IGP

Blown EPS beads for me.

I would try to keep it as simple as possible, and without knowing the layout etc, if I was in your position I would personally; Go as big as you can without being daft on loft/roof insulation. It's cheap and simple. Fill the cavities where you have them with blown EPS beads. If you're going back to brick/stone anyway - perhaps the vapour open insulating plaster (diathonite?) would be sensible over slapping PIR over it and introducing interstitial condensation risk. Have MVHR - I would prioritize 24/7 air quality and humidty control over an occasional log burning from an non-room sealed log burner. Air-tightness generally is key as I'm sure you're aware. Foam and tape everywhere! Go ASHP, if you're having UFH anyway make sure they are 100mm centres for the lowest flow temperature possible and continuous heat. Don't worry too much about losing too much heat to the ground - earth is insulating (otherwise GSHP's with loops wouldn't work), and the priority should be designing the heating system to get the lowest flow temperature as possible get the efficiency gains here rather than spending *loads* on fancy insulation like VIPs (unless you have some *crazy* thermal bridges). Get a really good ASHP that runs v quiet, I'm going for a Viessmann Vitocal 151-A which seems to be super quiet, v efficient and also has an integral DHW cylinder. This may or may not fit the bill, but there are other options out there for sure. That's what i would do, as you can go as far as you like with insulation but it it becomes diminishing returns quickly and having an efficient ASHP setup can more than make up for imperfect insulation levels.

As other state earlier, don’t go PIR in cavity, all too easy to get wrong. Example thread. Full fill all the way be that mineral wool batts or blown EPS beads.

You could just PIR in this zone being careful to foam and tape to stop draughts coming up between the PIR and joists? The PIR is a better insulator than fibrous insulation, so you can go thinner for the same performance - keeping that air gap for those joists. Then just carry on as you were for the rest of the floor, that’s what I would do with the info you’ve provided so far.

100% this. Example of PIR done badly is here

Wow, that’s er not good in the politest sense… I wonder if you could drill through the wall and through the PIR, and using a really long toggle to allow you pull the PIR to the inner leaf, working from the bottom up. Otherwise, given that the PIR is loose inside the cavity, I don’t suppose there is an option of removing it somehow, then once done, fill with blown EPS beads?

It didn’t make a difference to the air temperature as that set to a steady 20c, but the floor itself was like 12c prior to insulation and now is about 19c post. Can happily walk on the floor barefoot and not be cold at all. We’ve got about 180mm of mineral wool for the insulation layer. Definitely put a vapour membrane on the top and tape to wall, stops moisture from the room air condensing inside the insulation layer. Do it once, do it right.

I did the Ecological Building systems approach in my 30’s semi detached, and it’s made the world of difference. No draughts anywhere, and a warm floor in winter. Highly recommend.

I’d love to have gone Enerphit just for the warm fuzzy feeling of being in a highly insulated house. However, I just couldn’t make the sums work, and ended up focusing on airtightness, loft insulation, CWI, suspended floor insulation, MVHR. No major insulation work like IWI / EWI though. It’s a 1930’s semi detached. Then, I’ve done my heat loss, upgraded all the rads to run at 38c flow at -3c OAT and getting my energy use down further through high SCOP of my heat pump I’ll be installing later this year. So, I’ll be going from 18,000kWh+ gas/year pre-renovation to 10,000kWh now and then to around 2500kWh electricity (assuming all goes well with the HP as planned) for heating and DHW. But horses for courses and people do it differently 🙂

Don’t zone if at all possible. Adjust the spacing of the UFH loops to match the intended design temperature for particular rooms while running a single low flow temperature.

Yeah the design is like something your mate takes home at the end of night of a few jars, after he hasn’t had anything in a while. I’m going Viessmann Vitocal 15X-A, partly performance, partly just looks better than that monster.

I did something similar but used foil backed PIR, foamed and taped. Then put a vapour check membrane over that and taped that to the wall, floor and windows. So far so good, but I have MVHR now so that keeps the humidity low during the winter.

