[Greenbuilding] Relative humidity in heated houses

[Corwyn]

On 10/27/2010 10:09 AM, Sacie Lambertson wrote:
> Interesting the description of high RH.  I need a RH of at least 50 with
> 55 even better to preserve art in the house.  I fight this every year.
> And yes, I haven't had a blower door test yet (difficult to find a good
> tester in our area), but I believe the house is pretty tight--not air
> tight, but tighter than most.  That said, once we start burning wood, I
> am fighting the RH question all winter, trying to create higher relative
> humidity.  When you suggest a loose house is the reason for the lack of
> humidity but then say you want something lower than 50 I think we are
> probably talking at cross purposes.   Sacie

What constitutes high relative humidity is subject more to preference 
and other conditions than a hard number.  Lower humidity exacerbates 
colds while higher encourages more mold.  So, whichever of these you are 
more susceptible to will drive you opinion on humidity.  The best I 
could find in the medical literature is somewhere between 40% and 60% is 
most healthy (and that is probably for average persons).  Additionally, 
a tight house with a weakness in the insulation envelope somewhere (say, 
bad windows) will be more prone to condensation while one without such a 
weakness will allow a higher humidity with no problems.

This is currently something I am interested in, in relation to producing 
plans for incremental upgrading of old houses to Passivhaus standards. 
If you air seal first (which is probably easiest), humidity will need to 
be carefully monitored so that it isn't condensing on the relatively 
uninsulated sections.

Thank You Kindly,

Corwyn

-- 
Topher Belknap
Green Fret Consulting
Kermit didn't know the half of it...
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