pitch of roof

[climber101]

Calling the experts again please

for my planned ground floor extension (approx 3mx7m) I calculate the hipped roof pitches required to be between 14 to 15 degrees. (I reckon I can’t make the pitches any higher because I then reduce the roof flashing ‘upstand’ too much at one of the the sloping end pitches of the hip roof slope too much at corner of upper window)

Is that a lowish pitch or sound fairly common for extension I describe? (curious because it sounds low pitch to me)

Assuming I can find a match to my existing tiles that can handle that pitch with whatever overlap required could you advise please whether at that pitch is it common

a) to find tiles that will handle that pitch and ?
b) common to be having to put in extra defences against rain or not ? like double layers of breather fabric? and whatever else.

Many thanks

 

[noseall]

15 degrees is shallow but still within the tolerance of some interlocking concrete tiles.

What tiles are on the existing building?

 

[climber101]

thanks noseall, sorry I don't have a more precise description as yet but they are red concrete interlocking ones that look "wavy"! house is only 9 years old so believe they would be of a more 'modern' type

 

[^woody^]

This has been covered ( ) in the roofing section

Also some wavy tiles go down to a lower pitch than others

And don't design a roof pitch based soley on trying to acheive a flashing upstand by a cill. There are methods of detailing a tight cill/roof junction

 

[climber101]

thanks woody, i am intrigued with your comment about detailing a tight cill/roof junction so will go looking for any details of this . Currently where one of the side pitches is near to one corner of window cill i had left a bit over 150mm for upstand so if i can reduce this somehow to be tight to cill i reckon i can improve pitch up to 17 degrees.

Also some of the houses i have looked at dont seem to have a full length tile under the flashing at this interface? and the flashing seems to dip a bit making it look like i might not need the flashing to go as high as i think (didnt explain that too well)- i will try to find details of where you place top tile before putting flashing on etc.