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For info/inspiration here's something that I'm just in the process of finishing up - my garden shoffice (half shed, half office) Wall construction was (inside to out) - - 11mm OSB - Multifoil insulation (I was curious to see how well it worked..) - 4x2 stud filled with 100mm Knauf Ekoroll - 9mm OSB - Breather membrane - Horizontal batterns - Vertical cladding (gravel boards "good" side facing out) (there should be more air gaps and such, but it's a shed at the end of the day...!) Roof is EPDM on 18mm OSB, 4x2s @ 600 centers, mix of ekoroll and celotex, 11mm OSB internal finish Floor is 18mm OSB on 6x2s @ ~400 centers. Ekoroll supported by breather membrane looped over the joists Costs add up surprisingly quickly but saved money by sourcing all the joists from a nearby bungalow that was being scalped and turned into a house - the builder said it's a shame as it all treated, slow grown, dead straight wood but because it isn't graded he has to burn it or skip it. All the joist wood cost me £20 + labour for denailing etc. Smallest 9000btu ASHP for heating Still needs some finishing touches and another coat of paint/stain (Cuprinol Shades) but otherwise it's probably very close to what you're trying to achieve.

Sorry, but can I ask what's wrong with having a ramp/level access? We designed it in from the outset and cannot imagine why we'd want to replace it with steps and, as mentioned earlier in the thread, many of us may need such access in years to come (never mind for visitors).

I have a project to go off grid (because I can, not because I need to). The initial plan was to use 24 100Ah fork lift batteries as the cheapest option, but a lot more research changed my mind and I decided to use LiFEPO4 batteries instead. They seem to be more expensive per kWh, but in fact the cost in terms of real capacity is similar. When I did my calculations cheap FLA fork lift batteries would have been about £6,600 for a 48V pack with a notional capacity of 48kWh; I choose to use 400Ah LiFePo4 batteries with a cost of about £7,000 for a nominal capacity of 19kWh. In real life, in order get a long life out of the FLA cells you can't discharge them less than 50% which reduces the capacity to about 24kWh. The LiFEPO4 batteries can be run down to 20% without ill effect, which gives a capacity of about 15kWh for my example. Over the expected battery lifetime the costs per kWh were very similar. Having decided that the lifetime costs were similar the LiFEPO4 batteries have overwhelming advantages. They're much lighter and easier to handle, which was an issue for me as the chosen location is difficult to access. They are much more efficient - charge/discharge efficiency is over 90% FLA is of the order of 80%. They have low self discharge. They are low maintenance - no hazardous electrolyte to check and top up, no hydrogen to ventilate. They have simpler charge requirements, you don't need to do equalisation charges etc. Although some sort of battery monitoring system is essential in order to ensure that they don't get overcharged. Peukert effect (or equivalent) is virtually non existent. You can discharge at very high rates without significant loss of capacity. I wouldn't consider NiFE. They are very expensive and difficult to get hold of, but mainly they are appallingly inefficient, about 65%. There are a couple of useful discussions https://www.photovoltaikforum.com/speichersysteme-offgrid-f108/nissan-leaf-battery-in-an-sunny-island-setup--t102414.html discusses using Nissan leaf batteries in a Sunny Island system. This enormous thread http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069.html discusses real life use of LiFEPO4 batteries in off grid situations (boats) and has some useful information about how to ensure a good lifetime, unfortunately there's a lot of dross in there as well.

A self builder here is in a predicament. He is building a pretty well insulated house and detailing the air tightness well. But he has chosen not to fit mvhr. Instead he has a central extract system on each floor extracting from the bathrooms, kitchen and utility and trickle vents on the windows. After his air tightness test he was told it was "too good" and he is now looking at adding positive input ventilation as well (i.e mechanical ventilation without the heat recovery) I did try telling him mvhr was the way.......

What is stopping you adding your new sheds now under the PD rights for the existing dwelling, and then just not demolishing them when you remove the old ones? I am not sure when the removal of PD rights takes effect, but it cannot be before development starts. I guess it will be at the point you demolish. One problem might be if you have something like 'all existing sheds to be demolished' in your PP? What does it say?

Do I detect a little iddy biddy bit of something akin to guilt in the back of your mind? Partners can be all too good at detecting the surreptitious (not to say gratuitous, or even highly revealing) insertion of the word 'need' into a sentence. Teenagers are past masters at it.

If connecting to your existing boiler, is it a fully modulating one? If not, it's likely a small buffer would be needed tbh. +1 on more insulation, but if the tiles are smack on top of these boards then the floor will get hot enough, problem is that the medium to dissipate the heat is not great. Your pipes need to get hotter than normal, say in a screeded install, and you'll only have the tiles to absorb and convey the heat so may well prove to be uncomfortable if being used to heat an air leaky / high heat loss space. Retro fitting Ufh is not the best way, so if you choose this route be aware that you'll probably never turn it off in the heating seasons, just up and down ( comfort 21oC and economy aka setback at 16-17oC ) according to occupancy. That'll allow the house to stabilise and reduce response times. You can't increase the flow temp to speed up the warming times as you'll then get the overshoot that is mentioned above. Tbh that example is most likely just a poorly commissioned setup with way too high a flow temp so best not used as a benchmark. UFH works incredibly well, when fitted accordingly and commissioned properly.

What guys do up here is simply tape a bit of clear plastic over the floor. If you see any moisture under it, it's too wet to lay the flooring.

I'm sure the neighbours would move a few cars, people are generally very reasonable. Count yourself lucky I'm having to pull off a diplomacy miricle that frankly Kofi Annan would be proud of! Try explaining to builders that they have to take "1 hour quiet breaks" so a rescue horse in an adjoining paddock can "de-stress". I kid you not!!

Thanks @ragg987 meter working great :-) As a comparison I seal a calibrated (or so it says on box) cheap digital temperature and humidity meter in a plastic bag - gave approx the same reading:

There is another reason; MMC or Modern Methods of Construction. The drive to increase build speed and decrease costs by the big developers means that the supply chain have come up with a plethora of build elements that need very little skill to install/fit.

The main problem I see with your proposal is that the insulation is very thin so there will be heat loss down into the concrete slab and from there into the room below and/or the walls. You might be able to live with the increased running cost but the response time will be a lot slower. Do you have the headroom available to use thicker insulation say 80mm+? There is nothing peculiar to UFH that causes overheating. My guess is something else was going on. Perhaps too much solar gain? It is possible to have an issue with varying solar gain and a slow response time. Sometimes on a sunny winters day we get a lot of solar gain so the UFH switches off. Then when the sun sets the UFH takes awhile to respond to the loss of that heat source. The result is a small dip in temperature while the UFH catches up. They can be connected to a gas boiler using a mixer without a buffer tank. A correctly sized fully modulating boiler would be recommended if no room for a buffer tank. Buffer tank can help improve the efficiency but must be well insulated.