predominate roof shape 50%rule?

Hi All:

Im a bit confused when it comes to the 50% rule for predominate roof shape.

Can someone please help me better understand the rule in “ENGLISH”?

Lets say for example i come to a house that has hip on the right, rear and left side elevations but a large gable over the garage in the front? how do i determine the 50% rule?

Any help is appreciated.


Take class, start with Nachi’s free wind mit class. There is no 50% rule

Took the class.

This is from the online exam:

Predominant Roof Shape

Predominant Roof Shape

The predominant roof shape, that which is greater than 50% of the elevation, should be selected for that elevation. If an elevation has a Hip roof and it includes a gable and the total length of the gable bottom chord is greater than 50% of the wall upon which it sits, the elevation is classified as Gable. And elevation that has a Hip roof may also have more than one gable.
If the gable bottom chord of any ONE of the gables is greater than 50%of the wall upon which it sits, the roof shape for the elevation is classified as Gable. When more than one gable is located on an elevation, the lengths of the gable bottom chords are NOT to be added together in order to determine the greater than 50% rule. Even if a gable is less than 4 feet high at its highest point and the gable bottom chord is greater than 50% of the wall upon which it sits, the elevation is classified as Gable.
Elevations that have gables less than 4 feet high and have gable bottom chord lengths that are 50% or less than the wall upon which they sit are NOT classified as Gable.


I thought they updated that. Read the New 1802 form, that is not how it is figured now.

That is from an old class. The rules have changed. Time to take a new class.

ok well, i just took the online class from this site and passed the exam. So i guess the online class is outdated. Time for an update?

Im confused because i was under the impression that the rule was 10% of the total footprint.


ok all cleared up now. Great help from a fellow member. Case closed :slight_smile:

OK, got some other pics of roof geometry. Let me know what you think. It is predominantly a hip roof but has 3 of these modified gables. Is it a hip or do you have to measure them off to decide if it is a non-hip?

Add all of the perimeter of the home, divide the length of the total of all other roof areas by total of the perimeter. IF the answer is greater than 10% then it is not Hip.

Yep, already did the measurements and with its gables it is considered non-hip since those gables came out to 20%.

they look less then 4 feet tall to me. if so they are not considered?



The height is going to matter for the gable bracing, not the geometry.

Just wait, it will keep getting better and better. Before this is all done the rules will look like the tax code. No one will know whether to crap or wind their watch. Just when you think you it figured out, they change it again and as someone said, time for another school to try and figure out what the frapping form says this week. I love it. I just talked to a contractor last week or so and he asked if I was doing these and when I told him, “not any more” he said he wasn’t either until someone figures out what they want but he wouldn’t put his name on one of those forms due to the liabilities. What a cluster.!

The height is not a factor in this report

Gable bracing makes no difference in this report, you are wasting time figuring if it is braced, or not.

Dennis, right, it really doesn’t make a difference as there’s no credit for bracing or not, but not really wasting time since you still need to answer correctly because it is there. Just don’t knock yourself out trying to figure out if height is a factor. If the house was not built after 2002 than it’s a simple answer.

its not simple, it can be retrifitted, balloon framing, masonry,ect. but its still a waste of time because noone cares