mr rusty

The cost of a solicitor to try (an IMHO not succeed) in making this a legal condition of planning is most likely more than the cost of new DGU with frosted glass. It won't happen as the OP expects because if planners started to issue PP on the basis of the presence of 3rd party agreements a whole can of worms would be opened. Planning stands or falls on it's own rules

I'm not so sure you will need planning permission because you are not changing the footprint, usage or aspect of the building, but I'm not completely sure. What you will definitely need, and what may be a challenge is building control. It may be a challenge because that "conservatory" doesn't meet latest standards and I expect that re-roofing will bring the project in to the latest regs - You definitely need some good advice - whether that comes from some of the more knowledgeable people here or an external professional, you will still need someone to draw up some plans for a regs application. You might want to consider just upgrading the polycarb to maybe a 5 ply, much better thermally rated material which would then still give you the light and still improve the useability. This might restrict your regs application to just taking down the wall, and ignore the "conservatory" - depends on your budget.....

If it's a summer house with sofa beds which are very occasionally used, who'd know? who'd care?

As a someone this doesn't affect but have an interest, this looks like a huge tier of additional work and cost which can only reflect in the prices charged for new houses, which will drive up the cost of all housing. I came across this:- So if you are a developer, you have the option to buy another piece of land solely to improve the biodiversity to offset against the development. I hope no land sold for this purpose has any connection whatsoever with the panel determining the planning application.... Cynical? moi?

I had a similar condition on a recent planning. The tree survey came back with "during the build (of my garden room) building materials must not be stored in the root area of the tree (which otherwise they agreed was outside the development). The irony was that's where my stack of "may come in handy" building materials, rockery stone etc has been stacked for years.....

I did my most recent extension on a notice too. The key thing is to make sure the builder understands it is his responsibility to build to regs and final payment is subject to a completion certificate being issued. i.e. the builder is on a design and build contract. Do expect to pay a premium for the builder's risk though. In my case it wasn't an issue because the builder and the LA BCO had worked together loads of times and there was mutual trust and respect. IMHO this is a good way to go because it totally avoids any controversy between the designer and the builder passing the buck between each other if there is a problem with BC.

I feared this when we built our garden room which is only 8m from the house next door, but with a 2.1m fence already in place, and 2.3m eaves and 3.3 ridge I was able to show that the shadowing was well under the 25 degree limit described in BRE Site Layout Planning for Daylight and Sunlight: A guide to good practice (2011). 25 degrees measured from centre of neighbours habitable room window. I don't think shadowing of a garden is a thing. You could always point out to the neighbours that if they don't like your building you can always screen it with a row of 8m tall bamboo https://www.paramountplants.co.uk/blog/index.php/bamboo-for-screening/#:~:text=Fargesia Murielae grows to a,forming a dense elegant hedge.

This. And if you're survey doesn't highlight any structural issues, then it's nothing to worry about at all.

I expect, if you have PP for an annex for a relative to live in, that the decision notice says something along the lines of the annex is to be for ancillary use to the main building. My own PP decision notice includes "The proposal is for erection of a single storey outbuilding in the rear garden to be used as a garden room with use ancillary to the main dwellinghouse. " The key is "ancillary" rather than "incidental". As far as I understand it, ancillary means that you can do anything in it that you would do in the main house, but it isn't necessarily a separate accommodation unit (own address, council tax, services bills etc.) or is rented out as a business. If the PP says "incidental use", then it cannot become a separate accommodation unit, but my understanding is that if it is for "ancillary use" it can, and may or may not be subject to council tax depending on how it is used (by family etc or others). To avoid council tax implications I would ensure, if the council are involved, that you clarify it is only being used for incidental use even if the original PP was for ancillary use as an annex.

No big family houses?

I'm with @devildamo here. A purpose incidental to a house would not, however, cover normal residential uses, such as separate self-contained accommodation ( if it isn't self contained accom. this doesn't apply)or the use of an outbuilding for primary living accommodation (if it isn't primary living accommodation this doesn't apply) such as a bedroom, bathroom, or kitchen. The key thing IMHO is whether the use of the garden room is ancillary to the main house as planned/used. If it is, you can do whatever you like in it subject to building regs for electric and drains. Like most things this will depend on the facts. If it's got a bedroom, kitchen, toilet shower then it's very hard to argue it's not self contained accommodation. If it has a kitchenette, toilet but no bedroom, and these are not the primary facilities for the main house, it's easy to argue it's just for ancillary use.

I agree. Hardie or Cembrit cement planks have the advantage that they stay looking like they do on day 1 - no colour change/fading (in my experience at least with paler colours). They also have a very low thermal coefficient of expansion (from what I can tell from specs, about 1/3 compared to composite plastic and 1/10 of uPVC. )

Why don't you build it as two separate units with perhaps a canopy between and save yourself a lot of heartache - <30sqm internal and it is BR exempt.

...unless you use hooks

I think you have to ask yourself where the design risk sits. If you have a comprehensive design from an architect and pass it to a builder in the round and say "build this", then without too much doubt the design risk sits with the architect. If you have an outline design/specification and issue a design and build contract to a builder where he builds what you want according to a general specification, and the builder ensures all BR compliance, the design risk sits with the builder. If you have an outline design from the architect, and you act as project manager and employ trades people to complete work as and when you want it done, then the design risk mostly sits with you. Inevitably on the project there is a "risk pot" somewhere, so it's a good idea to be very clear who is holding it.