Wet cavity wall insulation in new extension

[jwpetal]

We are having an extension to our house built. Our builder has started building the walls and has added insulation. It has been damp with some light rain over the last 24 hours and he left the cavity walls uncovered. I went and felt the insulation along a side wall, where our doors will be, and it was damp. From the top, we can see that the insulation has shifted downwards - by the rain?. Should we have our builder redo the insulation? It is not soaking but he wants to do the roof over the weekend and we are concerned that the insulation will not be as effective if it was wet. Should we call in building control?

Any advice would be helpful

 

[jeds]

Sloppy work not to cover the cavity. Not ideal but it won't do any long term harm. The top of the cavity should be topped up before the roof goes on.

 

[noseall]

Cavity insulation gets wet then dries again.

It is nigh on impossible to keep everything dry. And if it were a case that we had to replace everything that got wet, particularly in the UK, all builders would be bankrupt.

Building control will not be interested in wet cavity insulation.

What do you suppose happens when cavity trays allegedly come into use?

 

[noseall]

Sloppy work not to cover the cavity.

Coming from a true site worker.
Sometimes, when it is getting late and the customers roof has been exposed to the elements and the guys are fighting the wind, rain and the dark and are trying to sheet up the the big hole in house roof, the cavity can sometimes get neglected yes.

Jeds, have you ever tied covering a cavity that has loads of sloping rafters in the way?

 

[jeds]

I'm half and half on this. Insulation does get wet and it's not a usually a long term problem. But I don't think it's unreasonable to expect it to be kept to a minimum where it's no big effort. Covering the tops of cavities isn't exactly hard - especially when the roof ain't on yet. It's like covering brick stacks. Some do it other can't be bothered.

 

[Pallatrax]

I have first hand experience of being the customer and diy builder subbing the brick laying out - so I have been up and down the roof trying to keep my rockwool dry recently.

As it is pretty repellent you'll find it won't really be as wet as it looks, but a 18" roll of DPC i had lying about proved just the ticked to covering up the cavity as the wind doesn't catch it!

Tom

 

[noseall]

Covering the tops of cavities isn't exactly hard - especially when the roof ain't on yet.

No it isn't, but builders have their priorities also.

Cavity insulation can get wet with no ill effects, however the customers home along with the electrics, plaster work, carpets etc, certainly can not.