How on earth do we sense check this estimate?

[londonloves]

We've had plans drawn up for possible extension to our three bed end of terrace, the guy is not a builder but a project manager so would do all the permissions, structural engineering etc. We are in south east London. Costs are coming out as follows:
Lift conversion with dormer - master bedroom, en suite and storage £45k
Double storey side extension (this would be : cloak room and storage in ground floor and new bathroom in first floor) £50k
Remodelling of ground floor (replace current family bathroom with downstairs loo, knock through from kitchen to make dining room, new kitchen, move some doorways around for fire regs) £20k
Total cost of project including 10-15% fee for project management = £130k ish.
This would basically give us four decent sized bedrooms, additional en suite and downstairs loo, significantly more downstairs living space. But would take six months...
Does this cost sound reasonable? We are basically clueless and have a LOT to learn!

Sounds ok to me but for such a lot of work it would be advisable to get more than one quote. Also expect some extra costs to be incurred - i think it is usual to have an extra 10 % available for unexpected things.

Is that an actual quote from a builder or estimates from your project manager? Estimates can be a long way out.

You could get a quantity surveyor to look at the plans. They will break down the costs into minute detail, which not only sense checks the estimate but also gives you an idea of where you might be able to reduce costs if you need to.

It's an estimate from the project manager who has done the plans. Should we be getting quotes from multiple builders based on his plans? He seems to have a builder he always uses, he was recommended to me by someone local who has had a similar project done recently.

that looks a bit cheap to me....if they have a large team they could possibly do in 6 months - our GF exentsion took approx 3.5months..

do you have planning permission ( i think you have to for double storey)

i would check for extras too - does that include your kitchen units ? if so whose and how many ....our not v fancy kitchen from diy kitchens was £3k ish not including worktop
how many plug sockets/lighting points - we had a quote from a firm that 'project manage' as well and they only included 4 sockets per room in usual quote and each other one was £75 - we had almost 30 put in our remodel......

electrics - new loft/kitchen could need new distribution board...
new bathrooms /loft could be new boiler...

dh was not keen on teh prject management company approach as you dont actually choose your builder.....
I know many that used it though and it really seemed to vary depending on which 'team' of builders you got....

what is covered by project management and how many jobs are they project managing at a time.......

we ended up going for the architect -got plans then got builders quotes approach - prices didnt vary massively once you evened out what they covered ! highlighters/excel were involved...

I think after the fact, knowing my builder was locally based - so i could go and seem at home if it all went pear shaped (it didnt but made me feel better i knew where he lived!) and i had spoken to some of his previous clients was the main thing

its a hard process but we very happy with end result .....

Don't know about your costings, but the timing sounds do-able. We had a wrap around and side two storey extension with a total refurb in the house. The builder said 22 weeks and he stuck to his schedule. Mind you we did have up to 7 people working here some days.

We haven't applied for planning yet - would need it for the side extension, yes. That's all included in the estimate in terms of cost of applications etc plus building regs, party wall, structural engineer etc.
We would def need a new boiler as we have an old fashioned one at the moment with tank in the loft. He said he's factored in kitchen and bathroom units at the lower end of the price range, which I'm happy with - don't want anything flash, thinking Wickes/Ikea vibes.
I think we need to ask him for a bit more detail on his cost breakdown and about his team of builders etc.
I really want the work done but I'm shit scared of taking on something this big.

Get more than one quote. Always!

If I had an idea of your location, floor areas, scope of works, I’d be able to advise better.

Sounds too cheap imo.

Always get 3-4 quotes.

Should I be getting quotes from builders? Or looking for other project manager type people?
Or quotes from all the different people involved - plumbers, decorators, electricians etc. Sorry if this is a thick question!

P.s. thank you everyone for advice so far, it's so daunting!

Cost seems v reasonable to me especially for SE London.

As to who to get quotes from it depends on what level of involvement you want to have in the build - if you want someone to manage it all for you then get other project management company quotes, although it may be too small a project for many. If you're happy to do some management then go with a main builder who has his own team of sub contractors (plumbers, electricians etc) which he will manage. If you're happy to project manage everything then get quotes from individual trades.

The main issue with project management of this sort of build is making sure that the right people and materials are on site at the right time and that you've planned ahead to ensure that happens (as best as possible) so you need a good understanding of the process of building - e.g when will you need the plumber/electrician for first fix, that the plasterer needs to be booked in before second fix etc.

Definitely get a number of quotes, take up references, look at previous projects etc.

Thank you, that is really helpful.

Seems cheap - I would get at least 2, ideally 3 quotes, do ensure the builders are fully insured and check references. We were quoted from £20k - £125k for the same job, we paid £50k in the end- cowboys and rip off builders are everywhere

This does sound cheap. There could be other expenses, has he done a ground survey for the double side extension? Are there any drains to be moved? If this is the case the Water Authoriy has to be involved, mega costs! Also what depth will the foundations need to be, depends on sub soil. All added costs.