Shed roof leaking by capillary action?

Lobster

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Jan 7, 2011, 3:39:38 PM1/7/11

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During the recent bad weather, I braved the elements and went down the
garden to my shed, which is just a glorified storage cupboard really.

Having spent a fair old time during last summer replacing the roofing
felt, I was a bit miffed to find a puddle on the floor inside. However
it's not at all clear where this has come from - after the snow had all
gone I checked the felt and it looks fine.

However, I'm wondering... the roof is pitched, and there's a 3" overlap
in the felt running the length of the roof, and the puddle was more or
less below this. The overlap is not nailed down, but glued with
bitumen-type stuff from a tin - admittedly not particularly well, but
certainly enough to stop the felt from getting wind under it, say.

At the time the snow was thawing - which was when I saw the leak - I
realised after the event that melting snow was being retained over the
overlap area by leaves, twigs etc which had landed before the snow. So
I'm wondering - is it conceivable that the soggy mess of snow and leaves
during the thaw could have allowed water to travel uphill, up the
overlap and through my roof?

If not I'm a bit stumped!

David

robgraham

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Jan 7, 2011, 4:00:52 PM1/7/11

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Is it possible that there was frozen condensation on the inside of the
roof that thawed when it got warmer ?

Rob

alans-computer.local

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Jan 7, 2011, 4:10:09 PM1/7/11

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Lobster <davidlobs...@hotmail.com> writes:

>
(snip)
It could be condensation on the ceiling because the ceiling was kept
below freezing by all the snow on top even when the air temperature went
above freezing.

Hugh Jampton

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Jan 7, 2011, 4:21:54 PM1/7/11

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On 07 Jan 2011 21:10:09 +0000, alans-computer.local wrote:

> It could be condensation on the ceiling because the ceiling was kept
> below freezing by all the snow on top even when the air temperature went
> above freezing.

I think you're right - that's the reason. Went into our loft just before
Xmas to get decorations and stuff. Was very worried when I found lots of
things wet - drops of water covering things. Could not find any leaks in
the roof. Took things back up there a couple of days ago and all was dry
again (thank heavens).

Also found similar in a shed - also no sign of leaks in the roof.
--
Regards,

Hugh Jampton

george [dicegeorge]

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Jan 7, 2011, 4:47:30 PM1/7/11

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I get leaks in my valleys with snow
cos the snow and ice lower down stop the melt water taking the usual
path, it finds its way between the lead sheets of the valleys, up a bit,
then drips in the house.
[g]

Lobster

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Jan 7, 2011, 7:16:10 PM1/7/11

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On 07/01/2011 21:00, robgraham wrote:
> On Jan 7, 8:39 pm, Lobster<davidlobsterpot...@hotmail.com> wrote:

>> At the time the snow was thawing - which was when I saw the leak - I
>> realised after the event that melting snow was being retained over the
>> overlap area by leaves, twigs etc which had landed before the snow. So
>> I'm wondering - is it conceivable that the soggy mess of snow and leaves
>> during the thaw could have allowed water to travel uphill, up the
>> overlap and through my roof?

> Is it possible that there was frozen condensation on the inside of the

> roof that thawed when it got warmer ?

Although condensation was the only other possibility I could come up
with, I rather discounted it as there seemed to be quite a lot of water
present in one puddle (half a cupfull?) whereas everywhere else was bone
dry - can't see why it would be so localised if condensation was the cause?

David

Donwill

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Jan 8, 2011, 2:55:56 AM1/8/11

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Perhaps the localised condensation inside was caused by low temperature
imposed by the localised snow retention over the overlap area as described.
Don

dennis@home

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Jan 8, 2011, 3:05:24 AM1/8/11

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"Lobster" <davidlobs...@hotmail.com> wrote in message
news:c1OVo.39409$B77....@newsfe29.ams2...

> Although condensation was the only other possibility I could come up with,
> I rather discounted it as there seemed to be quite a lot of water present
> in one puddle (half a cupfull?) whereas everywhere else was bone dry -
> can't see why it would be so localised if condensation was the cause?

Three inches of overlap isn't going to stop the water going up between the
strips if there is three inches of ice and snow covering it.
The ice and snow act like a dam and let the melting water underneath rise
up.
The glue might, but only if its perfectly sealed.

I have seen the same thing happen on my shallow angled plastic roof and that
has about 12 of overlap but no glue.
Its not an issue on a carport though so it doesn't need fixing for the odd
day it happens.
I have seen the condensation dripping too, but that happens along the
length, not just at the joints.

Tim Lamb

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Jan 8, 2011, 4:59:17 AM1/8/11

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In message <ig95s6$th6$1...@news.datemas.de>, "dennis@home"
<den...@killspam.kicks-ass.net> writes

Condensation will run down under a sloping roof and then drip at purlins
or some other discontinuity.

regards

--
Tim Lamb

Lobster

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Jan 8, 2011, 5:56:10 AM1/8/11

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On 08/01/2011 08:05, dennis@home wrote:
>
>
> "Lobster" <davidlobs...@hotmail.com> wrote in message
> news:c1OVo.39409$B77....@newsfe29.ams2...
>
>> Although condensation was the only other possibility I could come up
>> with, I rather discounted it as there seemed to be quite a lot of
>> water present in one puddle (half a cupfull?) whereas everywhere else
>> was bone dry - can't see why it would be so localised if condensation
>> was the cause?
>
> Three inches of overlap isn't going to stop the water going up between
> the strips if there is three inches of ice and snow covering it.
> The ice and snow act like a dam and let the melting water underneath
> rise up.
> The glue might, but only if its perfectly sealed.

ISWYM - yes that answer does make sense. Certainly the seal won't be
watertight in that context... but don't think I'll be ripping it all off
to start again any time soon!

David

harry

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Jan 8, 2011, 10:25:29 AM1/8/11

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This sort of thing is often caused by snow blowing in and then
melting. The snow will blow in through places rain can hever get
because it's so much lighter then rain drops. Even travels uphill.

robgraham

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Jan 8, 2011, 10:48:55 AM1/8/11

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Yep, I've seen that in a Scots' slated barn roof during a blizzard -
well slated but no membrane. Sarking would have got slightly damp but
was well ventilated so would have dried out quite happily.
Rob.

Skipweasel

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Jan 8, 2011, 11:35:02 AM1/8/11

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In article <f3aa2a04-971a-468f-8006-735aa26a6658
@fm22g2000vbb.googlegroups.com>, harol...@aol.com says...

> This sort of thing is often caused by snow blowing in and then
> melting. The snow will blow in through places rain can hever get
> because it's so much lighter then rain drops. Even travels uphill.

You also get snow and ice forming little dams that allow water to build
up and overflow a barrier which in normal circumstances would suffice to
exclude water.

--
Skipweasel - never knowingly understood.

John MacLeod

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Jan 8, 2011, 12:16:03 PM1/8/11

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Yes. Worth remembering that most Scottish roofs are both close-
boarded with sarking and roofed with Ballachulish slate which is much
rougher than Welsh slate and provides natural but controlled
ventilation for the sarking.

Mr Pounder

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Jan 8, 2011, 2:15:39 PM1/8/11

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"Lobster" <davidlobs...@hotmail.com> wrote in message

news:cSKVo.58829$Dz5....@newsfe27.ams2...

Strange things happen in very cold weather.
My garage roof leaked; it no longer leaks.
My driveway gates would not close, they now close.