Another low pitch roof thread - Marley Ashmore or Plain?

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Hello All,

I would be very grateful if you could share your thoughts on the dilemma I am facing.
I have a small lean-to roof (porch extension), one plane, no ridge tiles. Rafters length is about 1.8m. Roof pitch is 22.2 degrees. I was planning to install Marley Ashmore interlocking tiles (https://www.marley.co.uk/products/concrete-tiles/ashmore) as the minimum pitch recommended by the manufacturer is 22.5 degrees. However my roofer complained that they will be "horrible" to lay.

The problem with the roof is that the original old wall to which the roof leans is not perpendicular to the side walls (while the front wall of the new extension is) resulting in roof being effectively a trapezium with 2 right angles and the roof length on the left-hand side being 2 inches longer than on the right-hand side. This is indeed quite a lot of out-of-squareness for such a small roof. All this means that the battens will need to be laid out in some kind of fan pattern. The roofers say that with interlocking tiles the fanning is not possible. I'm not quite sure of this.

So they tried to convince me that plain tiles should be installed, because with plain tiles there is plenty of room for adjustments and closing this 5cm. The minimum pitch for any plain tiles is 35 degrees, but they say that the manufacturers are too cautious and "it will be fine" and also gave me examples of existing installations where it's been done. It's hard for me to believe that going down from 35 to 22 degrees will not impact significantly the performance of the roof. I understand the problem with fanning of the interlocking tiles, but I don't want to have a poorly-performing roof.

The hole extension is done under the BC application so I'm not sure what the building inspector would say about installing plain tiles on 22 degrees pitched roof.

Could you please share your thoughts?

Thanks,

Luke
 
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resulting in roof being effectively a trapezium with 2 right angles and the roof length on the left-hand side being 2 inches longer than on the right-hand side.
Oh my effing god.:(
Could you please share your thoughts
Run?

Starting from a square point i.e. the abutment at the top, set out the tile courses adding a diminishing course at the bottom.

22 deg's is too shallow for plains.
 
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I would love to run, but alas... The square point is actually at the bottom, at the newly built front wall (why would I ask to build out-of-square wall for the new porch?), but I get your point. How do you lay tiles in this situation? Do you keep all the tiles within a given row perpendicular to the batten or should they be laid parallel to the side walls? I attach two pictures where illustrate the arrangements, obviously the battens non-parallelness is greatly exaggerated (in reality it would be 5-7mm off on one side per batten).
 

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The Wessex tile is a good option and can go down to 15 degrees

https://www.marley.co.uk/products/concrete-tiles/wessex

I done a very low pitch job with Rosemary tiles(very similar to plain tile but clay) as specified by the architect, we had to install a sort of profiled tray under it to take any water to the gutter if it got under the tiles.
 
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Do you have a picture of how the walls actually look? or is it not built yet?
 
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you do not have to fan the battens. doing so slightly messes up head laps for one.
if the top of slope butts the wall then the 50mm can easily be dealt with by your flashing.
 
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The Wessex tile is a good option and can go down to 15 degrees
Could you imagine using a Wessex (or any profiled tile for that matter) whilst 'fanning' the rafter gauge? :eek:

Agree with Data, fanning is a stupid idea.
 
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Having 2 inches more flashing on the tiles on one side would be pretty visible, no? I'm not installing profiled tiles.
 
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you simply parallel it to the bottom of the tiles.. it'll look fine
certainly better than courses of tiles dogging
 
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Actually, after thinking about it I'm starting to warm up to this idea. I will discuss it with my (new) roofer.
 
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