loft conversion, new rafters?

[Jacko74]

Sorry if this has been done to death, really just cant find the definite answers.

Were at the very beginning of a loft conversion. Just trying to get quotes from architects for drawings and Steel calcs.
Today we had the first architect come round to view the space.

From trawling through this site and others like it, I thought (naively..) that I would be able to start pricing / sourcing materials. Timber, insulation etc.
The saying "A little knowledge is a dangerous thing" definitely applies to me, as a couple of things that he said threw me a bit.

#1 Rafters....
Straight away he said they would need to be 7" X 2"?
So that the Purlins could be pushed back / lowered. to get a 900mm wall.
(The current dimensions of the rafters are 4" x 2"/ 4.8m long / 2.5 M from purlin to ridge board)

#2 Insulation in rafters...
Needs to be 150mm?
I looked on Kingspans website and thought that diagram 2a would apply to me. Or have I interpreted this wrongly?? http://www.insulation.kingspan.com/uk/pdf/tp10.pdf

Also on a side note, he quoted £900 for the drawings, calcs, submitting plans. Is this competitive? I would honestly have no idea.

Thanks in advance for any advice.

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[Chukka63]

im currently doing a loft conversion.3.9 overall span with a centre wall.exisiting rafters are 3x2.i put 9x2 joists in,then built my dwarf walls approx 1200mm from floor to rafter.then battened the underside of the rafter to enable 75mm celotex between and 50mm underneath.
a 900mm wall is a bit impractical unless youre only 3' tall.with the new walls in place you dont need the purlin.
i would get a 2nd opinion.

 

[Jacko74]

a 900mm wall is a bit impractical unless youre only 3' tall.

You taking the p***??!!

 

[Jacko74]

i do intend to get other quotes, just seems that the architects I got hold of are in no rush to reply.

When You say dwarf wall from floor to rafter. Do you mean going from steel/rsj to rafters??

 

[Chukka63]

from the floor,no rsj etc needed in the one im doing