I am trying to reform. Change is hard. I can handle it.

I should build a gambrel. It would fit nicely with a clay/wood chip wall system. I would only have to deal with the small gable in the peak.

How about a broken back salt box, curb roof?

Tim

So does anyone know good proportions for a gambrel (the hipped gable, dutch gable) roof. specifically 0' to top plate, top plate to bottom of gable, to gable peak. It is hard to design looking at an elevation because of the fact it always looks taller than when its built (especially with a hipped roof).
Is it 2/3 to 1/3. Does wall height and width have something to do with it? 1:1.618?

Maybe a more basic question. How do you all determine the height of your walls compared to the width? Or is there even a relation? ..........roofs.

Mo,

I come from a Japanese carpentry background, so bear that in mind. I'll offer what lessons I've gleaned there in response to your question.

The hipped gable is called an irimoya roof in Japan and is one of the more common roof forms over there. The proportion of gable to the roof plane is determined on the basis of dividing the fall line down the roof plane (on the gabled end) into 5 or 7 sections, and then making the intersection of the gable at the hip a certain proportion of that 5 or 7 parts - 3/5, 4/7, 5/7th, and 4.5/7th, are some of the more common proportions used. The irimoya usually has a relatively large gable proportionate to the roof size, and in fact to maximize the size of gable it is typical make the hips irregular (i.e. not 45˚ in plan). That is to say, the slope of the roof at the gable end is slacker than the slope of the body of the roof on the non-gabled sides.

Tim,

who wrote, "How about a broken back salt box, curb roof?"

well, I'd like to see an illustration of that! And "why?" - I'm curious to know what advantages you perceive in that design.

Chris, that was just me. I was wondering if a broken back would fit into the curb roof definition.

Two pitches on either side of a structure. It doesn't say up or down, + or -, broken back or a hump.

One definition commented on two or more slopes. I began to wonder where one might see more than two. So I have a curb/half mansard and I'm planning on adding a shed roof to one side, it would have both, a hump and a broken back roof line. I see similar additions/wings on local buildings.

By the way I just tried looking for one of your first pictures which had just such a set up, am I right?

Didn't the Japanese have gambrel's?

The hip is a broken back, to one extent.

Tim

Tim,

the Japanese do list the Mansard roof type in roof layout texts - it is referred to as a 'koshi-o-re' roof, which literally means "hip-fold". It is not a common roof shape in Japan, though I was able to find at least one example:



As to your question, "I began to wonder where one might see more than two. So I have a curb/half mansard and I'm planning on adding a shed roof to one side, it would have both, a hump and a broken back roof line. I see similar additions/wings on local buildings...", I can offer some comments.

One thing I note about timber roofs peculiar to European timber framing traditions is that they are most often placed atop stone or brick walls. One reason for this relates to a scarcity of timber, historically speaking. Europe was in fact substantially denuded of forest by around 1500, and fully timbered buildings became problematic. Timber framing in Europe soon became largely confined to roof timbering, and that remains true to this day. Secondly, traditional houses had minimal insulation ,and lacked central heating until comparatively late. Third, most areas of Europe have long had greater population densities than most parts of North America, and a greater proportion of construction done in an urban context, where buildings are located quite close together, if not directly abutting, as in row houses. The Mansard was created in urban Paris, for example. All of these factors have produced architecture generally bereft of eaves, and less easy to add-on to with additions/wings, as you mentioned.

For those buildings constructed fully detached, the eaves were still minimal, as the stone walls were well able to withstand the weather. Lack of timber resources made additions and wings rather more difficult to integrate with thick stone walls, so they were rather less common. Now, I am speaking rather generally here, as for instance, Swiss timber/log farm houses typically have been all-wood affairs with deep eaves. Let's put that aside for the moment however.

