IanR

There's a number of different options, depending on what you are trying to achieve. If you planned a heated floor (UFH) that would be used all winter then it's worth considering something more complex, but if you do not plan to heat the floor then a cold bridge along the bi-fold frame to floor is less of an issue. The simplest option, to get a low threshold for the bi-folds would be to recess the raft to create a shelf for the bi-folds to sit in (cutting away the EPS upstand as required) and have a local step on the outside with a drainage path between the back of the step and the side of the raft. To take this much further you'll need to share more info on plan for upper structure, planned surface outside the bi-folds, generic section of bi-fold frame and where the bi-folds drain to.

Not complete rubbish. I used foil-back PB, which is vapour impermeable, although you end up with some gaps in it for sockets, switches etc. and fixings for PB on the externals walls and roof were specified as 150mm spacing. Payne Insulation were happy with that and there's no noticeable bowing of PB panels or of fixings popping. My (I-Joist) studs were at 400 centres - 600 centres would probably leave the PB insufficiently supported.

Ah, yes, depends on build up. Not an option for my "Value Engineered" structure, that doesn't include a service void across 95% of the external walls and roof. PB closes off the structure, so needs to be in place for the insulation fill. If you're including an OSB inner layer (+ battens) + PB, then yes, holes in the OSB only and can probably close of with stapled net, before boarding.

I've got 300mm walls and 350mm roof, filling an I-Joist Structure. Yes, would definitely do the same again. Thermal performance and acoustic performance exceeded expectation and are a large part of the resultant perceived high comfort levels. I was a little concerned about cutting Ø100 holes in the plasterboard at the top of every void, thinking the re-work of these may pop the plaster after a few years, but not one is noticeable after 7 years. Just remember to keep the discs you cut out.

Price would go up roughly pro-rata with increase in cavity thickness, if that's what you mean. They fill to a density, something between 55 - 60 kg/m³ iirc, so the thicker the wall the more bales of cellulose they require. I used Payne Insulation from Norwich - they did a really good job.

You've specified 600 centres on your studs, what happens to your U Value if you specify 400 centres?

No, breather membrane is correct, it's your cement particle board I believe. It's for wet areas, so assume vapour closed. Between it and your vapour barrier (@ 5) no moisture can get out.

Yep, since Ubakus can't determine how much of an issue it is. If there's a potential issue you then need to move to something like Wufi to determine how significant. Lack of drying reserve could be too high vapour resistance on both sides of the build up, so if moisture gets in it can't dry out quick enough.

PIR/PUR has good insulating properties per mm of thickness, but on its own is poor for sound attenuation and doesn't provide the best decremant delay. SIPs don't particularly make good houses, they're popular with volume builders as they reduce the skilled labour requirement on site. SIPs and PIR/PUR insulation are better when combined with a masonary skin as it improves the overall decrement delay and sound deadening, but less good with a lightweight structure. SIPs/PIR/PUR do offer a U Value advantage in a given wall thickness. By comparrison, celulose and rockwool are less good insulators (per mm of thickness), but do offer a better decrement delay for a lightweight structure. There is more to thermal perfomance and comfort than U Value alone. ie. to make an exageration a 1m thick stone wall has a much poorer U value than a 25mm thick PIR board but the temp profile inside the room will be very different. The PIR will react very quickly to outside temp changes but the solid stone wall will hold the two-week average temperature. The phase shift of your build up is just under 9 hours. I might accept a little compromise to the U Value (given that your side walls are width restricted) to swap out a material that gives a slightly improved phase-shift, to try and lift that to 12 or 15 hours. This would also likely come with improved sound performance. Since your front and rear walls are not thickness compromised, perhaps they could have a different build-up? ie. only compromise where you feel you have to.

I did. To me it's and insulated raft, but that's not the subject name of the thread, although it is the content of the thread, there are also others on the forum that object to this type of insulated foundation and floor system being referred to as a "raft", so I was trying to not ruffle old feathers.

