Hi William,

If the cavity has been completely filled then any vents would have a minimal affect on heat losses as the air path between them has essentially been cut off. I'm assuming the low level ones were blocked up.

I''m not saying this is the case with you but some houses do not lend themselves to full-fill insulation. Particularly areas of high exposure. Where in Wlaes are you? And what age and type of house?

In response to Mike George's questions:

1) The low level vents were not blocked, other than by the insulation.
2) The house is on the Gower peninsula.
3) The part of the house concerned is an extension built circa 1950 and the rooms in the extension have 3 external walls so keeping heat in is difficult.

We have been wondering about whether to additionally put aerogel or similar on the inside of the walls but before going to the trouble/expense of this wanted to see if there is any reason the CWI is not working as well as it might.

Just done a few knock throughs on cav. walls with eps beads and I was impressed with the quality of the fill, best I've seen , usually with rockwool or that white, all most foam like stuff, it can be quite patchy.

How much quilt you got up in the loft ( 300mm+ is good )
also do you have scaled ceiling , ie chalet bungalow, 1 ,1/2 storey . and if so is this area insulated ?

I got the impression that the guys installing the insulation were thorough.

There is about 300mm of soft insulation on the floor of the loft. The extension that has had CWI is 2 storey and the top of the wall is about 2 ft above the loft floor so that the cavity is ventilating into a cold space. If you look at the manufacturers website http://www.warmfill.com/presentation_1.htm there is a reference to the beads being ventilated. My concern is that the heat from inside the house is passing into the insulation and then rising through the insulation and venting into the cold roof space. On the other hand given that there is driving rain at times then it may be advisable to have some degree of ventilation of the cavity. Any expertise on this isuue would be welcomed.

An IR thermometer would be a lot cheaper than thermal imaging, though more tedious to use.

Posted By: williamdHowever the insulation does not seem to have had any appreciable effect in that this part of the house seems just as difficult to keep warm. Is it likely that this is because the cavity is open at the top?

Is the inner leaf block/masonry? Is it finished with wet plaster or plasterboard? If plasterboard then there's likely to be significant air leakage through the inner leaf. The air gap behind the plasterboard may be open to the loft/joist space above &/or a ventilated floor space below.

Posted By: williamdMy concern is that the heat from inside the house is passing into the insulation and then rising through the insulation and venting into the cold roof space.

If the insulation has been installed to the correct density then the quoted U value should take this into account. However, you could try sealing the top of the cavity with a piece of rigid insulation.

You've not mentioned the floors. Are they suspended timber floors? Are they insulated? Is there an air barrier? Could they be providing a source for the air going up the back of the plasterboard?

David

Yes
Air leaking can soon take the warm air away.