I'm not so sure on electricity being a one-way bet, unless all you're thinking about its price cap/fixed tariffs. Taking Octopus agile as the most extreme example of the smart tariffs, it's clear that the average price is in the 15-18 p/kWh range if you can avoid lots of consumption between 4-7pm. Given that a HP would run low and slow all day, the vast majority would be at these averages (you could also do a setback during the 4-7pm peak). There are numerous other smart tariffs, each with their own pros and cons but they usually mean there are bargains to be had if you want to take them.

Which is why I’ve come to the conclusion that we probably should be only recommending 300mm loft insulation, CWI (if have cavities wide enough) and upgrading to DG from SG for *most* properties, unless you happen to be doing more work anyway and can insulate more while there. New builds should be much higher standards. These are the highest impact per £ invested. And then HPs at <45c design flow temp as that is around at the point where SCOP for most HPs beats the spark gap and saves money for people (and be therefore can be seen as better, not just equal to gas). But that’s just my rules of thumb.

I have the same, I installed between the MVHR unit and the supply and extract distribution boxes. You want to attenuate the fan noise of the unit to the house, not the the outside to the unit - unless i'm massively mistaken! Hope that helps

I'm not so sure it's going to cost a ton in energy and can in fact be less. This is the Valliant Arotherm Plus table, which is probably there or there abouts a good approximation for most heat pumps. If say, I've got a property thats got a annual usage of say 10,000kWh of heating requirements which roughly approximates to a heat loss of 4kW at design outdoor temp (10,000 / 2500 degree days) and I run it at a 'bog standard' 55c flow , it gives a SCOP of 3.06, which would use approx 3268kWh/year elec. If I insulated the same property, and knocked of 1kW of heat loss of design temp (so now it's 3kW, 25% reduction of overall heat loss) by using IWI - that would be approx 7500kWh annually heat demand, and at the 55c flow temp would mean an annual use of approx 2,450 kWh / year. However, if i did nothing to the fabric, but instead upgraded the heating system to run at 35c flow at the outdoor design temp, that would give me a SCOP of 4.48, which would mean an annual electricity use of (10000/4.48) = 2,232 kWh / year.

Maybe I’m just a renegade, but when it comes to IWI - I’m usually of the opinion of don’t bother. Just make the sure the emitters are sized for 40c or less (ideally 35c) flow temperature on an ASHP and get the benefits there rather than potentially causing interstitial condensation issues with IWI. Much less risk and still high comfort with low energy inputs.

What @JohnMo says. Just slapping a HP in and guessing at the setup with doing proper heat loss calculations, system design and using on/off controllers is asking for trouble. What is your brother’s aim with the swap to the heat pump (apart from doing the right thing environmentally)? Is it low running costs, or low installation costs?

From what I understand, the manufacturers actually don't when they are pushed by people who know what they're talking about. They include buffers / LLH's in the manufacturers instructions, but it's just excess stuff to prevent callbacks.

There is also the Viessmann Vitocal 150 /151 A's, they also can integrate with the OVO tariffs (I assume any others that might work in the same way in future) and seem to be considered by some of the heatgeek engineers on twitter as the dogs danglies. I'm leaning that way when i move from my gas boiler to ASHP.

I think Glyn Hudson found this exact thing, he starts talking about it around 8mins in the video

Just remember you if you put any membrane down, it’s a breather membrane for the cold side and a vapour check membrane for the warm side, as well as don’t forget to tape it also. The breather membrane on the outside does the hard work of preventing wind wash, whereas the vapour check on the warm side prevents warm humid air crossing into the insulation and condensing. Ideally you need both. Or use foil backed PIR and foam and tape the area you install it. The foil prevents vapour moment, so getting a snug as fit as possible is key.

I’ll just leave this here re hydrogen. V interesting.

Depends. They have to be part of a strategy, and a very clear one at that. If it’s acknowledging that the skills base for low temperature heating isn’t there and there’s a very clear signal to industry to get their finger out and train and implement low temperature heating design by X date (say 2030 for argument) whilst also decarbonising at the same time and no new gas appliances after 2040. That could fly. If there’s no explicit strategy, then we have to go through the hard yards upfront in changing the culture to low temperature heating design, but it won’t be pretty. But if we throw hybrids in here, that just makes it worse as it’s extends this messy period where the training and culture of heating design isn’t moving on, possibly an even worse place to be.

It looks like he’s gone for what he’s losing in actual heat loss, making up (and possibly more) with efficiency of the system.