Tile vents

[Gazelle1]

We have a 1980s extension and the loft has old style bitumen felt and not much ventilation. It's very low pitched and small (about 20 m2). We noticed that in cold weather we were getting a lot of condensation so sealed the loft hatch better and put in 20 lap vents. All good and lots of airflow until the last couple of cold nights when all the condensation has returned.

We had a quote for tile vents (£500) but reluctant to spend this much unless it's going to make a significant difference. We're already getting airflow so I can't understand why the condensation is back.

Would tile vents make a significant difference?

 

[datarebal]

what is your insulation like? what tile do you have

 

[Gazelle1]

Insulation is fiberglass and 100mm thick. We've pulled as much back from the eaves as possible, as it was stuffed right down into them. There are three vents in the eaves but difficult to know how much ventilation they are providing. The tiles are standard clay tiles.

 

[datarebal]

100 mm isn't enough, you should be around 270 mm and there should no ceiling left without insulation.
loft hatch needs insulating too.
Standard clay tiles, i take it you mean clay plain tiles? these don't let a major amount of airflow in,
i'd first bump up insulation.
then if there is still a problem add vents

 

[Gazelle1]

Thanks for your reply. Would the extra insulation prevent warm air rising into the loft then? I've read conflicting information about extra insulation actually making condensation worse.

 

[datarebal]

That is the basic idea . Warm air in house not in loft, TBH your insulation is poor and insulation is cheap at the moment so you have nothing to lose

Loft venting is also important especially with bitumen 1f felt as you have

And dont forget to make sure any extractors extract to the outside

 

[Gazelle1]

Thank you, will give it a go.

 

[phatboy]

Having had much the same situation, that got worse after adding more insulation, I did some research the other week.

The extra insulation is keeping the house warmer, but holes for downlights and other things still allow moisture through, and that can travel through the insulation.

I added felt lap vents before i added insulation to resolve the basically sealed loft, and it was OK (Our tiles allow lots of air though). Since adding more insulation, it's been necessary to add vent tiles high up, and things feel dryer up there now.

 

[datarebal]

quite true about down lighters etc. but take the insulation out and see what happens

 

[^woody^]

You wont get rid of all condensation, so don't try and don't worry.

 

[Leofric]

Would the extra insulation prevent warm air rising into the loft then?

No, a vapour barrier on the warm side of the insulation is meant to stop moisture laden warm air rising into the loft. 300 to 350mm is the optimum thickness of quilt insulation at joist level. Recessed downlighters below roof spaces are a menace and should be fireproofed anyway . Cross ventilation at eaves level with some ventilation at high level is generally accepted as the best thing to do with cold pitched roofs.

 

[Gazelle1]

Thanks for your reply.

More worryingly, we have a separate very small roof space over our bathroom, with no access, no ventilation and recessed downlights. There's no way of checking the roof space so I dread to think how much condensation must be getting up there...it's survived 30 years so hopefully ok!

 

[datarebal]

drop a downlighter out and us a torch or your nose

 

[Gazelle1]

Couldn't see much (or smell anything, which is good...)