But with a strip foundation and plinth wall there's an easy solution to the bi-fold, that and insulated raft doesn't have...

But what you've done there is more typical, I'm assuming the recent poster has chosen this thread for the insulated raft, which does take the load bearing walls.

I'm not sure that too many people are putting insulated rafts/slabs under garden rooms, but I and others were happy to give suggestions to the OP who wished to. The perimeter EPS Upstand wouldn't be robust enough to directly take the loads of a Bi-Fold. When the doors are opened there are lateral loads being applied and I'd expect the upstand to move away the raft/slab. You're also not going to achieve robust fixings through the frame into the EPS, they're just going to pull out. There are a number of ways of achieving it, as there's plenty of Bi-Folds and other thresholds on insulated rafts in houses, but there's more detailing required. Are you putting UFH into the floor? If not, do you really see any benefit in using an insulated raft? Or are you just happy to experiment? If your set on using an insulated raft then post up what your thinking regarding your floor build-up and wall construction and I'm sure there will be a few suggestions on how to incorporate a Bi-Fold threshold.

There was one sold between forum members a few years back...

Twin-stud cassettes/panels and stick built I-Joist are almost identical in their performance, I'm not suggesting one is better than the other. From what I see MBC's twin-stud does need extra membranes to perform to the same level, but if that costs you around the same then it's not a problem. When I priced up a Touchwood I-Joist structure v. an MBC Twin-stud the I-Joist was 10% cheaper, but others have here have commented the opposite, so there's really not much in it. If you were putting the frame up yourself I'd expect the I-Joist structure would be cheaper, when you look at the build-up there's just less layers and less labour. But, if you're paying for an install then it depends on margins and how much detail they put into the quote. You could argue that a twin-stud structure can achieve a fully thermal bridge free wall-to-floor joint with a simpler (and therefore hopefully cheaper) insulated raft foundation. I did take some of the "saving" in the cost of the I-Joist timber-frame and spent it on slightly more complex perimeter detail on the raft, but if I did it again I probably wouldn't do the same as it's tiny improvements that are being achieved once your at that level of performance. Cullen Timber Design do an excellent service for designing and engineering a PassivHaus-type I-Joist Structure. They can supply a full cutting list to the likes of JJones I-Joists and Assembly drawings to show you how it goes together, or I can thoroughly recommend Wilkinson Passiv Homes (previously Touchwood), as their knowledge and experience of erecting a CTD I-Joist structure will deliver sub 0.2 ACH @50Pa

Blown cellulose improves airtightness and doesn't require solid studs to be squeezed between - it's good at fully filling irregular shaped cavities. I'm not sure how you'd fit earthwool in a twin-stud structure, and the wider gaps between the webs of an I-Joist structure may leave earthwool lose. Blown cellulose has excellent acoustic properties, helped by fully filling the void. I know earthwool does as well but I'd expect extra care would be needed to ensure no gaps are left as any good sound deadening material will fail if there are gaps for the sound to pass directly through. MBC's twin-stud "cassettes" don't necessarily take the full benefit of blown cellulose's airtightness properties as while each cassette will have good airtightness, you've still got to seal the joints between the cassettes which is I guess why MBC still use an airtightness membrane (afaik), whereas with a stick built I-Joist structure, filled with blown cellulose you can do away with the membranes. I believe earthwool offers similar decrement delay, so both are good for a lightweight timber structure that's not combined with a masonry skin and will give a better temp phase-shift than a PIR/PUR insulation.

Of course it doesn't. These are rural properties by their nature (off mains drainage). When flooding occurs it's with exceptional rainfall. Let's say the often quoted "a month's rain in 24 hours". As an underestimate call it 100mm of rain. A Hectare of ground will receive 1,000,000 litres of rain during the 100mm downfall. Density of rural housing, that in England has no access to main drainage, is on average substantially less than one property per hectare. It's several orders of scale difference to the treatment plant discharge that the OP is referring to. Feel free to point to some research suggesting that treatment plant discharge has any bearing on flood risk and I'll happily read it and reconsider. "big developers" are putting mains drainage in and not installing treatment plants. I lose track of all your areas of expertise. Are you saying you have been designing small treatment plant installations for decades?

