George

What does the Building Regs drawing show? Can you post it? # If it's a cold ventilated roof you'd normally have another sheet of PIR below the rafters. That can be taped or another (!) layer of PE can be the vcl.

Potentially but I was thinking more about compaction due to plant movement and material storage around the footprint of the structure. There's too many variables to give much advice - but some of the ideas in this thread will be good so you can challenge any consultants you use to make sure they're suitably experienced.

As an aside, 4m is quite close so there may be push back, since you'd be chopping through a large number of roots with traditional foundations. This is reduced with piles, but you are still blocking water from getting to the roots. Allied with that, during construction there may be a requirement to protect the roots/soil from compaction. This can result in building a temporary works platform over the roots area. I think to deal with any volume changes, and to protect the tree, I'd be looking at a screw piled foundation solution. Anything else is going to risk killing off the trees.

With clay sites you have to put stone down - think about where patios/gardens will be so you can just put it down and leave it. Dig down 150mm and stone up. Any type 1 stone would work as well as limestone. A 6" layer of stone won't sink unless something really heavy is on top. I'd also consider encircling the house with a French drain, or at least sloping the ground away, but that depends more on the surrounding elevation/geography whether that's really necessary.

Do you mean double overlapped clay tiles? This was surprisingly tricky to find one - loads of options for ~6000mm^2, but for MHVR really needed 20000mm^2, ended up going for this one but in grey: https://www.roofingsuperstore.co.uk/product/ubbink-ub19-plain-tile-vent-sepia.html

That's only for alloys known as 'weathering steels'; in appropriate conditions the rust develops into a protective patina. It needs to be used carefully - particular attention to water shedding details and corrosion losses built into the thickness of the steel. It's a pig to weld, too. But agree on the post - surface discolouring isn't serious and once encapsulated, shouldn't corrode any more.

- Will you need to access around the lantern for maintenance? - Consider the u-value of the lantern - it is likely much, much lower than the roof build up. if it's a very high percentage then the roof may be leaking a lot of heat - Conversely, consider how much solar gain you'll get in summer - Installation and laying the roof will be difficult with only 300mm to play with

I looked into it but couldn't justify the extra over cost compared to a radiator. Standard place for a rad is below the window because you don't often use the space under a window for anything else. And you look at a rad once then your brain never notices them again... I think in you case it's definitely a good shout. Maybe ask a supplier/installer if you can go see an installation and quiz the owners. Else, a 'feature' radiator rather than a normal boring one. Alternatively, electric radiant heaters which can be made flush with the ceiling, or something along those lines.

Agree re the gravel strip. Maybe 150mm against the side wall - line it up with the size of the gulley. By the book.... you should slope down to get to 150mm below DPC once past the door. However it's a relatively short length until you hit the fence so you'd just make it hard to use (as it'd be sloping and directing water to your neighbour). So I'd keep is level against the wall with the doors and slope uniformly away to the garden. You could put in a channel drain at the bottom of the patio as it'd be easy to direct it into the gulley pot. But if it's pretty free draining soil that's not really necessary. My soil goes a bit soggy immediately next to the patio but it all slopes away.

Remove the cladding, seal any gaps in the existing celotex and tape the joints. Then overlay with more PIR insulation boards, tape the joints and cover with a breather membrane. 50mm battens and then reuse the timbers (but replace anything rotten or badly warped). An extra 50mm of PIR will help, but you need to have a look at the eaves and make sure that will still work. If you go for 100mm you'll be toasty.

Anywhere with a floor going on top I'd finish the encasement flush. If this is going to form the FFL, then you could slope it slightly to allow water to run off. Paint bitumen on the steel and run it up to DPM level. It is smelly so don't go too far up. I'm not sure you need to paint the concrete - @saveasteading - what do you think? Galvanising is great protection. If it has damage then galvafroid can help repair it. But it is quite resistant to damage anyway as the zinc provides protection if it's within the same electrolyte. 150 years is ambitious... no building will last that long (no because things corrode, but because nature takes over) without maintenance so it's out of your hands I'm afraid. Build it as well as you can so it'll see you out. That's all we can do!

Before I answer that, a few clarifying questions... Is this all within the building envelope? Is anything going on top like a screed? Is the steel galvanised? Are you boxing in the columns? I would still paint the steel with bitumen if you have access. Usual detail is to encase with min. 100mm concrete surround and ensure it is well compacted between the flanges.

