Replies

1. GBA Editor
   Martin Holladay | Jul 26, 2016 06:08am | #1

   Rheems,
   Your question is a little confusing. I'll try to figure it out.

   First of all, I'm guessing (from the phrase "timber floors" and the spelling of "mould") that you are writing from the U.K. or Ireland. Am I correct?

   One point of confusion: You propose two options -- polyurethane foam or Icynene foam -- even though Icynene foam is polyurethane foam. (Icynene is a brand of spray polyurethane foam.)

   What you call the "sub floor area" is (I presume) what we in the U.S. call a crawl space.

   If you have a damp, moldy crawl space, the usual remedy is to install 6 mil polyethylene on the crawl space floor, and an appropriate insulation (either rigid foam or spray polyurethane foam) on the crawl space walls. Other water management measures (for example, exterior grading or changes to your roof gutter system) may also be necessary. These measures are described in this article: Building an Unvented Crawl Space.

2. 
   Dana1 | Jul 26, 2016 09:24am | #2

   Icynene is polyurethane.

   British spelling conventions such as "mould" or "vapour" are widely used in all commowealth and other former British colony nations- Rheems could just as easily be in (or from) Australia, Bangladesh, or Ghana. But since Icynene is a Canadian company, I'm putting two Loonys on the location being somewhere in Canada, or a Canadian ex-pat living in the US.

   A more precise location and more detailed information about what's under the floor is important though, since it makes a difference as to what works or doesn't.

3. 
   rheems48 | Jul 26, 2016 07:52pm | #3

   I am from Australia. In regards to the products I really wanted to know do I use open cell or closed cell foam? thank you

4. GBA Editor
   Martin Holladay | Jul 27, 2016 05:17am | #4

   Rheems,
   Assuming that you are describing a crawl space that is high enough for human access, the insulation belongs on the crawl space walls, not between the floor joists. The best type of spray foam in this location is closed-cell spray foam.

   Don't neglect all of the other measures mentioned in my article (Building an Unvented Crawl Space).

   Remember, exposed spray foam is a fire hazard. Check with local authorities to determine whether the cured spray foam can be left exposed. In some jurisdictions, it needs to be protected with a layer of gypsum drywall or equivalent.

5. 
   charlie_sullivan | Jul 27, 2016 07:25am | #5

   I would recommend rigid foam board insulation over spray foam, both for lower cost and for lower environmental impact, unless there's a specific need to use spray foam.

6. 
   Dana1 | Jul 27, 2016 08:59am | #6

   Oz, eh? So, do I owe Martin CDN$2 now? :-)

   Australia covers a significant range of climates- care to be more specific about location?

   In general terms, most locations would require a ground vapor barrier such as EPDM or polyethylene sheeting to limit ground moisture from migrating into the space. In many/most but not all Australian locations venting a crawlspace to the outdoors would be fine for purging what ground moisture finds it's way in. In other locations venting the crawlspace would bring more moisture in than it would purge, once a ground vapor barrier is in place.

   Rigid foam on the bottom of the joists puts all of the structural timber inside of conditioned space, where it's average moisture content will be stable and lower. But it may take less rigid foam to insulate the foundation walls rather than the under side of the floor framing, sealing up the crawlspace from the outdoors. In many parts of Australia would be the preferred method from a total energy use point of view. If insulating at the underside of the joists, foil faced polyisocyanruate would be the better choice. If insulating the foundation walls, EPS (expanded polystyrene- the stuff with apparent macroscopic beads used for everything from coffee cups & cheap picnic cooler) is preferable, since polyiso is hygroscopic and would wick up water if placed in direct contact with the ground.