Extension advice - Low / shallow pitch roof

Mike1983

Mike1983

Mike1983

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Hi all

In the process of getting some initial plans drawn up by an architect. Intending to have a single storey extension for the full width of the house by a projection of 4m.

The architect initially suggested this may not be feasible without a flat roof due to the shallow pitch that would be encountered.

I have however found some examples of tiles that are stated to work (and be guaranteed) down to 10 degrees (see example link below). My extension would be approx 12 degrees.

http://www.forticrete.co.uk/concrete-roof-tiles-and-slates/centurion-Reg--low-pitch-roof-tile.html

Does anyone have any advice / experiences of such things?

Thanks
 
There's quite a lot of caveats they use for the 10 degree pitch, your architect needs to agree these all can be met or it won't work.

The roof should be located in a sheltered geographical position. For example; Non coastal, not on open elevated sites, not in open countryside
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† Centurion® Roof Tiles – for use between 10 - 12.4˚: 1) The tile gauge (batten spacing) should be set at 285mm maximum and 275mm minimum. 2) The roof should be either a single or duo pitch roof shape without hips, valleys, tile vents, soil stacks, sun pipes, rooflights or solar systems. 3) The roof should be single storey only. 4) The roof should be located in a sheltered geographical position. For example; Non coastal, not on open elevated sites, not in open countryside. 5) The maximum rafter length of the Centurion roof should not exceed 5 metres (including overhang into the gutter). 6) Other roof areas above the Centurion® roof should have their own independent drainage system. 7) Down pipes from higher level roofs should not discharge onto the surface of the lower Centurion® roof. 8) The head or the tail of the tile should not be cut as this will impair the product’s performance. 9) Centurion® ventilation tiles should not be installed below 20º. 10) Centurion® tiles should all be clipped over the interlock and nailed (50x3.35mm) through the clip into the edge of the tile batten below. 11) Centurion® half tiles should be used at the verges by cutting off either the right hand roll or left hand interlock roll so that the central flat area protrudes between 38 to 50mm from the gable structure. 12) Centurion® verge clips should be twice nailed to the batten ends to secure the cut verge tiles. 13) Bonded double tiles should be used at the verge if using Continuous Dry Verge system. 14) Tiles should lie at a constant pitch across the roof and not deflect up or down over the fascia or gable wall ends which will cause gapping under the tile edges. 15) A felt support tray should be installed over the top of the fascia board to transfer any moisture contained in the batten cavity out of the roof. 16) The horizontal laps in the underlay should be a minimum of 300mm for pitches below 12.5º. 17) All lead work should conform to current Lead Sheet Association detail. 18) Forticrete recommend the use of roof ventilation in accordance with BS5250
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Tbh at that kind of pitch you're hardly going to see any of the roof so tiles will be an added expense (anything over 10 degrees isn't classed as a flat roof for your insurance fyi)
 
Thanks guys. I've passed on all the details to the architect who said he'd not heard of these tiles before but recognises the brand as a decent name. I've also passed on the installation criteria to ensure this is feasible before going any further.

Thanks
 
eviled said:
increase the pitch ?

either lower the external wall or increase the height the roof starts at
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Thanks for the idea but it's not feasible.
The outermost wall is as low as it will go to achieve the existing / standard 2400mm ceiling height and the roof starts at window ledge level of the upstairs bedrooms.
 
At the house we're buying the extension has quite a shallow pitch. Probably between 12-15 degrees. It has slate tiles over the felt to keep in keeping with the house and as far as i'm aware it hasn't been an issue (apart from for our surveyor!)

Same issues as you with the upstairs bedroom.

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I suppose one thing you could do would be to excavate further and put a step down in for a split floor level with the extension being around a foot lower which means you'd keep the ceiling height. I'm not sure i'd bother with that though!
 
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If i was doing something that Marvt74's house looks like, i would probably look to have a flat roof with railing around the sides and change that window for a door to give me a roof terrace to sit out in!
 
A flat roof is never flat to be honest and is always riskier when it comes to water collection, ingress, ponding, snow collection, etc.

15 degrees comes into my head for a shallow roof slope that's I've come across numerous construction projects where a "low" roof pitch was desired.
 
It sure of the actual degree of my ‘flat roof’ but it’s probably tiny. Width 7m by depth 4m, theres a 2 inch drop front to back and 2 inch side to side.
 
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