Best time to start an extension

[Getitdonet]

Hi all.
Im moving into my new place early January and will be doing a rear extension as well as redoing the bathroom. Given our lovely British weather this time of year when realistically is the best time to start this kind of work (rear extension)? Ideally I would like to crack on as soon as possible but I know the first part is all about getting the property water tight and mindful that Feb is a rainy time of the year.

Experiences/advice welcomed!

Ours was started last October and between December and February not much happened because of the awful cold weather and flu and colds among the builders. Bricks can crack if laid in below zero temperatures and it's very hard to dig out the foundations if the soil is frozen. We tried to use our builder on indoor jobs during the bad winter temps eg refitting our bathroom out so all wasn't lost

We ended up with no choice whatsoever as a builder was so hard to come by we just fit in with them. I think there're benefits and downsides to different times of the year and a lot of luck involved!

I agree with shutlingsloe - if you haven't got a builder lined up already and can find one to start Jan / Feb, I'd be really concerned! Good builders are booked up well in advance (we waited about 9 months for ours). Also, do you need planning permission? A party wall agreement (which must be served 2 months before you start work)? I would find a recommended builder and go with their timescales.

I have 1 that just did my friends full hs refurb so hes come in recommended. Im trying to list architects to come in for quotes for tge drawings although im finding those initial consultations are st times £250 is this normal? As ill rather get a competent one but serms like there isnt a concept of a quote first?
Im thinking of a 3m extension so within the permitted development scheme but i do have 1 party wall consideration given itd a semi (they have already done a loft conversion) plus the building reg so you have a point about notice.
There is the bathroom refit, plus decorationg upstairs to do plus an internal wall to remove which could take us into march i guess.