New build design & cost estimation opinions

[morgan_22]

Hi all, 

 

Me and my partner are currently in the process of buying a plot situated in West Wales to build our first home. I am an architectural technician and she's an accountant so the plan is to manage the whole design & build process ourselves to keep the costs under control as we are on a fairly tight budget. I'm hoping to build to passive levels if financially viable.

 

The plot is quite narrow & oddly shaped but is large enough for us to build a decent sized first home and it's in a good urban location so service connection costs should be relatively affordable. The perimeter & shape of the house will need to be retained (as shown on dwg PL02) due to a number of conditions so changing the shape & external size will not be possible. 

 

Please see attached (hopefully) the proposed design drawings & cost estimation spreadsheet. Any feedback or suggestions regarding the cost estimation (if I've missed anything) & proposed design will be much appreciated!

 

Thanks!

 

Cost Estimation 31 08 22.pdf PL02 - PROPOSED PLANS.pdf PL03 - PROPOSED ELEVATIONS.pdf

[nod]

It looks to low 

Site clearance and foundations are hard to predict 

Muck away can soon rack up As can stone in 

We spent over 10 k on muck away on our previous build 5 years ago 

[SBMS]

Too low. We are right in the midst of our self build so have a fairly good handle on current costs and I think nearly every single estimate is on the low end - perhaps except your services costs. 

[ProDave]

It's going to be a difficult site due to size so no option but muck away as it's dug etc and the logistics of building in a small space, access, material storage etc will be complicated.  That will likely all add more cost.

[morgan_22]

47 minutes ago, nod said:

It looks to low 

Site clearance and foundations are hard to predict 

Muck away can soon rack up As can stone in 

We spent over 10 k on muck away on our previous build 5 years ago 

Yes, the foundation cost was hard to estimate as we haven't had any quotes or had a soil investigation to see what the ground conditions are.

Can I ask what your G floor area was for your build?

[morgan_22]

35 minutes ago, SBMS said:

Too low. We are right in the midst of our self build so have a fairly good handle on current costs and I think nearly every single estimate is on the low end - perhaps except your services costs. 

Thanks for the feedback! 
Could you possibly be more specific? i.e. where do you think i'm way off with the estimates.

The only quote I've had so far is for the timber structure (inc. delivery, erection, cellulose insulation, airtight taping) which came to around £67.5k from a well respected timber framing company.

[SBMS]

5 minutes ago, morgan_22 said:

Thanks for the feedback! 
Could you possibly be more specific? i.e. where do you think i'm way off with the estimates.

The only quote I've had so far is for the timber structure (inc. delivery, erection, cellulose insulation, airtight taping) which came to around £67.5k from a well respected timber framing company.

I was going to say the only bit I can’t comment on is the superstructure as we are doing brick and block. 
 

I think as others have mentioned, your clearance costs are a bit low for muck away. Foundation costs are so variable, but just a 500mm extra depth dig for our foundations was an extra £5k. 
 

I think your glazing costs are optimistic we were over £20k for glazing and doors and that was double glazed. 
 

Surface and grey water drainage costs seem a bit low - we were 12k and that was for a scheme that was shared amongst 3 self builds so there were economies of scale costs. 
 

1750 for UFH is pretty low. Our ground floor is larger but our price is coming in at nearly

an order of magnitude higher. 
 

7k for electrics including an EV charger seems tight; unless you’re just going for pendant lights throughout etc. We worked on a rough basis of £50 per ‘thing’ (socket/ light etc) fitted. Crude but fairly accurate.

 

4k for MVHR installed? Ours is nearer 7k(installed).  
 

I’m just picking out a few things here. To be honest I followed the same logic as you when setting out - your spreadsheet seems logical but when you start getting quotes and getting into the detail of costings I think you’ll need an extra 25% unless you’re doing a lot of the work yourself. My original estimates were not dissimilar to yours and when we got quotes back I was out by around 25%. But the variability in quotes was pretty high so it does depend on getting a good builder you trust. 

[nod]

33 minutes ago, morgan_22 said:

Yes, the foundation cost was hard to estimate as we haven't had any quotes or had a soil investigation to see what the ground conditions are.

Can I ask what your G floor area was for your build?

