Does this sound a reasonable renovation plan?

[Hammertime]

Hello! I'm renovating a property and was wondering if you could sense-check my plans (banging my head against research brick walls has knocked all the sense out of me…). I've previously posted a question about solar when I was very early in the process and received very useful feedback. I now wanted to post about the plans more generally.

 

The property: just under 50sqm bungalow, one bed, all electric. Victorian but extensively remodelled in the 90s. It will sometimes be used as a holiday let (hence my concern about energy usage). Might have solar, but would only be a small array if so.

 

Insulation: I'm going as big as I can on this. 
Roof - upgrading roof areas to between 100-150mm pir as space allows. 
Walls - three sides are 1990s 50mm hollow cavity, fourth is Victorian solid sandstone c400mm (although altered in parts with modern brick and cement infill). Going to add 50-75mm pir direct to former, taped etc; for the latter, I’m either adding 25mm ventilation gap then pir studwork, or alternatively thermal plaster. Thermal plaster is not as good an insulator, but I’m wondering if this approach might utilise the thermal mass (sorry, I know that’s a controversial phrase) of the wall and help regulate room humidity? Can vapour open and vapour closed be used on different walls in the same room?

 

Heating: I’m taking out the old panel heaters. There is a log burner.
Considered: 
- ASHP would be brilliant, but it's a VERY quiet location. Also, I might just be able to squeeze in a slimline DHW cylinder but any other ASHP equipment would be a real push.
- High retention storage heaters might be an option, but I see mixed opinions of how effective they are. I also haven't seen many nice designs.
- Tepeo Zeb looks a nice idea, but I'm thinking 10-15 years ahead what happens regarding parts and support if buying from smaller companies.
- Offsetting electric usage by heating a slab with electric UFH. I have done some digging (literally) and found my floor buildup is only ~85mm (50mm jablite, 20mm chipboard, tiles), which makes this unfeasible.
- Some combination of pump and Willis external immersion heater to run wet ufh - I saw this discussed in other posts but was unsure of feasibility.

Currently intending to install oil filled radiators, and electric UFH in the kitchen (~14sqm) and bathroom (~4sqm) as secondary heating. Given the shallow build up, I'm thinking 25mm or 50mm vacuum insulation boards (expensive but hopefully worth it) on the slab to ensure as little heat is lost to the ground below.

 

 

DHW: I’m taking out the vented direct copper cylinder.
Considered:
- instantaneous water heaters and electric shower, but would mean paying for electricity when it's used. I started looking at time-shifting energy consumption.
- Mixergy tank, but main benefit would be the cylinder learning my water usage then heating required amounts accordingly, which isn't useful for a holiday let.
- Sunamp Thermino: a nice idea, but the footprint is similar to a slimline UVC so doesn't actually save much space. Also, the reviews of customer support/reliability seem mixed. If it was able to run heating as well as DHW like the tepeo zeb, that would be more attractive, but I don't think the newer ones do.
- Cylinder with integrated ASHP, but runs into the same noise issues as an ASHP. 

Currently planning to get a 'dumb' direct unvented cylinder as I can more easily upgrade smart thermostats like the Eddi as and when new tech comes out. Planning to oversize the cylinder as far as space allows, so that the on-peak immersion is rarely required, and choose one with good standing heat loss. Hopefully a better shower experience than an electric too.

 

 

Ventilation: 
Considered:
- MVHR was the original plan; however, the layout - coupled with conflicting advice about whether MVHR can be used with a non-room-sealed log burner - makes this tricky.

Currently planning to hit ventilation regs with DMEV in the bathroom, as it’s quiet, and DMVHR in the kitchen. I’ve read negative opinions about the effectiveness of DMHVR, but any help towards heat loss seems beneficial. I'll then get an air tightness test/gas spillage test for the log burner with the extractors running. Zero chance of being too air tight, not least because there are window trickle vents! But better to have it officially confirmed.

 

Does this sound a reasonable plan, or the mad scheme of someone who’s disappeared down too many research rabbit holes and surfaced with the wrong answers? 

 

Thanks!
 

[SteamyTea]

Post up a sketch of the layout.

Is there any reason you cannot put a horizontal DHW cylinder in the loft?

A properly sized and commissioned monoblock ASHP would be quiet, easy to install and cheap.

Get as much PV on the roof as you practically can, you may want to fit some batteries one day (they could be fitted outside).

MVHR should be fairly simple in a bungalow.

 

But layout sketch first, gives everyone an idea of what is where. Don't forget to put the roof orientation on.

Edited March 23 by SteamyTea

[IGP]

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.