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lackofunds 10-15-2007 12:10 PM

Insulate basement header with imbedded joists???
I have a 1962 house with insulated basement walls. Problem is the headers were not insulated. I have read that its wise to insulate basement headers where about 40% of heat is lost in cold winter climates like the one I live in (Wpg. Manitoba).

I have insulated the header at the wall where the header run parallel to the joists.

Problem: I have read that it is unwise to insulate headers where the joists are embedded in concrete although the reason was not given.

My floor joists are imbedded in concrete.....

Any suggestions about what I should do to insulate these embedded headers??



97catintenn 10-15-2007 11:39 PM

My guess as to why it is unwise to insulate where wood meets concrete, is due to condensation. The concrete being cold and wood being warm creates condensation and it needs to be able to breathe. If you insulate it, you will trap the moisture in and it will rot the wood.

I just saw this on Holmes on Homes earlier this evening, lol.

AtlanticWBConst. 10-16-2007 03:54 AM


Originally Posted by lackofunds (Post 68187)
Any suggestions about what I should do to insulate these embedded headers??

Hopefully all that imbedded wood is pressure treated. Judging by the age of your home, it may not be. If it is not, your best bet is to not touch it, for the reasons that the previous poster listed.
If it is PT, then you can use ridgid foam board attached with construction adhesive and galvanized fasteners (nails or screws)

chris33 10-19-2007 01:01 PM

Natural Resources Canada - Office of Energy Efficiency has helpful information on insulating basements (
They recommend not insulating the joist spaces where joists are embedded. Air sealing these areas is recommended.
I am about to insulate my 100 year old house which has embedded first and second floor joists. I guess the only way to totally insulate the exterior walls is to apply insulation to the exterior but I don’t want to cover up my brick.
Any other ideas on how to maximize insulation while protecting the embedded joist ends from rotting?

cabber24 12-02-2008 11:10 AM

Does it matter if the joists are above grade or not? Would spray foam work? or is that a bad idea too?

mwh 01-02-2009 12:39 PM

embedded joists
i have the same issue. i can't see why if you properly vapour barrier or use spray foam so there is no chance of moisture becoming trapped that it is a problem to insulate between joists. unless they're scared moisture is coming in via a crack in the foundation?

JCAHILL4 01-02-2009 05:03 PM

The joist are going to pick up ambient heat from the house and transfer it down the length of the joist to where they are embedded, where heat meets cold it will create moisture. Spray foam or vapor barrier isnt going to matter, therefore they will need to breathe. :( Some times 100 yr old houses suck.

Wildie 01-02-2009 07:23 PM

Hmmmmmmmm! My daughter has an older home that has a standard box frame construction! At some point, some enterprising sole filled the joist cavities with house brick! Mortared in place! I installed rolled insulation from the sill plate down to the 4 foot mark! ( it came with attached vapor barrier) Using R12 bat insulation, I faced the bricks in the cavities, and ran the v/b over top! The question is, am I facing the same problem as if the joists were embedded?

troyce1 01-03-2009 12:58 PM

what are embedded joists?

Wildie 01-03-2009 06:35 PM


Originally Posted by troyce1 (Post 206238)
what are embedded joists?

When the forms are built for the foundation, the joists are put in place before the cement is poured! The cement is brought up to the level of the top of joists, thus filling the joist cavity with concrete! Its my guess that this methed of construction died out in the period of around 1920. At least I have never seen this on newer buildings!

mwh 01-03-2009 11:59 PM

embedded joists
my joists are embedded in the foundation wall however extend through to the ouside 2x8 end plate, my house was built in '59. because my joist run to the outside end plate they will breathe to the outside therefore it shouldn't matter if i insulate the joist space...correct?

Schultz 01-11-2010 05:37 PM

Embedded Joists in Basement Header, Yes or No?

Originally Posted by Wildie (Post 205935)
some enterprising sole filled the joist cavities with house brick! Mortared in place! The question is, am I facing the same problem as if the joists were embedded?

Just like Wildie, I'm facing the issue of house brick mortared in between the joists (which otherwise sit on top of a poured foundation). The whole inside wall is plastered smooth; a quarter inch of plaster top to bottom, finishing the wall from the bricks up in between the joists right down to the basement floor.

I want to insulate the header area, but I worry these are effectively embedded joists.

Is it safe to insulate in this sort of semi-embedded header space? I can understand the moisture concerns... concrete will generate moisture, and wood will hold it. But my foundation runs high up off the ground and there's little hint of any moisture problems anywhere.

I'd like to go for it.

Gary in WA 01-11-2010 09:21 PM

  • Rim joist assembly must be insulated with air impermeable insulation
  • Interior air cannot access concrete condensing surface or rim joist condensing surface due to spray foam layer
  • Spray foam insulation layer is vapor semi-permeable permitting inward drying
  • Spray foam must be covered with fire/ignition barrier Highlights mine. From under Fig.4:
Another good read: There is also one on stone foundation insulation.

Be safe, Gary

gregzoll 01-11-2010 09:30 PM

I used Kraft faced R-13 around my basement Rim Joist & header pockets. It has helped a lot in stopping the cold. That along with using Window & Door foam to seal a few cracks between a couple of joints on the sills, and basement window headers. Next year, the windows are getting replaced with more energy efficient, since they have been in the house for over 70+ years, and when we reglazed them last year, used Lexan, because it was cheaper at the moment.

policestyle 12-03-2010 01:38 PM

Insulating Basement Headers...
This worry about trapping moisture is really a headache, and I wonder if it's even justified. Isn't concrete and brick ultimately breathable to the outside? In that case, doesn't moisture just find its way to the outside no matter what?

I could see if both the outside and the inside surfaces were sealed, leaving a warm wood channel to meet with cold concrete in a locked chamber...

This is driving me nuts because I had an energy audit done (on my 1905 house), wherein the auditor told me to insulate the basement headers. When I went back to him about this "moisture risk", he didn't seem to know/ think much about it.

Are we listening to these Holmes guys too much? Does anyone really know what's going on with moisture/ air/ heat??

Sorry, just venting (a pun in there to make me calm down).

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