Condensation in loft. 11 December 2022 at 5:03PM in In my home (includes DIY) MoneySaving 87 replies 6.4K views

stuart45

I think you are understanding it correctly. 
Although lap vents are seen as a DIY solution in the trade, if they work for you it's worth giving them a try. 
At least you went into the roof space, and spotted the problem.

grumbler

ashe said:

Another thing I have seen mentioned, which I have not checked in ours yet, is if you have a cavity wall make sure it has been capped in the loft otherwise any moisture in the cavity basically evaporates upwards. 

I am no expert, but to me upwards  is better than inside the house.

ashe

grumbler said:

ashe said:

Another thing I have seen mentioned, which I have not checked in ours yet, is if you have a cavity wall make sure it has been capped in the loft otherwise any moisture in the cavity basically evaporates upwards. 

I am no expert, but to me upwards  is better than inside the house.

I thought so too but seems from Googling building control suggest it. I guess should have some form of weep vents to the outer skin to let moisture out? 

stuart45

The theory of the cavity wall is that moisture condenses on the inside face of the external skin, and runs down to below the DPC. 
The cavity is normally closed to prevent too much convection and heat loss.
A small amount of ventilation is provided through weep vents. These are considered more important with timber frame houses.
With a timber frame house they are usually at DPC, at frames, and sometimes at eaves level.

locky123

Our property also suffers from condensation dripping from the bitumen felt in cold weather. Original roof from 1970s with open cavity wall tops, no additional roof vents, 270mm insulation, when the wind blows there is a good draft in the attic. 

I've seen the lap vents before but have yet to try them. perhaps it is time. More costly alternative is new breathable membrane but still not sure how effective in the long term it will be.

ashe

locky123 said:

Our property also suffers from condensation dripping from the bitumen felt in cold weather. Original roof from 1970s with open cavity wall tops, no additional roof vents, 270mm insulation, when the wind blows there is a good draft in the attic. 

I've seen the lap vents before but have yet to try them. perhaps it is time. More costly alternative is new breathable membrane but still not sure how effective in the long term it will be.

They're not showing as in stock atm but I got 10 of the vents from Amazon for £25 which is outrageous for that they are but if it starts to solve the problem I'm all for it 

_Sam_

Same here - just been up in the loft, 1950 bungalow and entire north side of the roof is wet, the wooden joist across is wet too from dripping I suppose    The the south side of the roof is all bone dry.

 

stuart45

There are lots of roof spaces like that. It's always a good idea to make sure there is enough ventilation when increasing the insulation .
The timber getting soaked is a purlin.

ThisIsWeird

The past few days have seen a combination of cold weather coupled with low wind speeds. Could it be that some condensation under these circumstances is actually quite normal, or at least not unusual? In most cases it should all clear away with no long-term issues as soon as a breeze builds up again, or the temp rises. I don't think that temporary drops of water should cause either concern or any real problems. (Although Sam's purlin looks strangely damp, as if it has been for a while). I think I would start by just monitoring the situation over the next couple of weeks. With luck it'll all return to normal, and fixes won't be required.

When it comes to hatches being accused of being a culprit, it isn't that they might not be insulated that can lead to additional condensation in the loft space, but that they might not be well sealed. If they allow a steady trickle of moist air up from the house below, then this is likely to condense out in the cold loft. So adding insulation on top of the hatch - whilst still obviously a very good idea - won't, by itself, reduce condensation, but just heat-loss from the house. Ensuring that the hatch seals against a nice soft draughtproof foam strip should reduce condensation - if that was one of the causes.

superstylin

I also wonder if this may be more of an issue related to current weather conditions rather than any issue in the loft? We've just been up in ours to get the Xmas presents for wrapping and the felt is covered in condensation which we've never had issue with before. A fair amount has dropped onto the presents and we're having to dry the boxes next to radiators.

Having said the above it's clear we have no vents and the insulation is only about 100mm thick which surprised me. Looks like I'm gonna be doing a bit of DIY.