[Greenbuilding] CONDITIONED crawlspace ventilation

[Jefro]

We are building in coastal Mendocino county, less than 100 miles north 
of coastal Sonoma county. 

Our inspector has read the Building Science stuff, but still highly 
recommends an insulated floor and vented crawlspace and a poly moisture 
barrier on the crawlspace floor (i.e. on the dirt).  Further, he 
recommends using unfaced batts in the floor so it can all breathe---he 
has seen problems with faced batts with the faces in either direction, 
as the moisture will condense on the batts themselves. 

This is what we plan to do (with unfaced denim batts), although not 
until we dry the underside of the subfloor completely---in other words, 
possibly not until spring. 

Michael McHugh wrote:
> Dan,
>
> With no forced air in the addition and hydronic tubes in the wood 
> floor, it sounds like you are trying to save heating energy. I don't 
> see how heating more space is going to save energy. I don't believe 
> Sonoma County has a hot, humid climate that will cause problems in a 
> vented crawl space. On the contrary, the cooling sea breezes should 
> allow for natural ventilation. A sealed crawl space that has vents 
> into the living space should also have a "rat" slab which will just 
> use more resources unnecessarily. I still believe an insulated floor 
> (weatherproofed as if it was an exterior wall) above a vented crawl 
> space would be better in your climate. I've never been to Sonoma 
> County unfortunately so I would recommend talking it over with the 
> locals or giving  Building Science Corp. a call and asking about your 
> particular situation. Conventional practice isn't necessarily bad but 
> let me know if you find that I'm wrong on this. Good luck.
>
> Mike
>
>
>   
>> Just to clarify,
>> Building Science Corp (http://www.buildingscience.com) has advocated
>> that crawlspaces be moisture-sealed, perimeter-insulated, and
>> mechanically ventilated as part of the conditioned space of the
>> building. (See their site for more information.) This results in
>> better moisture control and energy savings. Conventional practice was
>> to insulate the floor with batts between joists and vent the
>> crawlspace passively with screened holes. I've read that codes allow
>> a conditioned crawlspace if it is mechanically ventilated from the
>> conditioned space above.
>>
>> I was asking about an addition to a house right on the ocean in
>> Sonoma County, California.  I think I'll have energy savings if I
>> condition the crawlspace below the addition, but I need to link the
>> air volumes somehow, and since I have no forced air in the addition,
>> how do I do this? (The addition will have hydronic tubes in a wood
>> floor.)
>>
>> Thanks again,
>> --Dan
>>
>> --- Michael McHugh <mmchugh at vernerjohnson.com> wrote:
>>
>>     
>>>  Dan,
>>>
>>>  You don't indicate what climate you are in or what code you are
>>>  designing to meet. Could you insulate the addition floor and leave
>>>  the crawlspace unheated with screened vents only?  Is there
>>>  plumbing
>>>  and/or ductwork in the crawlspace?
>>>
>>>  Mike
>>>
>>>  >I am designing an addition to be built on a crawlspace foundation.
>>>  >I'd like to seal and insulate the crawlspace for energy
>>>  conservation,
>>>  >but I think codes require some kind of mechanical ventilation of
>>>  the
>>>  >crawlspace.  Since my addition has no mechanical ventilation, I
>>>  don't
>>>  >want to add a fan just for the crawlspace. Is there any way to
>>>  ensure
>>>  >an air change by passive means?
>>>  >
>>>  >If we put a heat recovery ventilator on the house, can I just link
>>>  >the crawlspace using air transfer grilles?
>>>  >
>>>  >Thanks,
>>>       
>>  > >Dan Johnson
>>     
>
>