Tile roof - insulation?

[qwertyuiop]

Can you please give me some advice.
I have a large Victorian semi. The roof is rosemary tiles. Not been replaced in 115 years. No underfelt. I cannot afford a re-roof (I am a pensioner).

I am proposing to:
Buy some 'airtec' insulation - silver foil bubble wrap type stuff that looks as if it may do the job for me. The intention is to just staple it to the joists on the inside of the loft space.

This is more or less what I intend doing (although it looks like in this case they do have underfelt on the tiles and I do not):
http://www.youtube.com/watch?v=qI9rflIIgiI

1. Is this a good idea, will it help much with insulation
2. Do I need to vent? The tiles will be about 4" from the airtec and will presumably 'breathe' because there is no underfelt.

Thanks for any help.

 

[Alastairreid]

You can do it that way if you like, You dont need to add additional ventilation.

Why are you insulating a rafter level though?

 

[qwertyuiop]

Thanks for your reply

I am insulating at rafter level because I use the loft space for storage and its really dirty with dust. So, if I do it at rafter level I can use the space better, I hope?? Also I do not like the fibre glass stuff it gets in my throat and itches me on my hands.

Out of interest why do I not need ventilation? Because I read somewhere to allow 2" at top and bottom. But another didn't seem to bother about ventilation. I don't know anything about it but I don't want to cause rot/damage to the timbers.

Thanks for any help

 

[Alastairreid]

You are getting the ventilation through the tiles and space between tiles and insulation.