My house was built in the early 80’s. Outside is traditional brick. Inside skin is grey block and plastered.

It looks like there is no cavity between the two skins, just a dpm. With the exception of below the windows- i think the interior skin is brick there.

I was a bit surprised by this as i thought post 80 cavities were pretty standard?

What parts of the structure have you looked at to draw this conclusion?

If it is a cavity wall it will be 250mm wide, if no cavity then probably 210mm and easy to measure at a door or window

Go into the loft and look at the gable end.  You’ll be able to see immediately if it’s a cavity wall.

Go into the loft and look at the gable end.  You’ll be able to see immediately if it’s a cavity wall.

I know I have a cavity – and that its insulated. I’ve had the windows/doors out and cut the back wall out the house so know for sure  But there’s absolutely nothing that would indicate it’s a cavity on either  gable end in my attic.

yeah I don’t think an 80s house without cavities would have been allowed – I’d be amazed if there weren’t some (or maybe a layer of something instead of a cavity, like insulation)

What makes you think you don’t have a cavity. It was common practice to close the cavity at all openings and stick a bit of dpm in to split the external leaf from the internal (we do the same now but it’s a thicker insulated strip) Beyond this I would expect 100mm gap with 50mm insulation, or 50mm gap minimum. Would be very very surprised if there is dpm splitting the leafs all over.

So as above measure it anything over 200mm suggests a cavity of some form. Would expect 300 at that age

What would about 240mm from outside edge of brick to inside edge of plaster suggest?

Seems a bit thin. Is it possible the inner leaf is 75mm blockwork? I would have expected a 50mm cavity, maybe partially or fully filled with insulation.

What would about 240mm from outside edge of brick to inside edge of plaster suggest

Render is generally 15-20mm

Plasterboard 12.5mm with a 3mm skim on top