Permitted development-I've thought myself into a loop-help!

[MsPickle]

So this feels like a really stupid question but I've been thinking and Googling and have thought myself to a standstill!

We're end of terrace on a road which to date has had little alterations made to the houses. We're looking at a loft conversion but because previous to us owning it the downstairs was made more open plan we've got to have a total new staircase and build a wall to re jig downstairs to meet fire regs. (Don't want to go down the mister route as where we are it would make the house unsellable/it's more expensive). This has got us thinking about the whole house as we'll have to figure out finances.

So my question: can we do a dormer loft conversion AND a small single storey extension under permitted development? What about if we rebuilt our plastic porch to brick-does that then count to total volume? I've read something about class A PD which covers the loft but then the extension would be class b, is it the total volume of everything together?

A dormer and single storey extensions come under different parts of the PD rights. You'd need to check the relevant class for each one. Try the planning portal website for useful advice.
I'm not quite sure what you mean by total volume as extensions are permitted by their measurements eg distance from the rear wall, height of eaves. The volume issue is about the addition of roof volume over and above the original roof - so only the dormer in this case as the single storey extensions wouldn't reach the roof (assuming you are not a bungalow).

Thank you @Takingabreakagain! I knew mumsnet would have the answer 😂 I'd got tangled as to whether the volume applied to the whole building or whether that was simply the loft part.

This is the government guidance document for permitted development for householders.

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachmentdata/file/830643/1909100TechGuideefor_publishing.pdf

Volume is the old way of working out PD rights. It’s worth reading the document linked by skiingisheaven above as it sets out all the rights, and you can do both loft and GF extensions.

Thanks @Charlottemh and @SkiingIsHeaven that's helpful.

Is it an old terrace or a new build?
Conservation Area?

As no others have been done, I'm wondering whether there are extra controls.