Cavity Wall insulation capping?

[TheMitchells]

If I add cavity wall insulation to my bungalow, with the intention of making it as airtight and insulated as possible for a limited budget, do I need to cap the top of the cavity?  I do plan to remove the first couple of layers of tiles and try to join the cavity insulation to the attic insulation.   So presumably not. 

 

I shall add something to ensure airflow into the roofspace. 

 

Then i need to ask about the vapour barrier and the best way to add that.  But one thing at a time. 🙂

[BotusBuild]

Just now, TheMitchells said:

join the cavity insulation to the attic insulation

 

From bitter experience this can be difficult to achieve from inside, so taking back tiles and "working from outside" maybe a clever solution.

Do be careful NOT to block off any designed natural ventilation to the attic space as you could end up with condensation problems up there.

 

I wouldn't cap off the cavity as again, there is probably some natural ventilation going on to keep condensation down in the cavity itself.

[ADLIan]

Generally a masonry cavity wall (insulated or not) should not be ventilated - nothing to do with reducing condensation risk. A open cavity must be sealed at the top and must not link with any ventilation into the roof space/roof ventilation route - it’s a fire safety issue.

[JackofAll]

Have left the top of our cavity open. The dritherm will meet the blown cellouse(when I get around to pumping it) is this a no no? Engineer seemed happy.