I went into our loft to put the Christmas tree away and the rafters were wet and some of the cardboard boxes up there were damp. At first I wondered whether some of the snow had melted and leaked through an iffy ridge tile but I've been told it is likely to be condensation. I'm puzzled how the warm air gets up there because there's a good ten inches or so of insulation (rolls). I've been told that once the cold spell goes everything will return to normal. I am concerned about the timber getting wet and all the boxes (and presumably their contents) getting soggy. Is it likely to just be condensation and nothing worse, and is there anything I can do to limit it? Would wedging slabs of insulation between the rafters help?
Unless you have foil backed plasterboard or some other vapour proof barrier moisture will migrate through the ceiling and insulation into the loft and then condense on the cold underside of the roof. You might limit the effect by ventilating the roof space but this will reduce the temperature considerably and if you have loft water tanks and pipes they may suffer!
Insulation (rolls)wont stop water vapour moving from of high vapour pressure area to an area of low Vp. your easiest and probably best solution is to make sure that your loft is adequately ventilated, also your habitable rooms particularily bathrooms and kitchen. Don
Youve got to get rid of the vapour before it hit the cold inside of the roof covering. This is done by venting through the highest part of the roof. Take the dodgie ridge of and replace with a vent ridge or a couple of vent tiles below the ridge.
It's interstitial condensation - and I've got the very same problem - and in my case, it's caused mostly by the steam from the bathroom that seems to find its way into the well insulated attic through various nooks and crannies [1] leaving tiny globules of frozen moisture [2] hanging on the underside of the roofing felt.
Normally this steam is vented from the attic with the airflow through the roof from the westerly winds that occur at this time of the year, but these winds have changed direction or stopped for fairly long periods leaving the moisture to collect - and because of the insulation, there is no heat in the attic now to simply dry it.
As a matter of interest, this situation has only occurred since we had the cavity and loft insulation installed about three years ago in a traditionally-built house of the mid-1970's (with absolutely no loft insulation installed at the time).
[1] I cannot persuade SWMBO to have a bath with the bathroom window slightly open to vent the steam for the life of me - and I've tried for many a year, but still cannot 'educate' here. Please don't show her this post or I'll be making my own breakfast tomorrow. LOL
[2] Glitters rather fetchingly in torchlight though - but roll on the return of the westerlies, and summer, to get rid of it!
There are some things to check, but it may be inevitable in this weather.
You need to make sure air is not moving from the house into the loft. Check for leaky loft hatch, oversize holes around pipes which pass through the ceiling, recessed spot lights, and any other holes. Check none of your extractor fans exhaust into the loft space. A cracked lath and plaster ceiling will let moisture through too. An ordinary plasterboard ceiling, even without vapour barrier won't let enough moisture through, subject to 3.
Make sure the loft tanks have close fitting lids so they aren't evaporating moisture into the loft. The CH expansion tank will get warm it times, and if uncovered in a cold loft, that can release lots of moisture. If the CH tank is pumping over, it will get hot, and the pumping over should be fixed.
The loft needs to be ventilated. If it doesn't have ventilation, eves vents can be easily fitted and will create enough air changes.
However, at this time of year, the roof surface will be colder than even the outside air temperature at night due to heat loss by radiation, and in this scenario, there's nothing you can do to prevent moisture forming in a ventilated loft (well there is, reduce both the ventilation and the insulation, but that's not realistic). This shouldn't account for large quantities of condensation though, so I would look at the causes above.
I'm following this thread with interest, as last week (putting Xmas decs back) I noticed with some alarm that there was moisture on the roof felt too. However I went through a process of putting loads of vent holes in my soffits 4 years ago, and haven't had any problem since.
Not wanting to panic, I had a good look round, and it seemed the moisture was concentrated ... wait for it ... on the bathroom side (we live in big "L" shaped bungalow). Of course sods law says that this is the part which is boarded over and used for storage as ... wait for it again ... it's nearest the hatch !
The bathroom ceiling is well sealed .. however the hatch is not, and I suspect this is where the vapour is rising through.
So what's the best way to seal a loft hatch ? And is it best to always assume there will be *some* moisture in a loft, and not store cardboard or paper goods, unless sealed with plastic ? Because (you guessed it) most of our stuff in the loft is in cardboard boxes (with lids ... when an old employer moved offices they over-bought on proper document archive boxes by 20 ... they are really sturdy and easily collapsed for storing flat)
From our point of view you may be heading for a rotting roof?????
And gathering that UK temps. have been similar to ours; offer the following comment..
Here in Canada there are several requiremnts.
1) Bathroom fans etc. to exit damp air directly to outside. Or open window.
2) Effective vapour barriers on the 'warm' side of all insulation. If not most types of insulation will get wet, cease to insulate properly and can cause rot and mould.
3) Attics to have minimum 0.3 per cent (that's 3 square feet per 1000 sq. feet of attic floor spac) ventilation arranged so as to permit cross ventilation. In some case fans, sometimes controlled by a humidistat are also used. Ignoring these measures can cause serious rot and mould problems can occur. Long winters here!
Couple of other points; another guideline is that, in our climates, not more than one third thickness of the insulation shall be inside the vapour barrier. This is because some warm and therefore moist house air will always penetrate the insulation, after all it's the air spaces that provide the insualtion!. Otherwise the warm house air will condense (same thing as 'sweat' on a window etc.) somewhere inside the insulation barrier and soak it.
It has been mentioned that while a 'proper' vapour barrier is required that sometimes a good coating of 'oil paint' can be used as a somewhat less effective vapour barrier.
Anyway here I am meticulous about not having vapour escape into and especially 'ice' (Yikes, snakes alive!!!) in my attic or on roof rafters. For the two houses we have built and lived in since 1960.
