mike2016 Posted January 28, 2021 Share Posted January 28, 2021 I was up in the attic a few weeks ago after upgrading the insulation and noticed a lot of condensation which was dripping onto everything. I was running a Positive Input Ventilation unit but reckon it was defrosting / using the heater which added a lot of heat into the attic over time as the landing wasn't freezing cold on those nights. Anyway, I turned this off and it's gotten a lot better but was up again yesterday and noticed the attic trusses are wet where they meet the roofing felt and there is still some but not much condensation on the inside of the felt although this is improving. I replace 100mm of fibreglass with cellulose between the joists and added 200mm knauf earthwool on top. I used glidevale rv655 baffles at the roof edges to maintain airflow. I've a few additional vents to open up the felt every other rafter or so on each side. The attic trusses on the side of the roof where the solar pv panels are don't have this issue, only the other side. I've a good seal on the attic hatch and been closing one or two old pipe holes but wonder if I've not enough ventilation or just have to wait for a windy day to help clear this out? I just don't like see the attic trusses wet like that..... all suggestions welcome! Link to comment Share on other sites More sharing options...
Temp Posted January 28, 2021 Share Posted January 28, 2021 Some guidance on ventilation here.. https://nhbc-standards.co.uk/7-roofs/7-2-pitched-roofs/7-2-15-ventilation-vapour-control-and-insulation/ Generally you need vents at the eaves equivalent to a 10mm wide slot the full length. Is there actually a slot in the soffit/facia area to feed air to the glidevale rv655 baffles you mention? You can also improve ventilation by using membrane lap vents.. https://www.roofingsuperstore.co.uk/product/felt-lap-vent.html Link to comment Share on other sites More sharing options...
mike2016 Posted January 28, 2021 Author Share Posted January 28, 2021 There's 3 x vents at the front of the house and 3 at the back. There would have been more gaps before I installed the Glidevales at the eaves. They have channels in them but I need something solid to hold back the loose cellulose. I have a few of those membrane lap vents, there are no ridge vents but it's a low pitch. I may try adding more membrane lap vents and see how that performs..... Link to comment Share on other sites More sharing options...
nod Posted January 28, 2021 Share Posted January 28, 2021 46 minutes ago, Temp said: Some guidance on ventilation here.. https://nhbc-standards.co.uk/7-roofs/7-2-pitched-roofs/7-2-15-ventilation-vapour-control-and-insulation/ Generally you need vents at the eaves equivalent to a 10mm wide slot the full length. Is there actually a slot in the soffit/facia area to feed air to the glidevale rv655 baffles you mention? You can also improve ventilation by using membrane lap vents.. https://www.roofingsuperstore.co.uk/product/felt-lap-vent.html I’ve just used these at my daughters home They work a treat £27 for 10 Link to comment Share on other sites More sharing options...
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