What's the shallowest allowable slope for a slate roof?
hulk hogan
degrees. Is that too shallow? Googling implies that 4:12 is the
shallowest you can go with slate. That's 20 degrees.
PS: does anyone have a digital copy of BS 5534 they could... 'make
available for download'?
Thanks.
neverwas
> My architect has specified slate on a roof with a slope of 16.8
> degrees. Is that too shallow? Googling implies that 4:12 is the
> shallowest you can go with slate. That's 20 degrees.
>
and artificial) can be used on lower pitches with a waterproof
sub-roof - design to depend on exposure, area etc. And that seems to be
the case from eg
http://www.marleyeternit.co.uk/products/TechnicalServices/FAQs.aspx?pcat=1&pcatname=Tiles+%26+Slates
and http://www.hayday-construction.co.uk/Hayday_Shallow%20Pitch.pdf. I
offer this only to help you search on. It is to be hoped that someone
with real knowledge will be along shortly.
--
Robin
meow...@care2.com
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
OG
"hulk hogan" <misterun...@gmail.com> wrote in message
news:0a783ccc-d5f0-4481...@j35g2000yqh.googlegroups.com...
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°.
Clive George
news:0a783ccc-d5f0-4481...@j35g2000yqh.googlegroups.com...
> degrees. Is that too shallow? Googling implies that 4:12 is the
> shallowest you can go with slate. That's 20 degrees.
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.
The Natural Philosopher
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)
hulk hogan
> hulk hogan wrote:
> > My architect has specified slate on a roof with a slope of 16.8
> > degrees. Is that too shallow? Googling implies that 4:12 is the
> > shallowest you can go with slate. That's 20 degrees.
>
> I've never used/lived with it but I was once told that slates (natural
> and artificial) can be used on lower pitches with a waterproof
> sub-roof - design to depend on exposure, area etc. And that seems to be
> and http://www.hayday-construction.co.uk/Hayday_Shallow%20Pitch.pdf. I
> offer this only to help you search on. It is to be hoped that someone
> with real knowledge will be along shortly.
> --
> Robin
Hmmm. That doesn't sound like what he's specified. The spec mentions
an underlay of 'Tyvek Supro'.
hulk hogan
> "hulk hogan" <misteruncalled...@gmail.com> wrote in message
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.
hulk hogan
> Clive George wrote:
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...
mark
"hulk hogan" <misterun...@gmail.com> wrote in message
news:0a783ccc-d5f0-4481...@j35g2000yqh.googlegroups.com...
If it were my roof and I couldn't make it more than 16.8deg I would
increase the overlap of the slates.
mark
Harry Bloomfield
Surely, within limits, what matters is the overlap? The greater the
overlap the more shallow the roof can be made.
--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk
meow...@care2.com
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
Bruce
>
>Surely, within limits, what matters is the overlap? The greater the
>overlap the more shallow the roof can be made.
They words here are "within limits".
Even with greater than 50% overlap, you won't get a watertight slate
roof shallower than 20 degrees.
The Natural Philosopher
Given a certain windspeed, what matters is how high the water can be
driven. if its more than the rise of a tile, it will climb up the tile.
The uber flat roof stuff is laid with interlocking joints I seem to remember
hulk hogan
> Harry Bloomfield wrote:
> > After serious thinking neverwas wrote :
> >> hulk hogan wrote:
> >>> My architect has specified slate on a roof with a slope of 16.8
> >>> degrees. Is that too shallow? Googling implies that 4:12 is the
> >>> shallowest you can go with slate. That's 20 degrees.
>
> >> I've never used/lived with it but I was once told that slates (natural
> >> and artificial) can be used on lower pitches with a waterproof
> >> sub-roof - design to depend on exposure, area etc. And that seems to
> >> be the case from eg
> >> and http://www.hayday-construction.co.uk/Hayday_Shallow%20Pitch.pdf.
> >> I offer this only to help you search on. It is to be hoped that
> >> someone with real knowledge will be along shortly.
>
> > Surely, within limits, what matters is the overlap? The greater the
> > overlap the more shallow the roof can be made.
>
> I am not so sure
>
> Given a certain windspeed, what matters is how high the water can be
> driven. if its more than the rise of a tile, it will climb up the tile.
