Mansard pitch roof

[markblue777]

Hi All,
Another roof related question. So after my other post with regards to roof joists Robin said about using a Mansard pitch roof instead. After looking at this and getting the missus approval I have a question with regards to pitch. How our house is there is a small kick off on the front that has about a 35 degree pitch then it goes to the main house (image below to show you what I mean) My question is can I have a mansard pitch so it has the 35 degrees at the front then say a 45 and the side and then a 28-30 degree at the back this way I can make the if the flat roof with a few skylights in key areas.


Circled in red is the roof we want to line up with



Cheers
Mark

 

[RogerBoyle]

Its possible to do anything you want. Once you have building control agreeing LOL

they will be the ones that say yes or no . the building of it is easy enough .

 

[markblue777]

Haha. Yeah I suppose that's the thing really. I just want to be able to draw something up to show them and then see what they say. If I can get it as close as possible to the end product all the better.

 

[RobinBHM]

Its possible to do, although the hips wont be at 45 degrees as viewed on plan. You arent looking for a huge pitch change so shouldnt cause any tiling problems, although it might make your chippie scratch his head a bit. One thing to be aware, this roof style will cost more as you are combining a tiled roof with a pitched roof and the more complex roof will take a bit longer to pitch.

You dont have to keep the same roof overhang on each side so could vary this if it helps with pitch angles

If you can tie in the new roof pitch with the existing one it would make the extension blend with the house well.

 

[markblue777]

Hi Robin,
The pitch selected for the front of the extension should blend in nicely with the existing so that should make it look as if it has been there.

I have a 34 degree pitch at the front (matching what exists already)
I have copied the 34 degree pitch for the rear as well and then finally the side has a pitch of 50 degrees.

Here are some shots of what I have done. Do I need to build in some run off for the flat section or can this be "padded out" when it comes time to laying felt etc.

Also I imagine that there needs to be 2 corners cut at a compound angle so the corners of the roof have something to run on when the tiles go over.

Is the general design of this of or is the structure well of. from what I saw it looks ok but i just need some like metal strapping to connect the joists to each other.

In the first image how could i get the 300mm wall to map into the roof correctly. I am at a loss with this section. I was thinking of just like running the tiles over it (as long as building control say thats ok) but I am not sure maybe there is a neater way to finish it

Thanks for the help all, Im just trying to get my head around it (trying to source some books / learning material on the subject to)

Cheers
Mark

 

[RobinBHM]

I cant tell if the ceiling is vaulted or a flat roof with ceiling joists at about top of wall level.

Assuming conventional flat ceiling, you will need structural timber or steel beams with short posts to support a ring beam that the common rafters fix to. The ceiling joists act as collars to stop the roof spreading.

The 300mm wall would have the tiles run over and finish to a verge, in the same way as a gable ended house.

To match an existing roof, work down from the tile line taking into account insulation as required. The tyvek site has an excellent download, showing detailing for pitched roofs, they recommend fully sealed warm roof with ventilation only at tile level

 

[markblue777]

Thanks robin I'll take a look at the site. The ceiling I am going for is vaulted. I know that alters the construction a bit. Is it just beefed up timbers (here I'm running with 2x6's

Cheers
Mark

 

[markblue777]

well change of plan. Going for the 34 degree slope at the front to match existing (tiled) then go onto a flat roof which will have epdm and then it will slope off the back at about 29 - 30 degrees (tiled)

I think this is the most straight forward way and it gives us some nice ceiling height in the areas we want with a good allowance for skylights.

Thanks for all the help it really allowed me to understand what is possible and that is not going to cost me the earth