They're functionally identical so long as they conform to: Type 1 in accordance with Specification for Highway Works, Clause 803 You can get virgin limestone, recycled, crushed aggregate etc, but the important aspect is that they're graded correctly. For blinding, sharp sand is better as it can be machine compacted.

I'm still not convinced and I wouldn't like to rely on vertical tie bars to transfer shear. I have specified plinths when other factors drive it, but by and large I prefer to get a direct load path to the footing. I've pulled 120 year old steels out of footings and, although heavily corroded at ground level, they're absolutely spotless where encased in concrete - and this was agricultural sheds so exposed to the outside. The combination of no oxygen, alkaline environment and being within the building envelope should mean risk of corrosion is minimal. I should hope no-one is attempting concrete pours in poor weather! Especially when HD bolts are being set. @kxi B - is the more normal detail.

It's not a direct answer to your question, but a new build basement under an existing building is not a good idea. Difficult, risky and expensive. The only places that do it are where the land values are super high (i.e. central London) and even then, they can go very badly wrong. Basement conversion is OK but still face challenges with waterproofing. You'd be better off doing the loft conversion and using the money saved (which would be a LOT) to put in solar panels and an air conditioning system.

How do you manage shear forces and significant uplift?

I don't like them because you're trying to get load down to the foundation. Horizontal forces especially are more difficult to transfer through a plinth. You can get round QA issues (although any decent groundworker should be able to manage HD bolts) with post fixed resin anchors. Steel encased concrete will take hundreds of years to corrode. Anyway - I'd be interested to see their detail OP, when it does arrive.

That's slightly unusual. Typically you'd take the steel down to the foundation level (and encase the steel with concrete) rather than to dpc. I'd wait because you may need to dowel the concrete upstand into the foundation below to take any horizontal forces, and/or cast in extra long holding down bolts.

Needs a specialist report. Typically there's no difference between single story and double story foundation on domestic houses. So even if you had footings which don't meet modern specifications, I doubt there'd be an issue with adding a storey. This can be further confirmed if nearby houses have similar footings but have two storeys. What you would expect is when the extra weight is adding you get settlement and some issues from that - cracking, broken drain etc. However, underpinning is a major operation and also causes similar issues (which is why I avoid it wherever possible). However you'd need to get a an engineer to sign it all off, which is the harder part. And I think you'd also have to agree to accept the potential for negative effects without the builder or engineer taking liability.

If you're not undermining the foundations of then the risk is low. However, in some circumstances you need to consider the footings can become a small retaining wall if you excavate the soil along one side so safest is to do it in stages, excavate a length, backfill, then the next section. It's a lot of 'it depends' - footing size, soil type etc but whenever you deal with ground conditions, excessive caution is never punished.

There are a lot of joists because 254mm deep joists is shallow for a 6m span. That's a span/depth* ratio of ~24 - achievable with a steel beam, but quite an ask for timber. This goes back to the architect setting too small a floor structural zone and on the SE/floor designer for not splitting the spans with a steel beam (although that would make service routing harder). *edit for clarity - span/depth ratios aren't for design purposes - they just gives an indication of how big a beam/joist should be

That makes more sense. Hope it works. At some point cost difference compared to a stand alone AC unit may reduce to zero...!

I would have thought that piping cooled water through radiators in summer is asking for condensation to form.

If it's the old nasty fiberglass I'd be tempted to chuck it - I think it slowly breaks down over time anyway. If it's the newer/less itchy stuff then do keep it. I would have thought a series of dumpy bags with a tarpaulin over the top would have been enough.

For a small structure it'd probably be easier to have a normal building but instead of roof trusses, use a ridge beam and single spanning rafters to get the vaulted ceiling. There are a few structural design features that should be employed for vaulted ceilings, e.g. plywood sheathing, stiffness of the ridge beam, lateral stability,rigid rafter connections... but is easier to build than a portal. If you really want a portal, I would approach timber frame manufacturers direct in case they have a more standard design. Avoiding building regs shouldn't be your primary motivation for sizing. If you want to use it as a habitable (i.e. heated) space, you'd be hitting BR requirements anyway. Anyway, whereabouts in the country are you.