battenburg

I have a Victorian terrace with a lean-to extension at the back of the outrigger. I imagine there are similar on thousands of houses all over the place. I have no idea when it was built and to my untrained eye it seemed fairly sturdy when I moved in – the roof is ‘formal’ with tiles and it was decorated much like the kitchen. I’ve since realised that a) its an extension to the original house and b) it is single-skinned brick, unheated, damp and without insulation. Its really not a nice room to be in and I’m desperate to make improvements. In reality, knocking it down and starting again would be the best option, but my budget won’t allow for that. Instead, my goal is to make it warmer, better ventilated and somewhere that I don’t want to immediately leave. I also have an aspiration to maybe take a sabbatical at some point in the next couple of years, so I’d like something that I wouldn’t feel morally compromised in renting out! The number one thing is to insulate the lean-to roof – currently it has no insulation at all. I’d also like to put a loft window in there to get a bit more light in. Multiple builders have told me there is no need for any Building Control involvement for ‘this kind of work’. However, they have also suggested that it would be worth replacing the timbers because its a small area and they will replace the membrane as well that will make it easier to have a greater depth of insulation, and I guess they could space the rafters to accommodate the roof window. My reading of the Building Regulations is that this then becomes replacing a thermal element, so needs to conform to certain standards for insulation – fine, happy with this and happy to submit a notice to the council, even if the builders say it isn’t necessary. What’s worrying me is that by changing the timbers and making them bigger, plus installing a roof window, does this then become a ‘structural’ thing and would I need to be conforming to other elements of the Building Regulations in relation to the room’s structure? I have no idea whether the lean-to has footings, or what depth those footings might be. There isn’t the budget to go about rebuilding/underpinning the room (or whatever one does if you add heavier timbers to a lean-to roof, if anything!). Obviously I don’t want the roof to cave in, but I’m getting so tied up in knots about this and wanting to do things by the book that I’m almost considering asking the builder to just do a like-for-like timber replacement and have less insulation so I don’t have to worry about it. None of the builders have expressed any concern or suggested I need structural calculations for installing deeper joists, so perhaps that just isn’t necessary. I'd imagine that its a very run of the mill job, especially as there are so many similar rooms on the streets around here. Can someone help explain how a situation with this would work in respect to Building Control? I realise that many many people would just get a builder to do the work and wouldn’t think about any of this. I feel like wanting to do things by the book has to potential to open up such a can of worms, so much so that I would almost rather not doing anything. The BC team at my council are very difficult to get hold of for an informal chat, but I understand that for something like insulation I could just submit a notice rather than a 'full' application. Apologies if my terminology is a bit muddled. Ultimately I want to make what improvements I can afford to a poorly built lean-to, and the whole process just seems overwhelming. I would really appreciate some helpful words that might make this situation a little less confusing to a layperson!