[Strawbale] Alternative tightening materials

[RT]

On Mon, 07 Mar 2011 01:14:52 -0500, David Neeley <dbneeley at gmail...>  
wrote:


> On a well detailed straw bale in which you have paid attention to air  
> sealing, don't you then run the opposite problem--having inadequate air  
> changes?
>
> Would it not in such case be prudent to also install an energy recovery  
> ventilator?

> On 03/06/2011 11:02 PM, RT wrote:

>> strawbale construction methodology is inherently conducive to yielding  
>> air-tight buildings


I don't think that there is any question of the necessity of paying  
careful attention to air-sealing
with any well-insulated building, whether it has straw in the walls or not.

Any air-leakage point is a point where bulk moisture from conditioned  
interiors will find its way into the envelope materials and condense  
somewhere within the cross section.

Once that moisture is in liquid form, it becomes more difficult (than if  
it were in vapour phase) for that moisture to get out again even if the  
skin materials are vapour permeable. (ie vapour permeable is not liquid  
permeable).

So what you have is moisture hanging around for a long time and like  
teenagers with too much time on their hands, trouble (in the case of  
building materials, microbial activity) is sure to ensue.

If one is relying upon air leakage through the envelope materials to  
provide the necessary ventilation air changes, then that ventilation air  
is going to be passing through mould/mildew/crud infested materials before  
entering the indoor air environment -- certainly not a scenario that is  
conducive to creating healthful living space.

So if air-tight construction is a necessity with well-insulated buildings  
to preserve the integrity of the materials and avoid potential deleterious  
health consequences to the building's occupants, then it necessarily  
follows that a ventilation strategy be implemented as well to ensure the  
necessary air changes to provide good indoor air quality.

And since the minimum (ie the worst that the Codes will allow) ventilation  
rate requires that the entire
volume of air inside the house (air which you have spent energy to  
condition) be changed a minimum of ~8.4 times a day  ... (ie you need to  
the empty the house of air that has been heated/humidified to 18-21 degC  
/~20 - 25% RH and replace it with fresh outdoor air (which might be at  
minus 20 or minus 40 degC and containing almost no moisture) that has to  
be warmed up to 18 - 21 degC at least eight and a half times every day ...  
and since any energy recovery ventilator worth considering will recover 75  
to 95 percent of the energy from the stale air exhaust stream, I think  
that the choice is a no-brainer (and a Code requirement here in Ontario).


-- 
=== * ===
Rob Tom
Kanata, Ontario, Canada
< A r c h i L o g i c  at  Y a h o o  dot  c a >
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