Loft extension or keep money and invest?

[Dutchhouse14]

We've recently inherited about 100k.
DH wants to spend the money on a loft conversion adding 2beds and a bathroom.
We've had quotes and it will cost about 80k.
It will be pushing the ceiling price of our house so hopefully break even point.
We are planning on staying here for another 10-12 years before downsizing and retiring.
We have 4DC late teens/early 20s.
The loft conversion has always been a dream (we've lived here 20years) but I have a niggling thought that it's about 10-15 years too late and we might be better using money for something else/investments.
DH is, probably rightly, concerned it would be slowly eroded and we would have nothing to show for it.
DS has just moved about 200 miles away with GF, his single bedroom is now doubling as my office and if he came back to visit with his GF it would be very tight for them to stay here and I don't want a barrier for them to come back and visit .
Oldest DD just returned from uni and likely to move out in next couple of years, her bedroom is our old dining room.
Another DD just started uni, autistic and likely to need a home with us for a while. Youngest DD has Autism more complex SEN and will need ongoing support going forward.
Having the loft extension would give us a second much needed bathroom, get my dining room back so lounge is less squashed/multi functional living/dining/ DH WFH space
But I think we could be down to 2 DC at home within next 2-3 years in which case need for loft extension would not be as pressing.
We work full time so weekends are spent doing housework, gardening, maintenance, ferriying around youngest DD so not sure I want to add more rooms to clean and maintain to the mix but having space for DS to comfortably visit with his GF (room would double as DH office) and having my dining room back would be nice.,as would a second bathroom.
We've never had money sitting in a bank account and I must admit I like the buffer and security it gives.
I would also like to give DC house deposits.
If we spend pretty much all the money on the loft conversion then we won't be in a position to do this unless we sell.
Sorry this is long! But what would you do?

I'm in a similarish position and will be using most of the money for home improvements/extension.

Where I'm different from you is that I will not be downsizing and will be future proofing to leave this house in a box when the time comes, and the additional spend will still be a long margin under ceiling price and still add value. I also have a financial buffer elsewhere.

I've always said I want a home my children and grandchildren can always come back and visit all at the same time.

10-12 years is a long time so if you will enjoy your conversion for that amount of time, I think it's money well spent.

In your position I would carefully consider all options. It sounds like your children are close to leaving home, building work at the moment is expensive as material costs are increasing. You would also need to factor in a contingency fund plus money to furnish the new space. Does the 80k include new bathroom etc or would this be extra?

What is your current financial position, do you both have pensions and investments? You didn’t mention how old you both are, how many years you more you plan to work, your retirement plans, existing mortgage and any other debts. I would consider all these factors before leaping into a project when you are at a stage of your life when your children could be close to leaving home.

First of all I would speak to an estate agent in the area and ask them if the loft conversion would be financially a good idea. In other words, will it actually add value to the house in the short term? If I added a loft conversion to my house, it wouldn't add that much value as my existing bedrooms would be much smaller plus the living space downstairs wouldn't be big enough to comfortably have 4 adults living here.
But… if it did add value, then its a great way of improving your living conditions plus increasing the value of the house when you do come to downsize in years to come.

Thanks fir your replies.
We've paid off mortgage, pensions are modest, no other investments or savings so will probably have to work until state retirement age, I'm 53,DH is 56.
We did have estate agent round to value house both with and without conversion, because it's a semi it has a lower ceiling price. If work comes in at budget it will be at exact ceiling price he said/break even point.
Price quoted is 76k incl bathroom but need to allow for decorating and carpets so I think it will be 80k ish all in.
We will move eventually, probably in10 ish years, as it's very rural no public transport and high maintenance old house with large garden so not ideal for retirement.
If we could do it and be comfortably under ceiling price and still have a good buffer of savings , I wouldn't have any concerns but we will be putting everything into this.

Whilst housing development is usually a reasonable way to invest - I’d bet that the historic growth may run slow for the next few years

I’d be tempted to pop it in pensions - you might get a lot out of being able to retire early

Your house will always be a semi.

Your right it’s a bit too late, don’t extend use both your stocks and shares ISA allowances. That’s 40k now and then another 40k in a few weeks with the new financial year.