BristolBuild2020

Combination of a few things, rainwater attenuation, green roof, on a slope, building up the garden to have somewhere to sit a 11m3 attenuation tank high enough to drain into the nearest sewer (forced to do this by SAB…!) The more I work on the numbers the less certain I think I’m going to go ahead..! Even if I remove all the things we don’t need we are still well away from where we need to be!

We're in the same boat now, we've now got Full Planning, SAB, Building Control... QS price (FWIW) came back as knocking on the door of £4k sqm (Gross) over 260sq.m including everything we've spent to date. Overall cost would be £100k over a realistic worth even at todays prices. Our budget has already gone from £1500 to £2000 sq.m and we're currently resizing the house (9% reduction in Net Area doesn't really solve the problem). Given Self Build mortgages want 20% ontop of an agreed build price (in cash that we have to tuck away) means we can't actually borrow enough to build. So plan is to chip away at it slowly over the next year or two to maximise progress for minimal cost...

Currently looking at UniBlock/Polarwall/Nudura having had to move from ISOTEX. Engineer myself so doing trade studies across all options. Also making sure I can pay on card for the protection (one bitten twice shy!) Pros and cons for all of them as you’d expect… UniBlock come pre-cut along with inserts for openings so it really is just an assembly job for the most part. 3m theoretical max pour height thanks to it being metal not plastic webbing. But minimum insulation thickness is 75mm so minimum wall thickness is 270mm (which for internal walls means doing your own shuttering realistically but if doing large homes then a few 10s of mm may not matter. Matters for us as we have some tight dimensions. Apparently a few previous Nudura developers have moved to this system (May just be sales pitch talk..) Polarwall has a slightly different system but all cut on site, so more work in that regard. But installing floors etc that much easier as you replace the insulation board with timber. Very modular system, 50mm all the way up to 180/200mm insulation. Need to ask if they can precut to make life easier on site. Not had hands on with Nudura yet. Quotes for 300sq.m broadly similar.

I should have mentioned that this room exists only because we are using the space above it as another parking space. The “main” house starts 5m from the border on both sides, from the road you’d not even know there was another room there. I’m struggling with this because having 1m down the side of the house we wouldn’t use for anything against having another 4m2 in this room seems like a no brainer..!

Currently tweaking the design of our new self build and one question I'm not sure the best answer to is how far to build from the border. We currently have a single storey that is built 15cm from the border, dug into a hillside such that the border wall would effectively become a retaining wall and the 'roof' matches the level of the driveway. There is currently no property built on the adjacent land but will in the future. Do I build to 15cm (with foundations likely up to the border, give or take a few cm) assuming that I will always have some sort of access or do I increase the distance to 1m to ensure we've always got access? As I understand it when next door builds, they may need to inform me if they build within 3m/6m (depending on depth of foundations etc). But I don't think we can prevent them from doing so? We are likely having an insulated raft as the foundations but that is TBC. Thoughts?

I assume 200L/day during the winter and 300L/day in the Summer. With a 7500L tank, the longest period below 10% capacity is 55 days ending 29th August 1976 and 174 days without overflowing ending 16th Sept 1976! Which ties in nicely with... https://www.countryfile.com/countryfile/great-drought-of-1976-what-happened-and-what-was-the-impact-on-britain/ Over the last 130 years the stats are... RWH Usage: 11,004m3 Mains Usage: 482m3

I assume your sand filter is before the tank? What does it look like? I might allocate the space for it and add it after the house is built, got enough to worry about at the moment...!

