I'm looking for suggestions about how to upgrade a vented cathedral ceiling covered with very nicely finished (albeit leaky) tongue and groove pine. Some specifics:


About 1/2 the assembly is vented from eave to ridge. The other 1/2 is tied into an accessible attic flat. Presumably, the 14" TJI's have poorly installed styrofoam proper vents. I don't believe they go all the way to the ridge and are not air sealed at all.


The 14" TJI is insulated with faced FGB (12"). The facing is installed to the warm side of the home.


There is a metal roof and the customer has no intention (or budget) to remove it and install rigid on the roof.


The tongue and groove is finished nicely with several coats of clear coat. It's a high end home and this assembly needs to be put back together perfectly.


The ceiling is peppered with recessed lights.


Each slope is 14' long and the room is 26' long.


I've noodled around with a few options based on the customer's budget and what we're hoping to achieve. They run the gamut from removing the T&G and FGB, installing sheetrock as an air barrier, dense packing the cavity, and re-installing the T&G. The ridge and eaves would be blocked and we'd have a hot roof. Moisture load in the home in low and managed.


Another option was to access the eave and ridge and 2 other area but removing strips of T&G. We'd then remove the FGB, block eaves and ridge, install 1" of CCF on the back side of the T&G (as an air barrier) and dense pack the cavity with cell. Might trap moisture, though?


How about removing sections of the T&G, removing FGB, and adding 3" of CCF to the underside of the roof then dense packing and re-installing T&G? Not a perfect air barrier but the likelihood of condensation is reduced from the foam.


Straight up dense pack the assembly? Just block the soffits/ ridge and keep the FGB?


I think creating a hot roof makes sense as it would be challenging to install a continuous vent from eave to ridge.


Like all T&G, the corners are leakiest although in this assembly, it was all leaky during my BD test.
Tongue and groove cathedrals without a proper air barrier (and poorly/ incorrectly vented) are a bugger! If anyone has any ideas on a reasonable way to make this assembly perform better, I'm open to suggestions.
Thanks!
Matt

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Replies to This Discussion

I hate to say this but budget wise & for looks, it would be easier, cleaner & cheaper to attack it from above. If you do remove the T&G look into a tool called the extractor as it is great at pulling the nails from the back

I don't know what the codes or exactly which climate zone where you are at in Maine but you need at least R20 air impermeable insulation added to either the underside or on top of the roof sheathing. If you come at it from below I would spray foam whereas from above I would lean more towards foam sheathing - 2 layers with offset seams For more: http://bit.ly/HotRoof 

Hi Matt,

Always super tough to fix these after they have been done so very wrong.  Tom Nichols just had a long thread on Linkedin on this very subject.  I didn't keep up with all of the posts but it might offer some advice.  I will read it later and re-post.

http://www.linkedin.com/groupItem?view=&srchtype=discussedNews&...

Can lights, no air barrier, and fiberglass insulation open to the flow of ventilation, not good.  R&R that T&G is going to be a bear, especially after it has been "finished nicely with several coats of clear coat".  Also, if that TJI is spaced 16" or 24" oc, then normal batt insulation does a poor job of filling the space between.  They make wider batts, but even with those it doesn't conform well around the bottom chord. 

I would avoid just dense packing what is there, moisture will still pass through the cellulose.  Any form of a hot roof, as Sean said, needs a substantial layer of spray or rigid foam to keep the inside surface above the dew point.  I'm assuming this is a year round home, not seasonal.

Back later.

Bud

The topic has been discussed ad infinitum at the linkedin group Bud shared.  I see this a lot; "High end home, but low budget."  Ironic to me.  If they want it fixed they need to pay the freight.  Do it right, or don't do it at all (or you'll buy it.)  My take; remove the t&g, throw the can lights away, remove the venting, install code-required insulation at a minimum, install drywall with finished joints/edges (durable air barrier), make provision for surface-mount light fixtures, reinstall the t&g, or find another nifty looking high-end finish product, and they'll likely go for it in a minute.

Hi Matt,

If you checked out Bud's link I'm sure you saw all of the ideas folks have on this.  Definitely no clear cut answers.  I would vote for the least intrusive method of opening the soffit, removing as much FGB you can and dense packing the rest to slow/stop air movement.  Reassemble and seal vent. 

For the lights, replace with sealed LED retrofits and caulk them in.

It's a tough situation no doubt.  Good luck

 Hi Matt,

The code in Maine does require a minimum of R20 impermeable insulation but it is important to note that this is based on a total insulation value of R49. If you can't get a total of R49 into the rafter space this R20 value isn't relevant.

Hi Thomas,  Ignoring the code for the moment we still need to follow best practices, like being sure the cold surface of that impermeable layer remains above the dew point.  Since local code officials have the final word, there is the place to start.  Once you know the total r-value required, then you can determine how much of that must be the outside impermeable insulation.

The unfortunate aspect here is air sealing is very important, but those beautiful T&G ceilings make that near impossible.

Bud

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