Damp Loft

Hi
Since the cold spell has arrived I've noticed a rather worrying damp in the loft. I went up to put some boxes up there and touched a small wooden table I was storing. This has green fur on it. You can run your hand on the under side lining of the roof and it comes away soaking wet, dropping big puddles of water. The carboard boxes I have up there are now "soft".
We only moved into our house back in January and I've not spotted these issues before.
Rather than felt on the back of the roof it appears to have a plastic lining, grey on the down side and black on the tile side. The house was built in 1985 by a skinflint. Does anyone know what this type of lining is? I've only ever seen roofing felt where the plastic stuff is.
Other details: standard single apex roof, tiled outside, (clear) airbricks at each end of the house, some visible light through the eaves, about 100mm of insulation, partly boarded. There's no vapour barrier over the upstairs ceiling boards. There are no extractor fans in the bathrooms and the loft hatch is a poor fit.
I guess a lot of hot air is getting into the loft and then condensing with insufficient airflow to get rid of it.
Painters10
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Condensation has three solutions:
ventilation, ventilation, ventilation.
Fit soffit vents front and back (and side if needs be) roughly equivalent in area to a 1cm slot all the way round.
That should be all that is necessary. If the loft hatch is in the bathroom (you don't say) seal it better as well.
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Bob Mannix
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Also, check for sources of high humidity up there, such as:
No lids on loft tanks. Pumping over of the central heating header tank (hot water coming out of the expansion pipe when pump is running). Holes though the ceiling into the loft, e.g. around pipes. These are particularly bad from high humidity rooms such as bathrooms, showers, kitchens. Poorly fitting lft hatch (not draftproofed). Extractor fans discharging into the loft. Rain leaking in (check for excessive dampness down gable iand party walls and chimney breasts -- elsewhere you'd notice it on the upstairs ceilings).
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Andrew Gabriel
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On Nov 24, 11:33 am, snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote:

.
Much of this discussion has centred on increasing the ventilation, but I would agree with Andrew that checking for an unexpeted source of water vapour is important. Are there actually any water tanks up there?
also: (following my own recent experience): does the boiler flue run through the loft and has it developed a leak or come disconnected?
nnd finally: does the soil pipe vent into the loft? I had a house like that where the soil pipe vented into the left with polystyrene plug in the end. If that plug were removed you might get warm damp air coming out of the vent each tim esomeone showered or bathed.
Robert
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Thanks for all of the excellent ideas and posts on this topic.
At the w/e I was able to get up the loft and look around more.
I discovered that there were only three places that hot air could get into the loft. 1) A soil vent from the ensuite loo. This was covered over with insulation and so I don't think there's too much of a problem with it. I have to vent the soil pipe into there anyway I think? However in the same soil stack there is our utility room with nasty condenser tumble dryer. There is a gap in the boxing down there that would allow hot wet air to go upwards. Whether hot air can come up all the way up to the loft I don't know. 2) The airing cupboard (with lagged hot water tank) had 6 holes in the ceiling all a fairly sloppy fit. I have now stuck loads of silicone sealant around them to make them airtight (or near enough). 3) The loft hatch on the landing. Just a piece of wood that you push up to get out of a recess. I am looking to replace this with the PVC insulated door that screwfix sell. Unfortunately this is next to a wall and so the coving gets in the way of having a full frame around. Head scratch time.
While in the loft I cleared out the airbricks at each end (they were pretty open anyway). These are 17.5x17.5cm each. In the eaves there are small round vents spaced about 35cm apart. There are no ridge vents.
Insulation is about 100mm deep all through.
The two cold water tanks are lagged but the lagging had fallen off the central heating tank. None of the pipes felt warm so I don't think there are plumbing problems causing this.
The loft is very cold, it's certainly not a sub tropical warm area at all!
The water was virtually streaming down the inside of the plastic lining. Every few seconds it drips down.
In the short term I've emptied anything out of the loft that had fabric or wood and I am storing it in the (relatively) dry garage. The missus was in tears as some of our baby storage stuff (toys, moses basket etc) have mould/mildew on them.
The plan of action is: - Silicone seal up any small holes (DONE) - Keep a window permanently open in the utility room for the tumble dryer (DONE) - Keep bathroom/ensuite windows open on the latch (DONE) - Change loft hatch to insulated type - Add humidstat extractor to utility room - Add humidstat extractor to bathroom
Stuff I'm still not sure on: - More insulation? I don't see how this helps without doing the other things? - More eaves or ridge vents? - Active extractor fan in the loft venting out through an air brick?
Once again thanks for all of the posts.
Painters10
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I just stuck a piece of Celotex on the back of the loft hatch. (Don't do this is the hatch is under loft tanks - it's supposed to leak heat to stop the tanks from freezing.)
--
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Airing cupboards are essentially dry. Landings are essentially dry. I would prioritise on the condensing tumble dryer which is the only source of the amount of water you are getting. A path from here to the loft would be fairly bad! Does the geographical distribution of the damp in the loft indicate where the problem is centred? Not sure what you mean about the soil stack - does it vent into the loft or not?
If you find and fix the problem, it shouldn't recur - lofts should be dry - and you can go back to using it. Are the eaves vents clear (the insulation hasn't been pushed into the eaves to block the air flow or anything? The insulation should not protrude into the space between the rafters at the edges. Can you lie down at the edge and put your hand down and feel the ventilators with no obstruction? - a foolproof test.
Once the problem is fixed, the time it takes to dry out will depend on the weather - right now it will stay as it is, you need some wind and low relative humidity (which is helped by higher temperatures as well).
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Bob Mannix
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Can you explain this in more detail? The soil pipe can vent into the loft, but it should have a large one-way valve on top which only allows it to draw air in, and not let anything out. Sometimes these are made of expanded polystyrene, although that's not for insulating (just cheap and light-weight). Is that what you meant by insulated?
I would take it off and make sure it hasn't got stuck open, so that hot moist air (due to hot water in the sewer) doesn't come up into the loft.
OTOH, if this pipe is from an extractor fan, then that shouldn't vent into the loft (but they often seem to).

