Is PP needed to insulate a flat roof?

[RobLe]

I would like to insulate our garage roof so it’s not so cold in winter, and also as it’s now the weakest link of our newly EWI-ed house.  We are link-detached - there is a mirror image house to our right, linked by the garage.  It’s a 1963 build, torched felt, no insulation, with a fall of only 1 in 100 with the lowest at the front, so it pools.  It’s not leaking though.  What I would like is to add shaped insulation making a warm roof (insulation, osb3, epdm), such that it is 140mm taller at the front, and 290mm taller at the back, giving a decent overall U value of around 0.13W/m2/K, and a fall of 1 in 40.

Do I need full planning permission to do this?  (Gah)
Is there anything sensible else I could do?

House plans attached, which I needed to do the EWI !

 

[A_L]

@RobLe,unless there is a heat source in the garage the insulation will do very little. Poor air tightness in the garage and uninsulated walls will strip the heat away. Is there EWI on the house/garage common wall? If there is there will be even less reason to insulate the roof as there will be less heat entering the garage  

[Onoff]

Garage doors are notorious as being big, uninsulated, heat leaky things.

 

I presume the outside of the garage didn't get EWI?

[tonyshouse]

I would EWI inside the garage against the house if it is a garage 

[Onoff]

& make sure any interconnecting house to garage door is good, in terms of insulation and air tightness.

[RobLe]

Thanks for the interest, I love that it's all energy related 🙂  Some details here:

The back of the garage is mostly wall - it is being EWIed, U approx 0.22W/m2/K.  I want a roof overhang detail to finish it. 

Between house and garage is a filled cavity wall, U=0.7.  Internal door is insulated, it's the original cardboard honeycomb inner with wood outers - I squirty foamed the honeycomb to insulate.

The side is a party wall to next doors garage, a mirror of ours. 

The personal doors are uPVC 3G all glass, fit well

up and over door has 50mm celotex on the inside so U=0.5.  It has rubber flaps around it, but will be leaky.  I wish it has a window in it, it's south facing. 

I've not EWIed the front of the garage - there's not a lot of brick there.  It would need PP.

Roof is uninsulated, I think it is the original.  

House and garage are uninsulated concrete floor.  I have perimeter insulated the house and back of garage, likely do front of garage too one day.

Rest of house is U=0.15 EWI, gas use last year was 4.5MWh, the gas boiler living in a small room at the back of the garage with token IWI.  The boiler has last Dec been replaced with a heatpump, but the pipe run is the same.  There is actually a rad in that IWI room - not convinced there should be as it's technically not house, but the plumber 15 years ago persuaded me.  It's never used.

I know without deliberately heating it won't get very warm, but I expect it would be warmer.  Right now it is 20C indoors, 5C outside (it was colder overnight), 10C in the garage.  Just a bit warmer would make it a nicer space to use for diy in the winter, and turning on a heater in it now would cause mental anguish.

 

[Temp]

How about persuading the neighbour to join you and replace with a pitched roof?