Documentation regarding cavity construction/airtightness resulting in elevated moisture levels

Edward Grove made this Official Information request to Ministry of Business, Innovation & Employment

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From: Edward Grove

Dear Ministry of Business, Innovation & Employment,

Please provide copies of all research documentation, analysis, internal reports and internal and external communications dating from 2013 onwards regarding the presence and potential ramifications of elevated (80% - 100%) relative humidity levels (with or without any associated condensation) within the wall structures of new (post 2005) timber framed cavity-constructed residences including in particular:

(a) Any analysis as to the impact of such elevated relative humidity levels (with or without any associated condensation) on timber framing moisture levels and decay and mould risks;

(b) Any research/analysis or correspondence as to the impact of the elevated (80 - 100%) relative humidity levels upon the rate of loss by diffusion of boron from timber framing, the impact of the elevated relative humidity levels upon the ultimate residual (equilibrium) levels of boron in the timber framing, and consequent impact on the efficacy of the boron treatment for control of decay fungi and mould. More generally, any research/analysis or correspondence as to whether or not boron treatment will be sufficient to prevent mould and/or decay fungi growth on timber framing in elevated (80% - 100%) relative humidity levels;

(c) Any field observations of (or correspondence/notes regarding) mould and decay-fungi growth in the internal wall structures of new (post 2005) timber framed and cavity constructed buildings where no material external liquid moisture entry (i.e. leaks) has been detected;

(d) Any research/analysis, notes or correspondence regarding whether or not current (post 2005) timber framed cavity construction is achieving, or is likely to achieve, or can/should be modified to achieve, compliance with the Building Code in light of the potential impacts of elevated interstitial relative humidity levels and/or any associated condensation.

Yours faithfully,
Ed Grove

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From: Ministerial Services
Ministry of Business, Innovation & Employment

Ref: 2021-2049

Dear Ed,

On behalf of the Ministry of Business, Innovation and Employment I
acknowledge your email of 14 April 2021 requesting under the Official
Information Act 1982 (the Act), the following:

“Please provide copies of all research documentation, analysis, internal
reports and internal and external communications dating from 2013 onwards
regarding the presence and potential ramifications of elevated (80% -
100%) relative humidity levels (with or without any associated
condensation) within the wall structures of new (post 2005) timber framed
cavity-constructed residences including in particular:

 

(a) Any analysis as to the impact of such elevated relative humidity
levels (with or without any associated condensation) on timber framing
moisture levels and decay and mould risks;

 

(b) Any research/analysis or correspondence as to the impact of the
elevated (80 - 100%) relative humidity levels upon the rate of loss by
diffusion of boron from timber framing,  the impact of the elevated
relative humidity levels upon the ultimate residual (equilibrium) levels
of boron in the timber framing, and consequent impact on the efficacy of
the boron treatment for control of decay fungi and mould.  More generally,
any research/analysis or correspondence as to whether or not boron
treatment will be sufficient to prevent mould and/or decay fungi growth on
timber framing in elevated (80% - 100%) relative humidity levels;    

 

(c) Any field observations of (or correspondence/notes regarding) mould
and decay-fungi growth in the internal wall structures of new (post 2005)
timber framed and cavity constructed buildings where no material external
liquid moisture entry (i.e. leaks) has been detected; 

 

(d) Any research/analysis, notes or correspondence regarding whether or
not current (post 2005) timber framed cavity construction is achieving, or
is likely to achieve, or can/should be modified to achieve, compliance
with the Building Code in light of the potential impacts of elevated
interstitial relative humidity levels and/or any associated condensation.”

Your request is being processed in accordance with the Act and a response
will be sent to you in due course.

If you have any enquiries regarding your request, or its urgency, feel
free to contact us via email at [1][MBIE request email].

