Anyone remember last year's minimum u value for cavity walls?

[davidmiller]

Hello. I'm working on an extension that had works started last may. Need help if anyone remembers what the u value was please?
Thanks if you can help.

 

[noseall]

Hello. I'm working on an extension that had works started last may. Need help if anyone remembers what the u value was please?
Thanks if you can help.

The same as they were post June 15 2022. When did the application go in - is the relevant question?

Since the June date, masonry cavities went up to 150mm when using the same product within. We now use expensive Unilin rebated PIR in the cavities in order to maintain a 100mm cavity. You can also beef up the thermal efficiency by adding PIR to the internal walls.

 

[davidmiller]

Morning thanks for your reply.
The application went in around 2021. Foundations were poured about this time last year. The building control company has been in touch by email saying that the new regs would be in effect if works had not started by a particular date in June last year as that was a year after the change.
I have been looking at pir. Seems you can get boards around £35 Inc vat. Which isn't much dearer than dritherm 37. I've always liked dritherm though. This pir didn't have tongue and groove by the looks.

 

[noseall]

Morning thanks for your reply.
The application went in around 2021. Foundations were poured about this time last year. The building control company has been in touch by email saying that the new regs would be in effect if works had not started by a particular date in June last year as that was a year after the change.
I have been looking at pir. Seems you can get boards around £35 Inc vat. Which isn't much cheaper than dritherm 37. I've always liked dritherm though. This pir didn't have tongue and groove by the looks.

You can't just throw in any old PIR. If you wish to fully fill a 100mm cavity, then the PIR sheets should be either rebated or have a sensible (25-50mm) gap, if not.
Unilin do a dedicated product

 

[Deluks]

Be wary of using Dritherm 37, it's readily punted out in quantity by the likes of Selco and Wickes, but with a standard brick/cavity/block construction, it might not be enough to meet required u-values, and any saving made by it's cheaper cost is negated by then having to use insulated plasterboard.
Dritherm 32 is a better product in this regard. Although more expensive and seemingly less readily available off the shelf.

 

[^woody^]

The standards that apply are those in force when the application was accepted.

 

[noseall]

Be wary of using Dritherm 37, it's readily punted out in quantity by the likes of Selco and Wickes, but with a standard brick/cavity/block construction, it might not be enough to meet required u-values, and any saving made by it's cheaper cost is negated by then having to use insulated plasterboard.
Dritherm 32 is a better product in this regard. Although more expensive and seemingly less readily available off the shelf.

DT 32 is much bulkier too. Your cavities need to take this into account when setting out the foundation masonry.

 

[Notch7]

I don’t know if builders generally use a 450mm trench or 600mm, but 450mm for a 350mm cavity wall seems a bit tight - would need to be pretty spot on on foundation dimensions.

 

[noseall]

I don’t know if builders generally use a 450mm trench or 600mm, but 450mm for a 350mm cavity wall seems a bit tight - would need to be pretty spot on on foundation dimensions.

We ALWAYS use a 600mm bucket. Trenches usually end up around 650mm wide.
I doubt a 450mm scoop is any use on a 350mm wide wall.