What's the shallowest allowable slope for a slate roof?

On Tue, 25 Jul 2017 11:54:03 -0700 (PDT), snipped-for-privacy@gmail.com wrote:


No probs with snow where you live?
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On Tuesday, 25 July 2017 20:08:07 UTC+1, mechanic wrote:



Snow load is not a problem for properly designed roofs.
NT
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On 7/25/2017 8:08 PM, mechanic wrote:

It does depend entirely on where you live. Also wind loads, and driving rain.
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On 25/07/2017 18:35, snipped-for-privacy@gmail.com wrote:

Can you give us a clue why we should believe you rather than eg BS 5534?
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Robin
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hulk hogan wrote:

I gather its too shallow to be watertight, but you can put a watertight layer underneath the slate to allow its use at any angle. Fibre cement sheet makes a good durable sarking.
NT
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Check your local library website - you may find that library membership includes online subscriptions. For example, miine includes the online OED, Times Digital Archive, Groves music and art online and BSI reports.
The relevant part of BS 5534 is
5.3.4.3 Roof pitch The recommended roof pitch and minimum head-laps for double-lap, natural, fibre-cement and other artificial slates, nail-fixed or hook-fixed, should be obtained from Table 4 and Table 5. The roof pitch should be not less than 20.
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You're lucky! My council libraries dont provide them at all - you have to go to the National Library. They have to retrieve the hard copy from off-site location. I'm trapped in the stone-age apparently.
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We had a low angle slate roof on a bit of our house. Didn't work, people couldn't make it work. Gave up, had the entire thing rebuilt with a proper roof.
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Clive George wrote:

Indeed. I had similar problems with IIRC pantiles. Slope (30 dgress IIRC)too shallow to b reliable in heavy weather.
If at all possible go for a more sensible angle. This is asking for trouble (though it CAN work)
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Problem is it is an extension of an existing roof - the existing is a cruddy felt construction and will get replaced. I the pitch of the roof could be steepened by taking one or two rows of bricks off the top of the wall to at least achieve 20degs...
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If it were my roof and I couldn't make it more than 16.8deg I would increase the overlap of the slates.
mark
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mark wrote:

Do you not think fibre cement sarking would be cheaper than 50% more slate? It would also look conventional.
The other problem with adjusting slates from 2 layers to 3 (cant think how better to explain it) is that it changes their angle for the worse.
NT
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On Tuesday, 17 March 2009 10:57:50 UTC, hulk hogan wrote:

I would never specify a slate roof at that pitch...Normally a min'm is 30 d egrees. At that shallow angle, you would need a waterproof sub layer and th e slates would have to be twice nailed at the head and at mid point otherwi se they'll lift if a strong gust of wind gets underneath. Marley Eternit do a slate appearance tile with a thin Edge called the Edgemere Duo which loo ks like slate. That has a guarantee of going as low at 17.5 degrees.
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On 14/08/2017 5:22 PM, snipped-for-privacy@googlemail.com wrote:

I will back that up. 10degrees is low.
In my experience re-slating, there is a noticeable set of water blooms on the slate below where the two upper slates bond. As you look at the slate they appear as an upside down rounded 'V'. At 30 degrees that bloom is as near as an inch from the top of the slate.
The lower the pitch the less the gravity comes into play.
Ray.
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