Insulating an unheated crawlspace - DIY Chatroom

indignatz · 10-16-2009, 01:58 PM

Hi guys,
I have seen all sorts of contradictory advice on the internet about the best way to insulate an unheated crawlspace. Let me give you the details of my situation.

I'm in Calgary, Canada so cold winters. The crawlspace is under an addition to the house. Originally this addition, but not he crawlspace, was heated with a second furnace and the duct was run through a hole cut in the dividing concrete wall between the original basement and the crawlspace. We've since consolidated the furnaces back to one although the duct still runs through this cutout and through the crawlspace, and the wall has since been finished on the basement side. That may be unnecessary information but I've provided it nonetheless.

The crawlspace is unheated and unventilated with access through an exterior opening approximately 2'x4'. This opening is covered with what is essentially a 'plug' constructed of wood and weatherstripping that fits snuggly into the opening.

I understand that I need to start with 6mil poly on the floor (which is dirt) and running up the walls, but what I'm confused about is whether to insulate the joists above the crawlspace or the walls, and what material should I be using?

Thanks in advance,
-Mark

ccarlisle · 10-16-2009, 02:05 PM

IMO the easiest is sprayed foam...acts both as insulator and thermal break. You have addressed the vapour rising from the floor but you'd still have to address the vapour getting out which means having a vb on the underside of the floor. Complicated. Look into Tiger foam tanks...

indignatz · 10-23-2009, 02:41 PM

Ok, so assuming I don't want to use sprayed foam, what are my other options.

Thanks.

ccarlisle · 10-23-2009, 02:52 PM

Then, 6" fibreglass - or mineral wool - batts on the underside of the floor you walk on, 2" rigid polystyrene boards on the crawlspace walls and poly on the floor.

indignatz · 10-28-2009, 12:56 PM

Thanks for that. Can you explain the logic behind insulating the walls and the ceiling? I've seen articles that say insulate the walls only and others that say insulate the ceiling only, depending on whether it's vented or not, but I haven't seen anything recommending insulating both.

**Scuba_Dave** · 10-28-2009, 01:28 PM

Are there water pipes or drains in the crawl space?
Do you know how cold it gets down there?

indignatz · 10-28-2009, 01:41 PM

No water pipes but there is some duct. The addition contains a bonus room and a bedroom. I'm not sure how cold it gets, I've only been down there in the summer, but the floors of the rooms above it feel colder than the rest of the house.

Wildie · 10-28-2009, 08:29 PM

Quote:

Originally Posted by indignatz

No water pipes but there is some duct. The addition contains a bonus room and a bedroom. I'm not sure how cold it gets, I've only been down there in the summer, but the floors of the rooms above it feel colder than the rest of the house.

Im in Ontario and I have a winterized cottage that has a complete crawl space.
It has 6 mil poly laid on the ground and held in place with stone weights.
I insulayed the inside of the concete blocks with R12 ROXUL insulation. ( We are lucky here in Canada that this insulation is available. It doesn't seem to be avail. in the US)
The insulation is held in place with insulation mounting pins. These pins have a perforated base and a gob of construction adhesive is placed on the surface and is pressed onto the concrete as required.
Once the adhesive has set up, the Roxul bats are pressed onto the pins. Then 6 mil poly laid over the top and pressed onto the pins as well.
Spring keepers are then pushed onto the pins to hold the plastic and insulation in place.
These pins are very sharp, so I bent the ends back in towards the wall to avoid accidental contact.
Roxul is is the ideal insulation as it is non-absorbant,and is very reasonably priced.
In Canada the crawl space should be conditioned. In the summer A/C will reduce the humidity and of course in the winter keep the floors warm.