GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Combining finished crawlspace with unfinished crawlspace

brucepeninsula | Posted in Energy Efficiency and Durability on

Hello all,

Our house is a ranch house built in the 1950s that has a finished, heated crawlspace (cinder block walls with a poured concrete base). There was a one room addition put on in the 70s that is unheated and does NOT have a poured concrete base, it is simply dirt with a vapor barrier laid over the soil. The crawlspace of the addition is not accessible from the existing crawlspace, nor any access door.

We recently did the flooring in the addition and had to open up the sub floor in the addition only to find that it was dripping wet, humid and had pools of water sitting on the vapor barrier, all causing rot of the joists. It was air dried as best as possible and then sealed back up with new flooring over top. There were some downspout drainage issues (sloping towards the foundation) that have been corrected since.

My question is would it be advisable to remove some cinder blocks between the two parts of the house to gain access to the currently inaccessible crawlspace to monitor the water issue down there? I just am unsure of how it will play into the fact that the addition is:
1) unheated as opposed to the main part
2) unfinished dirt floor vs finished concrete of the main part

The house is located in Ontario, Canada.

Any guidance would be much appreciated.

Thanks!

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.

Replies

  1. Expert Member
    Dana Dorsett | | #1

    Having some sort of access is important, even if only for inspection.

    Are the walls of crawlspace sealed & insulated?

    Is the floor of the room over the crawlspace insulated between the joists?

    Ontario is a pretty big place, with a wide range of climate. A more precise location may make a difference in what makes sense to do here.

  2. brucepeninsula | | #2

    Hi Dana, thanks for the response.

    The walls of the primary crawlspace are "insulated" in that there are 1x1 strapping on the cinder blocks with tentest insulating board on them (gaps on top and bottom, I've never understood what that was for) but no, they really are not. However they are heated with exposed pipes from the radiators that give off enough heat.

    The crawlspace of the room in question has insulation in between the joists but again, nothing on the walls.
    And our home is located in Collingwood.

  3. GBA Editor
    Martin Holladay | | #3

    Bruce,
    I looked up Tentest on Google. It looks like it is a type of insulation board made of cellulose, designed for roofing applications. This is absolutely the wrong product for a crawl space -- but you may already know that. For more information on the correct approach, see this article: Building an Unvented Crawl Space.

    Since you opened up your sealed crawl space and discovered a disaster -- everything dripping wet, puddles of water, and rotting joists -- I think you know the answer to your question, "Do I need an access door for inspection?" Yes, of course you do.

  4. Expert Member
    Dana Dorsett | | #4

    Collingwood ON has the characteristic of US climate zone 6.

    The insulation between the joists is making the moisture accumulation issue in the unconditioned crawlspace worse by keeping it (and the cold edge of the floor joists) colder. Leaving it in place is fine, but it's advisable to insulate the walls (and band joist) with at least 2" of EPS (any density) trapped in place with a 2x4 framed mini-studwall insulated with unfaced high density fiberglass or rock wool (~R15), and providing at least a minimal amount of active ventilation of that space with air from the primary crawl space.

    If there isn't enough headroom for that to work, 2" of EPS on the band joists (can-foam sealed in place) and 2" of continuous rigid polyiso cap-screwed to the under side of the floor joists (detailed as an air barrier with foil tape on the seams) can work. That will keep the moisture susceptible wood warmer (= drier), with a vapor barrier between the cold & damp conditions of the crawl space.

    It reads as if the existing insulation in the main crawlspace is also a problem. How much head room do you have to work with in either section?

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |