Rigid Foam Board in Crawl Space, Zone 3
I have a client in Zone 3 whose home is suffering from extensive air infiltration through the diagonally run dimensioned 1x subfloor that is covered with T&G hardwood flooring. The homeowner shows very little interest in encapsulating the vented crawl space and adding a dehu, and I cannot convince them to use SPF in their crawl space floor cavities either. They have read an article that suggests the installation of rigid foam board @ the bottoms of the floor joists. The floor joist cavities in the home currently have R-19 fiberglass batts installed in them that appear to be effectively in contact with the 1x subfloor material. I have reservations regarding the application of rigid foam board at the bottoms of the floor joists due to the air space void that will be created between the rigid foam board and the kraft paper faced fiberglass batt insulation that currently occupies the floor joist cavities.
我已经看到并在过去安装了刚性泡沫板，但是在过去的地板托牙腔内安装了刚性泡沫板，但刚性泡沫板是摩擦配合到腔内的摩擦力，以与底层材料接触。安装到空腔中后，将刚性泡沫板的所有边缘用填缝或喷雾泡沫密封，以消除空气泄漏的任何机会，以绕过刚性泡沫板。然后将玻璃纤维BATT绝缘在没有牛皮纸蒸气延迟器的地板托梁腔中，以增加所提供的R值。所有空气屏障和绝缘部件彼此接触，它们之间没有空气空间。我相信这个申请将有效，但它非常耗时。更不用说这个家庭中的地板托床腔内爬行空间在它们内部有很多对角线交叉支撑，并拆除支撑以摩擦配合安装刚性泡沫板进入蛀洞将是一个真正的痛苦并增加所涉及的时间。
Any thoughts on the installation of rigid foam board @ the bottoms of the floor joists? Does the air space void that will be created between the rigid foam board and the kraft paper faced fiberglass batt insulation create the opportunity for an issue to occur?
谢谢。
Replies
The batts insulation this home has now is worthless, as the floor sheathing should have been sealed. Installing a Dehumidifier would make things worse as you would be drawing moisture from the ground and outside.
You can install 2-1” layers of taped, sealed and staggered rigid foam under the floor joists (2-2” is better), or you could spray 2” closed cell foam. Make sure you seal/insulate all penetrations as well.
克里斯，
The basic problem is that the floor lacks an air barrier. A layer of rigid foam -- or, better yet, two layers of rigid foam with staggered joists, as Armando suggests -- will solve the problem, if the foam is properly installed.
为了创造一个空中障碍，您必须先密封地板组件的周边 - 边缘托梁区域 - 闭孔喷雾泡沫或刚性泡沫的密封矩形。一旦这些区域被仔细密封（限制空气渗透），您可以在地板托梁下安装一层或两层刚性泡沫。
最简单的胶带到胶带是面对箔的聚裂，所以这是我使用的类型。用高质量胶带胶带所有接缝。然后用填缝，罐头喷雾泡沫或来自SIGA或Pro Clima的高品质欧洲胶带密封周边（其中Polyiso符合爬行空间墙壁）。
An alternative approach -- one that your client has apparently rejected -- is to seal the crawl space vents and to insulate the crawl space walls. For more information on this approach, seeBuilding an Unvented Crawl Space。
Just thought I should mention an issue that comes to mind when I see this type of installation mentioned. Assuming the building is in an area where the NEC is enforced, how do you maintain the required access to any junstion boxes and splice points? I have yet to see an older crawlspace where there is not at least a few j-boxes mounted to the sides of the floor joists.
Nathan,
Good point. An electrician has to move all of the electrical boxes first.