Ask Ted!

If you have any questions you want answered, feel free to drop me a note. If you’ve got a question, chances are, there are lots of others out there with the same question. So ask away!

Note: all comments are moderated unless I’ve approved one of your previous comments. Almost everybody gets thrown off by this, but I moderate comments to avoid spammers. The downside of this is that you won’t see your comments post until I’ve had a chance to review and approve them. Sometimes this can take days (sorry!) Thanks for your patience.



1,130 thoughts on “Ask Ted!

  1. Ted, I have read your description of how to insulate an attic and cathedral ceiling, and many of your related blog entries. Thanks for a good resource. My builder installed T&G directly onto the rafters of the cathedral ceiling, with only a partial and imperfect vapor barrier at that. During the course of the winter when the outside gets really cold and then warms up, I get random dripping water here and there in the room, especially around the chimney, but also in some other random locations as well.

    To fix it, I will be removing all the T&G and insulation. Treat the mold that I find, then putting it back together right. To do it right, I want to put 2″ of XPS spaced 2″ from the roof deck. Then fiberglass insulation up against that. Then, to air seal it, I will staple plastic sheeting to the rafters, and put rubber tape over the staples along the length of the rafters. Finally, I will put the T&G back up, nailing through the rubber tape into the rafters for a good seal. I can send you a diagram of my strategy if you’d like to see it.

    Is this a good strategy, or am I missing something?

    • Michael, sorry to hear of your T&G ceiling issues. It is dismaying that builders continue to take the same old failed approach to constructing these types of ceilings, forcing homeowners to have to reinvent the wheel and re-do the building of their homes.
      The potential issue I can see with your solution is trapping moisture in the region filled by the fiberglass. The XPS and the plastic are slow vapor retarders, so any moisture that gets past the plastic is going to get trapped in the fiberglass without any way of getting out. A safer solution would be to place the fiberglass under the roof deck, with a gap for air flow, then put XPS under that (towards the inside of the house). Then a thinner layer (maybe 1/2″) of XPS or poly-iso foam covering everything (imagine replacing a sheet-rock ceiling with foam). This creates a durable, moisture resistant barrier.
      Then, you can put whatever aesthetic ceiling in place you’d like. The T&G could be applied directly at this point.
      With this construction, any moisture that slowly works its way up to the fiberglass layer will easily be flushed out. Moisture that passes the T&G would be mostly stopped by the thin foam layer, which will be essentially at the temperature of the inner ceiling, so condensation risk is minimal. And since there will be minimal seams between the large sheets of the thin foam, you can tape these seams for a fully continuous barrier.

      • Hi Ted,

        One other consideration here is whether the space between the roof deck and the T&G is actually ventilated. If it isn’t then this solution will create the same problem that the OP’s solution creates: the fibreglass is sandwiched between two vapour barriers (the XPS and the roof shingles) with no means of letting moisture escape.

        So for the OP, by ventilated I mean are there soffit vents and roof and/or ridge vents on the roof above your cathedral ceiling?

        Apologies for hijacking this response!


      • Good addition input, thanks Jeff.
        The risk is slightly reduced, even in an unventilated roof assembly. I wouldn’t want much moisture getting in there, but using multiple layers of foam board would reduce the moisture migration to a tiny amount. Any residual would likely be so little that it would diffuse out of the cavity through small air leaks that are likely to exist. But, as Jeff notes, best be safe and ventilate properly with continuous soffit and ridge vents.

    • Ted, you’re right of course that there is a minimal chance of moisture being introduced from the interior of the home through multiple layers of XPS board (in fact, I find there is a lot of fear mongering with regards to how much moisture transmission there actually is through most construction materials in most real world scenarios).

      I always side with Murphy’s Law in these situations though… for example, what if there is a roof leak? Now there is water between the roof deck and the T&G with no chance of escape. So you’re suggestion of ensuring there is a ventilated space below the roof deck is the safe bet in my opinion.

      Again, sorry for jumping into this discussion. I just found this situation an interesting one.


  2. I am trying to figure out if I have mold between hardwood floor and subfloor. Old house with dark floors. What can I do?

    • Unless the floors have been allowed to remain wet, there’s little reason to suspect that they’re moldy. Does the floor feel “squishy” like it’s rotting? Are there any other symptoms besides some discoloration? Wood will naturally discolor from water damage such as under flower pots or repeated animal urination on carpets (trapping the moisture between the carpet and floor).
      If you have significant reason to suspect mold issues, you might have to have someone remove the hardwood floor in the damaged area so they can examine the wood below. However, this is a fairly drastic solution that requires cutting and prying out the boards and should only be done as a last resort

  3. Ted,
    I’m very aware of your disdain for recessed cans due to their flawed characteristic of having a 5-6″ infiltration area into your attic space and unconditioned air. Would you still dislike them as much if I built a box out of insulation board to enclose them in the attic? I know they have the LED retrofits for existing cans now which may help with cutting down on air infiltration, but honestly, I’m not a big fan of the hue of LEDs yet.

    Much thanks!

    • I’ve built boxes in the attic for my pre-existing recessed lights, so it’s certainly a feasible solution.
      However, it was a real pain due to the hardware on the attic side that got in the way of the boxes, requiring me to notch the boxes and fit them into awkward spaces. I made mine out of foil-faced poly-iso board. Foil tape sticks to this very well making construction relatively easy.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s