[Strawbale] code required vapor retarder

[Rob Tom]

Wayneapple at aol.com wrote:

> I just got hit with a code official requiring a vapor retarder(MBC  
> 1403.3)"Vapor retarder. An approved vapor retarder shall be provided.
>    Exceptions:
>          1) where other approved means to avoid condensation and	       
> leakage of moisture are provided.
>          2) Plain and reinforced concrete or masonry exterior		walls  
> designed and constructed in accodance with		Chapter 19 or 21  
> respectively."

> 	What do you think is the best way to get around this?	We were planning  
> on using earth plaster on interior and	exterior with a lime plaster  
> final coat on the exterior.

> I will try to argue "1)" but that seems a stretch.
> I really don't want to use a vapor barrier latex paint on the interior.


Wayne;

I think that you may need to explain the supposed intent of the Code  
requirements WRT the "vapour retarder" requirement to your Building  
Official and then explain how you have addressed those issues (namely (1)  
bulk moisture transport via air leakage (ie your air barrier strategy) and  
(2) vapour diffusion) in your design.

In 1999, a similar matter went before the provincial (Ontario) Ministry of  
Municipal Affairs and Housing for an appeal to the then Ontario Building  
Code requirements  WRT a SB house in Mississauga, Ontario.

John Straube (before he received his doctorate)  appeared as an  
independent expert witness. I think Don Fugler did too but I can't seem to  
find him listed as being such.

The bottom line was:
(if you read nothing else from the bureaucratic bafflegab  below, at least  
read the last half of the sentence in "8. Reasons" near the end.)


=============== Copied from BUILDING CODE COMMISSION DECISION ON B.C.C.  
#99-56-712
IN THE MATTER OF Subsection 24 (1) of the Building Code Act,  
1992.================


7.	Commission Ruling
It is the decision of the Building Code Commission that the proposed  
non-structural insulated wall assembly composed of compressed, stacked  
straw bales enclosed by metal lath and covered on both sides with a 15 mm  
layer of cement stucco and coated (on the interior surface of the inside  
only) with a waterproof finish provides sufficiency of compliance with  
Sentences 9.25.2.1.(1), (2) and (4), Sentence 9.25.2.3.(1), Article  
9.25.3.1., Article 9.25.4.1., Sentence 9.25.4.2.(5) and Articles 9.28.4.2.  
and 9.28.4.3. on condition:
i.	That the appointed independent consultant who is a recognized building  
science expert and a registered professional engineer in the Province of  
Ontario and that the architect of the project who is a registered  
professional architect in the Province of Ontario provide their  
professional stamps on the architectural drawings and details provided to  
the municipality;
ii.	That the independent consultant ensure that the recommendations  
regarding straw bale construction contained in his report to the  
Commission are adhered to in the subject building;
iii.	That the independent consultant review and approve the as constructed  
building and submit written confirmation of same with the municipality;
iv.	That the proposed straw bale wall assembly be used on the ground floor  
only of the subject dwelling;
v.	That the proposed straw bale wall assembly be used in a non-structural  
situation only;
vi.	That the proposed straw bale wall assembly be constructed with a  
system of horizontal stabilizers consisting of a top ladder and bottom  
sill plate connected together with a series of pretension vertical tie  
down wires;
vii.	That the proposed straw bale wall assembly be further constructed  
with angled re-bars laid flat on each course of bales at the dwelling's  
corners and that a series of spikes, having a length of more than twice  
the height of the bales used, be driven vertically downward into the bale  
courses;
viii.	That the proposed straw bale wall assembly be further constructed  
with wire mesh installed on both the interior and exterior surface of the  
straw that spans from top to bottom of the wall and which are fastened to  
the top ladder and the bottom sill plate and that both wire meshes are  
tied together by a series of tie backs running horizontally through the  
straw;
ix.	That the window and door units in the proposed straw bale wall  
assembly be supported with wooden framing members that are attached to the  
top ladder and bottom sill plate;
x.	That the proposed straw intended for use in this dwelling consist of  
prestressed, two-string bales with a minimum density of 113 kg/m3 and a  
minimum RSI value of 3.00 (for Zone 1);
xi.	That the proposed straw be treated and dried prior to installation in  
the subject dwelling and that it be kept dry at all times during  
construction;
xii.	That the proposed dwelling be constructed with a roof projecting 900  
mm over the walls of the subject house; and
xiii.	That the proposed dwelling be constructed with a 710 mm high masonry  
splash skirt surrounding the ground floor perimeter of the house and  
attached to the subject straw and stucco wall assemblies.

8.	Reasons
With conformance to the above conditions, the Commission is satisfied that  
the proposed wall assembly will be properly designed by a licenced  
architect and reviewed, inspected and approved by a certified engineer  
expertly qualified in this field, that the wall assembly will be used in  
the appropriate circumstances for the subject house, that the wall  
assembly will be constructed with adequate vertical and lateral support,  
that the walls be sufficiently air tight and vapour permeable as required  
in engineer's report, that the straw will be appropriately treated and  
handled before and during construction, and that the house itself will be  
designed to protect the exterior walls from excessive exposure to moisture.

=================End of copied material===========================


The full document WRT the appeal and ruling may still be available on-line  
at the Ministry website:

    www.obc.mah.gov.on.ca

but if not, let me know and I'll put up a copy into the FILES section at  
SB-r-Us.



-- 
=== * ===
Rob Tom
Kanata, Ontario, Canada
< A r c h i L o g i c  at   C h a f f Y a h o o  dot  C a  >
(winnow the chaff from my edress in your reply)