Warm / cold roof space?

[pmcbythesea]

1977 bungalow with 100mm fibreglass loft insulation between joists and now an additional 200mm fibreglass insulation on top of that across the joists. At roof edges where roofing timbers meet the ceiling joists and external walls, it was very leaky - it was possible to see right down to the soffits and the loft space was pretty well ventilated by accident rather than design. Timber soffits with no ventilation built in but over the years they seem to have shrunk back from the walls giving airflow to the loft.

 

Now that extra insulation has gone in, the extra 200mm has blocked off the views down to the soffits and therefore the airflow.  And the only other ventilation in the loft is via an odd tear or two in the roofing felt. No breathable membrane, no ridge ventilation, etc.

 

Question is do I re-open at least some of the previous gaps down to the soffits (i.e. take the extra insulation away from the edges)? It is worth pointing out there is a cold water supply tank up there which is insulated but could be prone to freezing in very cold weather if there is a significant airflow through the loft.

[ProDave]

You need airflow in a cold roof to prevent condensation, so you will need to open up some ventilation.

 

There is a product, which is basically flat plastic board, to insert down between the rafters to create a gap down to the soffits, but I don't know it's proper name.

[Gone West]

I think @ProDave might be thinking of things like this.

 

https://www.amazon.co.uk/Vents-Prevents-Condensation-Attic-Ventilation/dp/B00M97O5YY

[ProDave]

No not that. But I have found it

 

http://klober.co.uk/shop/product/loft-vent-tray

 

It creates a ventilation space, while still allowing the loft insulation to go as far as possible.

[pmcbythesea]

Thank you, that's very helpful. I was thinking of sticking some pipes in. I guess in 1977 people didn't think too carefully about loft ventilation.

[pmcbythesea]

Moving on then.......at some time in the faraway distant future existing timber soffits and facias will be replaced and that's an opportunity to put in proper air-flow. However in the meantime, I am inclined to go round existing soffits, drill holes in them and put in these:  https://www.amazon.co.uk/gp/product/B004E5HB5Y/ref=as_li_ss_tl?ie=UTF8&tag=daniweadroof-21&linkCode=as2&camp=1634&creative=19450&creativeASIN=B004E5HB5Y

 

Has anyone done that, come across any issues?

 

[joe90]

Yes they should do it, I worked on a house that the mortgage supplier insisted they were fitted when the customer bought the house but I discovered when I did work on the house that the walls extended right up to the back of the roofing felt so the vents did no good, but if you can see the soffits then you have an airway.