Posted By: Nick ParsonsThe 'Bristolian's guide...' is good, but IIRC the author is fairly dogmatic that 60mm WF should not be exceeded. Other opinions exist. I usually used 100mm Pavadentro (with its 'mineral functional layer') when it was available, but do your homework. 60mm would be 'safe', I think, in most situations (on the right sort of substrates, of course), but be prepared to stand your ground when BCO is looking for 0.3W/m2K. (The 'get-outs' are in AD L1B)

Nick, thanks for that, I’ve seen a post regarding the building regs clause on limiting thickness that needs to be cited for building control purposes. And I’ve heard you speak favourably about Pavadentro before. What do use now that it’s discontinued?

you might learn something from spending 30 mins watching this who knows ?

https://www.youtube.com/watch?v=UYTbMi2Jgfk&feature=emb_rel_end

Posted By: Daveking66 the Steico supplier (Ecomerchant) has advised that their boards should be covered with a layer of waterproof plasterboard if used in a bathroom -

Good news, two suppliers (Unity Lime and Mike Wye) have now advised that I won’t need to add a layer
water resistant plasterboard in the bathroom.

There’s obviously a risk I’m listening just to the advice I want to hear, but the addition of a water
resistant Layer of board (to prevent ingress of water moisture) seemed to defeat the whole
purpose of a breathable system.

Just need to find a system for insulating the pitched section of ceiling now! (which I’ve raised in another post). Thanks for all your comments

Posted By: Nick ParsonsIf they are happy and the walls are not (and are never) going to be covered in impervious coatings/sheets then go with their view. They are both reliable sources. NBT used to do 'free' (you paid for it in the material price, of course) WUFI (interstitial condensation) calcs, which were v useful. I don't know of any supplier which does these now, and if anyone tells me of one I will probably use them!!

The Celotex technical department did a free condensation analysis for me. This was for a different set up though - IWI using PIR onto a cavity wall in which the cavity is filled with Rockwool fibre.

Posted By: Nick ParsonsThe 'Bristolian's guide...' is good, but IIRC the author is fairly dogmatic that 60mm WF should not be exceeded. Other opinions exist. I usually used 100mm Pavadentro (with its 'mineral functional layer') when it was available, but do your homework. 60mm would be 'safe', I think, in most situations (on the right sort of substrates, of course), but be prepared to stand your ground when BCO is looking for 0.3W/m2K. (The 'get-outs' are in AD L1B)

Can anyone advise which part of the L1B regulations will help me fight my corner in regard to the application of a thinner layer of insulation to reduce condensation risks in a solid brick walled Victorian property? Nothing jumps out at me so far

Works for me:

"Historic and traditional buildings where
special considerations may apply

"3.8 There are three further classes of buildings
where special considerations in making reasonable
provision for the conservation of fuel or power
may apply:
a. buildings which are of architectural and
historical interest and which are referred to as
a material consideration in a local authority’s
development plan or local development
framework;
b. buildings which are of architectural and
historical interest within national parks, areas
of outstanding natural beauty, registered
historic parks and gardens, registered
battlefields, the curtilages of scheduled
ancient monuments, and world heritage sites;
c. buildings of traditional construction with
permeable fabric that both absorbs and
readily allows the evaporation of moisture.

"3.9 When undertaking work on or in
connection with a building that falls within one
of the classes listed above, the aim should be to
improve energy efficiency as far as is reasonably
practicable. The work should not prejudice the
character of the host building or increase the risk
of long-term deterioration of the building fabric
or fittings.

"3.10 The guidance given by English Heritage 3
should be taken into account in determining
appropriate energy performance standards for
building work in historic buildings.
In addition English Heritage has produced detailed
technical guidance on how to implement specific
energy efficiency measures. (See list of available
guidance documents at http://www.english-
heritage.org.uk/professional/advice/advice-by-
topic/climate-change/energy-efficiency/.)"

Unfortunately the building regs and the "guidance given by English Heritage" are quite subjective, lots of phrases like 'reasonably practical” but nowhere does it say XX W/m2K. This for the reasons mentioned at the top of this page.

Something official-looking from an insulation supplier might be what you are looking for, but remember that Victorian properties can be retrofitted to BReg standards, so the building control people might have a good point?
Eg https://research.historicengland.org.uk/Report.aspx?i=15746

https://buildingconservation.com/books/retrofit2017/files/assets/common/downloads/publication.pdf

Brief mention on page 8:

Moisture monitoring at New Bolsover
has been carried out continuously
since 2011. During this period seasonal
fluctuations have been observed, with
walls becoming wetter in winter and
drying out during the summer months.
So far, no conclusive evidence of moisture
accumulation behind either insulation
system has been observed, but monitoring
is continuing

WillnAberdeen Cheers for digging those out and pasting up. Much appreciated.

Quite a marked difference in the findings of those reports. I was surprised they found no differences in condensation build up in the walls treated with PIR and those treated with wood fibre board in the New Bolsover end of Terrace Victorian House in the Historic England report.

I found myself wondering if I’d backed the wrong horse, favouring woodfibre insulation, until I read the building conservation report,
page 23, internally insulated walls, which compares a building insulated with 40mm of woodfibre board (Shrewsbury) and one insulated with 100mm PIR (Drewsteignton)

https://buildingconservation.com/books/retrofit2017/files/assets/common/downloads/publication.pdf

Maybe I’m listening to what I want to hear, and although there are a number of factors at play in terms of wall type and aspect, the big takeaway for me is the conclusion:

“In conclusion, we find that the performance of these walls is in part conditioned by their individual material components, including changes made to the fabric to improve energy efficiency. Interstitial condensation has been a particular concern, yet the internally insulated brick wall at Shrewsbury, which uses a limited quantity of insulation and does not incorporate a VCL, has stable vapour responses that operate within safe limits. In contrast, at Drewsteignton, where insulation has reduced the U-value of the wall to a fraction of its previous heat loss and a VCL limits the movement of vapour towards the internal side of the wall, vapour conditions are deteriorating.”

Indeed! And one of those places is on Dartmoor so unsurprisingly it gets wetter in Winter and dries out less in Summer than the other one in Shropshire......

One is cob, the other brick.

That's the problem that daveking is wrestling (and me) - there's so little clean data available! And because the 'right answer' seems to depend on how much water gets into the wall in winter (location, orientation, exposure, surface treatment, construction), nobody can give out a one-size-fits-all target U value, not even in building regs.

Interesting piece in that historic England link about trying to make WuFi prediction match up with what actually happened in real life. WuFi seems to be used lots by architects before renovations. The key parameter was the "rain adherence fraction" (how much of the rain soaked into the wall, instead of running off) and depending what number was picked from 0 to 0.1, the software predicted either doom or happiness. Unfortunately the correct value couldn't be found until a few years of site data were collected after the renovation. Without that, the architect would have to guess a "cautious" or "risky" value.

The heritage building conservation folks and the climate conservation folks obviously have different ideas of what 'risk' means, and the householder has to balance the two!

Also interesting that historic brick was more moisture tolerant and more insulating than the data WuFi used for modern brick, because old brick was more porous.