Reflective VCLs and internal wall insulation - Am I over thinking this?

[TinRobot]

Hi folks - 

 

I have spent hours looking at different solutions to make my bungalow conversion as good as possible within some sort of budget. For the old existing walls (most north and east facing) I have come up with the following:

 

25mm x K Rend

100mm x Standard Brick 

65mm x Blow in Knauff Superfill 34 CVI (this will blow out the nasty stuff in there currently) 

100mm x Standard Block (0.15 W)

1mm x DuPont AirGuard Reflective VCL (was considering the 6mm superfoil but not sure if it makes any difference - could do with some advice on this one) 

25mm x Baton - 600mm centres (to provide air gap)

57.5mm x Kingspan Kooltherm K118 Insulated Plaster Board

3mm x Plaster

 

Total internal depth lost 86.5mm

 

Does this sound a logical approach? 

 

I am like a rabbit in the headlights! 

 

[Nickfromwales]

Hi.
You don’t need an air gap internally, more a service void for pipes and cables etc. 
You can get liquid membranes also, such as Passive Purple ( check out Intelligent Membranes online for more product info / suitability etc ) which can go internally.

Other than that, it sounds as though your on the right track. 
What nasty stuff is currently in the cavity? Beads or wool? If wool, that needs professional removal first, as this can have problems later in life which you may not be insured against if not removed ( and certified ? ). 

[TinRobot]

Thanks Nick. The current cavity insulation is suspected to be urea-formaldehyde foam. It is like dust and I cannot believe it is doing anything good. 

 

We have been told by a cavity insulation company that they can blow it out as they pump in the Superfill stuff. Originally they were going to put in Superfill 44 but I have asked them to use the better 34 product. 

[nod]

K Rend will be 15 mil rather than 25 

Rest sounds good 

[Iceverge]

Kooltherm is very dear compared to alternatives. At your thickness it's £33.91m2

 

70mm Knauf omnifit + plasterboard is about €13/m2

 

50mm PIR  + plasterboard is similarly about £13.50/m2. 

 

 

All have similar U values. 

 

 

 

If it was me, I'd have a good look at the state of the cavity insulation as is. It mightn't be as bad as you think. 

 

Then probably 70mm mineral wool between battens and plasterboard or.... 

 

40mm/50mm PIR foamed and taped at the joints and then 22mm battens for a service cavity and then plasterboard and skim. 

 

 

[TinRobot]

Thanks for the response. You're right of course on cost. My problem is two fold - first I am living here currently and it is freezing. We have no central heating and everything has been bodged or done on the cheap. Being half frozen isn't helping my fear that I am not insulating enough. 

 

The Kooltherm seems to have 0.019 thermal efficiency whereas standard PIR is 0.022 and normal wool slabs are at 0.32. I think I would prefer to spend the extra - it is just finding the best I can for the price. I just don't want a cold house that costs a fortune in electric to heat and 0.18 seems to be the min for building regs now so that would be ideal !

[Iceverge]

Have you considered EWI as you are rendering anyway? 

 

No loss of internal space either. 

 

£30/m2 would buy about 200mm of EPS Which would probably boost you to about 0.13 W/M2K. 

[TinRobot]

24 minutes ago, Iceverge said:

Have you considered EWI as you are rendering anyway? 

 

No loss of internal space either. 

 

£30/m2 would buy about 200mm of EPS Which would probably boost you to about 0.13 W/M2K. 

 

Hi Ice 

 

I initially wanted that solution but I am really struggling to find a supplier who will render as well. The costs go through the roof. I live on the coast and the old walls are very exposed. In our small village we have some renders cracking etc. so I am not that confident (I am dipping into savings and this is a one shot at getting it "right" - I won't be able to afford fixing this stuff in 10yrs). 

 

The other issue with EWI is the I have a new flint wall coming off of one of the walls that needs insulating and the EWI hasn't been accounted for (I am not that impressed with architect). 

 

Constant panic trying to weigh everything up. Thanks again for the suggestion. 

[Iceverge]

Coast = Windy = Airtightness+windtightness as #1 priority. 

 

Have you considered closed cell foam in the cavity and maybe a battened service cavity inside or insulated plasterboard. 

 

Don't forget airtightness needs to go with ventilation, mechanical preferably.