The G F area was 150m2 Nice flat site 

But trees five years ago Prices have more than doubled since then 

 

Our current build No trees Boulder clay hardly any top soil Shallow foundations 

Should save a few quid this time Wrong as soon as I started digging I hit pockets of sand 

Muck away would have been horrendous Luckily we own the two Acre field behind I chose to strip back the top soil on half the field and bury the 1000 tones plus of muck After a day of getting nowhere with my borrowed 8 tone digger I hired a bulldozer 

£500 per day and £300 per day fuel 

It’s the only part of the build that is impossible to predict 

I dug twelve test holes prior to full planning which the SE based his foundation design on and all seamed well 

 

Hopefully you are lucky with ground conditions But allow a contingency Just in case 

[morgan_22]

15 minutes ago, SBMS said:

I was going to say the only bit I can’t comment on is the superstructure as we are doing brick and block. 
 

I think as others have mentioned, your clearance costs are a bit low for muck away. Foundation costs are so variable, but just a 500mm extra depth dig for our foundations was an extra £5k. 
 

I think your glazing costs are optimistic we were over £20k for glazing and doors and that was double glazed. 
 

Surface and grey water drainage costs seem a bit low - we were 12k and that was for a scheme that was shared amongst 3 self builds so there were economies of scale costs. 
 

1750 for UFH is pretty low. Our ground floor is larger but our price is coming in at nearly

an order of magnitude higher. 
 

7k for electrics including an EV charger seems tight; unless you’re just going for pendant lights throughout etc. We worked on a rough basis of £50 per ‘thing’ (socket/ light etc) fitted. Crude but fairly accurate.

 

4k for MVHR installed? Ours is nearer 7k(installed).  
 

I’m just picking out a few things here. To be honest I followed the same logic as you when setting out - your spreadsheet seems logical but when you start getting quotes and getting into the detail of costings I think you’ll need an extra 25% unless you’re doing a lot of the work yourself. My original estimates were not dissimilar to yours and when we got quotes back I was out by around 25%. But the variability in quotes was pretty high so it does depend on getting a good builder you trust. 

Very helpful thanks! 
 

I'm hoping to do most of the site clearance & excavating myself as we have a fair few members of the family with building experience that will be able to lend a hand but will still need to cart away & dispose the waste which will come at a cost (unless I can find a local farmer that'll take it).

 

Can i ask what was your builds total floor area and where was it located? 

 

One of the main parts of the brief was to keep the design as simple to keep costs under control and all this feedback is very useful.

I think the best way forward will be to start getting approx quotes from local tradesmen & companies to try and get a realistic estimation of the costs as we're still working off planning drawings.

 

[morgan_22]

14 minutes ago, nod said:

The G F area was 150m2 Nice flat site 

But trees five years ago Prices have more than doubled since then 

 

Our current build No trees Boulder clay hardly any top soil Shallow foundations 

Should save a few quid this time Wrong as soon as I started digging I hit pockets of sand 

Muck away would have been horrendous Luckily we own the two Acre field behind I chose to strip back the top soil on half the field and bury the 1000 tones plus of muck After a day of getting nowhere with my borrowed 8 tone digger I hired a bulldozer 

£500 per day and £300 per day fuel 

It’s the only part of the build that is impossible to predict 

I dug twelve test holes prior to full planning which the SE based his foundation design on and all seamed well 

 

Hopefully you are lucky with ground conditions But allow a contingency Just in case 

Yes prices have gone through the roof in the last few years! Hopefully costs will start to settle in the next year or so as they say that the best time to self-build is in a recession when there isn't much work about for local builders.
 

This is also a relatively flat site, but as said earlier it's small & awkward which won't help the costs.

 

 

 

 

[SBMS]

8 minutes ago, morgan_22 said:

Very helpful thanks! 
 

I'm hoping to do most of the site clearance & excavating myself as we have a fair few members of the family with building experience that will be able to lend a hand but will still need to cart away & dispose the waste which will come at a cost (unless I can find a local farmer that'll take it).

 

Can i ask what was your builds total floor area and where was it located? 

 

One of the main parts of the brief was to keep the design as simple to keep costs under control and all this feedback is very useful.

I think the best way forward will be to start getting approx quotes from local tradesmen & companies to try and get a realistic estimation of the costs as we're still working off planning drawings.

