How to build a cylindrical roof on a victorian style house?

Question

Its an 8 sided roof which is 157" wide, here is a picture of our house plan, building the last house on the page (HA2142DR: Victorian With Appealing Veranda). The roof is on the left side of the house.

http://www.house-plans-advisor.com/victorian-house-plans.html

Answer 1

http://www.diynetwork.com/diy/ho_trellis...

That should give you an idea. Not a perfect match but...

Answer 2

Find an architect.

Answer 3

Beautiful house.  I hope you get along well with it.  I am a bit concerned with the question, though.

The plans should give you a fair amount of detail as to how the roof structure goes together.  You really need the plans to build this one, even if you are not in an area that requires building permits or planning approval.  There are some issues that require expert direction, the plans would be your best source.

It sounds like you do not have a copy of the plans.  The house you refer to does not have any 8 sided roof areas that I can identify, nor does it have any roof areas that are 157" wide.  Perhaps you are building an altered version or just something similar?

I'm bored, so I'll give you a bit on this one.  First the veranda roof.  This one is fairly simple.  The link to diynetwork.com provided by Docar should give you a bit of visual.  This roof structure will be similar, but the top will be clipped off.  A ridge board from each outside point up to the corresponding point on the house with rafters filling the space between.  Any experienced carpenter should be able to frame this without too much trouble.  If you are building on your own, this would be a good place to get a bit of help as the angle cuts can be fun to figure out.  I suppose this one would have 8 sides if it were continued to complete the shape.

The roof over the master bath is the other questionable one.  It certainly is not 8 sided.  The front view gives the impression that it is 6 sided, but in reality is should be 5 sides -- 3 equal sides on the front, 2 larger sides on the back.  If it were built with 3 sides on the back, the middle section would create a trough with the roof behind which would cause ice dam issues and certain leaks.  2 sides will divert the water away from the structure properly.

In modern construction, there would be a carrying member across the master bath in line with the front of the house.  Trusses (or roof framing) for the main part of the house would be put up first with this structural member carrying the ends.  The front 3 sides of the roof would be built similar to the diynetwork pictures, the back would be "over-framed" or built on top of the main roof for the house.

A professional should specify the size and type of the carrying member.  Again, this should be specified in the plans.  Also, there is another related structural problem with this design.  On the first floor, there is a very short wall segment between the front door and the room below the master bath (office, perhaps?) that will bear a significant amount of weight.  The plans should also detail the type of framing required to carry this weight to the foundation.  It may just be extra studs, might take a steel column.  If the framing is not sufficient, you will get cracked drywall and perhaps problems with the door at some point in the future.

Short version, if you don't have the plans you should get them before you go any further.  If what you are building is different from the design, you really need an engineer to address the structural issues involved.