Our temperature today and yesterday was around plus 1 or 2 Celsius (Mid 30s Fahrenheit). S'posed to go below zero tonight and a couple of centimeters of snow tomorrow? Previous snow all gone, only used the new snowblower couple of times. Studded snow tyres on all four wheels of the vehicle. A 2 WD pickup truck that is inherently, when unloaded, light light at the back. Cos haven't yet put the extra weights in the back. Must do that tomorrow Saturday.
Hope these comments help. Roofs can be expensive! And not easy to work on.
Treated roof timbers in my case, and one this cold spell finishes, the roof will dry out.
No fan fitted - and impossible to train the wife to open the window when she's in the bath.
True, but with retrospective insulation in a 30 year old + property, the expense would exorbitant in rip-off UK.
No problem with ventilation here normally, under 'normal' conditions, I could 'fly a kite' in the draught in the roof space.
Quite true.
I presume that you would apply that to the underside of the ceiling? I use emulsion paint there.
As an 'old retired carpenter' I'm not that worried as long as there is enough roof space ventilation to get rid of it - and this is normally the case here where we have more rain than snow (usually). :-)
We don't normally have more than a thin layer of snow where I live in the UK - so the lot we are having now is rather unusual - and causing some rather unnecessary problems to some.
Thanks for that info Terry, and its nice to see some of the differences in construction between our two countries.
I use sticky tape as the hatch isn't a very good fit. I hardly ever go into the loft - it's not used for storage.
If the loft is used for storage bear in mind that every time you open the hatch lots of warm moist air from the house rushes into the loft and condenses as it cools.
Does your roof have breathable felt or traditional?
If breathable - these can be used without ventilation (according to the manufacturers), provided that there is a vapour barrier underneath and all the rooms producing moisture have adequate ventilation (i.e., extract fans). They say that some interstitial condensation could occur, but that it will evapourate and be ventilated through the membrane in summer.
If a traditional felt- this should be ventilated at the eaves along two opposite sides. You can do this with breathable felt too. Make sure the gaps are free and not blocked by insulation. Again, try and reduce the moist air entering the roof space by draught-stripping the loft hatch and using the extractor fans and trickle vents.
As others have said, insulation isn't a vapour barrier. Once the vapour's in the roof space, you need to allow it to ventilate away. What you don't want to do is block any ventilation path by putting insulation between the rafters.
I have seen roofs covered with breathable membranes literally dripping with condensation. If I had a roof like that, I wouldn't leave anything up there that could be affected by moisture.
I do have some holes around the pipes in the airing cupboard and either the loft hatch of its recess isn't square so there's a bit of a gap (a few millimetres) at one end, so these require some attention.
They do.
There are no vents in the soffits but there are none in any of the (identical) houses in the street. There are a couple of air bricks in the gable end but strangely, only in our house; none of our neighbours have them.
Thanks for the reassurance that it is "just" warm, moist air from the house condensing on the unusually cold roof. Hopefully when this unusual weather goes away, so will the problem.
We do have a fan in the bathroom but it's a 4" connected to flexible ducting, so it's not ideal. Sadly the window lintel got in the way and prevented us fitting anything bigger or better.
Likely non breathable I would guess. If it looks black and shiny and like it's made of sackcloth painted with black gunk, it's probably old style sarking which is not breathable. Not sure what else they used then but although Tyvek (breathable) has been around since the late 60's I not sure if it was widely used then - probably very expensive.
Best seal all gaps between rooms and loft inc' ceiling roses and pipe entries. Have a loft hatch with a seal. Then paint the loft floor with oil based paint.This will seal enough to prevent water vapour moving from house into the loft where it meets cold surfaces and condensates. Some paint the ceiling with oil based paint and mat paint over. This will also keep the house warmers as hot air is not moving out of the house -you pay for that in energy bills.
From our point of view you may be heading for a rotting roof?????
And gathering that UK temps. have been similar to ours; offer the following comment..
Here in Canada there are several requiremnts.
1) Bathroom fans etc. to exit damp air directly to outside. Or open window.
2) Effective vapour barriers on the 'warm' side of all insulation. If not most types of insulation will get wet, cease to insulate properly and can cause rot and mould.
3) Attics to have minimum 0.3 per cent (that's 3 square feet per 1000 sq. feet of attic floor spac) ventilation arranged so as to permit cross ventilation. In some case fans, sometimes controlled by a humidistat are also used. Ignoring these measures can cause serious rot and mould problems can occur. Long winters here!
Couple of other points; another guideline is that, in our climates, not more than one third thickness of the insulation shall be inside the vapour barrier. This is because some warm and therefore moist house air will always penetrate the insulation, after all it's the air spaces that provide the insualtion!. Otherwise the warm house air will condense (same thing as 'sweat' on a window etc.) somewhere inside the insulation barrier and soak it.
It has been mentioned that while a 'proper' vapour barrier is required that sometimes a good coating of 'oil paint' can be used as a somewhat less effective vapour barrier.
Anyway here I am meticulous about not having vapour escape into and especially 'ice' (Yikes, snakes alive!!!) in my attic or on roof rafters. For the two houses we have built and lived in since 1960.
Our temperature today and yesterday was around plus 1 or 2 Celsius (Mid 30s Fahrenheit). S'posed to go below zero tonight and a couple of centimeters of snow tomorrow? Previous snow all gone, only used the new snowblower couple of times. Studded snow tyres on all four wheels of the vehicle. A 2 WD pickup truck that is inherently, when unloaded, light light at the back. Cos haven't yet put the extra weights in the back. Must do that tomorrow Saturday.
Hope these comments help. Roofs can be expensive! And not easy to work on.
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