Thursday, May 22, 2014

Crawlspace Insulation

Crawlspace insulation under enclosed porch

The current project on the perpetual house (perpetual building mode, that is) is insulating the crawlspace. Anything in a crawlspace is a pain, but insulating in a crawlspace is particularly painful - insulation in your eyes, breathing insulation, insulation on your skin, etc, etc. I wear a mask, glasses and a Tyvek suit to make it a little less onerous.

We are doing this ourselves because we can and our labor is free. We is me and Rich, my brother-in-law. Also I believe that no one else will do the same quality work. I don't know that to be true, but I suspect it is true based on the insulation work I've seen done in the past by others and the fact that no one else cares as much as I do and no one else is as willing to do this painful job as I am.

Ok, so here is the plan for insulating under the porch - the floor joists are 8" which works out to a 7.5" space for insulation. I have 2 different kinds of insulation that could be used for this area: -
5.5" Roxul mineral wool insulation which is listed as R-23
2" Roxul Rockboard insulation (about R-8).

For the 7.5" space, we installed the 5.5" Roxul first and the 2" Rockboard to finish filling up  the joist bay. The 5.5' Roxul batts were easy to apply, but the 2 ft wide Rockboard was a pain. We had to cut it to fit each of the floor bays which ranged from 21" to 23" wide. Then we had to wedge that stuff in. It was awful. I don't find Roxul to be as horribly itchy as fiberglass, but it does aggravate me, especially when I have to wedge it in with my shoulder and the stuff is going down my neck. Some of it was a little loose so we put strapping across it to hold it until I install the DA vapor permeable membrane from 475 Building Supply.

Larger view of the crawlspace insulation under the enclosed porch. Strapping is to hold it in place until the DA vapor permeable membrane is installed by stapling it to the floor joists. 
Lynn warned me about critters under the house, but other than the Carolina Wren nesting on one of the piers that we are having to work around, and an occasional wasp, critters have not been a problem. There is a dead critter present though. You might be able to see on the pier on your right. See the close-up below.

A little dead bat. I keep meaning to take it down, but I really don't want to touch it even with gloves on. 
I have to fill 2-3 small gaps where we did not abut the Roxul Rockboard together very well and I need to foam the gap between the floor joists which you can see above the bat. That is the space between an open part of the porch and the area below the door to the enclosed porch. 

Well, that's where we are today. I am off tomorrow so I will work on insulating the rest of the floor under the house. It is forecasted to be a tiny bit cooler tomorrow - in other words, it is not supposed to reach 90 tomorrow. Little blessings. Thank you for reading.


  1. Hi I'm wondering two things- what do you hope to gain by the membrane and is it a problem to leave an airspace above in each space if you have the same rvalue below, and if no problem why not use the r-30

  2. Ms. Reingold,

    I'm sorry I'm so late answering your questions.

    You asked about the purpose of the membrane. The Pro Clima DA membrane under the floor joists serves 2 main functions - it serves as an air barrier so air does not "blow" through the insulation diminishing it's effectiveness as insulation and as a vapor retarder. It is not a vapor barrier which would totally prevent water vapor movement - moisture is able to move through the membrane, but not as easily as it would without the membrane. We live in the very humid south so reducing moisture transfer from outside is important. But should the flooring above or insulation get wet there is still some ability for the insulation and flooring to dry outwardly as well as inside the house.

    We also have a pretty healthy animal population here - ants, wasps, and even possums. My brother's trailer had possums in the duct work for the HVAC. This membrane will not prevent a really determined possum from digging through it, but it will deter the possums. Insects will have a pretty difficult time getting through the membrane as well.

    I don't really understand your second question. I am going to post a really detailed description of the under floor insulation, but it will be a few days since we are getting so close to fully finishing the home.

    Thank you for reading the blog.