A reader's Roofs and roofing question: Rancher extension?

Cathy J.   from   Puyallup, United States   had this Rancher extension question.

We are considering an addition on the back of our home which is a ranch style with I believe a Cross Dutch(hip)Gable, it is T shaped. We want the addition to make the back of the house be straight across which would actually make the house look L shaped. We aren't sure just how to do the roof with the two different angles, and how we go about adding on to the existing roof?
Sure would like to hear whatever advice you can offer!

Bill's answer

We had a couple of emails back and forward, with Cathy sending me a floor plan and a couple of photos, and me saying that the floor plan was well done as this is always hard to do without really messing up the amenity of the rooms that lose their windows. And Cathy writing back (no doubt quite pleased) and telling me it was her own design etc. etc. I got down to the most important part with any job like this.

My old boss used to say to me "Let's give it a couple of coats of looking over" and that's what I did. Time spent thinking about it is never wasted.

Rancher extension - This is what the existing house looks like in a simplified form.

Rancher extension - The roof plan as if draw from scratch.

At the right is a plan of what it would look like if we had started from scratch with an "L" shaped plan. Just a larger full hipped roof. Except that the two dutch gables are not real gables anymore. Half and half gable and dormer window?
It is definitely easier to leave them in and I don't think they will look too odd.
This option is a lot of extra work, with only two roof surfaces remaining unchanged.

Below is a view that gives a better idea of the same layout.

This is the best layout if cost is no object. The roof slopes stay the same and no problems with it not matching up. It would look just "like it grew there".

It would shed snow just as easily as the rest of the house roof.

Rancher extension - An alternative simpler roof layout.

What I have tried to do here is to keep it as simple as possible, that is not altering the existing dutch gables. In fact there are only two extra roof surfaces.

The new roof extends from the original ridge, but covers a greater distance, so it has to be a shallower pitch.

In all these sketches I have drawn the existing roof at 25 deg. pitch. That is about 5 1/2" in 12". The main new roof going up to the existing ridge slopes just about half of that.

There are other layouts that you could do, keeping the same roof pitch, but they involve something like a separate roof over the addition, and this would give you a level or almost level box gutter over the inside of the house.

This layout here might not be workable either, it depends on how low a roof pitch you can go with the shingles that you have.

Snow loading is another thing, you have plenty of walls under to support the roof and extra weight, but I am not to exactly an expert what is the minimum pitch.

Rancher extension - Sketch of the roof with the curious little triangle in the plan now showing as a dormer window.

When an existing room, especially a kitchen loses it's window, a skylight, or a dormer window as I have drawn here could make it a lot more pleasant.
I'd keep the pitch of the dormer same as original roof.