Building extension in the rain?

[Heathofhares]

The builders finished the walls last week and are due to do the roof next… they have left the walls open at the top ( cavity wall with mineral wool insulation between) now the forecast is for heavy rain. Should the wall tops be protected or does it not matter?

Shouldn't be a issue. Bricks are designed to have water pass through it. Hence the drain points above sills.

Thanks- do you know about the insulation too?

It’s best to cover the cavity over at the top, if the insulation gets very wet it stays wet for ages , I’ve even seen water go all the way down and come out the weep holes.

Cover the cavity job done. .

thanks chumly, walls are 10’ high, its going to be easier said than done... am I right in thinking the builders should have done this before they left?

Yes they just normally put a piece of plastic or damp proof membrane over it and bricks on top to stop it blowing off, or place scaffold boards across it . Anything you can find will do as long as it keeps 90% of the water out and won’t blow off.

Hmm, spoken to the builder and he reckons it’s fine and will just dry out… do I believe him or try and rig something up?

Depends on how much rain your going to get and how long before the cavity is water tight. If it just a bit of rain and with it being summer it should be ok. If it was winter and chucking it down then it wouldn’t dry out. It’s good practice to cover brickwork over whatever the weather.
It’s good practice to cover any building materials over , it’s much easier to work with them when dry.