Insulation

[TShort]

Sorta off topic, but it's for my RV shop...
I'm getting ready to insulate the shop. The ceiling has 2x8 joists, so 7 1/2" of space. Is it better to get the 6" insulation bats and almost fill the space, or to get 9+ inch bats and cram it in?
I have not been able to get a consistent answer. Some say even though the thicker stuff is crammed in I will get a little more R value out of it. Others say cramming it in is a bad idea. I'm going to drywall over the insulation, and ventilation is not an issue as it is an old building and the floor above (attic) is 1x6 boards.
Any thoughts?

Thanks
Thomas
-8 ailerons

[Captain_John]

ME? I would stay loose with the smaller batts. It is all about dead air space. If you cram in a larger batt, it is more densely packed and defeating the purpse of the thicker batt and costing you more loot to boot!

Also, do a vapor barrier. Either kraft faced batts or plastic sheeting. It will keep humidity to a minumum and be less drafty.

CJ

[robertahegy]

I agree with CJ. Also make sure you have some air flow through the insulation via soffet and ridge or gable vents. If the insulation can't dry out it will be worse than not having any.

Roberta

[Captain_John]

YAH! What Roberta said!

They call them soffit vent spacer things Raft-r vents or something. They are top hat shaped and provide ventilation from eaves to attic.

Know whatta mean?

CJ

[Rob Hanberg]

Thomas,
Stay with the thinner insulation. When you confine the insulation with sheetrock the insulation tends to expand over time. It will make your sheetrock push away from the rafters.
Rob

[jimpappas]

If you can find an installer close by and can justify it try Icynene foam.

I had it done on the three walls of the basement shop I could get to. They removed the old vapor barrier and pink insulation which the mice loved and sprayed in the foam. It's water based and cures in 20 minutes with no vapor barrier and it's great if someone in the house has breathing problems.

It's a little more than plain batting but best of all it seals any opening and gets in all the little gaps no air leaks or drafts at all!

Now I work in the basement in a Tshirt and with the basement vents closed and it's sometimes almost too warm just from the residual heat from the ducts and furnace going to the rest of the house.

It's amazing stuff and I'd use it everywhere if I didn't have to rip out existing finished walls to do it. It's really that good.

Besides I need to save some money for the next part of my kit