Extension build

mirrormatrix

Looking for advice. Getting a small extension built. Current plan is for hollow block walls with plasterboard backed internal insulation on the inside. However, i thought that hollow block was done away with years ago.

What is the most normal/recommended construction method these days for a new wall?

Pat734

100mm block, 100mm cavity, 100mm block

10-10-20

https://www.boards.ie/discussion/comment/123707136#Comment_123707136

Or 150mm cavity if it's habitable.

muffler

https://www.boards.ie/discussion/comment/123707155#Comment_123707155

Exactly. It's 10 years or more since I last specified or seen anyone else specifying a 100mm cavity. The norm these days would be 150mm.

BorneTobyWilde

Porotherm insulated block no cavity

mirrormatrix

Thanks. Assumed alright that cavity would be the norm. Would foundations need to be increased to account for add weight of cavity wall? This is what I was told when I asked about having a cavity wall instead of single layer hollow block.

muffler

https://www.boards.ie/discussion/comment/123709133#Comment_123709133

Yes foundation width would have to increase but no one here can tell you the width as it can vary depending on the load bearing capacity of the ground and that aside structural detailing isn't permitted as per forum charter. Talk to a local engineer.

mirrormatrix

Thanks. Have an engineer for the project. Not looking to know width but builder has said it would cost more so just wanted to see if that sounded sensible.

I am being told that hollow block with internal insulation is perfectly good construction and well insulated, with gains from cavity wall not being that great vs additional costs. But what I'm reading elsewhere is that no one uses hollow block any more. So I'm not sure what to believe.

sydthebeat

Hollow block of easier on the builder, that's why they are championing it.

It's hardly ever used outside of Dublin.