IanR

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...

That may explain why Adam at Wilkinson Passiv Homes will now do the ground works as well as the timber frame build. Previously AFT would have supervised the raft install.

Advanced Foundation Technology Ltd. would be my first choice, but it's worth doing some searching on this site.... lots of options. AFT and Wilkinson Passiv Homes do a number of projects together.

The newly extended area wouldn't qualify for Class Q Change of Use.

That crossed my mind too, you just need to get your roof lights agreed with the initial Prior Notice application.

Hi Lottie, and welcome. You've mentioned "Agricultural", so assume you are referring to the Class Q PD rights that have been in place since 2015, but were recently amended. If so, then yes, Class Q requires the building in question to have had an Agricultural Use within an established Agricultural Unit (commercial farm business). It must also have been in Agricultural Use on or before a date in 2014, and if it came in Use after that date then there is a 10 year wait before Class Q rights could be used. From what you have outlined, your building does not fit within the Class Q rules. ie. it's not been in Agricultural Use, at no point has its use been within an established agricultural unit.

Yes, no distinction is made between rural housing and urban housing within the PD rules for an occupied dwelling house. But, for all housing, the LPA can restrict PD rights when approving a permission. ie. If they feel any further development would be over-development, they can place a condition that removes any further PD Rights. For info, Class Q does this automatically, if you convert under Class Q, all PD Rights (other than green PD) are removed from the completed building. That doesn't mean you can never extend, just that you are required to put in a planning app to do so. I don't believe that would achieve anything larger than a single application that sets out what you want and tries its best to justify your request. When you put in the second planning app the judgement will be based on the original building and will consider the development that has already occurred.

Is the site in open countryside? By that I mean not within the settlement boundary of a village. At 8 acres I'm assuming it is in Open Countryside. If you obtained an approval for a Class Q development, then you have established the right to convert a home of the approved size and massing. This can be used as a fall-back for a full planning app, but you're unlikely to be able to push the size up by much, if you are in Open Countryside. You may be allowed to increase by the size that PD would allow if it were already a house, but unlikely to be any more. For single unit developments LPA's tend to treat Open Countryside in the same way Green Belt is treated, where any development is considered harmful to the openness of the countryside, so if Class Q has established the right to a house of a certain side, any further enlargement of it would likely be considered harmful, with few options to mitigate. Without Class Q you are relying on the clauses of Paragraph 84 of the NPPF: From those, (c) and (e) are you options, and only (e) would allow a significant increase in size. However, you should do some reading on what are termed Para 84 homes (previously known as Para 80/Para 79/Para 55), it's a very expensive route to planning approval, with no garuntees.

You'll just need to state that's what it was as part of Such'n'such Farm, and as long as there's no evidence that contradicts your statement, it won't be challenged. That's the effect of how the legislation is written. The building must have been occupied for the purpose of agriculture, within an established Agricultural Unit, and it's the Agricultural Unit that has the 1000m² and 10 property limit. Sorry, that's not an area I've looked at in any detail so can't help with how the rules are applied, but a google search brings this table Ref. https://www.gov.uk/government/publications/technical-housing-standards-nationally-described-space-standard/technical-housing-standards-nationally-described-space-standard Which suggests the minimum area for a 1 bed single occupancy is 37m², if there is a shower rather than a bath. To increase the size of the existing building would be development and from the info you've set out I'm not aware of any permitted rights that would allow you to increase the size without planning permission. Class Q will only consider the building now present on the site and whether or not it meets the requirement. What was there previously has no bearing. With a full planning app it may help, a little. Good question, and one I'm considering myself on my own site. It's obvious when a building is adjacent to a public road and the main entrance is on the side fronting the road, but less obvious if the building is in a field, approached by a farm track that is perpendicular to the public road, and the building entrance is neither on the track side or the public road side... I believe the legislation is attempting to allow an extension that is the least harmful to the openness of the country side, so they've added some words that hopefully places the extension on the least visible (to general public) side of teh building. My guess is that this one will cause some Appeals, and when it finally goes to the High Court to appeal an appeal decision, then there will be some case law that gives a better definition. For me personally, I'll be presenting my next Class Q in a way that maximises the extension option in the best manner for the development, and I will label the rear view of the barn as the one where I want the extension even though it has the main entrance. Typically farm yards are a square of concrete with buildings on 2 or 3 sides, with the buildings' main entrances off the square of concrete. The least visually impactful extension would be into the farm yard, but most would call that the front of the building. Hopefully there will be some other Class Q applications raising this same question before I submit my own so that I can be guided by how the LPA's interpret the new rules.

"Agricultural Unit" has a specific planning definition: and, "agriculture" or "farming the land" terms when used in planning mean the commercial business of farming. Since Agricultural Use bestows certain development rights it's been much tested in the courts and case law now defines it as being a commercial business able to support a farm worker. It's not just farming-type activities. So, if the 8 acres and cattle shed were split from the ownership of the original Agricultural Unit and continued with an Agricultural Use as part of a separate Agricultural business then yes, it would have turned into 2 Agricultural Units. But, if the 8 acres and cattle shed are no longer owned as part of an agricultural business then they are no longer part of an Agricultural Unit. If it didn't work in this way the 1000m² conversion limit would have a massive loop hole, ie. if a farmer wanted to convert more than 1000m² of farm building they'd just need to sell it off to someone else. The building however doesn't need to still be part of an Agricultural Unit, but it must have been at some point in its history and must have been in Agricultural Use prior to 20th March 2013, otherwise there is a 10 year wait. This would come down to the LPA's interpretation of the building's Use. Since you are keeping items in there it's Use is continuing, but is it Agricultural Use or is it residential storage or industrial storage, the latter two no longer being an Agricultural Use. As an example, a building used by a farm contractor to store their farming equipment that they use to contract on other's Agricultural Units is not classed as being in agricultural use, but in an industrial use. Difficult to judge how an LPA would interpret the use of your cattle shed, it would be better to clear it and have it considered to be now redundant with its last Use being Agricultural. If the only item stored in there is a tractor (not a ride on mower) that's been used to maintain the connected track and hedges then the LPA may accept that the shed still has an agricultural use. Yes, the land has continued with an Agricultural Use while leased to a farmer. At that point the land was being used as part of the farmer's Agricultural Unit. But, you've not mentioned the building being used by the tenant farmer, and it's the building's use that is considered here. Unfortunately this 2.5m x 4.5m lean too couldn't be considered as part of the Class Q. You'd first need to establish its "legality", ie. under what permission was it developed, then you'd have to wait 10 years after it began an agricultural use within an established agricultural unit.