One of the difficulties with the Mansard roof type is that the lower pitches of the roofs are quite steep - thus to add any significant amount of eave projection requires the roof extend quite far down toward the ground. To create even a modest overhang then, one would end up with a dark and cramped under-eave space. The Mansard doesn't really work so well as it is, when you try to put eaves on. Obviously, the solution is to reverse/fold the roof back at the eave transition so as to create eaves, as you will note I have done in the pictures of the Mansard I framed. This is not a novel solution by any means, however what I noticed in looking at lots of Mansard roofed structures, with the reverse roof fold at the wall plate to effect eaves, is that the way the eave is added on is structurally weak in most cases.

The typical way the eave extension is added to the roof is by scabbing it onto the steeply slope lower rafters. And the weakest point of all is the corner of the eave, where it projects out from the side of the building and forward at the gable. I saw lots of Mansard roofs with added eaves where the corners of the roof were sagging.

After looking at the problem for a while, along with studying Mansard roof framing shown in several 19th century carpentry texts, I came up with a solution using some ideas I took from Japanese carpentry. I made the eave rafters cantilever off the interior wall instead of scabbing them on to the lower rafters. I then parked the lower rafters directly atop of the eave rafters at the fulcrum point, which was directly atop the wall plate. The eave rafters then attached to a ledger which was affixed to the interior timber wall of the upper story.

Here's a picture showing the cross-section of the roof to give you an idea:




The circular line visible in the drawing is there to show how I arrived at the basic proportion of the roof planes.

For dealing with the weak outer corners of the eave I employed a diagonal cantilever, which is essentially, in form, a backed hip rafter sliced in half along its length. There are better solutions to this problem but in consideration with the budget for that project, this seemed a good compromise.

The term 'broken back' is something I would rather avoid - not because it doesn't make sense, but because the word 'broken' doesn't, uh, market so well to describe any aspect of a roof. Another term for a hip rafter that makes sense to me is 'descending ridge'.

I really wish I could re-edit these posts after putting them up.

Well, I wrote above, "For dealing with the weak outer corners of the eave I employed a diagonal cantilever, which is essentially, in form, a backed hip rafter sliced in half along its length. There are better solutions to this problem but in consideration with the budget for that project, this seemed a good compromise."

Here's a picture of that diagonal cantilever:



This solution carries the very end rafter quite well, however the next two rafters in from the corner are not so well supported. There is a perimeter fascia strip running along the lower edge of the roof, atop the rafter, and this helps carry those two rafters with marginal support. I also used timber screws to fasten them in place, and they were decently rigid after that.

Thinking more about the terms 'curb roof' and Mansard, and following on from the definition of 'curb roof in the link provided on page 2 of this thread by Will Truax, A Dictionary of Architecture and Building, Biographical, Historical, and Descriptive, I though it might be helpful then to illustrate the curb roof in comparison to Mansard roof. These are my opinions, for what they are worth, and I welcome further commentary. Roof terms, from the searches I have done on the web, seem hopelessly confused, and misinformation abounds - it wouldn't hurt to try and straighten out the mess, surely?


So, to start with, here's an example of a roof I think that fits the description of 'curb roof' the best, since the white band defining the break between roof pitches does look a lot like a curb (kerb for those of you in England!):



Here's a picture of another 'curb roof', with 2-sides, from Williamsburg VA:



Here's another 2-sided curb roof:




This then would be a 2-sided Mansard, due to the lack of 'curb':



And finally, here's a 4-sided Mansard:

Thanks... if you find some more "evidence," like a book, please pass it along.

Thanks Chris.

I am always interested in "barn ethnicity."

Given the fact Mansard (previously dubbed "gambrel") roofs are of French origin, I would guess French barns would have them, as they make good haylofts, etc.

But do we see French barns built this way?


And to interject another point, the picture of the thatched Dutch barn you posted (#17195, bottom) actually seems like an "inverted Mansard," meaning the lower section is not as steep as the upper. So the relation of pitch in a Mansard can create convex or concave forms, it seems.