On 04/05/2021 20:48, George Miles wrote:
I'm planning a small extension,
walls to be brick on the outside,
then a cavity, then blocks

The blocks hold the roof beams up,
the bricks are to look nice and stop rain.

Presumably sealed in at the eves/soffits?

I see videos of people putting insulation -
(wool or kingspan)
in the cavity.

But wouldnt there be a thermal bridge leaking heat both at the bottom and the top of the cavity insulation?

No more so than if left uninsulated.

Wouldnt the same amount of insulation be more effective if on the inside of the block wall ?

Or take the chance to do both - more overall, and less loss of internal
space.

A bit depends on what kind of occupancy. Insulation inside is good for
intermittent use spaces, since you can raise the internal temperature
quickly since its decoupled from the bulk of the thermal mass of the
masonry.

Full time occupancy can be better with more thermal mass inside the
insulation since it takes longer to slew in temperature, thus keeping
temperature swings down and reducing influence of very hot/cold days.



--
Cheers,

John.

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