I ran into an old friend today who told me about some problems he
had/his having with his roof, and I would welcome any advice/comments
from anyone here who has any experience with such matters.
He lives in a bungalow, which was built in the sixties, and about two
years ago he started having problems with the roof leaking. He got a
firm in, who had been recommended to him, to look at it and they advised
a new roof - they quoted him £11,000 for the job, including UPVC
guttering, soffits, etc, which he agreed to.
The new roof was fitted 18 months ago. At the time he queried the felt
they used, which he said was no thicker than wallpaper - whereas the old
felt was quite thick - and he was told that this was what everyone used
nowadays and that it conformed to the current British Standard. After
the new roof was fitted he started getting quite bad condensation
problems, so he got the roofing firm back in.
They said that their roof was perfectly ok - but they didn't know what
was causing the condensation problem - although they advised fitting
ventilation in the soffit area. He had this done but the problems still
persisted. Things got so bad that he called in a surveyor, at further
cost, who advised fitting ventilation tiles along the ridge. Again he
has had this done (by another roofing firm, having lost confidence in
the first), at more cost, but things are no better - in fact the new
firm said that the ridge tiles hadn't even been fixed properly, so it
seems that the first roofers did a fairly poor job anyway.
It is definitely condensation, there are no leaks, and he -
understandably - is at his wits end. He is convinced that the problem is
caused by the flimsy roofing felt - the sale of which, we understand,
has now been discontinued - and I tend to agree with him.
Can anyone offer any advice or hope whatsoever for this poor chap - who,
to add to his worries, has just suffered a bereavement (which is why I
happened to meet up with him again)?
Until I see him again I can't tell you much more than I've already told
you about the ventilation. He has had eave ventilation fitted, and now
ridge ventilation, but the problem still persists. The thing is, prior
to the new roof - when he had no ventilation fitted - there were no
condensation problems. Can you explain this?
Thinner felt. Not as good insulation but probably fits better than the
old stuff so doesn't let the air flow. Warm moist air coming up and
condensing on roof. Probably needs better loft insulation plus more
ventilation. I've noticed new roofs in our road are all fitted with
quite large roof vents that were not needed previously.
On Sat, 06 Jan 2007 19:31:28 +0000, a particular chimpanzee named
The 'felt' could have been a breathable membrane (such as Tyvek,
Klober, Permoforte, etc).
The traditional way of preventing condensation from causing damage to
the fabric of the building is to keep the roof void ventilated. This
was (and still is) done by allowing enough space at the eaves to
permit air to flow through the roof void. In most roofs this is a
continuous 10mm gap to the soffit or the equivalent area. Where the
roof void is not a big open space (such as a loft conversion, or a
mansard roof), then a gap between the rafters needs to be maintained
and ventilated at the top and bottom. The gap at the top should
always be less than that at the eaves (off the top of my head I can't
remember exactly why, but it is for a good reason). The ventilation
at the ridge should be equivalent to a 5mm continuous gap, and the
eaves increased to 25mm.
Breather membranes work differently. They are designed to allow water
vapour through from inside, but not liquid moisture in from outside.
They don't require cross ventilation. What they do require, however,
is for the ceiling under to have a vapour barrier to the warm side of
the insulation, and any gaps, such as loft hatches, downlighters,
etc., sealed. There should also be no ventilation to the eaves or
ridge to prevent moist air from the outside being drawn in. I have
seen some roofs fitted with breather membranes dripping wet on cold
winter days. The manufacturers claim that this will evaporate quickly
and doesn't cause any permanent damage.
If one is using these membranes, you should either ventilate it in the
traditional way, or seal it and allow it to 'breathe'. One of the
problems (IMHO) is that builders/roofers tend to do a mix of both
methods, i.e., they think that a breather membrane will allow them to
reduce the amount of ventilation without reducing the amount of
moisture penetrating the roof void. OTOH, traditional felts were very
vapour resistant anyway, so unless the roofers did something to block
the ventilation, there won't be any more moisture up there than there
If your friend has now gone down the route of ventilating the roof
void irrespective of the type of felt, he needs to make sure it's done
-Have at least a 10mm gap to the eaves, and make sure that the
insulation doesn't block the air path (but see above if it has dormers
or is a chalet bungalow).
-Seal up any loft hatches with draught-strip, and seal any other
-Ensure that any water tanks have close-fitting lids.
-Add additional insulation to reduce the temperature difference
between the felt and the internal air (and save money too).
"If no-one on the internet wants a piece of this,
It would be interesting to know what the original outer roof covering was
and age, example, Natural Slate, Clay Rosemary type. And what as it been
replace with now.
As regards of re roofing again, in my opinion, that going over the top.
There's got to be a better option. £11,000 sounds a lot, unless its a
complicated very large roof.
To have the roof sprayed will be the biggest mistake he'll make. Its
condemned by the National Roofing Federation. This method is the last straw
for a roof on a building that is shortly being pulled down in the near
future, just to keep thing from falling off.
