Basement insulation and furring

The framing is great for wiring and plumbing. The foam board is a good idea. The strapping is not. I get a laugh at TOH shows and videos. When they glued the foamed, did you notice the spacing of the beads? http://joneakes.com/jons-fixit-database/743
Walls, including basements, need to be fire-stopped every 10’ lineally as well as at top and bottom, per Code. Otherwise a fire could start in an outlet and rapidly travel to the other end of the basement or in the floor joist cavities above and surface upstairs across the house. So the strapping needs fire-stopping with fiberglass or other approved materials; http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_3_sec002_par031.htm

It is of premium importance to keep the basement air from reaching the concrete; http://www.buildingscience.com/documents/information-sheets/5-thermal-control/basement-insulation Strapping will allow an air leak at an outlet box to travel everywhere the strapping is installed, both horizontally and vertically. The air current there would negate the insulation R-value; a piece I put together earlier: http://www.diychatroom.com/f98/biggest-loser-fiberglass-insulation-90438/

The rim should be foam board and canned foam, again the stop the air, not with air permeable fiberglass insulation: http://www.buildingscience.com/docu...arriers/critical-seal-spray-foam-at-rim-joist

Use ADA with drywall: http://www.buildingscience.com/docu...rs/air-barriers2014airtight-drywall-approach/

Without a top plate in the video, fire could get in to the whole basement wall above, in the joist spaces, especially with the board run up into them.

TOH appears to know what they are doing, I give them that…..

Gary

Thanks for the information and links.

A few questions:

1) It's not clear to me if a firestop is required every 10' along the vertical axis here, since the basement is masonry construction. If it IS required, how do you achieve this AND insulate the wall with the foam in contact continuously with the wall?
2) Since the foam insulation IS in direct contact with the basement wall floor to ceiling, the temperature of the foam facing the interior of the home should approach that of the interior itself (that is why we insulate). If so, what's the driving force for convection between the drywall and strapping?
3) Can the vertical fire stop (every 10' horizontally) simply be attained by using spray foam at the air gap left between the horizontal (first set of straps) and second (vertical straps)? This is only a 3/4" airspace.
4) Using the strapping method, electrical boxes (if full depth) would actually be cut into the rigid foam. Seems to me that this would be less likely to leak air the a regular stud wall with fiberglass insulation. Careful caulking around penetrations into and around the box should negate any airflow around it.

Simply trying to understand advantage / disadvantage of the strapping method shown in the video. It certainly reduces the amount of wooden material required (and thickness of the wall) relative to building another 2x4 framed wall in front if the rigid foam.

Thanks again.

"Fireblocking shall be provided in wood-frame construction in the following locations:
1. In concealed spaces of stud walls and partitions, including furred spaces and parallel rows of studs or staggered studs, as follows:
1.1. Vertically at the ceiling and floor levels.
1.2. Horizontally at intervals not exceeding 10 feet (3048 mm).
2. At all interconnections between concealed vertical and horizontal spaces such as occur at soffits, drop ceilings and cove ceilings." From the public codes sited previously. (Because of the wood strapping).

(2) Any air leak under the wall plate, at the electrical outlets, above the wall if you didn't air seal (fire-stop) there--- close top plates from drywall to concrete. A basement air leak to the dead air space created by the strapping would be a “closed loop” unless I’m reading it wrong,: http://www.aecb.net/PDFs/Impact_of_thermal_bypass.pdf

Even in the basement, air convective loops are present because heated air rises and colder air sinks. I would use some medium or high density fiberglass batting at the strapping to create smaller chambers or cavities in the chance there is a small air leak in the drywall it would be limited to that small confined area. Then the air at the strapping would be truly “dead” with no movement. http://www.explainthatstuff.com/heatinsulation.html

Your plan sounds good to me. You lose more heat above the frost-line: http://www.quadlock.com/technical_library/bulletins/R-ETRO_Value_of_Basement_Insulation.pdf

Yet, there is a limit when cost outweighs the R-value; http://www.enersavesystems.com/pdf/Economic-Thickness-of-Thermal-Insulation.pdf

Check locally on the foam. Let me know what they require, if you would, please. One AHJ required drywall directly attached to the foamboard, not on the frame wall face only.


Gary

Best Practices for Basements

Hey klmeenan,

The standard accepted method for insulating a basement is fairly straightforward.

1. Glue or screw 2" thick XPS, Extruded Polystyrene, foam insulation board to the concrete block walls. XPS is semi-permeable so it won't trap moisture behind the walls creating mold and rot. 2" or XPS = R10, which should be enough for your climate.

2. Tape the seams between the foam board panels with Tyvek tape, or some other strong acrylic based tape. This will prevent air from leaking through the XPS foam insulation board at the seams.

3. Use expanding foam insulation like Great Stuff to seal any gaps between the foam board insulation and the floor. Also air spray the foam in any service penetrations where your electricity, phone, cable, gas and water mains enter your basement.

4. Air Seal your rim joists and bottom plate with scraps of the XPS foam board and Great Stuff. Start by cutting pieces close to the right dimensions. Glue those pieces to the rim joist. Air seal around the perimeter with Great Stuff.

5. Frame a 2X4 wall in front of the insulation. Use a piece of Trex or composite decking for the bottom plate to prevent water from wicking up into the framing.

6. Run your electrical wires, outlets, light switches, plumbing and HVAC ductwork through the walls.

7. Drywall, tape and mud. But be aware that the paper on drywall is food for mold spores. The new types of paperless drywall offer the promise of mold-free basements.

For extremely cold climates, adding 3 1/2" of fiberglass insulation or rockwool insulation between the studs will boost your r-value. Insulating the floor with 2" of XPS and installing a plywood subfloor over top will also increase comfort and energy efficiency.

Controlling moisture in basements

One other thing I forgot to mention...

If your basement seems to be damp or have mold or moisture problems, you probably have a lot of moisture in the soil that surrounds your basement. This moisture can pass through concrete block and poured concrete walls very easily.

In order to control the moisture in your basement, you need to eliminate the water that is getting into the soil around your foundation.

Most of this water comes from your gutters and downspouts. Connect extensions of some kind to your downspouts. Make sure the water is sent at least 10 ft. away from your foundation. Although I'd personally channel it to the street, drywell or french drain for extreme weather situations.

The other way water gets into the basement is through improper grading. Improper grading is when the grass or landscaping next to your foundation is lower than the soil near by. Water always follows gravity and so it flows down hill and collects right next to your foundation.

Proper grading directs water away from your foundation. It may require adding extra soil next to the foundation to raise the grade. Or you can remove the high spots near foundation walls.