Some updates, due to the poor infiltration rates we are now putting rainwater down a combined sewer at 0.1l/s. However in theory you shouldn't use Driveway run off for RWH... Thus I need at minimum now two tanks, one at-least 10m3. So call that two 7500L (as cheaper than an actual 15m3 tank) to leave me with 5000L that I can use to irrigate the green roof in the summer plus one more for actual use for RWH. Talking with some suppliers, they are quoting BS8515 resulting in a 3000L tank (just collecting off the non-green 54sqm at the moment). However having got the rainfall data for my location for the last 130 years, even with a 3000L tank there a long periods whereby its effectively empty (I assume empty at 200L remaining) and long periods again when it never overflows, yet apparently BS8515 is what we have to design to to ensure fresh water ever 15 days (not quite sure how you can maintain that if it doesn't rain...) At 3000L the cost of the whole system just doesn't make sense for the returns. Thus I think I'm going to ignore BS8515 and store 7500L from the 54sqm (due to the layout of the pipework, if it is determined that the runoff from the Green roof is not that stained then I can divert at least part of the runoff to my primary RWH tank) and then store whatever is left-over after releasing at the relevant attenuated rate. I'm currently not planning to use a header tank (don't actually have anywhere to put it...)

Looking for updated RWH thoughts... since this thread: I'm currently in the process of specifying my RWH tank, but a number of issues are coming up and I'm really wondering if its worth it, however with this recent drought I really want to store big numbers as even with a 7500L tank at ~200 litres a day for toilets/washing machine thats only 35ish days. I may also need to store large amounts due to soakaway issues (low infiltration rates...) I also want to irrigate the green roofs with the stored water when its really dry, otherwise pretty pointless using mains water to irrigate the roof! I've collected the data for my location of rainfall for the last 60 years, so I know the best/worst conditions and its not ideal. The issues I have come across: 1. Staining 70% is green roof thus discolouration due to solubles due to the substrate is likely. So I could collect from just the 60-70sqm that isn't green, but barely fill 7500L most years and never fill 15000L. I was thinking that the majority of the staining is flow through the substrate, thus if I had a way of diverting low flows (<0.1l/sec) to the soakaway then I'd only be collecting runoff and maybe minimise the discolouration? I can't imagine that even from a non-green roof that its perfectly clear as the leaves/etc that get stuck in the gutters etc also cause a little discolouration? 2. Pollen/Surface pollutants Apparently the tanks should overflow 'regularly' a few times a year, however again using the data, very rarely do they overflow (removing the top surface) unless I pick a pointlessly small tank. So either I need to find something that can skim off the top of the tank irrespective of level or pre-filter the water to remove the top surface again. I have an idea in my head so I might need to sketch it up to see if it works but wondering if anyone else has come across this before? Thinking about a large sand filter somewhere on the site to pre-filter the water, but may struggle in downpours... All rather tricky...!

I shall contact the SE to get his input. Does it matter if we're going Durisol or similar ICF? 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!

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...

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!

Evening, Having a bit of a battle with the SAB authority and I'd like to get it confirmed where their authority starts and ends. We have submitted a SAB design assuming no contribution from the green roof nor the RWH tank to size the soakaway. However the pre-application screening is asking for details on the green roof & RWH (tank, size, pump, pre/post-tank filtration), etc... I'm not quite sure why they need some of this information if it does not size the system, so could someone confirm where their jurisdiction starts and ends? If they *do* need details on all this, do they require specific products to be defined or specifications only (5000L, 2 rpm @ 3.5 bar, 800W, 0.65mm external, 0.35mm internal tank filter... etc..) Reference to any regs would also be useful but probably contained in a BS EN spec that costs £££! Many Thanks!

Having used Durisol on a site for a few days I’ve been planning to use them for my build ever since. Not quite sure where the negativity comes from but I’ll be looking at a Plan B in any case.

So to confirm my understanding then: I can trim bushes, etc. that have nothing to do with the build. I can get a tree surgeon in to cut down dead trees, trim others that are well outside of the building footprint. I can dig holes outside of the footprint of the house (Soakaway?) I can dig holes inside of the footprint (to check for utilities because for example a cable detector has detected something...) as long as I fill it in again? I assume I can't for example start building a retaining wall for the garden (as we are on a slope?) I can't start any digging within the footprint of the building? Many Thanks!