We currently live in a modular home that was built in 1989. The middle of the house has vaulted ceilings, the two ends of the home, where the bedrooms are, have regular ceilings. There is only attic space access on one end of the house. I was wondering what would be the best way to install extra insulation in the attice space that we can't get to, and in the vaulted ceiling part. I know in the middle of the house there can't be much in the way of insulation between the ceiling inside and the roof outside. We are planning on new shingles in 1-2 years. Is taking the sheeting off and putting insulation down, replacing the sheeting and the roofing a good way to do it, or is there a better way. Thanks.

1st thing I would do is open a small portion of the ceiling to see if it is insulated, or consult the original plans to see if insulation is listed on the making of the ceiling.
If insulation is still desired or needed:
Either way your going to have to open up the ceiling or the roof.
New shingles and taking up the ply-wood to insulate sounds like the easy and cleanest way to go. Ripping off the ceiling drywall has a few down sides.
Messy in the house.
If the sheetrock was hung properly, the walls help support the rock on the ceiling.
Vaulted ceilings is tough to mud and sand.
Then prime/paint!

Personally I'd do the roof even though I hate roofing.

Usually in modular homes the insulation is the blown in type not the batt type. You might want to add to the insulation from the inside of the home not through the roof.

How far do you want to go to insulate the house?

1 way would be to remove the shingle roof,add a product called 'nailine'(I believe this is the name,I'll check to be sure)Nailine is a wood/solid insulation/wood sandwich which applies the product in one step.I have used this on a few roofs in the past.

Thicknesses very as per need and insulation value.

It was pricey,and with the gas prices going down,, well you decide what you want.

This is a site for the product I have explained.

http://www.insulatedbuildingpanels.com/

You could also consider a roof-over. This adds the extra insulation you want and also redoes the roof so you don't have to redo your roof with shingles. It is usually a metal roof with insulation under the metal roof. You do not have to ditch the existing roof to have the roof over installed. It is a route I went when I owned a very large double wide. You might want to look into that versus ripping up your existing roof and adding insulation under it.

If you decide to take down the ceiling at insulate from the inside, I would go with Icynene spray foam. It's more expensive than bat, but you'll never regret it. I just had the stuff installed in my Cape Cod and I'm currently saving 30% on my natural gas usage. And these figures aren't just quoted from some sales rep, I just did the math from my last bill.

I did spray foam insulation for several years. It is expensive, but incredibly efficient. I would go with a closed cell type, not icynene. Icynene is open cell, it works pretty well but will absorb water like a sponge if there is ever a leak.