Tuesday, October 7, 2008

A Little-Known Wick-Stop in a Foundation

By Dan Morrison

Even though I stopped working at Fine Homebuilding ten months ago, I still get letters from readers asking questions about the articles I developed. Here's one from an engineer in Tennessee asking a question about a drawing we ran in Scott Gibson's article Does Fiberglass Insulation Still make Sense? The article featured a drawing illustrating how insulation is used: in basements, walls, and roofs. It shows a good system and a better system. On both sides of the drawing there's an arrow pointing to the joint between the footing and the foundation wall with a label that says "Paint on damp proofing"

The reader wrote:

To whom it may concern –
I recently purchased the winter 2008 issue of “The
best of Fine Homebuilding.” Cover article is Energy-Smart Homes.
Scott Gibson’s article titled “Does Fiberglass Insulation Still Make
Sense?”, starting on page 26, ends on page 31 with a cross-sectional view of a
house with all of the recommended types of insulation. At the bottom of
the page there is an arrow pointing to the line between the footers and the
poured concrete walls labeled “Paint-on-damp-proofing”. Was this
intentional or is the arrow suppose to point at the outside surface of the
concrete wall? I’ve never seen anyone paint anything on top of the footers
before pouring the walls. Please clarify.
Many thanks,
Jackson, TN
My response to Brian:

Nope, not an oversight. The capillary break staop water from being absorbed
through the footing into the wall and up to the framing. If you’ve got foam sill
sealer on top of the foundation wall then the wall framing is probably safe, but
the concrete slab can still absorb water through the footing. I know, I know,
but there’s foam under and around the slab. If that’s the case, then you’re
probably fine. But when you ask Joe Lstiburek, Bruce Harley, and Andres
Dejarlais to give you a drawing, you get plenty of belts and suspenders.

The main point is that this is a spot most people never realize is
a good wick-stop. Does everybody do it? No. Does anyone? Probably. If you don’t
use continuous rebar between footing and foundation, the building inspector may
have a problem with it because this is technically a slip joint, but using a
keyed joint (as is shown) fixes that problem.

Thanks for noticing
the little things,
Brian's response back to me:

Thanks for the quick response.
Damp-proofing the
footer-wall boundary makes sense and is defiantly something I plan on doing
that I understand the reason for it.
Again, thanks for your
reply. I’ve enjoyed reading your publication and am looking forward to
reading the next issue.
Brian Cotton, PE

Always happy to help. That was some of the most fun of working at Fine Homebuilding -- getting good info to people that care.

--Dan Morrison is the managing editor of GreenBuildingAdvisor.com

Thursday, October 2, 2008

The Environmental Consequences of Excavation

Pete and I visited some job sites in Southern California last week. One site, a rather large home buing built to be a net energy producer, was an excellent example of how important integrated design is. Here, Peter talks with the builder and the structural engineer, Bruce King about how the team re-thought the foundation system.

One of the challenges in this part of the country is earthquakes, so most foundations need to be somewhat over-engineered. The original design was for a pier and grade beam system which required a huge amount of excavation. Bruce wondered if switching to a mat slab would be a better use of materials and on paper it seemed like it was. Once the team started moving dirt around, though, the builder asked some questions. Bruce sat back down at his desk with a fresh pencil and discovered the hidden environmental cost of trucking out dirt and trucking in gravel.

Editor's note: please excuse my cruddy video editing skills. I just wanted to slap this together for a free-lance writer to watch as background info for an article. The picture and sound quality are not what we will get once Rob gets back from Virginia and edits this thing for real.

--Dan Morrison is managing editor of GreenBuildingAdvisor.com