Nâku noa, nâ

MINISTERIAL SERVICES

Corporate, Governance and Information

Ministry of Business, Innovation and Employment

Level 4, 15 Stout Street, PO Box 1473, Wellington 6140

NZBN 9429000106078

 

[2]www.govt.nz - your guide to finding and using New Zealand government
services

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From: *OIA
Ministry of Business, Innovation & Employment


Attachment image001.png
30K Download

Attachment Scion final report Nov 2012 A826150.pdf
2.5M Download View as HTML

Attachment framing final copy 1.pdf
655K Download View as HTML


Hello Ed

 

I’m writing in regard to your request to MBIE for the following
information:

 

Please provide copies of all research documentation, analysis, internal
reports and internal and external communications dating from 2013 onwards
regarding the presence and potential ramifications of elevated (80% -
100%) relative humidity levels (with or without any associated
condensation) within the wall structures of new (post 2005) timber framed
cavity-constructed residences including in particular:

 

(a) Any analysis as to the impact of such elevated relative humidity
levels (with or without any associated condensation) on timber framing
moisture levels and decay and mould risks;

 

(b) Any research/analysis or correspondence as to the impact of the
elevated (80 - 100%) relative humidity levels upon the rate of loss by
diffusion of boron from timber framing, the impact of the elevated
relative humidity levels upon the ultimate residual (equilibrium) levels
of boron in the timber framing, and consequent impact on the efficacy of
the boron treatment for control of decay fungi and mould.  More generally,
any research/analysis or correspondence as to whether or not boron
treatment will be sufficient to prevent mould and/or decay fungi growth on
timber framing in elevated (80% - 100%) relative humidity levels;    

 

(c) Any field observations of (or correspondence/notes regarding) mould
and decay-fungi growth in the internal wall structures of new (post 2005)
timber framed and cavity constructed buildings where no material external
liquid moisture entry (i.e. leaks) has been detected; 

 

(d) Any research/analysis, notes or correspondence regarding whether or
not current (post 2005) timber framed cavity construction is achieving, or
is likely to achieve, or can/should be modified to achieve, compliance
with the Building Code in light of the potential impacts of elevated
interstitial relative humidity levels and/or any associated
condensation.  

 

MBIE holds no research, analysis, or reports that would fall within the
scope of your requests (parts a, b, and d). However, there are two pieces
of analysis that technically fall outside the scope of your request but
may provide the information that you are looking for: Scion’s Report on
the Efficacy of Brush-on Remedial Treatments on Radiata Pine Framing from
2012 and the research article Effectiveness of on-site remediation
treatments for framing timber, by Singh, Page and Bennett. Both have been
attached for your reference.

 

With regard to correspondence or notes relating to the information you’ve
requested in parts a, b, and d, MBIE staff are not aware of any
information within scope of these parts of your request. Definitively
determining whether MBIE holds any notes or correspondence that mention
the topics you’re interested in would require MBIE to search through a
significant quantity of emails and documentation. As such, unless you are
able to narrow the scopes of the four parts of your request, MBIE will
likely have to refuse them under section 18(f) of the Official Information
Act, as the information requested cannot be made available without
substantial collation or research.

 

With regard to part (c) of your request, MBIE is unaware of any documents
or correspondence specifically related to such field observations.
However, some reports or other documents related to Weathertight Home
Resolution Services (WHRS) investigations or Financial Assistance Package
(FAP) repairs may record individual observations of such issues if these
were identified in the course of weathertightness investigation or repairs
to a specific property.

 

Given the number of investigations and repairs carried out, unless you are
able to narrow the scope of this part of your request, perhaps by
including a particular address or claim number you’re interested in, MBIE
will likely have to refuse this part of your request under section 18(f)
of the Official Information Act, as the information requested cannot be
made available without substantial collation or research.

 

To set up a time to discuss whether you would like to refine your request,
or if you are satisfied with the documents we have provided you here,
please contact me as soon as possible.

 

Sincerely

 

Jon Little

SENIOR MINISTERIAL WRITER

Corporate, Governance and Information

Ministry of Business, Innovation and Employment

[1][email address

Level 4, 15 Stout Street, Wellington 6011 | PO Box 1473, Wellington 6140

[2]cid:image001.png@01D5FDFB.FA9ADF50

 

 

[3]www.govt.nz - your guide to finding and using New Zealand government
services

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From: Edward Grove

Hi Jon

Hopefully the below is of assistance. I could be completely off-base with my concerns, but in any event hopefully the below somewhat clarifies where I'm coming from.

As recorded in BRANZ study report SR344 "Vapour control in New Zealand Walls" ([2016] - G Overton) BRANZ undertook two years (elsewhere referenced as three years) of testing from 1 May 2014 onwards of cavity construction methods, with a particular focus on the potential for interstitial condensation, due to (amongst other factors) "growing anecdotal evidence" of problems with interstitial condensation.

