Joined
·
1 Posts
I have been asked to roof a geodesic dome house. Does anyone have a simple way or formula to measure the number of squares on the house? Carl
Roofing a Geodesic Dome house
1 - 20 of 24 Posts
Here you go - http://en.wikipedia.org/wiki/Dome_(mathematics)
I'm not a calculus expert, but I don't think there is a formula for measuring surface area of a geodesic dome (a geodesic dome is not really a dome, but a polyhedron, so the link above is not much help).
From what I could tell after a google search, you have to know the surface area of the individual planes, and sum them. I.e. figure out how many shingles it will take to cover each triangle, multiply by number of triangles that size (may be that all of them are the same size, I can't remember), and then throw in some ungodly waste factor because it's all hips.
I don't know how the ones we did were estimated either, but I could ask if you're still around.
From what I could tell after a google search, you have to know the surface area of the individual planes, and sum them. I.e. figure out how many shingles it will take to cover each triangle, multiply by number of triangles that size (may be that all of them are the same size, I can't remember), and then throw in some ungodly waste factor because it's all hips.
I don't know how the ones we did were estimated either, but I could ask if you're still around.
Joined
·
1,237 Posts
The surface area could be approximated by the surface area of a sphere minus an estimated percentage that is truncated at the bottom. Try and figure out you drip edge, there is a challenge. But seriously I would imagine there would also be a pretty high waste factor on the roof .
Was the rest of your post not serious?
No. Drip edge == circumference.
What I would do is tell them straight up that it is going to be a job where the materials are just what they are. The surface area of a sphere should be greater than the dome so that gives you a max, but then you have to add waste so the sphere may be closer to right. Just one of those things where they have to understand that the cost is very hard to set beforehand, and if wasn't sure I would either turn it down or try to talk them into letting me charge them by the hour.
Joined
·
156 Posts
I would use a waste factor of at least 20%. If you have never done a dome home, you are bound to make a few mistakes and use up material in a hurry!
I have know 2 different roofers that have done dome homes and they both told me to run away!!
I have know 2 different roofers that have done dome homes and they both told me to run away!!
Joined
·
1,237 Posts
Each of the polygons making up the dome has interfaces with the adjoining polygons. Rake edge, drip edge, some kind of flashing, hip/ridge caps, nothing at all. I was reflecting on the one or two I have seen locally and in I could not recall what was used.
The rest of my post was serious.
Tough crowd
Tough crowd? Maybe, but you can't post gobbleygook on most forums and not get called out.
You said: "The surface area could be approximated by the surface area of a sphere..."
And you were absolutely right. Then again we can approximate the surface area of a cube with a sphere too, depending on how accurate we want our approximation to be. Or, we can measure the area of one face of the cube and multiply by six, and have more than an approximation.
"...minus an estimated percentage that is truncated at the bottom".
Most I've seen aren't a truncated sphere, but elongated slightly at ground level, like a short squat bullet. A lot of the ground level vertical walls will be broken up with windows, doors, siding, etc- so add another guestimate to the approximation and estimated percentage.
The drip edge thing was just the third strike, and what I decided to comment on. I see your point now though, and yes that is a difficult detail to figure out. Ours has lasted a couple seasons leak free (knock wood), but I'm not sure we'd do it the same.
Anyway, you were right about the waste factor.
You said: "The surface area could be approximated by the surface area of a sphere..."
And you were absolutely right. Then again we can approximate the surface area of a cube with a sphere too, depending on how accurate we want our approximation to be. Or, we can measure the area of one face of the cube and multiply by six, and have more than an approximation.
"...minus an estimated percentage that is truncated at the bottom".
Most I've seen aren't a truncated sphere, but elongated slightly at ground level, like a short squat bullet. A lot of the ground level vertical walls will be broken up with windows, doors, siding, etc- so add another guestimate to the approximation and estimated percentage.
The drip edge thing was just the third strike, and what I decided to comment on. I see your point now though, and yes that is a difficult detail to figure out. Ours has lasted a couple seasons leak free (knock wood), but I'm not sure we'd do it the same.
Anyway, you were right about the waste factor.
Joined
·
1,237 Posts
I get your points, but it was not IMO gobbleygook. It is a closer approximation to a sphere than a cube. Truncating a base and allowing for windows and doors and a sort of apron the comes down to the ground would certainly be part of the take off.. I would not expect the OP to bid the job directly off a few internet posts. My suggestions may or may not have helped the OP, but it would be an approach I would likely take.
I am not a smart-ass or a wise-guy. You will find most of my posts have substance and will be useful to the topic.
Further
Levity is is used with mixed results on the web. Aside from sticking in a winking smiley or a LOL here and there, one's intent can easily be misconstrued.
I know. I enjoyed your post about ice in the gutters so much that I didn't care you hadn't done an intro. You obviously know what you're talking about and I'm sure there is a lot I could learn from you (esp re: metal).
Let's agree to disagree on the dome, but for the record I have done one. When you actually start roofing it, you realize each triangle took x shingles, and that you could fairly easily have estimated almost the exact number of bundles, even though the waste is ungodly. That mathematics agrees with this real world method is complete coincidence.
I could definitely use some work on my levity. Apologies and cheers.
Joined
·
1,237 Posts
It's all good and I prefer to begin with mutual respect. Later, when there is a serious disagreement we can have a real pissin' match :laughing:
One of domes I have seen locally IIRC had ***xx facets.
A tip for your next one. The manufacturer recommends dutch-lapping the hips. Do the flat bottmed ones first passing the hips 3", do the intersecting ones coming back over 3" again. This gives a 6" dutch lap.
Attachments
1 - 20 of 24 Posts
Join the discussion
Join now to ask and comment!