# Finishing a basement



## Windows on Wash (Aug 30, 2011)

I am highly suspect of the quoted R-Value on the core foam.

Even if the interior of the block is insulated, this has little to no impact on the R-Value where the block is solid to the outside and the thermal bridge is not interrupted.

I prefer ISO board to XPS but there may be issues with its compatibility with moisture. 

I think you would be well served to stay within the accepted and tested wall construction methods. 

Paging GBR :whistling2:


----------



## Gary in WA (Mar 11, 2009)

Welcome to the forums!


I agree with WW, above, especially on thermal bridging and the shape of the block leaves un-insulated areas from the outside in. These would be similar to wood studs changing the whole-wall R-value: http://www.coloradoenergy.org/procorner/stuff/r-values.htm
Scrolling down the list, notice your 8” ? concrete block is a *little over R-1* for its thickness between the insulated cells. Looking at the inside cell section you may have 3-1-1/2” areas of solid concrete that is not insulated, per 16” ? each. So 25-30% of your total wall area is insulated to R-1.

After reading these results of a study with foam thickness, scroll to the main page for more reading: http://www.buildingfoundation.umn.edu/FinalReportWWW/Chapter-5/5-optimum-main.htm Compare your Heating Degree Days to the cities listed.

Did you notice page #9 at BSC: http://www.eere.energy.gov/buildings/building_america/pdfs/db/35017.pdf

Did you catch page 10, on thickness here- quite similar: http://www.buildingscience.com/documents/reports/rr-0202-basement-insulation-systems

The *thickness* of board counts, and also *where* it is installed: http://www.quadlock.com/technical_library/bulletins/R-ETRO_Value_of_Basement_Insulation.pdf

No air gap to insulation: http://joneakes.com/jons-fixit-database/743

My guidelines without sites (unless questioned, lol); 
Air (sill) sealer under p.t. bottom plate (as per code)- h.d.galv.nails, air-tight drywall (as per code), rim joist foam board with air seal, fire-block top plate to floor joist cavities and every 10’ horizontally (as per code).

Gary


----------



## econger (Nov 20, 2011)

Thanks for all the input. Makes sense. I know what I need to do to do it right.


----------

