I am ready to insulate my basement, Northeast area. Poured cement 9′ walls that has a foil-faced R-3 blanket nailed on the top half of the walls, bottom half is exposed. I am planning to keep the blanket on the walls, frame 3″ away from the wall & install faced R-11. Right?
Question 2: should I use a heavy mil platstic over the faced insulation or plastic on/over the wall?
Question 3: Use no insulation, use only the heavy mil plastic before the wallboard?
Edited 3/23/2005 11:38 am ET by tjb22
Replies
You should go to homesience.com. They say to never use poly to
put up ridged foam board before you frame then frame in front and
insulated like a normal wall.
Get a copy of FHB 169, the second most recent issue. There's a halfway decent article in there on just that topic. Also, visit http://www.buildingscience.com.
Andy Engel
Senior editor, Fine Woodworking magazine
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
Hey Andy, nice article. I was re-reading the article last night and I have a question about one of the drawings. It shows the floor built so the plywood extends to the walls, minus an expansion gap. Wouldn't it be better to install the foam on the walls before the floor so the plywood stays well away from wall and does not wick moisture from the wall or catch the occasional water drip behind the foam wall?
Thanks,Billy
Thanks for the good words. That detail didn't show well in either the photo or the drawing. The plywood is at least half an inch from the walls. The void is filled with expanding foam.
One emailed criticsm I received made some sense. It was from a fellow whose company does mold remediation. He liked most of the details, but had a problem with the flooring extending below the walls. His point was that if the basement ever flooded - burst pipe, whatever - then most insurance companies would insist on all of the flooring being removed. That's a bit harder when it runs under the walls. I'm on the fence - I think the floor under the walls is a better detail from the standpoint of moisture migration and insulation, but only marginally. And he's right that it would be hard to tear out. Andy Engel
Senior editor, Fine Woodworking magazine
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
Thanks Andy. I also like your use of EPS. I've used XPS on recommendation from Building Science but now they changed their recommendation to allow XPS only if it is under 1" thick. It makes sense to use the EPS to allow easier drying to the inside.
It's a tough call on the floor. If the basement has walls that leak before the floors then it makes sense to put in the wall foam first. But leaks should be dealt with first, of course, but sometimes there's a minor residual problem or the occasional plugged downspout.
What kind of 1/2" exterior plywood did you use? A/C or B/C? I'm doing a basement room next week and it will be the first time to try your floor system.
Thanks,Billy
The first rule in finishing basements is to be sure that any water problems are fixed. And will stay that way. Basements are like boats or ships. They all leak. Knowing that doesn't stop people from using them though, they just plan on removing the water. So, a basement needs either a sump with a pump, or a daylight drain before I'd consider finishing it. I prefer daylight drains because they don't require power.
To your question. I used CDX plywood. It's subfloor. There's no need to use AC or BC ply.
AndyAndy Engel
Senior editor, Fine Woodworking magazine
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig