Wall Insulation

bifl

Hi,
From reading on here I had my mind set on a 250mm cavity fully filled with beads. Main reasons
-it gives a good U-value perhaps around the 0.12 mark
-gives me thermal mass on the inside of the envelope for the geo-thermal UFH
- beads wont rely as much on good workmanship to fit and will fill up nicely around the windows

Getting a provisional BER done the initial design is using a 150mm board in the cavity from a main Irish manufacturer giving a u value of 0.14. This raise a few question in my mind

- would the 150mm be better as a small cavity comes back to a more traditional build that people are used to working on and less emphasize on the correct 'detailing' on a wide cavity build.
- why go to the trouble & expense possiblly (???) of going wide or extra wide (how ever you want to look at it !!) when something smaller would do.

Any advice would be appreciated.

Thanks
Bifl

hexosan

How are you guaranteeing that the 150mm boards will be fitting correctly in the cavity by the block layer

dfader

If you want a U value of 0.14 in theory go with the board insulation in the cavity, if you want it in reality pump the cavity.

Selfbuilder14

bifl wrote: »

Hi,
From reading on here I had my mind set on a 250mm cavity fully filled with beads. Main reasons
-it gives a good U-value perhaps around the 0.12 mark
-gives me thermal mass on the inside of the envelope for the geo-thermal UFH
- beads wont rely as much on good workmanship to fit and will fill up nicely around the windows

Getting a provisional BER done the initial design is using a 150mm board in the cavity from a main Irish manufacturer giving a u value of 0.14. This raise a few question in my mind

- would the 150mm be better as a small cavity comes back to a more traditional build that people are used to working on and less emphasize on the correct 'detailing' on a wide cavity build.
- why go to the trouble & expense possiblly (???) of going wide or extra wide (how ever you want to look at it !!) when something smaller would do.

Any advice would be appreciated.

Thanks
Bifl

We are also building starting soon and have opted for 150 cavity full fill. No drylining using walls as thermal mass. My other half is,a civil engineer and he thinks going for a wide cavity makes the build more difficult. Our architect also preferred a slimmer wall design. I am sure both systems work well if built properly.

JD6910

i put in a 200mm cavity. cant remember the u-value but it was excellent.
250mm does create structural issues and detailing issues.

id stick with 200mm. cant be a huge u-value difference going up to 250MM.

BryanF

You need to do the heat loss calculations for the overall envolpe, no point looking at this in isolation.