All Activity

Experience speaks. Agree, a ground bearing slab will benefit the overall u value calcs.

For me I can see how folk are going for the MHVR, high end glazing, home automation etc. I do think UFH is a great solution, if kept simple like @JohnMo advocates. I think lot's of you are not actually being eco friendly at all. I think many are trying to do this as hobby to satisfy your need to appear eco friendly and not looking too deep and forensically about what you are doing. Some just want to play about with tech stuff. Some folk buy sports cars..but they don't kid themsevels on they are something they are not. Many of you are specing high end glazing that only has at most an 7 -8 year warranty. How do you jusatify that? Some are specing ventilation and home automation that will be redundant in ten years time. But if you really want to make a contribution then I would love to hear about eco friendly ideas that are going to work for 50 years plus that are easily and cheep to maintain, by someone else, say a young couple buying you home. I think many should be honest with themselves and just ask are we really being eco friendly or just being liberal twats so we look good. To make a point here. I have three young Chartered Architects on my books at the moment that have come to me to assist on the design of their own houses. They are all really clever and innovative designers. I'm loving working with them. I bring to the table my experience and say let's do this so we maintain / enhance the value of your house, lets look at the best way we can design for the short term.. so you enjoy realising your design but also make sure you can sell the house for a good price later and make sure some surveyor is not going to devalue if you have introduced some tech stuff that is a liability.

Ah.. First thing I think is that are you building a small house on a very valuable plot? If you are putting a 1.8m value house on a £250k plot then the warranty is far too cheep. I do claims work from time to time against the warranty providers. There are new comers to the market and you really nead to read carefully their T & C's. It bad enough for me going up against the NHBC as their T &C are not the same as they used to be. My last experience with Protek was.. the computer says know.. they are relatively small compared with the huge contingency ( all be it ring fenced) that the NHBC hold. One of their surveyors came to my office and I found him very competant, had a huge depth of knowledge about the building industry but a good bit of the liability rested with him, not Protek Unfortunatly the Protek management came over as a bit twatish..and a bit financially niaive about the self building industry. I think the main guy was about 40 years old.. still clearly in primary school. but with a bit of tough love they seemed to wake up and smell the coffee and we agreed a sensible premium that balanced their risk against mine. For the keen, folk that are familiar with how policies are written.. many waranty providers are shedding risk to independant surveyors and SE's to keep the cost down.. the banks are just burying their heads in the sand lending wise. I recently (not be named) one waranty provider wanted me to take on the contaminated land risk.. for £100 quid.. they are either out of their mind, or low IQ or just chancers! It's business so the latter is most likely. In this insurance business there are no friends in the desert! I know and make claims agianst them.. on the wanker ratio they are often above 5. Some are actually competent individuals.. but why do they take the mickeal out of ordinary home owners that say just work for the NHS... like my wife? You must understand how limited the cover is you are going to get for 4.0k.

Post what they are asking for. One thing about dealing with planners and BC is that you can end up being a useful idiot. Some treat you as a bit of CPD on their CV! Some make the mistake of providing info that just opens a can of worms.. again you become a CPD candidate. Now actually I have a good relationship with the planners, BC, locally I have known some for 40 years or more.. when we just were kids. Think about the balance.. you want to be helpful but not too much in writing. If you can the best way is to lift that old thing called the telephone and have a chat.

Are you sure? This could come back to bite you unless you know your stuff! By asking the question I can see you don't!

Actually this is more common than you think. Even if it's load coming down from large openings. Now you may have a full structural and very stiff raft and that is a different animal. When we design lighty loaded "insulated rafts" we often have point loads. There is much confusion around this. Unless you are an SE or experience Civil Engineer for example with the ability to analyse these things you won't really know about this mistique and the thoery. @Nickfromwales.. has done a lot of them but many don't know the theory, how they behave and the long term implications on the structure you are putting on top. The art of design is to look at each element from the soil up and understand how all these fascinating materail interact. It's part science and part craft.. that makes design exciting.. and eh profitable!.. In isolation if looking for a quick fix and safe, all we do is to recognise that the insulation is a bit more "squashy" and design for that. An insulated raft just has a more flexible layer before it hits the hard core. I've copied below a bit of my conservative calculations that I present to BC for a ground bearing slab, they need to tick a box.. The calcs are for completness, so I have go conservative to head off any questions from a checking Engineer. It lets you see how I'm taking the compressive strenght of the PIR insulation and reducing deflection. I chose to set a limit of 1.0 mm on the screed deflection as BC can't argue otherwise. Normally on insulated rafts I'll pick a different value.. I'm not going to tell you what that is as it's my intellectual property and that is why I get paid as an SE! ..