>
> The uber flat roof stuff is laid with interlocking joints I seem to remember
I think I'll be ensuring that the pitch is at least 20degrees by
raising the high end of the roof further up the wall of the main
building (it's a lean-to). At that pitch at least there will be
specified acceptable head-laps etc given in BS5534. You'd think it
specifies a minimum pitch for a reason, and upping the headlap by a
'finger in the air' amount at lower pitches has no guarantee of
success. I looked at the interlocking 'slates' such as Redlands
Cambrian, but if plain real slate is possible, it'd be preferable,
since it looks better. Apparently the interlocking joints on these
single-lap systems work like miniature gutters which direct water down
onto the lower course of slates.
The architect has been saying things like 'I think 17 is within the
tolerances' and 'remember the underlay membrane is a second line of
defence' both of which I think are... well, he's not a roofing
contractor.
I couldnt find anything about using fibre cement sarking on the
internet - is the idea that the roof would be waterproof even with no
slates, making the slate decorative?
Jim
>The architect has been saying things like 'I think 17 is within the
>tolerances' and 'remember the underlay membrane is a second line of
>defence' both of which I think are... well, he's not a roofing
>contractor.
>
>I couldnt find anything about using fibre cement sarking on the
>internet - is the idea that the roof would be waterproof even with no
>slates, making the slate decorative?
This thread is quite interesting since we've just been having an exactly
similar conversation with our architect, who has drawn a roof at 22
degrees inclination and has specified it as a flat roof with slates for
decoration.
I emailed Marley and they sent me a "Below Pitch" spec which describes
laying sarking, two layers of felt, and a membrane under a normal slate
roof at these kinds of angles. It's a bit belt-and-braces but sounds
like the correct thing to be doing.
I haven't had a roofing contractor's opinion yet on it.
meow...@care2.com
Yes. The slate also has one more function: its the robust layer, it
stops falling objects breaking the fibre cement. So it takes both
layers working together to provide all the required functions for a
long lived functional roof.
NT
Mike Barnes
We had a new single-storey extension roofed with slate at 20 degrees
about ten years ago, and despite being in an exposed location in a wet
part of the country, it hasn't given any trouble at all.
We were constrained by the height of the first-floor windowsills, and in
order to get as much as 20 degrees slope and still have adequate
headroom at the low end of the roof, we sloped the floor. It's about
three inches lower at the far end, which in practice is virtually
unnoticeable.
--
Mike Barnes
Bruce
>
>I emailed Marley and they sent me a "Below Pitch" spec which describes
>laying sarking, two layers of felt, and a membrane under a normal slate
>roof at these kinds of angles. It's a bit belt-and-braces but sounds
>like the correct thing to be doing.
>
>I haven't had a roofing contractor's opinion yet on it.
I'm not a roofing contractor but that roofing system is clearly designed
to makes the slates, or tiles, redundant.
hulk hogan
> We had a new single-storey extension roofed with slate at 20 degrees
> about ten years ago, and despite being in an exposed location in a wet
> part of the country, it hasn't given any trouble at all.
Good to know.
The Natural Philosopher
My experience of that was that after a while the felt goes.
And a costly strip and redo is in order.
Jim
>> I emailed Marley and they sent me a "Below Pitch" spec which describes
>> laying sarking, two layers of felt, and a membrane under a normal slate
>> roof at these kinds of angles. It's a bit belt-and-braces but sounds
>> like the correct thing to be doing.
>>
>> I haven't had a roofing contractor's opinion yet on it.
>
>My experience of that was that after a while the felt goes.
>
>And a costly strip and redo is in order.
The other option seems to be to use a modern plastic tanking membrane,
hot welded at the joints, rather than felt. But it's unclear whether
most contractors would be familiar with this approach, or what the cost
implications are.
The Natural Philosopher
> In uk.d-i-y, Jim wrote:
>> hulk hogan <misterun...@gmail.com> wrote:
>>> The architect has been saying things like 'I think 17 is within the
>>> tolerances' and 'remember the underlay membrane is a second line of
>>> defence' both of which I think are... well, he's not a roofing
>>> contractor.
>>>
>>> I couldnt find anything about using fibre cement sarking on the
>>> internet - is the idea that the roof would be waterproof even with no
>>> slates, making the slate decorative?
>> This thread is quite interesting since we've just been having an exactly
>> similar conversation with our architect, who has drawn a roof at 22
>> degrees inclination and has specified it as a flat roof with slates for
>> decoration.
>>
>> I emailed Marley and they sent me a "Below Pitch" spec which describes
>> laying sarking, two layers of felt, and a membrane under a normal slate
>> roof at these kinds of angles. It's a bit belt-and-braces but sounds
>> like the correct thing to be doing.
