BristolBuild2020 Posted July 7, 2022 Share Posted July 7, 2022 I've been working through my big spreadsheet for costing the build and the one area I'm struggling to cost is the foundations, if its £100,000 or under we are OK and we can proceed without making the house smaller, if its more then I might spend some time rearranging everything to get the size down. Research and the odd random quote have ranged from £50k to £150k for 200 sq.m of raft foundations. On top of that struggling to find a builder that will respond let alone quote so I have to go to Plan B, work it out roughly myself (and at this rate I may actually end up doing it myself... TBC.) There is an added difficulty that it is on a slope of about 1:5... Based on the provisional structural drawings to date... Materials 150mm of Type 1 = 30 m3, 0.42m3 per 800kg bag = 72 bags = £63/bag = £4,500 50mm binding concrete = 10m3 = £200 m3 = £2000 Average Raft thickness of 300mm = 60m3 = £200m3 = £12000 200sq.m of rebar = £2000? Labour £250/hour, 8 hours = £2000/day Four weeks(???) = £40,000 Total = £60,000 Plus 20% due to site/inflation/unexpected costs = £72,000 or £360sq.m, which based on website values of £250 sq/m doesn't seem too far off. In addition some of the initial ground works (retaining bank, soakaway, RHW tank and garden level) will be done by me anyway which will involve digging some of the house out so contractor wont be starting from scratch. In any case, what else am I missing? Many Thanks! Link to comment Share on other sites More sharing options...
Olf Posted July 7, 2022 Share Posted July 7, 2022 31 minutes ago, BristolBuild2020 said: Based on the provisional structural drawings to date... Do you have a proper design of the raft (by a structural engineer)? It's hard to do precise figures based on vague assumptions 26 minutes ago, BristolBuild2020 said: 0.42m3 per 800kg bag Can you not get lorryloads of hardcore? 26 minutes ago, BristolBuild2020 said: 50mm binding concrete Why use binding concrete under concrete raft? 26 minutes ago, BristolBuild2020 said: Average Raft thickness of 300mm Sounds a lot, especially for an average. 29 minutes ago, BristolBuild2020 said: £250/hour, 8 hours = £2000/day That feeds 6-8 people, I'm not sure if there is enough room for them not to bump into one another. Saying that, this is surely the are where biggest savings can be achieved, search for many stories of those that had fun with diggers on their builds Link to comment Share on other sites More sharing options...
JohnMo Posted July 7, 2022 Share Posted July 7, 2022 Your prices seem well over the top. Our foundation, consists of the following for 194m2. Level site Reinforced strip foundation (2m wide at front of house) 70m perimeter. Hardcore and blinding sand, DPM. Stub walls, 100mm PIR insulation in cavity 160mm deep reinforced slab over whole area 200mm PIR insulation 100mm concrete finished floor. I install the insulation, contractor did the rest £36k. U value 0.09. If your buying sand and hardcore, buy direct from quarry, about half the price the builder merchant charges. You need an engineered design, based on your site. 1 Link to comment Share on other sites More sharing options...
ToughButterCup Posted July 7, 2022 Share Posted July 7, 2022 1 hour ago, BristolBuild2020 said: ... at this rate I may actually end up doing it myself... TBC ... In any case, what else am I missing? Please ask a properly qualified SE to do the design for you. We used Tanners: very experienced in this sector, and very keenly priced. (£1008.60 ) 3 Link to comment Share on other sites More sharing options...
Dreadnaught Posted July 7, 2022 Share Posted July 7, 2022 (edited) Price seems a little high. I would recommend splitting the job in to two parts. Groundworks in preparation for the raft. And the raft itself. Personally, I would say neither part is suited to a general builder. Use a groundworks specialist for the preparation. I used a team I found locally that were digging up the streets to lay new cables. I just stopped in the road and asked them if they were interested in some side work. For the raft itself, get a local concrete specialist to do it. He will have spent most of his time doing commercial jobs (such as the floors of warehouses) but will have no problem adapting to your needs. You'll get a much keener price. I agree with the others: make sure an SE designs and specifies your raft. From the SE, you should give the dimensions drawings, detail cross-sectional drawings showing steels, and a steel schedule to your concrete guys. He will pass the latter on to his local steel supplier. Edited July 7, 2022 by Dreadnaught 2 Link to comment Share on other sites More sharing options...
Russell griffiths Posted July 7, 2022 Share Posted July 7, 2022 Your building a house, not a patio, why are you talking in 800kg bags, you get 3 15 tonne truck loads at £450 a truck. Stop thinking Like a diy bloke and think like a construction guy. 1 Link to comment Share on other sites More sharing options...
saveasteading Posted July 7, 2022 Share Posted July 7, 2022 Everybody above is correct. £250/ day not per hour , easy error to correct. Concrete at £200 / m3 is high. Stone by the lorry, and find what options available...type 1 spec'd as standard but ask for crushed concrete and other options. BUT first. Not knowing the circumstances of course, but my gut reaction on that slope is for beam and block, not raft. As well as saving materials it makes it all easy for traditional trades. Also removes retaining walls or banks that are not in your budget. Spend some of the saving on a good local SE. Question all suggestions politely and stress value. If you pay an SE for 10 hours work then they cannot test alternatives. The extra £1,000 can be repaid many times over IF you choose the right SE. 1 Link to comment Share on other sites More sharing options...
