Crawl space insulation options
House is 1-story 1200 square feet, CA climate zone 3, zip code 95062, about 1/2 mile from the ocean. Existing ventilated (passive vents) crawl space has 18″ clearance, 48″ OC 4x floor joists under sub-floor, perimeter foundation and piers along joists. Clay soil is damp, but downspout diversion and french drain in back yard keep the space from having standing water. House is heated by hydronic radiant heat system, on top of subfloor in 1/2″ sleepers.
Looking to for recommendations on how to retrofit the crawl space. Goal is higher IAQ in the house, so minimize infiltration and delta T between house air and crawl space. Air sealing between house and crawl space is a must, but I’m not sure about the other steps. I don’t want to make anything worse (such as block air from the crawl space to house but make it easier for mold to grow).
Option 1 is to leave the crawl space passively vented, and to spray closed cell foam to the underside of my subfloor (2″ thick, as recommended by spray foam contractor).
选项2是将R-5最小刚性泡沫添加到茎壁上并托架托梁，用相同的刚性泡沫密封通风孔。空气密封到外面。这将需要“条件”的空间，这就是我挂断的地方。我可以添加一个排气风扇（连续或在潮湿或其他控件上），但我不想有被动的通风口，所以供应空气从何而来？
Any feedback appreciated, thanks!
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Replies
菲尔，
Option 2 is the standard advice for those who care about energy efficiency and home performance. If you install a small exhaust fan in your crawl space, along with a floor grille to allow conditioned air from the house to enter the crawl space as makeup air, you won't get any crawl space odors or moisture in your house.
所有细节都在本文中解释：Building an Unvented Crawl Space.
All of that said, Option 1 would work in your climate. Note that most green builders try to minimize the use of closed-cell spray foam because of the global warming impact of the material's blowing agents. If you decide on Option 1, a better approach (from an environmental perspective) would be to install a continuous layer of foil-faced polyiso on the underside of the floor joists, with all penetrations and seams carefully sealed to make the layer airtight.
如果有任何更便宜的情况（由于安装更容易，可能是这种情况），在基础墙上也将击中R5的一英寸闭合泡沫，并且本质上是气密的，没有很多细节。爬网空间的总平方英尺可能小于您正在考虑的地板区域的1200'。在许多地方，用浓郁的油漆喷洒泡沫会通过召集火灾代码。
爬行空间地板需要蒸气屏障，例如EPDM（膜屋顶）或重乙烯。如果使用爬行空间来容纳热水器或空气处理器等物品，则用2英寸混凝土鼠式覆盖它来保护它。和鼠板）走上这条路线。
Thank you both for your responses.
Martin, I am hesitant to install a register between the house and the crawl space for makeup air. We have existing radiant heat installed, so finding a location for this new penetration would be difficult. We also have no air conditioning or forced air at all, so is our indoor air actually considered conditioned enough to work as the makeup air to the crawl space?
我也感谢您对环境影响的注释。
Dana, I will ask about insulating the foundation walls instead. If I go with spray foam under the floor, would I need to paint as noted for fire? Also, we have no appliances in crawl space. Not planning a rat-slab.