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We recently put forward an offer on a detached house in Brent which has been accepted.

The house however will not be suitable unless we do a single story extension that is at least 4m.

We have since learnt that the house had previously been extended (in 1990) and that it is located in a conservation area.

Please find below a screenshot of an ordnance survey map showing the property taken from a planning application for a nearby property (google drive link):

https://drive.google.com/file/d/1av3I50ZKumwmjZ8Zplowr-hqPM_RNtV7/view?usp=sharing

I highlight below the portion that we think has already been extended (ie. was not part of the original house as at 1948):

https://drive.google.com/file/d/1ZHHs6nJgAKPddNK8wiCmjkwMtLjGV3gA/view?usp=sharing

I highlight in yellow below the additional extension we require:

https://drive.google.com/file/d/1ALKE55MZwKIiZfzCvXr3txZpXyhXM9jP/view?usp=sharing

The 'Permitted development rights for householders - Technical Guidance' makes it clear that we couldn't do this under permitted development rights, but if we were to submit a planning application along the above lines, how would you rate the likelihood of such a plan passing or does it seem completely unrealistic?

Thanks in advance!

Even though you’re within a CA, there would be no impact on it as it’s all be concentrated to the rear.

It would ultimately come down to the impact on the neighbouring properties. Look up your LPA’s policies on outlook, amenity and daylight in particular 25/45/60 degree lines, etc…

Thank you for the advice Damian :)

Just a few follow up questions following on from Damian's advice.

1. Please refer to the image below. The property we wish to purchase is the one in the middle.

https://drive.google.com/file/d/1eOiMdCpOkqctyQXrURmiFyZ1JLgxsxdo/view?usp=sharing

In terms of the 45 degree splay lines - which ones have been drawn correctly: red, blue, purple and/or green?

2. Would a single-storey GF extension bound by the splay lines shown in the following image be acceptable in terms of outlook and amenity? (The Brent Council Design Guide does not offer very much by way of guidance in this regard).

https://drive.google.com/file/d/1mqnyL2PfQEJGYc3T3pPiWmjV_KZPgEuk/view?usp=sharing

3. Would any of the trees shown in the following images need to be taken down if we were to do such an extension? If so, would this be difficult to get permission for, given the area's conservation area status (the trunks are more than 75mm in diameter)

https://drive.google.com/file/d/1qLkvDagKmLeT2PlDQFZNR6GxJ4kQH7gG/view?usp=sharing

4. The house is next to a grade II listed building - will this cause any problems?

Any further advice would be much appreciated! Thank you!

Instruct an architect/designer who should be able to go through all of that and any other questions you may have.