wall insulation

[junglejim01]

So here we go...getting frustrated with BC! I'm renovating a 1960s lean-to extension. I'm trying to achieve a much better thermal performance and keep the building inspector happy but finding this tough. He's approved new windows doors, floor, roof insulation. But the sticking point is the walls. It's a narrow room and is going to become a kitchen so we'd wanted to go for 22mm insulation on the external wall. Any more and we're going to struggle with the ktchen fitting. The BC has been in today and is insisting on 50mm+12.5mm plasterboard. I know it's not a massive difference but we were already sacrificing space with the 22mm. I can't believe that we can be improving something so much and still not the BC's not happy.

Any thoughts?

 

[freddiemercurystwin]

Just offer to add more roof insulation to compensate, although 22mm is better than nothing it is hardly anything.

 

[junglejim01]

sorry...bit of confusion...it's not the roof insulation. It's on the external wall

 

[tony1851]

He knows that; what he's saying is that while 50mm is the accepted standard for walls, if you go less than this thickness, you can offer to compensate by adding extra insulation elsewhere - usually best in the roof.

The idea is that the total heat loss should not be any worse.

There is a provision in the regulations which allows a lesser standard of insulation if the normal standard is not practicable.
I think your inspector is trying it on and not giving you the whole story.
Read Approved Document L1b.

 

[RonnyRaygun]

sorry...bit of confusion...it's not the roof insulation. It's on the external wall

What Freddy is saying is that you can put more insulation in the roof to offset the heat loss from having insufficient insulation on the wall.

Then the BI might accept 22mm.

 

[tony1851]

Beat you by 60 seconds!

 

[junglejim01]

Thanks for thr replies and clarification...ok that's interesting. I'm not sure which will be most workable then as the lowest part of the roof at the eaves is already going to be tight on height with an extractor.

 

[tony1851]

Google AD L1b (2010 edition) and look at page 18 (retained thermal elements).
It states that your lesser standard of insulation should be no worse than a U-value of 0.7; you will easily better that with 22mm + plasterboard.

 

[junglejim01]

Thanks, just read that but i'm not sure that i would meet the criteria for a 'lesser standard'. I wouldn't be loosing 5% of floor space. However, crucially for me, i would be loosing enough to have to loose a small cupboard.

 

[RonnyRaygun]

Thanks for thr replies and clarification...ok that's interesting. I'm not sure which will be most workable then as the lowest part of the roof at the eaves is already going to be tight on height with an extractor.

Or you can add more insulation to the floor (might not be practical).
Or you could add more insulation elsewhere in the rest of the property.

 

[junglejim01]

Thanks, can you direct me towards where the regs say i can improve another thermal element to make up?

 

[RonnyRaygun]

http://www.eastherts.gov.uk/media/pdf/d/1/18_-Technical_Leaflet_-_L1B_extensions_May_2011.pdf
Page three of the above document...

 

[freddiemercurystwin]

When you say 22mm do you mean 22mm insulation or is that 22mm including the plasterboard so actually only 10mm insul?

I'm not sure it actually says that in there tbh (it may do I probably ought to read more of the Regs ) it seems to be a given that most inspectors accept such a compromise at least that's been my experience.

What is in the Regs is that if you can justify why an improvement is not technically feasible (ie your kitchen won't work) or the 15 year payback doesn't add up (ie you won't save the money on heating bills spent on the additional insulation over a 15 year period) though proving that is easier said than done. I think someone posted a link to a simple calculator for that on the forum once.

When you say the kitchen won't fit surely you could fit say a 500mm unit instead of a 600mm unit and the kitchen would still work? And the walls would be warm too.

 

[freddiemercurystwin]

http://www.eastherts.gov.uk/media/pdf/d/1/18_-Technical_Leaflet_-_L1B_extensions_May_2011.pdf
Page three of the above document...

Yes but that's with SAP calcs, which will cost more than the additional insulation, though will get him out of the hole and frankly the inspector would be a hole if he insisted on SAPs.