To build extension or not

[KLCG]

Hi I haven't posted in many years but I am in need of advice.
We are in Godalming, Surrey. We have had planning permission to build on top of our kitchen since May 2018. We have had builders out to quote and we are getting quotes of £80-90k before VAT. We have £250k left on our mortgage, house is currently worth £425k. Mortgage renewal is due in October this year. So we would need to do additional borrowing. How would we do that?? Or do we wait??

The main goal was to give our son (10), who has Autism, a larger bedroom. (Our daughter is nearly 15 would move into our room, son move into her old room. )The architect talked us into a loft extension too but we are not going ahead with that as my Husband would not be able to stand up in most of it. He is only 6ft. So will just board that out.

On the plans, the ground floor was going to be a shower room and my utility was going to be absorbed into the kitchen. I now plan on making the shower room an office instead and keeping the utility room as is.

Since Brexit and now the CV we have ummed and ahhed about whether to go ahead with the build. Husband is on a very good wage and I work part time but he is worried we will end up negative equity and will be stuck or lose the house completely.
We could live with the smaller bedroom but he will soon be a teen and might want to spend more time in his room and he has lots of "things" he collects. So does my Husband ..

I wanted to start it last year but husband wanted to wait. Daughter starts year 11 in September so I would want it done soon so it wasn't too disruptive for her.

What's everyones thoughts. Is it too risky? Should we just do it and if there is a housing market crash or a recession then we ride it out?? Feel like I am going around in circles.

Why not sell and buy a bigger house?

That would give you £515 available for a mortgage.

I doubt you’ll get your money back in a slightly bigger bedroom 3 bed house

How do I edit my post - changed my username too so looks like different person.
Once the extension has been completed the house will have an extra bedroom, an ensuite, an office and we would keep the utility. I would take down the wall between the kitchen and the downstairs back room too. Making it a larger room that can be section off with foldaway doors.

It seems like a lot of money for what you will gain. Why not just go with a loft conversion with a dormer to gain more headroom?

Hi ShellieEllie, we are not allowed a dormer where we live. Planning permission rules. There are two windows in the plan but my Husband wouldnt be able move around up there. Plus the staircase has to go through the smallest room and so house would still be a 3bed. There is also no room for an ensuite either in the loft. IF the extension went ahead and we opted not to do the loft, we would effectively have a 4bed house with a study (5th bed?), a utility room, downstairs toilet, ensuite in New room and family bathroom. For £90k at the very least. Moving costs are so much higher than the extension.

Unless you manage it very well you will probably find the £90k increases somewhat. We had a very tight contract and good builder but extras came along that we wanted etc

Yes, very likely. I think that's the real fear.