Its got to be a problem with venting.
I think it had those square interlocking concrete tiles, and I believe
that they have been replaced with something similar - I'll clarify all
of this when I speak to him again.
I'm not necessarily disagreeing with you, because you clearly know more
about roofing than I do, but how do you explain the fact that he never
had the problem before with the original, thicker felt? Surely if the
inside of the roof lining - felt, membrane, whatever the correct term -
is cold then the warm air rising from within the house will condense on
that surface? Presumably the only way to stop that would be to fit a
membrane that maintains a differential temperature between its two sides?
Something that makes me slightly skeptical about the ventilation
solution is what I observe in a wood-shed that I have at the bottom of
the garden. This shed - a typical construction for storing logs,
open-front, slatted sides, etc - has a roof made of box-profile steel
sheets. At this time of the year, ie when it's cold, the inside of the
roof fairly drips with condensation. Now this shed is almost as well
ventilated as the middle of a field but, because of the inevitable
temperature difference between the interior and exterior surfaces of the
roof, moisture quite naturally condenses on the inside.
I have a similar problem in my small workshop, even though the door is
left open all the time, which has the same type of roof as the
wood-shed. I had decided some time ago that next summer I would take the
sheets off, fit some plywood or chipboard sheets, and refit the
box-profile sheets on type.
I'm pretty sure that will solve the problem, but what I am doing is
surely analogous to fitting a thick insulating membrane on my friend's roof?
I've tried to give as much info as I can on your behalf to
free.uk.trade.roofing . Please feel free to add as much more as you can to
help resolve your friend problem.
One more thing that might help is, as the loft ceiling insulation been
altered while re roofing. can you give any details. On both groups so I
don't have to re post.
Is there a personal first name Mr Giles ?.
Giles will be fine, thank you Keith. I will post this to both groups, as
The loft insulation has not been changed in any way. To answer some of
the other points raised: I'm not completely sure why the roof had to be
replaced, he told me that there had been problems with leaks and that a
new roof was advised. He did tell me the type of tiles that were fitted,
but I have forgotten the exact name - they were definitely Redland
something or other, and I think the name 'Wold' came in to it. The new
tiles were almost an exact match for what was on there previously.
The condensation problem affects the loft space only, and there were no
problems before re-roofing. The property is in Birmingham, and was built
in the early sixties.
If Redland or Marley tiles have been used, both companies do have a
technical departments and
technical support that will answer any question. I have spoken to Redland
for there advice but not knowing the full history I can't answer all there
questions. They want to know if there as been a specification, type of
tile, pitch of roof and it would be handy to have the surveyors report
ready. Redland Technical on 08708702595 Wait for a representative to answer,
you may have to wait for one to be free. If its Marley tiles then phone
Marley, If you have problem finding the phone numbers let me know.
Many thanks, Keith, this is very helpful and obliging of you. I did post
a reply to an earlier post of yours, but it hasn't appeared on my server
so I will repeat it here:
"Keith, I will be speaking to my friend later on today, and I will try
to find an answer to all your questions - why the re-roof, etc. Redland
Stonewolds were the type of tile that he said. He did also tell me
something about the new tiles that were fitted - but largely that the
roofer used tiles that cost about £2.30 each when he could have got
something similar for less than a pound.
I have already passed on your advice about the foam - which was actually
my suggestion (blushes deeply), and that idea/thought has now been
firmly abandoned. I am very grateful for your considerable help here. It
is not my problem, but my friend is going through a bad time at the
moment and I would like to help him as much as I can.
I spoke to my friend again this evening and asked him for more
information about his roof. He said that the reason for the re-roof was
because there had been a few problems with leaks which had apparently
been difficult to locate, also some of the rafters had bent under the
weight of the tiles and needed replacing. In addition to this some of
the felt had also rotted away. The tiles themselves were in reasonable
condition, but he decided to have new ones fitted when they stripped the
He said that the new felt/membrane that the roofers fitted was called
'Cromar Protect 1F'. He also tells me that in the last few days he has
had some additional ridge ventilation fitted, so now it is a matter of
waiting some time to see if this helps the roofspace dry out - a
surveyor looked at the problem yesterday and said that the roof timbers,
and the brickwork of the chimney that comes up through the loft, had
very high moisture levels.
I think that I've covered everything.
Cheers - Giles
Right, I've been on the www site of 'Cromar Protect 1F'. It states "a non
breather membrane that requires venting" There's is your answer to the
problem. The only thing you haven't mention or didn't ask is, what pitch is
the roof. If as I think, its a low pitch roof, this will add to the
problem, extra vent required. Lets hope that the additional vent your friend
has had put in is a success.
Yes - sorry, I forgot to say - the roof does have a low pitch. As you
said, we will now have to hope that the extra venting sorts the problem out.
Many thanks for your advice, you have been exceptionally helpful.
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