Insulating small pitch in roof??

Im getting a list of things that need doing to my property and was just wondering the following:

i have insulated the main part of my loft but there is another part which is basically in the shape of a half pitch - hopefully thats the right word. To get through that part it would mean either mean squeezing through the rafters which would require a relatively slim guy or is it normal to cut one of the beams to gain entrance into that part to insulate it and then replace the beam. The reason Im hoping there is a solution is because to that part of my property it is a lot colder. hopefully someone can help me.

thanks.