I am located in Huntington Beach, CA (US Climate Zone 3; CA Climate Zone 6). I am looking to replace my roof and attic insulation soon. Based on my research, the best thing to do would be to convert my attic to an unvented attic, and move my insulation to above and below the roof deck.

I contacted my local building department to confirm that unvented attics are allowed per code, and they said

"All concealed attic spaces need to vented per code. There are different ways to do it per designer’s choice."

So I looked up the CA building code and it says the following on unvented attics

"R806.5 Unvented attics and unvented enclosed roof framing assemblies created by ceilings that are applied directly to the underside of the roof framing members and structural roof sheathing applied directly to the top of the roof framing members/rafters, shall be permitted where all the following conditions are met:

1. The unvented attic space is completely within the building thermal envelope. [...]"

I have 2x4 roof trusses. Is the bottom chord where the ceiling is applied considered "the underside of the roof framing members"?

I am trying to figure out if I should push back on the building department.

After watching a video with Joe Lstibuerk, I'm just going to leave my attic vented, and go with insulation at the bottom of my roof deck and at the ceiling. The trouble and cost to go unvented is not worth it in the climate I live in.

I can't link the video, but search YouTube for "Building Science Insights: To Vent or Not to Vent". At the 41:55 mark, he goes over a design that convinced me.

I'll probably be making another post asking for advice on what type of insulation I should use. Fiberglass batts or blown-in cellulose.

Yes, that sounds like the best idea to keep it vented.

Fiberglass is cheap and light. Cellulose is I think 3 times the weight but denser and for tight space provides more R per inch.

Joe knows his subject matter very well and he is highly respected in the industry. Vented attics have been used forever and have a well established and successful record. I would vote for blown in fiberglass...much lighter and less effected by moisture long term.

Be sure to use soffit vent channels so the blown in insulation doesn't block these vents and so you can get the required insulation depth around the perimeter. Be sure to follow the recommended ridge to soffit vent area ratio so as to get good ventilation performance without creating large negative attic pressure that increases your living space air infiltration and reduces the energy efficiency.

Thanks for the advice on the insulation. I do have a question about air sealing at the ceiling level. I am about to get the interior of my house painted. It currently has 36 recessed lights throughout the house. Of those, 28 will definitely be removed.

There are 5 that are in the kitchen that I would like to remove as well, but I just don't know what to replace them with. 2 are over the sink and 3 are over the space between the wall cabinets and the island. Any suggestions what I can replace them with? I was thinking track lights, but I have 8ft ceilings and I don't think they would like nice.

Why do you want to remove them? Most people would dream to have that many? Air sealing?

We used the new type of recessed lights that only requires an octogonal electrical box. I spray foamed the back side of every one.

You can find new led lights that fit in old style recessed light boxes that seal pretty well with a foam gasket around them.

The boxes could also be replaced with a completely sealed type...

https://www.alliedmoulded.com/residential/vapor-seal-air-sealed-electrical-boxes/

Here is the octagonal box I used.

https://www.amazon.com/Carlon-Outlet-Box-Polycarb-Blk/dp/B00Y78P3CQ/ref=sr_1_1?dchild=1&keywords=carlon+outlet+polycarb&qid=1595849560&sr=8-1

The recessed lights I have are the 6" remodel type housings. About 16 of them are not "air-tite". I can probably make those lights air-tite or replace them. Another issue with the lights is that they act like heating lamps in the summer. Granted the existing insulation is a mess in the attic, but because of the height of housing, they extend beyond the existing insulation and just absorb the heat in the attic and transmit it back into the house.

I'm trying out a low profile LED light that does not require a housing, but I don't think you can effectively air seal it while still being able to replace it when it eventually fails. Also if you have blown-in insulation, that's another mess to deal with when replacing the light.

Are there any solutions for 6" recessed lights for air sealing and insulating effectively? I couldn't find anything

We frequently use the various flush and semi-flush mount LED lights. They typically have some type of spring mechanism that keeps them tight against the ceiling while still allowing them to be easily removed for replacement. They also have gaskets for air sealing. We also completely foam over their electrical boxes so they are absolutely air tight. I don’t think anyone uses recessed lighting anymore, especially in energy efficient homes as they are challenging to get air tight. Some examples of flush and semi-flush mount LED lights may be found here:

https://www.lowes.com/n/buying-guide/flush-mount-and-semi-flush-mount-buying-guide

I removed one of the existing housings to try out the light in the link below. The clips and gasket don't appear to really give a good air seal. And whenever I will need to replace a light, I will have to go up into the attic and move the blown-in insulation out of the way to prevent it from raining down when the light is removed. Maybe I can install a plastic sheet over it to prevent that.

https://www.homedepot.com/p/Commercial-Electric-Slim-Baffle-6-in-New-Construction-and-Remodel-Color-Selectable-Canless-LED-Recessed-Kit-91302/306079881

I wish these were 4 inch lights so that a simple JB like this one could be installed in their place.

https://www.homedepot.com/p/Carlon-1-Gang-18-cu-in-Round-Old-Work-Electrical-Box-B618RR/100404072

Yes, retrofitting flush and semi-flush mount LED lights is way more problematic than just installing them in new construction. The clips and gaskets should give a good seal, but this seal is secondary in any event. If the electrical boxes are foamed in properly, they will be absolutely air tight even without the lights installed.