Angle of roof extension

[billm]

A friend is planning a single storey extension to his semi as per this diagram.

A newly qualified Architect has done the plans and has told him he can't have an extension that is 3.5m long (even if he gets planning permission) because the angle of roof won't be sufficient for water run off. But he can have a 3m long extension as then the angle will be OK. And a 3m extension doesn't need planning permission.

So now my friend is having to redesign the kitchen/interior layout and boiler location to make up for the loss of the extra 0.5m.

Is there a minimum angle for a tiled roof and will an extra 0.5m length on the extension really make that much difference to rain running off the roof or is the Architect just quoting the theory from his books rather than practical knowledge which he has yet to learn.


image shack

 

[Alastairreid]

He can go to the 3.5m depth if the pitch of the roof is adequate for the tile he will be using, this seems to be the architects problem.
He can either change the type of tile to suit the pitch or raise the pitch to suit the tile by engineering a lead roof around the window cill.

 

[billm]

Thank you, I have found this explanation after reading your post. Perhaps choosing a different tile will solve the issue.

http://www.myredlandroof.co.uk/general-advice/why-pitched-roofs

 

[^woody^]

Sack the architect.

A tile for a lower pitch can be used - down to 11°, or a sealed sarking is fitted below the tiles

 

[Alastairreid]

At a guess the architect will be trying to specify the same roof covering as the main roof, he will know the minimum pitch required for those tiles, cant get it at 3.5 so shortens the depth to 3m to get the pitch..

 

[Jerrythezinc]

Alternatively your friend could consider a metal roof and retain the 3.5m depth and only need to raise the roof by 200mm keeping well below the upstairs window

 

[Alastairreid]

Aha another metal man!

Welcome aboard jerry.

 

[Jerrythezinc]

Its always good to have more than one opinion, thanks for the welcome!

 

[Adrian80]

Look on the tile manufacturers website. The minimum pitches are all listed.

Just use trig to calculate the angle of the pitch of the desired roof.

tan-1 (opposite / adjacent)

tan-1( height below window / 3.5m)

or
tan(minpitch) X desired length to give the minimum height of the window from the top of the garage.

Personally, i would withhold some of the fee, buy them a maths school book, and tell them to read it.

 

[garyo]

'normal' roof tiles have a minimum pitch of around 35 degrees. Some interlocking tiles will go down to around 20 degrees. I used the Marley Ashmore why I was in a similar situation:

http://www.marleyeternit.co.uk/Roofing/Concrete Tiles/Ashmore Interlocking Double Plain Tile.aspx

As other posters have said - you need to tell us the angle you're aiming for.

Gary

 

[pinenot]

The last .5 could be sprocket ed, thereby matching the original tile/pitch and achieving the original extention length! if this is of any help -

View media item 60246

 

[^woody^]

The last .5 could be sprocket ed, thereby matching the original tile/pitch and achieving the original extention length! if this is of any help -

View media item 60246

You wont get tiles to fit and be weathertight at that sort of connection of two pitches

Plus the loading on the horizontal joists would need much deeper ceiling joist sections. Let alone how the eaves would be finished with such deep ceiling joists

 

[freddiemercurystwin]

View media item 60246

LOL

 

[RonnyRaygun]

Well, everyone else has made a suggestion so here's mine. You could have a crown roof.
Google it for pics, but basically it means you can have the same tiles and pitch as the main house until the height limit is reached, then flat roof to wall.

 

[hardmetalking]

there'a only room for one zinc king on here.......

That makes you the Prime Minister of Zinc Jerry....... you have been elected but you'll never be king!