SBMS

Did you do similar detailing re DPC as suggested? Were you on PIR for cavity insulation or beads?

@Dunc that’s really useful thank you

So, unlike @JohnMo’s suggestion you’d advocate some marmox instead of aerated blocks? I wonder what the payback would be based on additional cost of marmox.. we’ve got 50m perimeter.

With that DPC - how would we get the beads below the DPC?

Thanks. Out of interest if this is as effective as marmox thermablock - why would anyone use them instead of the above detailing?

Thanks. Architect has specified PIR upstand around screed (not on engineer drawings above). Is that what you mean? Just to clarify - your two courses of aerated blocks - are they the ones directly below FFL (adjacent to the slab, insulation and screed?) Where do you mean regarding the DPC movement?

Would that not be based on the joist depth?

We currently have the following 'standard' detail for foundation arrangement: We are using EPS beads for cavity insulation. Have seen a number of different schemes to reduce thermal bridging. Enhancement one: the 'denby dale detail' where the bottom four courses of inner block are switched out to aerated concrete. Enhancement two: putting a course of marmox thermablock adjacent to the screed to minimise bridging (about £1400 additional cost for that). Enhancement three: instead of the concrete cavity fill before ground, we could bring the beads right down below ground level. Which of the above would recommend incorporating into the above detail with regards to a cost vs benefit analysis?

Dave - really useful, have you got any more photos (especially at corners) of the installation?

Currently specifying the posi joist to wall junction. My plan is whichever detail we use, we'll still paint the junction internally with passive purple. As I understand it, the tony tray method is 'tried and tested' and clearly works - but there can be issues with on site installation (tearing when joists are lifted on etc). Is there any reason why a joist seal such as https://www.manthorpebp.co.uk/air-leakage/joist-seals-wide-range-sizes-and-permutations/joist-seals isn't an easier, less risk prone solution?

I don’t think that would be clearly justifiable or necessary. The principle when granting planning permission is that the new dwelling that is approved is assessed for approval in the context of retaining its PD rights. The removal or those rights via a condition should be justifiable in the context of the application and site. For example, a contentious site that only just passed in green belt would typically have PD rights removed so as to afford the LPA the ability to control future development of the site. It should be site specific and necessary and justifiable. Our LPA no longer adds this condition by default (it used to) following a number of successful applications to remove the condition post approval by a fairly industrious local planning consultant… each time he asserted the test of necessity and justifiable to the site and the LPA didn’t even question it. I think an earlier post regarding appeal inspectors dim view to removal of these rights is valid.

Yes I don’t quite understand it myself - but makes sense it’s an exponential simulation. We are in the north west (Lancashire) so…wet! Our site area for positively drained area is 0.3ha - does that make a difference? Yours is roughly half; could that account for the 2x difference??

Is it vaulted if you’ve got a ceiling effectively 1.4m from the ridge? If youve got a steel there anyway could you not get rid of the collar?

@Alan Ambrose, our ground floor sqm footprint is 206m2 (garage + ground floor). My basic maths: my 206m2 / your 470m2 = 43%. So of your 24.7m3 storage would be around 43% at 10.6m3. Then there's the discharge rate - mine is 2.6l/s whereas yours is 1.9l/s. my 2.6 / your 1.9m2 = about 136%. So that 10.6m3 is about 7.8m3. I'm not sure why the figures I've tried to normalise above are still double when removing the 'permeable' area, and adjusting for the lower discharge rate.. However I suspect that the simulation isn't linear (i.e. half the sqm doesn't yield half the required attenuation) and is possibly more like an exponential curve... someone smarter than me can answer that? What I would say is counting your permeable areas as impermeable seems up for debate and might drastically reduce your storage requirements. Secondly - how did they calculate your discharge rate? Our site is currently brownfield and they adjusted it 'up' as if it was greenfield (so there is a betterment), but still theres a 30% difference.. maybe one to investigate? And finally, the great irony in all this, is that currently, every single bit of our site - where the house is going, the driveway and our garden - totally 1500sqm - is currently a thick concrete slab (brownfield, former piggery and stores) with some rudimentary drainage discharging to the local beck about 160m away. The site never floods, and neither does the beck, so anything we do - probably even without attenuation - might be entirely unnecessary??

Is it enough? He’s done the storm calculations and says it is - that’s what we are paying him for, so got to assume that his climate adjusted 1 In 100 year storm figures are correct? One thing I have noticed is some engineers count the driveways (even if permeable) into modelling/attenuation figures and some don’t - did yours (assuming your driveway areas are permeable?)

Thanks @Dave Jones - I spoke with the engineer today after these comments and he basically said we could go with either. He pointed me at some manufacturers of plastic manholes that were cheaper but fundamentally said we need 4m3 of attenuation with a hydrobrake and said we could use crates or a manhole. He suggested speaking to our groundworkers to price up the most cost effective route. Seems like a pragmatic response at least.

It was over engineered. Our house was one of 3 self builds at the site and we inherited the scheme that had been approved and discharged with the council. The owners of the site had responsibility for implementing the scheme. Our builders, the ground workers and another drainage engineer I asked to have a look at it said it was entirely unnecessary and some crates would have sufficed. Fundamentally 500 sqm of driveway was used as attenuation. This was dug down, lined with membrane and then filled with stone with a hydrobrake at the end to discharge. Ironically it was an absolute silty mud pit by the end of the build when the crates went down and likely totally impermeable below the crates. In any event… Agree with your comments on the chamber, seems really expensive way to do it

Ah okay - that gets a bit closer then - a set of attenuation tanks to do 3.5m3 (the 2100mm chamber option) is about £500...so it might be a wash price wise or a few £100 more? Do you think the 'ease' of install balances the slight increase in materials (saving on labour costs for digging two holes for example?)

Editing my previous message… I was thinking of the radius not diameter so got you re the 2m2 of crates. Do sokeaway crates do the same job as a manhole?

We’ve had our SUDS compliant drainage plan designed by our engineer. Compacted clay so no chance of soakaways etc. I had asked to minimise attenuation tanks etc - to be compliant the engineer has designed for water to be attenuated in the surface water pipe work and oversized manholes. The big one is a 2100mm diameter by 1m deep manhole with a hydro brake limiting to 2.6l. This will run off into a distant stream (via an existing drain). I’ve looked online at the concrete ring which is about £900 so not obscenely expensive. our last build was eye wateringly over engineered to the point of having the entire driveway effectively be the attenuation system with layers of stone, membrane and then crates on top. Very expensive. The manhole above looks like it’s about £900 so seemingly not too bad. Has anyone put something like this in before? It’s been sited in what will be the garden - how much of it has to be exposed? The full 2.1m, or can it be turfed over (or partially turfed over)?

What’s the umbrella company called?

Thanks @JohnMo, a fair point. I'll ask the floor engineer to design to minimum depth, based on the SE arrangement and then increase as needed. My question was really, if the floor manufacturer can do a 202mm does this even work for services.

We're looking at specifying our posi joists for our intermediate floors. For a number of reasons )mainly head height) we want to specify the minimum depth joist we can. The posi joists we're looking at have the following minimum clearance depths between the flanges: 108mm 131mm 159mm We'll be using flexible MVHR ductwork which should be fine with any of these. I think our biggest service will be any 4" soil pipes with bends etc. What would be the minimum recommended depth for this?

Thanks @Mr Punter what’s an intermediate pitched roof? We were looking at blown cellulose - what would you recommend?

Thanks. Why would you not advise mixing PIR on top and Rockwool in between? also - what are your thoughts on warm roof for pitched roof?