Mansard Roof construction

robbshowe · August 22, 2012, 04:41:26 AM

I have been asked to design and manufacture a cafe which has a mansard roof. Has anyone had experience with this style of roof and can possibly share some ideas? I have sketched my thoughts down and feel that the use of dragon beams and ties at the external corners will provide a suitable base for the principal corner rafters, similar to a hip roof construction. Any advice would be appreciated. I can provide photos of what I mean if this helps.

Jim_Rogers · August 22, 2012, 07:55:56 AM

Years and years ago, I drew a dragon and cross joint for a client for his small shed design idea.
It was never built.
I didn't like his choice for plate meeting tie joint in the corner.

But here it is:

There are methods for joining the cross to the tie and plate when they are at different elevations.
And you need to consider the assembly sequence when you design it so that you can put it together.

I got this design from a book written by a man from England. I'll find his name and the title of the book if you need it.
I'm sure you would be able to purchase one over there.

Usually a Mansard roof has a pretty steep slope.
What were you thinking about the slope for the roofs?

Jim Rogers

robbshowe · August 22, 2012, 01:57:38 PM

Hi Jim. The cafe has a 45 degree slope, which is quite short in length. The length of the slope is only 1.2m, sorry I mean approximately 3'9" in old money! I have successfully made a hot tub enclosure using a dragon beam/tie arrangement which worked out fine. I used a half lap where the wall plates met which simplified things considerably. My main design issue is how best to make the remainder of the roof! - never having made a Mansard roof of any kind before. I have ideas but thought there is little point re-inventing the wheel if someone has done this before. I imagined making a series of long principal roof trusses linked by purlins but need to sketch this in some detail for you to evaluate. Is it possible to attach a pdf file if I scanned in an A4 sheet of the architects concept drawings or even my sketches so you can get a better overview of what I am face.d with? The roof has a large flat expanse with a short slope on three elevations. I will be working on the design tonight so should be able to supply you with firmer ideas thereafter.

Jim_Rogers · August 22, 2012, 02:05:59 PM

Robb:
Yes you can attach a pdf if it doesn't go over the file limit.
Or you can email it directly to me, if you wish.
Email address is jrsawmill (at) verizon (dot) net

See link below post window for adding attachments and file limits.

robbshowe · August 23, 2012, 05:10:48 AM

I will attempt to send a couple of pdf's to indicate what I think will work. One sketch merely gives an overview of the general roof structure, the other gives a bit more detail for the external corner showing the hip rafter set up. I've yet to look at the internal corners required in other areas of the building! Please let me know your thoughts.

robbshowe · August 23, 2012, 05:45:46 PM

Had a call from the client today who has had feedback from his local planning department and they have insisted on a more traditional pitched roof construction. This will consist of a series of principle kingpost truss assemblies linked by purlins. Back in my comfort zone - that's a result! However, I must thank you Jim, for taking the time to provide some advice. I have always found you Americans to be most helpful, having trained with Steve Chappell of Fox Maple fame! He ran a course in Asturias in northern Spain which I attended a few years back. He spoke well of you Jim - presumably he either knows you personally or perhaps merely of you? Anyways, I do enjoy the design challenges I meet every day and appreciate the repository of information freely shared by the Framers Forum - thanks!