Mr Punter Posted July 7, 2022 Share Posted July 7, 2022 Another vote for beam and block. Try to keep the beam lengths fairly short as it makes the floor feel much more solid. Once the beams are craned out it is a diy job to finish. If you do get a crane for the day you can use it to distribute packs of blocks and bricks around the site. Link to comment Share on other sites More sharing options...
jayc89 Posted July 7, 2022 Share Posted July 7, 2022 B&B is likely cheaper if you're getting a contractor in to do the work. A slab is certainly cheaper if DIYing. As has been said, get your aggregates in by the truck load. We paid £15/t for recycled MOT 1 last year. Link to comment Share on other sites More sharing options...
BristolBuild2020 Posted July 7, 2022 Author Share Posted July 7, 2022 (edited) All many thanks, hopefully the following answers all the points raised to date... 1. To be clear a SE has done some detailed draft drawings for me for quoting purposes (cross-sections, 1st floor/roof posi-joist details, retaining wall/openings reinforcement, etc). I can upload them if it will help for you lot to look over them? 2. I had used 300mm as an average because I wanted to be conservative and over-estimate, quite a bit of the slab is 300mm due to retaining walls at the front of the house, however if I calculate it more accurately it seems I was well off... A more accurate volume is: Raft Edge: 0.4m deep x 0.6 Wide x 32m along all specified edges = 7.7m3 300mm Area: 0.3m deep x 48m2 = 14.4m3 150mm Area: 0.15m deep x 52.5m2 = 7.9m3 Total: 30m3 3. Regarding binding concrete... No idea, SE specified it...! 4. SE has not specified anything regarding insulation or final floor finish. I've accounted for the underfloor heating separately, I've added two more lines for 200mm PIR + 100m concrete based on John Mo's comments in my spreadsheet: (72 (2 spare) sheets of 2.4x1.2x0.2 @ £180/sheet = £13k, £4k of concrete as technically this step is after I've built the ICF walls. 5. For clarification we are hoping to get to the point of the foundations being done before selling the house we currently live in, as well as making sure that it is closer to £50k rather than £150k, as the former means we can crack on as is and not sell earlier than necessary and secondly don't have to change the size of the house. 6. I shall investigate splitting the job to groundworks and concrete, thanks @Dreadnaught 7. Regarding bags vs bulk - I googled MOT Type 1 and the first page on google for me is only bags... revised on a local company doing recycled MOT type 1. 8. The "ground" floor is buried along the front of the house, so a retaining wall is necessary. 9. Regarding raft vs B&B, if this has any bearing on it I am aiming for Passivehaus standard (although I'm not going to go out of my way to necessarily 100% meet those standards, aiming for decent U-values, decent airtightness and that'll be it. U-values + 1:4/1:5 slope + retaining walls may drive it towards a raft? Finally an updated value seems to be... Materials 150mm of Type 1 = 30 m3, 0.67m3 per ton = 45 tonnes --> £15/ton recycled as suggested = £675 (bit better than £4k!) 50mm binding concrete = 10m3 @ £200 m3 = £2000 (Shall challenge) Raft Concrete of 30m3 @ £200m3 = £6000 200sq.m of rebar = £2000? Labour £250/day, four weeks = £5000 Now down to £16k, which given I've been given quotes of £60-100k makes me wonder A) What I'm missing and B) If they were just quoting high just incase... Edited July 7, 2022 by BristolBuild2020 Link to comment Share on other sites More sharing options...
Mr Punter Posted July 7, 2022 Share Posted July 7, 2022 You can easily reach PH standards with beam and block. You will not need any rebar or concrete / blinding / type 1. Given the gradient it may make sense. Link to comment Share on other sites More sharing options...
JohnMo Posted July 7, 2022 Share Posted July 7, 2022 (edited) Not sure where you are getting your prices. Insulation Celotex 100mm sheets £37+vat https://www.insulationhub.co.uk/product/100mm-celotex-ga4100-2-4m-x-1-2m/ Not £13k, but £2.6k I did the insulation, UFH pipes and finished floor concrete, prior to the walls. Way easier, just pumped the concrete in. Filled the UFH with antifreeze mix and pressurised. Edited July 7, 2022 by JohnMo More details Link to comment Share on other sites More sharing options...
BristolBuild2020 Posted July 7, 2022 Author Share Posted July 7, 2022 (edited) 22 minutes ago, Mr Punter said: You can easily reach PH standards with beam and block. You will not need any rebar or concrete / blinding / type 1. Given the gradient it may make sense. I shall contact the SE to get his input. Does it matter if we're going Durisol or similar ICF? 22 minutes ago, JohnMo said: Not sure where you are getting your prices. Insulation Celotex 100mm sheets £37+vat https://www.insulationhub.co.uk/product/100mm-celotex-ga4100-2-4m-x-1-2m/ Not £13k, but £2.6k I did the insulation, UFH pipes and finished floor concrete, prior to the walls. Way easier, just pumped the concrete in. Filled the UFH with antifreeze mix and pressurised. I just googled 200mm PIR and picked Travis Perkins! Revised with those sheets though as you suggested. I would like to clarify that when the time comes to actually order I shall be shopping around, at the moment I'm trying to build up a reasonable cost of each step to the nearest £5k or so. I shall also consider doing the PIR + concrete myself, seems reasonably straight forward. Also I note from your photograph, did you do three courses of ICF and then do the insulation without filling the ICF first? Given the retaining wall requirement for the Ground floor I might do the first 8-10 courses and then do the ICF foundations. Thanks again! Edited July 7, 2022 by BristolBuild2020 Link to comment Share on other sites More sharing options...
JohnMo Posted July 7, 2022 Share Posted July 7, 2022 I had the ICF blocks there, but they all got moved, so were rebuilt the next day. I thought I would get ahead, but didn't. The insulation was done prior to the ICF blocks being placed into position. Link to comment Share on other sites More sharing options...
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