PIR in cavity wall and avoiding air gaps

[Dave Jones]

On 23/02/2022 at 22:16, Simplysimon said:

why oh why do you still build with a block inner leaf instead of a timber kit down there? move into the 20th century folks, heaven forbid, you could actually move into the 21st century with i beam kits......... ?

because double the price isnt double as good.

[dpmiller]

1 hour ago, Dave Jones said:

because double the price isnt double as good.

I'd love to see some actual data on that, if you have it?

[Dave Jones]

5 hours ago, dpmiller said:

I'd love to see some actual data on that, if you have it?

 

not rocket science ask any kit builder to supply you at the m2 rate of blockwork and see the reply.

[dpmiller]

1 hour ago, Dave Jones said:

 

not rocket science ask any kit builder to supply you at the m2 rate of blockwork and see the reply.

not how it works. You made the assertion...

[SteamyTea]

5 hours ago, dpmiller said:

not how it works. You made the assertion...

How dare you question Dave Jones, he never needs to shows evidence, only his opinion matters in his tiny world.

 

[Chathura]

Even though this is an old thread, I believe this situation is still valid and more relevant to 2023 due to 2022 and 2023 amendments in Building Regulations - Part L which requires a wall construction with a U-Value of 0.18W/m²-K.

 

Our engineer has made a mistake or probably his draughtsman has copied-pasted a detail diagram from one of his old AutoCAD drawings. Therefore, the footings of our extension were already built following the specification below. This was sent to me somewhere in the middle of 2023—but this does not even remotely address the U-value requirement. But unfortunately, I trusted them and never had a secondary verification from someone else. The building control officer also never gave me a straight answer (I've seen it from many authorities in the UK. They don't give an answer that they would hold accountable. They give double-sided responses so we have to stay prepared to waste time and money if they suddenly say something else in the end. This also happened when I was getting approval from the water company for a public sewer diversion).

Therefore, I now have a few options to correct this.

1. Undo the oversite, break the footings and redo it with 150mm cavity instead of 110mm above. 
2. Undo the oversite, build another layer of blocks in the inner skin and allow space to create a 150mm cavity.
3. Keep the footings as is and improve the insulation thickness to create a fully-filled cavity. (This saves me time)

• 100mm×1200mm×2400mm PIR is the cheapest option. Also, one board would cover the entire height of the wall giving the best possible performance. But, I don't know if the bricklayers could manage it with 11kg heavy boards. (calculated down to a U-Value of 0.166 W/m²-K)
• 100mm×1200mm×450mm PIR is light (2kg) and easy to manoeuvre. However, this does not come with a tongue and groove edge. We are living in a Sheltered Area on the Exposure Zone Map (given below)—therefore, this might be fine and I can use something like Stormdry for extra protection from rain penetration.
• Celotex Thermclass 90mm×1900mm×450mm is probably the PIR that was created for this purpose. It has a tongue and groove edge for easy installation and protection from rain penetration. However, this is about 1.7kg heavy and twice the price of the above-mentioned (calculated down to a U-Value of just 0.18 W/m²-K)

I am waiting to discuss these options with the builder and choose the best option out of these three. Meanwhile, I appreciate it if anyone has a better idea or opinions on these options. I'll also update the thread accordingly as we proceed for the use of anyone who finds this thread in future. 

 

 

 

[JohnMo]

Insulated plasterboard inside the walls? No undoing or redoing work.

[Chathura]

6 hours ago, JohnMo said:

Insulated plasterboard inside the walls? No undoing or redoing work.

That's a very clever solution as well. But when considering the costs for both PIR insulation boards and insulated plasterboard together, that's going to be really expensive, isn't it? 

Edited November 18, 2023 by Chathura