I didn't think so either but it does say that the area is the same for either style. It's in the fine print. :D

Remle · February 27, 2015, 04:50:11 PM

LeeB
Upon further examining the calculator I'm confused by the statements that the area is the same for either style in the fine print.
Please tell me if I am interrupting this wrong..
The triangle method came up with 608 sf +/-
Using the fine print of the calculator method, I get 24 x 24 x 4 x .33 = 760 sf.
Have I some how got the fine print wrong ?? Either the calculator falls apart or I'm having a mental block.. ??? ???

1938farmall · February 27, 2015, 05:38:39 PM

beenthere gave the definitive answer right out of the box. lucky no one wants to panel the sistine chapel

LeeB · February 27, 2015, 08:46:26 PM

GABLE OR HIP ROOF:
A gable roof and a hip roof of the same length and slope will have identical areas.   Enter roof dimensions below for your roof in feet, (or slope as inches rise per foot.)
If you enter only L-1, W-1, & H-1, the result will be the area of a single straight gable roof.
If you enter all six values, the result will be the actual exposed area of both roofs. You cannot enter values for Area 2 alone.
The values calculated for roof 1 and roof 2 are independent. The total will not equal their added values, as the calculator subtracts the hidden area from roof 1 at the intersection, and displays only the actual exposed roof area for the total.

   L-1W-1H-1slope1
-OR- /12   Area 1
= ft2      Total Exposed,
Areas 1& 2
Combined:
ft2      Roof 1 Hidden
ft2
Roof 2 Ridge Length
ft
L-2W-2 H-2slope2
-OR- /12   Area 2
= ft2