New build - insulated plasterboard worth it ?

MackDeToaster

Hi, doing a build with 150mm xtratherm solid insulation in the cavity. With this and everything else (heat pump, mhvr etc) house is estimated to be A3 or better.



I'm debating putting 62mm insulated plasterboard on all external facing walls as well but engineer is so/so about it and some builders providers are actually saying don't bother, while others are saying it'd be well worth it. Cost would be 3,200 just for materials then labour as well, circa 6k in total.



I think at that price it'd be a very long time on payback, if ever, but don't know whether the house would feel significantly warmer (assuming it hits A3 without). Any opinions ?

sydthebeat

no

BryanF

Spend the money on thermal junction /air-tightness 1:5/10 details. So you can hand the builder actual drawings as opposed to him winging it.

Baymax2020

Simple answer is no. You'll get better air tightness from sand and cement followed by skim. Have you had a BER assessor in. What size is your cavity

tedimc

Apart from the insulation aspect - one other small element to consider is screwing into the wall for curtain rails, etc when you have insulated boards.

Its a f**king pain!!

For what's it worth - I bought the standard insulation boards from that crowd in Monaghan. Fixed them to the wall myself, filled any gaps with foam, applied foil tape over the joints and then got a crowd in to slab the whole lot with regular plasterboard.

Maybe not worth it, but it worked out a little cheaper and allowed me to be more particular about gaps, etc. I was also told that because the normal boards have foil on both sides, they are slightly better.

However - my own situation was a renovation and I only had a 75mm cavity. My preference would have been to have all the insulation together in the cavity if the width permitted it.

MackDeToaster

Thanks for the replies. I've decided to give it a miss as it's just not worth it financially. Already have plenty of stuff for airtightness - window tape, air tight membranes for ceiling, thermally rated expanding foam, sprayable air-tightness paint and so on.

MicktheMan

MackDeToaster wrote: »

Hi, doing a build with 150mm xtratherm solid insulation in the cavity. With this and everything else (heat pump, mhvr etc) house is estimated to be A3 or better.



I'm debating putting 62mm insulated plasterboard on all external facing walls as well but engineer is so/so about it and some builders providers are actually saying don't bother, while others are saying it'd be well worth it. Cost would be 3,200 just for materials then labour as well, circa 6k in total.



I think at that price it'd be a very long time on payback, if ever, but don't know whether the house would feel significantly warmer (assuming it hits A3 without). Any opinions ?

As others have said....
Noooooooooooooooooo

Gumbo

MackDeToaster wrote: »

Hi, doing a build with 150mm xtratherm solid insulation in the cavity. With this and everything else (heat pump, mhvr etc) house is estimated to be A3 or better.

It would want to be. That’s the minimum requirements. Every new house in the country is A3.

Penn

Yeah I would have thought with 150mm full-fill cavity insulation, heat pump and MVHR, you'd almost definitely be at or near an A2 rating. Internal insulation won't really have much of an effect at all at that stage, you'd nearly be better considering a small solar PV installation. Would have a shorter payback period by lowering your energy bills.

Yellow_Fern

Possibly as the ceiling for the rooms below the attic.

If you have drywall room partitions, worth adding sound proofing in the wall build up.

Yellow_Fern

Gumbo wrote: »

It would want to be. That’s the minimum requirements. Every new house in the country is A3.

Every house in the country is designed to be A I think A2 now but I emphasis designed. Many wont be.

sydthebeat

Yellow_Fern wrote: »

Every house in the country is designed to be A I think A2 now but I emphasis designed. Many wont be.

assigned certifiers are looking for final BER as proof

so many WILL be built as A rated.

its a nightmare trying to get a new final over the line of compliance.

Air tightness test and report has to be done
Heat Pump Designer / Install form has to be signed off
SR 50 calcs have to be done for rad systems
ACDs have to be signed off
Design plans of associated ACDs has to be signed off by assigned cerftifier
full construction specifications have to be signed off

the paperwork is immense

Yellow_Fern

sydthebeat wrote: »

assigned certifiers are looking for final BER as proof

so many WILL be built as A rated.

its a nightmare trying to get a new final over the line of compliance.

Air tightness test and report has to be done
Heat Pump Designer / Install form has to be signed off
SR 50 calcs have to be done for rad systems
ACDs have to be signed off
Design plans of associated ACDs has to be signed off by assigned cerftifier
full construction specifications have to be signed off

the paperwork is immense

The final BER is only a general guide. The BER tests the design not build.

sydthebeat

Yellow_Fern wrote: »

The final BER is only a general guide. The BER tests the design not build.

That is not 100% correct.
A new final BER is competely build based.
A provisional BER is design based.

Remember, the DEAP methodology is the only "test" there is at the moment

As I said already, it requires an air tightness test (which tests the build) and it requires certifiers thermal bridge factor sign off as well, which is build based.

The rules for final new build bers, to show part L compliance, are very strict.... And currently this is the ONLY prima facia way to show Part L compliance.

Calahonda52

Penn wrote: »

Yeah I would have thought with 150mm full-fill cavity insulation, heat pump and MVHR, you'd almost definitely be at or near an A2 rating. Internal insulation won't really have much of an effect at all at that stage, you'd nearly be better considering a small solar PV installation. Would have a shorter payback period by lowering your energy bills.

Payback without FIT, is about 25 years for normal domestic.

Yellow_Fern

sydthebeat wrote: »

That is not 100% correct.
A new final BER is competely build based.
A provisional BER is design based.

Remember, the DEAP methodology is the only "test" there is at the moment

As I said already, it requires an air tightness test (which tests the build) and it requires certifiers thermal bridge factor sign off as well, which is build based.

The rules for final new build bers, to show part L compliance, are very strict.... And currently this is the ONLY prima facia way to show Part L compliance.

In fairness you are correct with the airtightness test. This is build test but its the exception. BER assessors wont even check lofts for attack insulation and there is absolutely no way for them to check wall insulation.

sydthebeat

Yellow_Fern wrote: »

In fairness you are correct with the airtightness test. This is build test but its the exception. BER assessors wont even check lofts for attack insulation and there is absolutely no way for them to check wall insulation.

i dont know what BER assessors you know, but ones that wont check an attic for insulation will not last long...

there are ways to check for wall insulation, usually the meter box. i myself have an endoscope for this.

but you miss the point for a "New Final BER" in order to check Part L compliance.

as an assessor i need all the documentation that ive already listed. I need specifications signed off from the certifying inspecting engineer. i need to do a site survey myself to check whatever i can physically see and confirm.

im doing one at the moment where i have the following information:

1. invoices from the hardware suppliers for insulations product, showing quantities (13 in total)
2. acceptable details signed off from certifying engineer for thermal bridge factor (as uploaded to BCMS)
3. design drawings indicating locations of ACDs for thermal bridging (as uploaded to BCMS)
4. Heat Pump designer sign off sheet, indicating flow temp and hours of operation (vital for compliance!)
5. product fiche for heat pump for me to manual upload to DEAP library
6. written specification of construction signed off by certifying engineer
7. data sheets of (every single!) window installed.
8. installer certification for attic blown cellulose insulation

and i am awaiting the air tightness test result currently.

I think youll find it is very much a build based assessment