 

I posted on a similar thread back in March here with our square meterage and costs breakdown:

 

 

[saveasteading]

2 hours ago, nod said:

It’s the only part of the build that is impossible to predict 

 

Everything is predictable. Groundworks often has potential for clever designs to minimise muck away.

Simply avoiding overdigging (wrong sized bucket) can be worth a great deal.

[nod]

5 hours ago, saveasteading said:

Everything is predictable. Groundworks often has potential for clever designs to minimise muck away.

Simply avoiding overdigging (wrong sized bucket) can be worth a great deal.

Regardless of design If BC comes along and says Let’s have it another 500 It’s going to cost If you use the wrong size bucket You probably shouldn’t be in the digger in the first place 

 

We sat our treatment plant in 1 cube of concrete on our first build and 6 cube on our second 500 quid extra 

You can possibly account for this 

[SBMS]

7 hours ago, saveasteading said:

Everything is predictable. Groundworks often has potential for clever designs to minimise muck away.

Simply avoiding overdigging (wrong sized bucket) can be worth a great deal.

Nothing is predictable!  As nod said - groudworks especially so. Our BC asked us to go another 1/2 meter deeper because he was worried about a tree that had been felled.  Wasn't to the NHBC guidance, but he's a belt and braces guy. Cost us 5k extra.  Our chamber floor was supposed to be here weeks ago - but they've got transportation issues because of the fuel costs (theyre trying to keep to quotes by optimising their deliveries) - certainly wasn't predictable when they quoted in January before Ukraine etc etc

[AliG]

I like the efficiency of your design.

 

But you are a bit too low I am afraid.

 

A few things.

 

1. Site

I think muck away is around £50 a cubic metre.

I think scaffolding will be at least double if not treble the amount estimated.

 

2. Windows - Actually you don't have a lot of glass, so the estimate looks OK to me, if not high.

 

3. Heating - Looks OK to me, we paid the same amount for 140sq metres of UFH pipe and manifold. 

 

4. Electrics - Looks OK to me, PV should be less than 5k

 

5. Finishes

 

If this is for wooden floorings looks, too low. OK for carpet

 

6 Fit out

 

Staircase looks too low

 

Kitchen/Utility room looks way too low. Unless you get the very cheapest appliances they could eat up much of that budget on their own.

 

Plasterboard - I think you have around 250sq metres of wall at a rough guesstimate. I would expect plasterboard and skim to cost maybe 3x your estimate.

 

I am assuming that the kit includes the roof insulation otherwise this is quite a large cost not allowed for.

 

Net I reckon you are maybe £25k too low. TBH it is more realistic than most estimates II have seen recently. This assumes that you manage all subcontractors yourself, otherwise a main contractor will probably add 20% to your costs (combination of mark up and them not spending as much time getting lowest costs)

 

[JohnMo]

Looking at the sunamp, big cost for little advantage, have you considered a normal UVC?  Perhaps make the downstairs shower slightly smaller and use that space to site it?

 

Willis heater assume is for UFH, you should install two, one for backup as an installed valve isolated spare.

[morgan_22]

1 hour ago, AliG said:

I like the efficiency of your design.

 

But you are a bit too low I am afraid.

 

A few things.

 

1. Site

I think muck away is around £50 a cubic metre.

I think scaffolding will be at least double if not treble the amount estimated.

 

2. Windows - Actually you don't have a lot of glass, so the estimate looks OK to me, if not high.

 

3. Heating - Looks OK to me, we paid the same amount for 140sq metres of UFH pipe and manifold. 

 

4. Electrics - Looks OK to me, PV should be less than 5k

 

5. Finishes

 

If this is for wooden floorings looks, too low. OK for carpet

 

6 Fit out

 

Staircase looks too low

 

Kitchen/Utility room looks way too low. Unless you get the very cheapest appliances they could eat up much of that budget on their own.

 

Plasterboard - I think you have around 250sq metres of wall at a rough guesstimate. I would expect plasterboard and skim to cost maybe 3x your estimate.

 

I am assuming that the kit includes the roof insulation otherwise this is quite a large cost not allowed for.