If only there was a way to nicely automate this I’d be on it as we currently use the cheap period on Cosy to heat the DHW for evening showers at 1pm (or PV if the sun is shining) using the ASHP.

You, sir, are correct. I now routinely dissuade anyone from 'diverting' excess PV as these days it's either going into a battery or they're getting paid for the less complex method of selling and buying back. KISS at its finest. Hoooooooooooooooooooooooooooooooowever....... I would like to interject. In terms of promoting longevity for ones ASHP, I suggest that my clients use the ASHP at dawn, and again at dusk for recharging the DHW, and only topping up at midday off the grid, via the immersion, if it is at all necessary. I dislike the idea of having the ASHP jump from a relaxed state of cooling to a panic state of DHW recharging, and the subsequent downturn in COP. I like to look holistically at how the M&E is presented at the design and concept stage, but furthermore, how long the homeowner will have a reliable system that doesn't need replacement prior to it delivering a ROI. Most ASHP's don't come with a warranty longer than 7 years, which is pretty crap, gas boilers around 10 max, so anything simple that can stave off a premature replacement of a bit of kit in the multiples of thousands, is a worthwhile pursuit imho. Kicks the beloved BUS grant saving into touch if you need to replace these any sooner than expected.

Maybe there’s scope for the physical panel install - that’s probably 2/3rds of the work.

I didn’t install a solar diverter for our PV as I figured I’d get a better COP from the ASHP than a 1:1 using a diverter. The ASHP is also run from the PV anyway so, in theory, I believe I’m using less PV to get the tank heated.

I did try cooling the slab with the ASHP but the family discipline closing windows and doors during the hot periods was iffy so gave up. On sunny days the UVC is 67c with the immersion / PV diverter by 10am. The lower ground floor bedrooms are north and east facing with smaller windows so not an issue. The first floor bedrooms with vaulted ceilings are the warmest and AC is just so effective and the running cost offset by PV (+FIT).

You can always run the pipework for AC, and first fix it.... Then in future years install the expensive bits either end. Could do it all for a few £100... MVHR is too invasive and there is no retrofitting.

Usually PV would sort that, or just a midday blast on the immersion heater, direct from the grid, so the cooling can just plod on in the background.

True but that’s a fraction of runtime really - and can be scheduled in the early hours (when it’s cheap). Personally I think simplicity is having one system doing both, but maybe it’s my OCD not wanting a unit sitting there unused half the year.

But can’t cool while the hot water tank is heating, right? I also considered fan coils and floor cooling but it was getting complicated and seemed like a lot of faff. having separate AC and ASHP just kept it simple for me.

I considered whether to install AC or not but have decided to fit fancoils to the first floor bedrooms and landing areas and have a two zone ASHP system. So can cool to proper AC levels in summer if needed. Wasn’t hugely more than a standard ASHP and was roughly the same as not doing UFH upstairs. And installed MVHR as well.

I like to look out at the blue sky so have AC to allow that if I wish to! We also have blinds to help with overheating but I don’t want to live in a house in permanent shade during the summer months.

They get it all year round. We don’t .

Like all those miserable people in the Mediterranean climate. It's OK.

If I remember properly, I read it that I would put a notice up in a suitable place , such as in a services zone, so that any future owner or maintenance orsin would have it explained. Ie just an explanation of the system. More formally it would also be in a maintenance manual, but that would get lost.

That's a good price. 0.002% of your build cost....

Agreed, but it’s a little like being imprisoned by the sun, and also that’ll be on the handful of nice days where you want to be able to look out of those lovely (and very expensive) glazed elevations, to the views outdoors. In the villa we stayed at in Faro (Portugal) there were a few days where dropping all the external shutters was necessary, as well as AC running, but it was horrible to sacrifice the views. For those current projects I’m on, we’re using solar reflective glazing, and the blinds etc will only be needed for privacy. The AC on these will only react to a slight rise in temps, and will have very little to do, so it won’t be a cure it’ll be a prevention.

And 450mm isn't enough to justify beam and block. The very clear difference is that below a slab you can have ground, (which insulates) or insulation, whereas below beams you have a draught.

@Indy https://forum.buildhub.org.uk/topic/43530-mvhr-who-needs-it-i-dont/#comment-611326

Depends on whether the one without had trickle vents? You know me and my impartiality lol. “Resistance is futile” 🤣