To vent or Not to vent

Recently had an energy audit done. I was told that it is no longer being recommended to vent a roof. I was told that if the insulation was installed correctly there is no need for ventilation. I was told that the recommended method for insulation would be a dense pack cellulose into the rafters. They also said that Fiberglass bats would also work. The critical part was that I had to ensure that there are no air pockets left between the decking and the insulation material. When I was told this they said the idea of not needing venting is fairly new and anyone I talk to would say it is crazy. I am hoping to get some good feedback on anyone who is hearing this in the field. I was shocked but it is coming from someone who is the best in the field and well respected. Please have an open mind when replying as things in all industries do change.

I would like to add that it is a late 20s colonial. I am having cellulose blown into the empty walls and tightening up the foundation and attic areas. It is considered a 2 1/2 story with stairs to the attic space that I plan to finish and use, minus the storage on the edges.

You should do a little research on Building Science by visiting

If that doies not link correctly, since I typed it from memory, try Googling: Joe Lstirbruk and unventilated attics.

It is a new theory here in the states, but more openly accepted in the Canadian region.

Your location will be a main deciding factor and also stopping ALL air leak passage ways from entering from the conditioned interior living quarter climate into the attic. The most likely candidates are the wall plates and ceiling can lights.

Sprayed Polyurethane Foam has a higher R-Value than what options you had mentioned, with it being adhered to the underside of the roof deck sheathing.


Cellulose was recommended, if I can remember correctly, because it offers a higher R value if packed in correctly to the proper density. I think cost was another factor. So if I remember it is cheaper and has higher value “IF” done right. Please correct me If I am wrong. I looked up Joseph Lstiburek. This guy is the real deal. It will make some interesting reading. Thank you very much.

I don’t recommend installing asphalt shingles.

I am a slate and copper roofer. :smiley:

There are a lot of variables involved here, the biggest one being " IF installed correctly".

Make sure you do your homework on this one.

My biggest concern with spraying the rafters and decking, is that when the roof leaks you may not know about it until the roof decking and rafters are rotted away.
Not recommended at all for a slate roof.

Good luck.

I am not sure I understand. Are you saying I should get a slate or copper roof and skip insulating. Is copper or slate even affordable. Why would blown in be any less affective with those materials as opposed to asphalt shingles. How would I insulate the area of the roof just above the living space?


That was just a poor attempt at humor.
As in, was the person who said that nobody recommends ventilation selling a product that does not use ventilation?

Of course a slate or copper roof is better than an asphalt shingle roof, and affordable. Relatively speaking.

You don’t insulate the underside of a slate roof because the slate needs to “breathe”, or dry from both sides.

You will find a lot of disagreement on the subject, but done properly, it can be a good choice.

Too new in my area for me to have any documented real life experience with.

Sorry about the misspelling of the guys name.


just spoke with my energy guy. I mentioned Joseph Lstiburek and he said “I am glad you looked him up, he is one of (if not) the best out there.” He also mentioned “I worked with him on a bunch of projects”. I was extremely happy to hear that. Now I am completely confident that I am getting great advice. I always over analyze stuff. My wife tells me “It doesn’t have to be perfect, just do it!” Did I mention everything I do takes a long time to complete. Anyway I wanted to thank you guys again for the responses.