 

Net I reckon you are maybe £25k too low. TBH it is more realistic than most estimates II have seen recently. This assumes that you manage all subcontractors yourself, otherwise a main contractor will probably add 20% to your costs (combination of mark up and them not spending as much time getting lowest costs)

 

I've tried to keep it as square & simple as possible without making it look like a box with a roof on top! 

 

1. Ok I'll work the cubic meterage out & alter my estimation to suit. 

 

2. Yes the amount of glazing is quite low as I've kept the amount of NW & NE facing glazing to a minimum so hopefully I have over estimated a bit on the glazing.

 

4. PV is one of the optional extras at the minute but as we are going for all electric heating & DHW a PV array could be very economical with the way energy prices are going.

 

6. Will increase staircase.

The utility will just be a large plant room / corridor (1.8m long x 1.8m wide) with floor to ceiling cupboards to hide the MVHR & washing machine, this job could be done on the cheap as we have a few carpenters in the family.

The kitchen will be a howdens/stock kitchen with standard appliances as I would much rather spend £25k extra on the building envelope than on a designer kitchen, but I will increase my estimate as it is a bit low.

Will increase plasterboard & skim finish estimate as to tell you the truth I had no idea how much it would cost!

 

The kit includes all wall and roof structure, insulation, internal & external sheathing boards and airtight membrane & taping.

 

Yes I'll be managing the project & subcontractors myself as I have experience in the industry.

 

Very helpful comment, thanks!

 

 

 

 

[morgan_22]

1 hour ago, JohnMo said:

Looking at the sunamp, big cost for little advantage, have you considered a normal UVC?  Perhaps make the downstairs shower slightly smaller and use that space to site it?

 

Willis heater assume is for UFH, you should install two, one for backup as an installed valve isolated spare.

To tell you the truth I haven't looked into the different electrical heating possibilities as of yet but if a normal UVC would work out cheaper to install & run with the PV then I'll probably get one. Yes I'm currently in the process of re-jigging the downstairs shower room layout around to make the third bedroom/snug a bit bigger and give more storage space in the plant/utility room.  

[saveasteading]

9 hours ago, SBMS said:

Cost us 5k

But I would have known, and so should your SE or architect. And your SE trumps the BCO.

I will modify my statement if you like  to 'predictable to those whose subject it is'. But then that applies to every element: I don't know much about electrics.

 

A nasty extra cost for you whether justified or not.

Many bco's have a default of asking to dig deeper, because they can and the groundworker does it and the client gets the cost. These aren't usually best pleased when told "no," or asked to prove the need. 

 

If there had been a deciduous tree nearby then he was probably right, to some extent at least.

 

The biggest unpredictable aspect of groundwork is the weather....I admit to that bringing surprises.

[Mr Punter]

I don't see an allowance for a sprinkler system, which are mandatory in Wales and would be advised anyway as you have a staircase open to the kitchen.

[SBMS]

3 hours ago, saveasteading said:

But I would have known

How would you have known?

[saveasteading]

2 hours ago, SBMS said:

How would you have known?

It was my training and job.

Study the site: on the ground , the geology and surroundings. Dig holes. Look at trees and watercourses. Look at nearby projects.

Design the building to suit the conditions.

Other Engineers are available.

[Dave Jones]

you need to cost your big unknown the foundation. Have you had a ground test done by an SE? What about a warranty ? Provision for hiring plant, telehandler etc ??

 

Then get the plans properly QS'd its cheap and you will have every brick, block and nail costed. Unless you are funding the build from cash the bank will want this anyway.

 

Very lucky to get it under £2.5k m2 and thats with a lot of work and time for free coming from you.

[shuff27]

The roofing estimate is low - I paid c.£20k for 100sqm using Spanish slates.  That did include a lot of leadwork & valleys (3 dormers & attached garage) but your figure of £3.5k seems optimistic unless you have a very cheap roofer!

[SBMS]

16 hours ago, saveasteading said:

It was my training and job.

Study the site: on the ground , the geology and surroundings. Dig holes. Look at trees and watercourses. Look at nearby projects.

Design the building to suit the conditions.

Other Engineers are available.

Fair enough. It was a difficult one to predict as the tree was in a neighbours garden, 20 meters away, felled 9months ago (before we bought our plot) and was only discovered because BCO asked to use their toilet and spotted it in their garden. 

Edited September 2, 2022 by SBMS