>>
>> I haven't had a roofing contractor's opinion yet on it.
>
> We had a new single-storey extension roofed with slate at 20 degrees
> about ten years ago, and despite being in an exposed location in a wet
> part of the country, it hasn't given any trouble at all.
>
I think the crappy extension I had failed after about 15-18 years.
It was really the last straw that broke the camels back.
With water coming in in several places, the overhead cable that stopped
the roof pitch being decent was undergrounded, the house was demolished,
and proper angles used.. ;-)
> We were constrained by the height of the first-floor windowsills, and in
> order to get as much as 20 degrees slope and still have adequate
> headroom at the low end of the roof, we sloped the floor. It's about
> three inches lower at the far end, which in practice is virtually
> unnoticeable.
>
Thats generally why this is done. I have to say I had a bloody valley
join with an existing roof, and they are buggers. If its a leanto or bow
window type thing, there isn't the huge volume of water in on spot.
If you have interlocking machine made tiles, then its not so bad. The
water can't drive around the interlock easily.
But I still say unless there are overriding reasons to have a low pitch,
don't. And know what you are getting into.
Martin Bonner
The slate would provide pretty good UV protection for the felt though,
so the felt should last longer.
Bruce
Oh, absolutely.
But a slate roof at the right pitch should last much longer.
meow...@care2.com
Sounds like someone did it wrong. If you use fibre cement sarking,
overlapping at any joints, the felt etc isn't even needed. The slates
act as a windbreak, so there is much less tendency for water to be
driven up the sarking overlaps than occurs with the slates. I've
experience of such a roof with no felt or membrane, and no trouble at
all.
NT
colinh...@gmail.com
Phil L
Cheers for the ancient info.
Roof tiles can go as low as 22 degrees
tabb...@gmail.com
> Hey boys dont even bother laying slates any lower than 30degrees Forget that underlay etc keeping it watertight Wider slates can go slightly lower Dont try and change whats been tried and tested our years Architects Dont try and reinvent the wheel 👹
NT
mechanic
tabb...@gmail.com
> > On Tuesday, 25 July 2017 18:35:10 UTC+1, colinh...@gmail.com wrote:
> >
> >> Hey boys dont even bother laying slates any lower than 30degrees
> >> Forget that underlay etc keeping it watertight Wider slates can
> >> go slightly lower Dont try and change whats been tried and
> >> tested our years Architects Dont try and reinvent the wheel ��
> >
> > Not sure why you bring this up now, but fwiw my one very shallow
> > roof has been doing fine for a long time.
>
NT
newshound
rain.
Capitol
Martin Brown
and freeze thaw will shorten their life. This typically only shows up as
a problem after many decades and on paths that have also been weakened
by walking on - notably the path up to the TV aerial on a chimney.
There are special tiles for low slope roofs with a second underside
ripple on them to make them more weather proof against bad weather.
--
Regards,
Martin Brown
Vir Campestris
> Roof tiles can go as low as 22 degrees
Andy
Robin
> Hey boys dont even bother laying slates any lower than 30degrees Forget that underlay etc keeping it watertight Wider slates can go slightly lower Dont try and change whats been tried and tested our years Architects Dont try and reinvent the wheel 👹
>
--
Robin
reply-to address is (intended to be) valid
Andrew Gabriel
This is done by having the waterproof layer under the tiles
(I think it's glass fibre resin laid on ply), and the tiles are
really just a decorative layer on top.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
Andrew
angle the greater the overlap needed, and *most* importantly with wide
tiles, they absolutely must be laid flat. Never 'curved up' at the
eaves. As a consequence the undercloak (?correct term) must tilt down
by about 3 degrees to stop water running back under and down the top of
the barge board at the gable end.
However, just try telling that 19 out of 20 'professional roofers'
who haven't a clue.
LSR
>>
> Marley Modern can go down to 20 degrees (AFAIK)
--
Reentrant
dave...@googlemail.com
> My architect has specified slate on a roof with a slope of 16.8
> degrees. Is that too shallow? Googling implies that 4:12 is the
> shallowest you can go with slate. That's 20 degrees.
>
> available for download'?
>
> Thanks.
I would never specify a slate roof at that pitch...Normally a min'm is 30 degrees. At that shallow angle, you would need a waterproof sub layer and the slates would have to be twice nailed at the head and at mid point otherwise 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 looks like slate. That has a guarantee of going as low at 17.5 degrees.
RayL12
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.