There's got to be a really major source of moisture for this to be happening. Is the plastic lining smooth/shiney on the inside? It should have a slightly furry surface if the right stuff has been used, and it's been installed the right way round -- this is to stop condensation pooling into droplets which then run down and drip off, although if you have a high moisture content up there, then it's going to do this anyway.

The comments in the thread about adding more insulation to solve this are misguided.

None of these sound bad enough to explain what you're seeing. My suspicion would be some route from the tumble drier into the loft, maybe through the boxing you mention, or maybe through the soil pipe vent if it's stuck open.
Also, check the paths from any extractor fans -- can they leak air into the loft?
--
Andrew Gabriel
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OK I will try and explain... there is a soil pipe that comes up through the ground floor, branching into the utility room for the washer. The pipe carries on up into an upstairs ensuite loo. In both the utility and ensuite there is a boxed section that the pipes goes up. These are floor to ceiling in both rooms. In the loft this box is open into the loft space. There is no sign of a polystyrene bung etc. Just some insulation laying on the top of the opening. I cannot see into the boxing to see if there is a one way valve on the pipe in the ensuite.

The box opening is deep in the eaves of the loft but I will do this to see if I can shine a torch down to look.

There are no extractors in the ensuite/utility or bathroom so its not those.

It looks like plastic sheeting with a raised squares pattern on it. It is grey one side and black on the tile side.

I've now blocked up the path from the utility room (tumble dryer) so that no air (or not much) can go up there anymore. We have had some trouble with smelly pipes - sink/bath overflows in the summer. I thought the fix was to flush out the drain outside (it seemed to work), but I wonder if the vent pipe is stuck open whether this would also explain the smells?
Painters10
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Andrew Gabriel wrote:

Would be interesting to know whether it's that wet up there when the weather is cold but dry. In other words, in the current conditions, I might be wondering about a leak, maybe on the ridge?
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As a follow up I think I have worked out the cause of the condensation. I racked the brain to work out why the loft wasnt damp etc when we moved in last January and looked like it had been dry for 20+ years, yet within 11 months of us being here we had damp and condensation. It had to either be a repair issue, or something we'd done.
I blocked up the hole in the utility room that had the condensing tumble dryer in it as I am sure that was the main cause of moist air getting up there (through the boxing around the soil pipes). There were no roof leaks and no other large holes to admit enough moisture.
To try and dry the loft out I hoisted a dehumidifer up there and put a 1KW fan heater on a timer to put some heat into there for a few hours a day. After running about 10days the roofing lining (plastic) is now bone dry and the damp smell has largely gone. I am drying it further so that I can put extra insulation up there (Wickes had it on special offer).
The one odd thing is that I have found a warm pipe up there. I think Andrew Gabriel suggested this as a cause of humidity: Pumping over of the central heating header tank (hot water coming out of the expansion pipe when pump is running).
This appears to occur - a small'ish pipe tees-off a main hot pipe in the airing cupboard and goes up into the loft. How can I stop this pumping up? Is it effectively telling me the pump pressure it too high? The boiler is in the garage about 15m away and was retrofitted (it used to be downstairs in the utility room - 5m away).
Thanks for all the help guys.
Painters10
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where does the small pipe go? or is it a pressure relief safety thingummybob?
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A warm pipe won't cause a problem but very hot water coming out the end of it will.

The problem is generally having the expansion pipe just after the pump, so it's usually more a pipe arrangement problem. It should go vent, feed, pump along the flow (some say but roughly that). Other than that there's a blockage or some other problem.
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Bob Mannix wrote:

Bear in mind that the added ventilation could result in lower loft temperatures. Make sure any plumbing in the loft is well insulated.
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That about sums it up I think.
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Painters10 wrote:

You need more insulation, and insulate on top of the hatch, and more ventilation, obviously eaves vents would be better (if they aren't already installed), but for now you can just add some more air bricks at each end.
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Phil L
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Phil L wrote:

No - more insulation just lowers the effective loft temeprature even more and so can cause more condensation.
Insulating and sealing the hatch could help.
Eaves vents should be a lot easier to install that air bricks I imagine.
cheers
David
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DM wrote:

It can't cause /more/ condensation, more condensation can only be achieved with more moist air getting into the loft to condense on the cold suface of the mono, which is what is happening now.

I don't think taking the gutters, fascias and eaves down on each elevation is easier than knocking out a few bricks. YMMV
The fact is, it doesn't matter if there is *no* insulation up there, water will still condense on the mono because it is the only thing seperating the loft from the outside air, unless you count the tiles, which are full of gaps and are open at the bottom anyway.
He needs to provide more ventilation and in the meantime, remove the water which is in the cycle of dripping, evapourating and condensing again, adding more insulation will reduce the evapouration bit, and more ventilation will take some of the moist air away, personally i would get a dehumidifier up there for a week or two after adding more vents and fibreglass.
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Phil L wrote:

Sort the insulation out and I'm sure there won't be any need for extra ventilation.
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but isnt normal roofing felt permeable to water vapour, but the builder used some kind of cheap plastic which is not permeable, so the water vapour from the bathroom etc is going up and getting stuck at the roof level..
hence need ventilation in the bathroom, and more ventilation in the roof because of vapour from human breath, kettles etc etc and vapour from warm air downstairs going up to a colder loft and dew-pointing up there...
[g]
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