Wednesday, September 28, 2011

Lucarne Et Nolet Sur Arêtier

Finally into some new territory with the Mazerolle book. Up next was a dormer parked on a hip corner, or 'sur arêtier'. There was only half as much text to plow through, however this drawing also had its peculiarities and challenges to overcome  - and mislabeled portions of the drawing. I'm ready for this sort of thing now and don't let a few hiccups (or 'hiccoughs', as you may prefer) slow me down. As with the other dormer problems in the book, this one revolves around determining the shape of the noulet, which are irregularly-shaped pieces of wood that are employed instead of valley rafters. In a future post I'll take a look at this French traditional solution in comparison to other methods of dealing with dormer valleys.

Here's the drawing in the text, plan view at the bottom right, elevation views at the top:

Click on any drawing to see a larger version.

The illustration of the plan shows the noulet and their relationship to the rest of the dormer and the main roof:

The upper surface of the noulet conforms to the upper surface of the dormer roof, while the lower surface of the noulet has to conform to the top of the main roof's hip rafter, which is at a different slope than the dormer roof.

Here's a close up of the plan drawing of the noulet - notice that on their left side they are shown abutting the side of the diagonal strut which helps carry the load - note point 'L' as the intersection point:

Point H' in the above drawing appears to be the end of the hip rafter resting upon the central support beam in the dormer, however all the hinge lines in this drawing are actually at the top of the molding, which sits a bit above the wall plate. Thus, what appears to be the end of the hip rafter in the above drawing is actually, in my drawing, 3 cm above the true end point of the hip. That raised hinge line adds to the drawing difficulty.

So, I followed faithfully along with the drawing and what it indicated should be done, until I had completed the plan and the 3D development of the noulet. I then placed the noulet into the roof. Tah-dah! However there was a problem - notice the lower end of the noulet at the top of the wall plate:

Another view:

You can see that there is a hole there are the lower meeting point of the noulet, the dormer wall plate, and the side of the strut. That won't fly. That's not sound constructional practice.

Here's a look at the top end of the noulet, where you can see the triangular section which results when it must conform to both the hip rafter and the ridgeline of the dormer:

I realized that a better solution - perhaps the intended solution (?) if I assume a mis-drawing in the text, is that the triangular shape of the noulet can only join cleanly here if the lower end of the noulet can rest partially on the bevel on the hip support strut, and partially on the plate. So, I redrew, which involved raising the elevation of the plate and the dormer rafters in reference to everything else, and a whole lot of cascading little issues arose as a result. When I had straightened everything out again, I produced a new noulet section and slid it back into the dormer roof. Here's the result:

Another view:

This is a much cleaner and more workman-like solution I feel. No gaps, and the noulet conforms to the required intersecting planes, the dormer roof, the wall plate, and the hipped main roof. That's my solution and I'm sticking to it until someone can show me some way that the text's proposed version can work cleanly. In the above drawing I have sized the bevel on the strut to coincide exactly with the inner top corner of the noulet, however the bevel could be made larger with no effect upon anything else in the structure.

By the time I was done, I had built myself a virtual dormer on a hip:

A look at the plan view, with the noulet in yellow:

I then placed that dormer into another drawing where I am aggregating all the dormer models, along with who knows what else I might dredge out of Mazerolle:

A closer view, showing, among other things, the raised molding along the dormer wall plates:

From the inside looking toward the dormer - this shows the hip strut bracing more clearly:

Side elevation view:

And in context with the other dormers I have completed so far:

A plan view of all the dormers:

That's 4 dormers down and just one more to go now. The last one shown is a dormer which is situated higher than the ridge of the main roof. It also is a noulet problem though I'm sure I'll learn a few other things as well. Mazerolle hides the secrets in these drawing,s and I keep uncovering more of them as I move along.  Despite the problems in the book with the illustrations, and details omitted in the text portions, it is a brilliant work, and there is much to learn if one puts the time and effort in.

Thanks for coming by the blog today. Comments always welcome.


  1. hi chris,

    definitely my personal favorite among the dormers. the interior rendering shows how nicely it opens up the room as well.


  2. Michael,

    yes, I also like the lines. Thinking to about how a eventail dormer might look placed on the hip...

    Many thanks for your comment!



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