Insulation, Radiant and Vapor Barriers - Insulation in between roof joists

I'm making plans to remodel my garage and one of the things we really want to get out of this is a storage loft. One of the issues with the garage is that it gets VERY hot in the summer (Los Angeles) so I plan to put r30 batting between the bare roof joists and I have a few questions:

1) I'm planning to use r30 batting but I've heard people descripe using a styrofoam insulation when insulating between roof joists. I've also heard of some kind of reflective insulation. Is batting the right material to use?

2) As this will be right up against the roof, do I need to worry about a vapor barrier? If I do need a vapor barrier, would it face the roof or the garage?

3) I saw a home remodel show on TV and one of the things they did was put batting in between the floor joists that were accessible through a crawl space. They used metal rods that were just a little longer than 16" so that they would be sprung between the joist to stay in place and hold the batting. Is this a good method to use...I can't find these rods at the local home improvement store

4) I'm not planning to insulate the walls. It never really gets cold enough here to be a bother when in the garage during the winter. I think that the vast majority of the heat coming in during the summer comes through the roof but is it a mistake not to insulate the walls? (The only heated wall is probably insulated but it it is not, I will insulate that wall)

By the way, as this loft will be effectively "cut off" from the puny little air vents near the ground on the outside wall, I plan to install a thermostat controlled vent fan and also a vent to allow "cool" air in.

Thanks for your input!

Insulation will not stop the heat. Haet is from radiant heat. Only way to stop the heat is with a radiant barrier or a closed cell foam

How much ventilation is there? How many square feet in the area?

Insulation will not stop the heat. Haet is from radiant heat. Only way to stop the heat is with a radiant barrier or a closed cell foam

Is this something that is sprayed on or are you talking about styrofoam that is cut to fit and then put in between the joists? Is this something that I could tackle myself (I'm pretty handy but don't always hae specific expertise with specific solutions).

Thanks!

Spray Foam can be a do it yourself project. One of the bigger brands out there is Tiger Foam. It’s not cheap from what I have heard. There are radiant barrier paints on the market. Most or over $100 a gallon. I’ve heard mixed reviews on these, so do your homework. You can buy rolls of radiant barrier foil that you can staple to the roof joist.

How much ventilation is there? How many square feet in the area?

The garage is roughly 23' x 18' with 3 small vents near the ground on one wall. I will be putting in a loft at the 8' level with the roof height sloping from a high of 5' down to zero at the other end. There is currently no ventilation in that space but I plan to put a gable fan at one end and open a vent about 2/3 of the way back.

Thanks!

Spray Foam can be a do it yourself project. One of the bigger brands out there is Tiger Foam. It’s not cheap from what I have heard. There are radiant barrier paints on the market. Most or over $100 a gallon. I’ve heard mixed reviews on these, so do your homework. You can buy rolls of radiant barrier foil that you can staple to the roof joist.

Airman.1994, thanks for the pointers. The Tiger Foam looks really cool on the website but to do my 200 sq ft garage, it was going to be about $2,000 to do it myself...so yes, it's not cheap.

I did order some radiant foil barrier and the minimum order gives me twice as much as I need but the cost with shipping and a roll of tape is just over a hundred dollars...should get it on Monday.

Thanks again!