? This is treatment plant discharge, it plays no part in adding to a flooding risk. It's several orders of scale smaller than surface water drainage. @Lincolnshire Ian just follow the General Binding Rules where Environment Agency, who are responsible for reducing surface water flooding, have worked out what is best to do with you treatment plant discharge.

Assuming you are in England, you need to follow the General Binding Rules https://www.gov.uk/guidance/general-binding-rules-small-sewage-discharge-to-a-surface-water The above section is specific to discharging to surface water. It's not a last resort in England, perfectly OK to do, if you fit within the rules. If you do fit within the rules then no further permissions or permits are required, although you are criminally responsible for meeting the rules. Read all the caveats, but as long as you meet them then the storm drain will be fine if, for most of the year, it has water running in it. If it doesn't then there's an option to discharge to ground, within the storm drain, with a partial drainage field (length of perforated pipe) as described by @crispy_wafer

It's a badly worded question. I converted under Class Q, which excludes any further PD after conversion and reclaimed the 5% at the end of the build + the 20% for the materials I purchased directly. I don't remember that question when I claimed (2017). It maybe clearer with an added comma, ie. "Do you have planning permission*,* which includes permitted development rights?" ie. Is some of the conversion you have completed been developed under PD (and therefore not shown on your planning permission documents). If so you may need to get the LPA to agree it was legal via a "certificate of lawful development".

Insulated rafts, that are often used for PH type builds, are typically sitting on 300mm of EPS insulation, plus a perimeter insulation that may be around 150mm thick, isolating the floor and foundation from any contact with the ground. Detailing of the floor-to-wall joint is still required to achieve a cold bridge free design. U value would typically be around 0.1 The video at the attached link gives a good explanation of AFT's Eco Raft. Not their highest performing foundation, but further gains start to become marginal. https://www.advancedfoundationtechnologylimited.co.uk/our-products/timber-steel-icf-framed-building-foundation/

Many rafts and slabs are just over-engineered. It's not due to the EPS, I assume they've not been optimised by the SE. My own, similar to many on here, has a single layer of A193 Mesh, in what is generally a 100mm thick "raft". The thickness is increased to 300mm under the external walls with a second layer of mesh and some extra rebar. The cost of the steel was easily covered by the reduced concrete, reduced muck away and no screed.

Hello & Welcome. And quite right he is to, although the edge detail needs marrying up with your chosen wall build up to achieve a fully thermal bridge free design. There's no reason why an insulated raft would not be more cost effective than a standard strip foundation (if comparing like-for-like), but, as they remain a niche product some company's continue to charge a premium for them, definitely shop around. Are you going with Kithurst's I Joist wall build up? Looks pretty good, although there's potentially some cost that could come out of it without effecting performance. My own is an I Joist wall and roof structure, filled with cellulose fibre. From inside to out it's foil backed plater board, 300mm or 350mm I Joist, T&G DHF Egger board, breather membrane, battens, rain screen. The PB is the vapour control layer and the Egger board the airtightness layer (and racking strength), with no separate vapour or airtightness membrane (although all T&G joints were sealed with a butyl sealant). Really very simple and easy to make make very air tight. Cullen Timber Design designed and engineered my frame, and in conjunction with Wilkinson Passiv Homes (previously Touchwood Homes) have completed quite few similar builds.

"non-residential" means the plot has not previously been a residential plot (ie. previous house knocked down or was the garden of a house) AND development has not commenced. Just having planning permission does not make a plot residential. "residential" means either previously residential or development has commenced in line with an Approved planning.

That will take a significant re-write to un-pick WBS and Biomass boilers from the legislation, and still leave the fossil fuel ban in place, which appears to be her intention. Perhaps it's just the announcement of a Review for the sake on an upcoming election...