DevilDamo

Being a corner plot, you have more PD restrictions... https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/830643/190910_Tech_Guide_for_publishing.pdf (Page 16)

Maybe the definition of ‘principle part’ should instead read... “The main part of the house excluding any front, side or rear element of a lower height (regardless of these being part of the original house or subsequent additions)” It’s a little confusing when the definition states ‘extension’ but the part in brackets then talks about being part of the original house. In theory, it’s one or the other unless they’re referring to extensions up until 1948 that are deemed original. I also think the additional storeys should be limited to two for a single storey property and one for a two storey property, both of which would result in a three storey property. We took advantage of the change in policy to add a single large storey to this property.

An outbuilding 15-30sq.m (measures internally) constructed substantially from non-combustible material is exempt from BR’s.

Yes it does... https://www.planningportal.co.uk/info/200130/common_projects/158/additional_storeysextending_upwards “The additional storeys must be constructed on the principal part* of the house” “Principle part The main part of the house excluding any front, side or rear extension of a lower height (regardless of these being part of the original house or subsequent additions)”

Just out of interest, why didn’t you look at the option of a rear dormer? You’d have to make sure the volume of the dormer including the roof over the two storey rear extension does not exceed 50cu.m. Similarly to the additional storey rules, the dormer can only go above the ‘original’ part of the dwelling.

The additional storey cannot go over the top of an existing extension. Looking quickly at your plans, you had shown the roof of the existing two storey rear extension to be raised.

If it’s between 15-30sq.m and 1m away from the boundaries, it’s exempt from BR’s. Or are you asking if you can take it closer to the boundary with the highway?

Depends if the new build has certain withdrawal of PD rights. The guidance states... ”Although solar photovoltaics and solar thermal equipment (i.e. solar panels) are not permitted development under Class C, they may not require an application for planning permission if they meet the requirements set out under Part 14 of the rules on permitted development in Schedule 2 to the Order.”

Can you provide a satellite image or even photos showing the position of the house relative to the highway?

As per the link above. To be exempt from BR’s, construct it using masonry as it’s very difficult to achieve the required fire resistance with a timber frame structure.

Can you provide a link to that?

I’d suggest you referring to this room more along the lines of a Cupboard.

Who advised you to submit a NMA application... the LPA, your architect/agent or builder?

SketchUp?

LPA’s do vary on their ‘Do not scale...’ policy. One of my LPA’s state... “All plans must be given a drawing reference number and ‘do not scale’ disclaimers need to be removed from all plans.” I get around this by having the following note... ”Do not scale from this drawing, except for Planning purposes.”

So this room is currently accessed via the Landing, has its own door but not a suitable escape opening?

As above. The 400mm only applies to doors that swing across a landing, not away from it.

Not under PD I’m afraid so whatever you decide would have to meet Planning policy.

Never ideal to have a washbasin below a window to the En-suite. Where would the mirror go?

Both of those are fine prior to the formal approval of a Planning application.

It’d be deemed Lawful after four years anyway so you could do that should you want it all tied up properly.

Why do you need Pre-Planning/application advice? Even if you did, it could cost you a lot more than all that should you carry out the works without approval. Is it really worth the risk for what is a very minimal outlay?

If it’s PD, there is no ‘granting’ of Planning permission. Btw, be weary as to what the LPA may consider as being adjacent to a highway, in particular this bottom corner. Anything higher than 1m that wraps around the front would in theory require Planning.

As a result of the pandemic and if anything, I wouldn’t be surprised if the rules on amenity space became more of a priority and determining factor. As @ProDave mentioned, does your LPA have any guidance or policy on amenity space? You’d usually expect houses to have gardens of at least 10m, which would allow for a 3m patio and 7m grass area.

LPA’s are always keen to try and maintain the symmetry and balance of semi-detached properties. If they offer it, you could look to seek the LPA’s pre-application advice before formally applying. I assume your attached neighbour has no interest in doing the same?