Also refer Mr Overton and BRANZ's 2015 paper in the Canadian Journal of Civil Engineering "Hygrothermal performance of New Zealand wall constructions - meeting the durability requirements of the New Zealand Building Code" which reported upon the same experimental results as BRANZ study report SR344.

From SR344 the majority of the cavity-constructed wall sections were found to have "measured (relative) humidity of 100% for significant periods of time”. The only exception (construction having an SVR installed) maintained a constant relative humidity of approximately 90%.

Wood moisture contents were recorded at above 18% over the period July – October annually.

Vapour pressure (relative humidity) was regularly higher than both the internal or external relative humidity, meaning that, to quote Mr Overton "moisture is somehow being added to the [inter-wall] space".

It seems clear that the stack-effect is being disrupted. i.e. warm humid air from the interior is cooling, including by mixing with cooler air entering from the exterior, within the wall-space rather than being able to (as in non-cavity construction) pass through the wall structure so as to cool (and release moisture) outside of the building envelope.

As Mr Overton records in BRANZ study report SR344 "high humidity within structures can support mould growth and corrosion/decay without condensation occurring. For this reason, ASHRAE 160 has a series of failure criteria relating to different averaging periods for the relative humidity on any surface, specifically that:
(a) 24-hour average should not reach 100%
(b) 7-day average should not exceed 98%
(c) 30-day average should not exceed 80%.
The third criterion is specifically aimed at preventing mould growth and corrosion".

Mr Overston's conclusion was that: "The humidity in New Zealand walls typically exceeds ASHRAE criteria and is at risk of supporting mould growth.... Going by the ASHRAE failure criteria, in particular, the 30-day average criterion, very few of the wall constructions in this analysis would be deemed acceptable"..."If the cavity moisture levels indicated by WUFI are accurate, the models suggest that current typical New Zealand walls are at a high risk of damage due to mould growth".

The MBIE in its report for BCTRAG of 21 February 2020 headed "Airtight Buildings Causing Moisture Issues” (authors, R Almand and R London) also noted that the increased air-tightness of buildings was raising internal humidity levels and giving rise to a risk of deterioration of building structures and health risks, - particular relating to decay and mould fungi.

In BRANZ study report SR361 "The selection and hygro-thermal modelling of new New Zealand dwellings" (November 2016) it was reported that:

“At this stage, the assessment of risk of timber decay is not possible as insufficient data is available on the various decay species. However, projects are underway that will start to fill this gap, at Lund University and others. In addition, a related BRANZ Levy proposal is being considered”....“Currently, no consideration can be given to decay of timber due to insufficient data being available, but the use of WUFI Bio or the MRD post processor from Lund will enable the assessment of mould growth potential on wall surfaces and inside the construction.”

In BRANZ study report SR341 “The role of Ventilation in managing moisture inside New Zealand Homes” [2015] (S McNeil, M Pagmann, P McDowall and M Bassett) the authors noted that “observations of the presence of mould and mildew were made at several of the homes studied”.

In BRANZ study report SR399 “The effects of humidity on gypsum plasterboard used as lateral load bracing for buildings” (June 2018) the authors noted that there were significant reductions in strength of plasterboard, of potential concern where the plasterboard was being used for lateral load bracing, at relative humidities beyond 75%, with “continued decreases in strength up to 97% RH, the maximum RH tested for this project”….”Observable changes in performance were only observed at RH levels starting at 80% …These humidity levels are in general greater than what would be expected to occur in the interior of residential buildings and also for typical laboratory conditions, even for spaces that are regularly exposed to exterior conditions”.

i.e. as well as the observed raised relative humidity levels posing a potential for increased fungal activity, there are potentially adverse effects on the strength of structural materials exposed to the elevated relative humidity levels within the building cavity that were observed in BRANZ study report SR344.

In terms of the risk of mould and decay fungi growth, the key issues appear to be:

(a) What wood EMC is likely to result from the raised relative humidity levels, and will this be sufficient for mould or decay fungi growth? If so, over what time period will material effects manifest?

(b) To what extent will current boron treatments inhibit or eliminate such mould or decay fungi growth?

It is now well established that decay fungi and mould can establish in all pinus sapwoods (but not necessarily other sapwoods including that of non-pinus conifers) well below fibre saturation, and indeed well as low as 17 – 20 % EMC. Growth will however be less vigorous than at moisture contents above fibre saturation.

