Blocks between joists

[Peter500]

I'm doing a flat roof with joists sitting on a block wall. I'm planning to put blocks between each joists i.e. almost 600mm between the joists. I was wondering how high the blocks should go and perhaps what their purpose is? Are they just there to prevent twisting of the joists? Is it best to finish the blocks approx 10mm lower and then just foam/seal it to help with air tightness, or dothey need to be a really tight fit?

 

[Wayners]

Blocks block air flow Vs x wood.
Blocks can be a fire break and stop the twisting.
Whatever works best for requirements. Do you need airflow?

 

[Peter500]

I don't want air flow. I will be having MVHR in my main room. The other 'room' is a garage, so air flow doesn't really matter in the garage.

 

[noseall]

I'm doing a flat roof with joists sitting on a block wall. I'm planning to put blocks between each joists i.e. almost 600mm between the joists. I was wondering how high the blocks should go and perhaps what their purpose is? Are they just there to prevent twisting of the joists? Is it best to finish the blocks approx 10mm lower and then just foam/seal it to help with air tightness, or dothey need to be a really tight fit?

You can do it with masonry or solid bridging (timber) and PIR for insulation continuity.

 

[Peter500]

You can do it with masonry or solid bridging (timber) and PIR for insulation continuity.

Timber is a good idea. Blocks will be cheaper as I already have them, but timber would be much quicker

I'm planning to continue my insulation (Dritherm 32, not PIR) through the cavity either way.