Return to the Basements Forum | Post a Follow-Up

Basement insulation

Posted by doogan123 (My Page) on
Sun, Jan 4, 09 at 23:09

Hi all - So I am reading through all these posts, And need to decide what to do with my basement walls rather quickly now, I am rebuilding my house from the basement up. I Also need to insulate my basement to bring into the envelope.

So - its concrete block basement, Full height. Walk out in the front, about 6 ft under in the back. I really do not get any water in there. There was a point where very little water was seeping in - not even pooling - just heavy dampness, this was when i also had standing water outside the wall - this is all remediated now - I have not see this for months at this point

The walls have not been treated in many many years ( well before I bought it) and they are in pretty good shape. There is some flaky paint, and some mild mortar crumbling in places - I don't feel its that bad.

So from my research - I have figured that i should do it as follows. This diagram is from building

Basement Wall

A couple of questions -

Instead of Icyene on the walls - can i just pin on some Rigid Board (1.5-2 inch)?
I would spray the Rim Joists - with a DIY Kit (Am doing all of the house with this)
Do i need a Vapour barier inside the Rigid board - or just bang it straight on to wall?
Should I coat the walls with Drylock first before the Insulation?
Finally - on the floor - on top of the insulation - can I just lay a wood floor (2*3 and Plywood). I really do not want/need concrete

Thanks for you help - I need to start on this next weekend

Follow-Up Postings:

RE: Basement insulation

XPS (extruded polystyrene) or EPS (expanded polystyrene) is acceptable according to BSC. No additional vapour barrier is required. Drylock not needed.

Pouring another concrete slab atop the existing slab is more suited to new construction. Instead, you can use the XPS under plywood. Or Delta FL. Or Dricore. Two inch XPS on the floor will reduce headroom and is costly.

RE: Basement insulation

Should th board be foil faced or is that the same as having a vapour barrier?

Do I need to insulate the floor - or is it silly not to. Are there any other more cost effective options for insulations. I am looking into the 2 other flooring materialy you listed also


RE: Basement insulation

The board you put on the wall should not be be foil faced. Shiplapped board is best. If not, tape all joints with builder's tape from Tuck or Tyvek, for instance, or with fiberglass mesh and mastic.

As a DIY project, the most cost effective would usually be one inch of XPS on the wall followed by conventional framing (on top of a strip of XPS) with the space between filled with fg. An alternative would be Wallmate or equivalent. Here's how it's installed. (Scroll down to interior.) But this may pose challenges in wiring.

Building Science does give the nod, too, to EPS. But it has to be thicker, as the R Value is lower. And you will have to be careful about summer humidity levels. (The same applies to XPS, I find.)

Smart vapour retarders, the only one of which I know is Membrain, are another possibility. They permit the use of fibrous insulation. But unless your conditions match those of the only test I've seen, I would be hesitant to use it unless my soil conditions and climate were similar to the test subject.

If you use XPS on the floor, you are insulating it. It will be more comfortable. But I notice that not even the US Department of Energy has any recommendations on R values for basement floors.

In an extremely cold climate, I can see floor insulation as cost effective. Is Sarah Palin your governor?

Note: Whenever you are air-sealing and insulating a home you should pay attention to any fuel burning appliances that depend for their supply air on air leakage. It's advisable to buy and install CO detection devices. And you may also have to provide direct air supply venting to furnaces, water heaters, fireplaces etc. Spend $49.95 and save your life.

Here is a link that might be useful: Department of Energy Recommended R Values

RE: Basement insulation

nah..I am far far from Sarah.. I am just north of Manhatten - about an hour.

So I have this right - I need to pin on XPS to the wall. I can then put 2*4 framing outside - but i need to sit the bottom plate on a strip of XPS - Correct?

Do you recommend using the Enka Drain as shown in the above diagraim to protect against any future breakdown that may allow water in - this way its guided under and out?

RE: Basement insulation

The enka drain is for under the slab or exterior walls.

Since you have experienced some small seepage in the past, it might be safer to use the Dricore, Delta FL or equivalent on the floors.

i need to sit the bottom plate on a strip of XPS

At the least, rest it on 6mil poly, which prevents water vapour going into the wood.

I prefer the strips of XPS, as they provide a thermal break and lift the wood off the floor, protecting the plate from water that might end up on the concrete floor. Yes, it's stable, just use concrete screws or percussive charge fasteners through the plate and XPS at once.

RE: Basement insulation

Worthy - thanks for your help.

couple of more questions

In the event of moisture hitting the Strips of XPS under the plate, should i include a capiliary Break along with the XPS - or the XPS should be sufficient under the Plate? i.e. will moisture absorb up thru the XPS over time and into the wood?

I have someinterior Block walls coming out of the external wall. What should i do when the insulation hits this? i guess its either just butt it up against it, of shoudl i bring it out along the interior wall?

Finally - is there a Glue or a Caulk that i can use that will bond to the concrete wall/floor and the XPS to seal it ?

thanks for your help

RE: Basement insulation

XPS is more than enough.

interior Block walls coming out of the external wall
If these are short projections--a foot or so--they're probably pilasters to hold up beams. I would insulate them too.

glue or caulk to bond Construction adhesive designed for foamboard may be used to adhere it to the wall, though Building Science recommends that the board be mechanically adhered. Foamboard fits tightly on a block wall and no extra caulking is normally required.

De nada!

RE: Basement insulation


PL300 is what everyone uses to glue XPS to the walls. Dab it on and hold to the wall for some time till it holds itself on the wall.
Tuck tape the seams

 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!

Return to the Basements Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.

Learn more about in-text links on this page here