Similarly, it is well established that boron leaches from wood surfaces when exposed not just to liquid moisture, but also when exposed to moisture vapour (i.e. humidity), but (it would appear) only to a material degree when the wood moisture content is at least 20%. Refer “Reducing Leaching of boron-based wood preservatives – A review of research” (Obanda, Shupe and Barnes), Bioresource Technology 99 (2008) 7312-7322. The authors note that that such leaching by diffusion appears to self-limit at levels above (unstated) toxicity levels. Per Krabeenhoft (2003) the movement through, and from, wood of boron by diffusion would appear to require consideration of the diffusion from/through bound water, water vapour and free water within the wood, but analysis is (or, at least, was then) hindered by the lack of established diffusion co-efficients for boron.

Consequently we need to know:

(a) The relationship between relative humidity levels with the rate of loss, and the ultimate equilibrium levels, of boron in wood. One would expected that so long as there is constant replenishment/movement of the humid air at the wood surface/air boundary (so as to provide a boron sink) increasing relative humidity will increase the rate of leaching and decrease the ultimate amount of boron retained in the wood; and

(b) The boron retention required for mould and decay fungi toxicity at the moisture and temperature levels likely to be present in the wood during the observed periods of elevated relative humidity.

There is, as BRANZ has already observed, a considerable degree of variation in the reported toxicity levels of boron to decay fungi.

Certainly per Scion’s 2010 report “Durability of Boron Treated Radiata” (Hedley, Page, van der walls, Nasheri and Durbin) at the very least when wood moisture is maintained well above fibre saturation (45% moisture content reported as average in the report) boron exhibits high toxicity even at extremely low concentrations.

However, most researchers dating back to the 1950s have reported much higher required levels of boron for toxicity than Scion’s research.

One possible explanation may be that boron appears to display higher toxicity when present in solution in free-water within the lumen, rather than within the cell wall. i.e. boron is more toxic to decay fungi when wood moisture levels exceed fibre saturation.

That would be consistent with the experimental results reported in the Record of the 1983 Annual Convention of the British Wood Preserving Association (“Borate Diffusion Techniques for the In-Situ Treatment of Joinery”, Dicker, Dickinson, Edlund and Henningsson) where it was reported that boron treatment:

(a) did not fully inhibit decay fungi growth in sapwoods at a wood moisture content of 22%, while being wholly effective at moisture contents of 24% and above; and
(b) did not fully inhibit decay fungi growth in juvenile wood at a moisture content of 25% or below, while wholly effective at moisture contents of 28% and above.

Growth was observed to be slowed even at the lower wood moisture contents compared to untreated controls.

To quote the authors “at moisture contents above 25 per cent sterilisation of relatively large infections in the inserted dowels is achieved in sap, heart and juvenile wood and below this moisture level colonisation from the dowels is prevented to a large extent to a point where this lack of moisture becomes the limiting factor for growth”.

So, we have a scenario where:

(a) the majority of cavity construction methods tested are causing elevated relative humidity levels within walls, to the point that high (but below fibre-saturation) moisture levels within timber framing can be anticipated. Those moisture levels could, but for boron treatment, be sufficient for very slow, but nonetheless overall exponential decay and mould fungi growth (per Vittanen’s formula);

(b) boron can be expected to slowly leach from the wood, to some (it appears, currently unknown) ultimate equilibrium level, into the water vapour in the air. The equilibrium level is likely to be somewhat dependent upon the relative humidity levels to which the wood is exposed. Indeed higher relative humidity levels should theoretically increase the rate and extent of leaching, ultimately resulting in lower residual/equilibrium boron concentrations in the wood;

(c) boron can, possibly, be expected to have reduced toxicity (but still some significant inhibiting effect) on decay fungi (and possibly mould fungi) at wood moisture levels below fibre saturation.

Overall, what we need to know is whether there is now a risk of very slow, but nonetheless exponential, mould and decay fungi growth in a significant number of timber-framed and cavity constructed residences in Auckland (and similar climates).

If so, are we facing a potential wave of material structural failures (from decay fungi) or heath/habitability issues (from mould fungi) and if so, of what magnitude and over what time-frame?

A secondary consideration is what other adverse structural impacts the increased relative humidity levels might have, whether in terms of structural materials such as plasterboards or other lining materials, or corrosion of fasteners, or impact upon the integrity/durability of adhesives.

Yours sincerely,

Edward Grove

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