Prior approval query

I don't have a straight forward answer for this as it depends on various factors. Firstly, what moved your neighbour into objecting? Would he write a letter of support now? Were both applications submitted with a Prior Approval for large extensions? The loss of light can potentially be dealt with with either solar studies or a decrease in the height of the extension. Usually if you can ensure a shadowing volume no higher than 2.5 meters (as this would be the height of an outbuilding under permitted development).

I encountered a similar issue with Prior Approval on a job recently. The application for Prior Approval for 6m extension was rejected due to an objection with one of the neighbours. I advised my client to speak to both neighbours in a friendly way, to try to negotiate and compromise on the issue. I then essentially redesigned the roof of the extension to be slightly smaller to please the neighbour, but kept the 6m. We then submitted again for Prior Approval with 6m and it was approved. So I suggest try your best to deal with your neighbours. If not, prior approval may not be appropriate, and going for full planning may be more suitable dependant on the context.

There are different approaches if you want to extend your property to the rear. 1- If your house is a standard mid terrace property with Permitted Development Rights, generally you should be able to build up to 3m depth (and eaves 3m high) without planning permission. 2- You could go for up to 6m deep if you submit a prior approval application for a larger extension, which I imagine is the path you took. This option totally depends on your neighbours and if there are no complains and all the other limitations are respected (roof height, remaining garden area, etc), the Council should give you the approval without questioning. 3- The third option is a Householder Planning Application, in which your Local Authority will look at your site and will assess if it is acceptable considering your neighbours' properties, overshadow, overlooking, etc. Even an extension that would be approved through the previous routes could be rejected by the Council. It is in this case when they would normally suggest the 45 degree rule. Answering your specific questions, you could extend the size of your opening and avoid the 55cm from the edge by making it structurally safe, normally a steel box frame would solve the problem but you would need to get a structural engineer involved and get the calculations approved by Building control. Also, regarding your options to get a rectangular 4m extension, you could still try to agree a depth with your neighbour that is less than 6m, but still more than 3m, and submit again a prior approval for a large extension making sure they won't object this time. You could also offer to lower the roof height if that is the reason why they are objecting. I hope that helps and you can eventually get the most of your property