calculating angle of pitched roof?

[xdrive]

Hi.

Just trying to work out angle of roof. Aiming for 15 degrees.

maximum height (from ground to bedroom window sill) is 3.85m

Extension length is 4m out. The height in the current lounge is 2.5m which I wanted to aim for (but don't think it would be possible if I want to get the right angle.)

I've used tan15=0.268x by 4m (adjacent) to give 1.07m for opposite. If I take this number away from the height of 3.8m I get 2.7m. floor to ground level is 0.3m (have a couple of small steps to get out). So that would give internal height of 2.4m?



Am I missing something? Do I need to take away the height of the rafters (6 by 2) ? Also I would have to remove a few cm under sill for flashing right?

Also Is the 15 degree angle critical for velux
Or would 13-15 be acceptable.

cheers

 

[noseall]

You need to also take into account the thickness of the rafter, the depth of the b/m, the space needed under the sill to accommodate the lead/tile/batten and the depth of any lintels or beams that span any large width openings.

 

[noseall]

The Velux need that minimum - absolutely. Shallow pitch roofs do not like the flow of water to be interrupted. They need to be simple and the roof (tiling, lead, membrane etc) needs to be carefully constructed.

 

[tony1851]

At 4m out on a conventional house, you will struggle to get 15 degrees and still come under the cill; as Nose suggests, you need to take into account rafter depth, battens, tile thickness and at least one course for a flashing.
You can do a small cut-out in the roof below the cill, lined with lead, but it spoils the interior of the vaulted roof, and is another potential source of leaks if not done correctly.

 

[Leofric]

For a low pitch like that if you are doing it in tiles you need to consider the type of tiles, battens on counterbattens on membrane on sarking board on rafters. Tanalised battens of course.

 

[tony1851]

For a low pitch like that if you are doing it in tiles you need to consider the type of tiles, battens on counterbattens on membrane on sarking board on rafters. Tanalised battens of course.

Not forgetting, of course, that there's the Velux (15 degrees min.) to consider

 

[xdrive]

At 4m out with an angle of 15 degrees rise is 1.07m. with rafter, battens, redland regent tiles, (0.25m) plus flashing (0.1) and step outside (0.3m) I'm looking at external wall height of 2.13 max. From what I've read a door with frame and lintel requires 2.1m (ideally would have liked min 2.2m and showing a small gap below bedroom window for aesthetics).

But at 2.1m I could potentially achieve 15 degree angle or pretty close to it with calcs above.

 

[^woody^]

Not forgetting, of course, that there's the Velux (15 degrees min.) to consider

Unless the OP buys and fits a low pitch kit.

 

[xdrive]

Unless the OP buys and fits a low pitch kit.

So I can potentially fit velux under 15 degrees with the kit? Interesting

 

[tony1851]

Unless the OP buys and fits a low pitch kit.

Yes, they tilt the velux up relative to the roof, but they don't look very good externally.