Posted By: Ed Davies

Posted By: JC48Hi _ I have gone for full fill batts 32 dritherm equivalent and found a supplier almost 50% lower than the rest at a little over £4M2 for 650m happy to say who it is if anyone interested as this saved me £3K

Please do. I, and I expect others, would be grateful for a whisper if you feel it's rude to point publicly for some reason.

and me please, why not post it for all to see (unless you are associated with the company?

JC48 just post it up we all wont to know ?

On thing with pur/pir in timber frame , you don't very good sound proofing . Friend just did a 2nd floor extension with timber stick build and PUR inbetween and inside joists , now lays in bed on a Sunday morning listening to the kid play in the garden next door. wouldn't get that with rockwall

Hi the material I bought is Superwall 32 batts and the price was £4.25 from Encon Insulation Witney - hope that helps - wasn't sure of the etiquette re naming companies - I have no connection whatsoever other than as a customer with Encon

I used Encon in Glasgow for all my insulation. Cheapest by far and MOL deliveries (Mechanical Off Load). Also for plasterboard.

thanks JC - and local too!

Posted By: borpinIs there anything in the fact that a 'wool' type insulation allows a certain amount of air to circulate V a PIR EWI type construction that is sealed so no air reaches the inner leaf?

Would you see a significantly reduced insulation effect in an exposed area?

The issue of air movement in mineral wool insulation comes up for discussion a bit here in Sweden, (normally by sales guys trying to justify why their cellulose insulation is double the price of mineral wool).

So before deciding on using mineral wool myself I did a search for research on the subject.

I did find a research project by Gothenburg University (I don't have the link to hand but if anyone is interested I can see if I can find it again).

The main points were that air movement within mineral wool (or glassfibre) insulation can reduce it's effectiveness by as much as 50% but some simple measures can ensure that you don't have air movement within the insulation.

So you should first take steps to ensure that you don't have wind blowing through the insulation, this can be as simple as a layer of building paper, it doesn't need to be airtight just act as a wind barrier.

Even with this wind barrier in place there is still the possibility of air movement within the insulation as a result of convection currents, however the research found that convection currents can only be established when the temperature difference across the insulation is greater than 30ºC, assuming an interior temperature of 20ºC then the risk only arises when the outside temperature is below -10ºC.

Again it is easy to combat this. If you are in an area where temperatures regularly dip below -10ºC then you just need to place a wind barrier at some point within the insulation so that you don't have a delta T of greater than 30ºC across any one portion of the insulation. So for example with attic insulation a layer of building paper between layers of insulation will do the trick.

I'd imagine that there are fairly few areas of the UK where temperatures regularly dip below -10ºC?

To me this cries "Shelter Belt", but perhaps I'm indoctrinated by large gardens :-).

Ferdinand

Posted By: davidfreeboroughThe general rule with mineral wool insulation is not to allow any air movement adjacent to the insulation.

How about a full fill cavity? Still needs vents does it not? If there is no air movement then they are pointless anyway.

Posted By: Chris P BaconI know very little on the subject but my understanding is that in a wall the wind break needs to be in the vertical plane parallel to the inner and outer surfaces. In the situation you are describing you will still have your total temperature difference across one continuous section of insulation.

Doh! Yes, you're quite right. The reason I was thinking about my approach is that convection is also supposed to be suppressed by a lack of height. So short windows don't suffer from downdraughts in the same way as tall windows, for example. But then again, the U-value of a rooflight is worse than that of the same window in a wall, supposedly because of convection. I don't understand how it all hangs together :(

So I would be interested in a link to the paper you mentioned if it comes easily to hand.

Posted By: borpinHow about a full fill cavity? Still needs vents does it not? If there is no air movement then they are pointless anyway.

A masonry cavity fully-filled with mineral wool insulation doesn't need ventilation. However, any cavity trays would normally be drained by smaller "beak weeps" or similar. Interestingly the Denby Dale Passivhaus seemed to dispense even with these. The stone outer leaf used lime mortar & so didn't need the beak weeps.

David