Basement subfloor retrofit insulation options
We recently renovated our 1897 brick workman’s cottage here in Chicago. We’ve done our best to upgrade the energy efficiency of it including insulation upgrades– although based on some of threads, may have made a few not optimal decisions (closed cell soy foam interior – we’re in an historic district so we cannot make any changes to the exterior.). We’re now seeking to tackle our basement floor, specifically insulate it.
This is an existing floor poured by the previous owner in the early nineties. It is a 4” thick slab sitting on a sand/soil base – our ground is very sandy in our particular location. We have no leaks and very little moisture except for one area (6”x 36”) where the below grade exterior brick is absorbing moisture from the ground soil. Our plan is to dig out this area (exterior) and install an exterior water vapor barrier in the Spring. In the interim, we want to begin insulating the floor and installing a ‘finished’ floor. I’ve read through all of the threads as well as a number of building science corporation articles and believe the below is the best approach but am looking for any experience/feedback.
• 1” XPS foam board with taped seams – directly on slab
• .5” plywood mounted perpendicular to the XPS and anchored to the slab through the xps using tapcon screws (necessary to anchor?)
• .5” plywood mounted perpendicular to and anchored to the first plywood layer
• Finished floor options include: floating cork floor, simple sand/stain and seal of the plywood, tile, FLOR carpet tiles, etc. No wall to wall carpeting.
My questions are:
1. Is it necessary to anchor the first layer of plywood if a second layer is being installed?
2. Is it possible to install a single layer of a material such as Richlite (‘skate park boards’) instead of two plywood layers?
3. Is it possible to install a single layer of hardiboard instead of two plywood layers?
The 1” XPS is a definite but we’re flexible on the other methodologies. I’m trying to avoid old school sleepers (poor insulation, height) and simplify installation as much as possible as this will be a DIY as well as retain as much headroom (8’6”) as possible.
Note: The walls are already finished () with the bottom wall stud sitting on the concrete slab.
Posted Nov 30, 2010 5:49 PM ET
Edited Jan 21, 2013 4:34 AM ET
Other Questions in Energy efficiency and durability
Is it OK to step the slab thickness over the footings to accommodate insulation between the slab and the footings?