What is the best way to get my properties to an EPC rating of C?

You are not alone, there are tens of thousands in the same situation.
First make sure you have a combi condensing boiler, 400mm loft insulation, good DG windows and controls on all radiators except for one, then do nothing.
The government needs to find a solution therefore wait until they say something.
Finally, get an Energy Assessor to do a survey, then pay them to run different scenarios on the software to find what you have to do at its most efficiency, then you can rely on that.
Alan

do absolutely nothing until the government makes their mind up about what their 'cunning plan' on EPC's is exactly.

Expect potentially a bit more waffle in the New year ahead of the next GE....

I entirely agree with what others have said about the details of new EPC implementation not being completely known at this point.

I would suggest that the best preparation is to shop around and find a friendly and helpful EPC inspector who can review your property accurately as each inspectors approach, assumptions, opinions and calculations can come to so some very different conclusions, ratings and advice.

Finding the right inspector could be considerably less expensive than implementing the recommendations of the wrong inspector.

Double glazing, thick roof insulation and modern boilers and heating controls go a long way and get you into C territory if your walls have a cavity.

I worked with the EPC guy to know what got me the most points.
Loft insulation was the best £ per point.
I also added uPVC double glazing as the very old single pane timber windows were expensive to maintain.
I went from a very low D to C with just those two (I did this in 2023)

Double glazing, thick loft insulation, combi boiler, radiator thermostats, programmable thermostat with zones if large house, led lights 100%. Simples. Choose a good surveyor as they often have options in modelling the house.

A modern gas boiler will be more efficient and save your tenants money, but it has a higher carbon footprint than electric storage. And since we don't yet know what the revised EPC algorithm will favour, nobody can really know which of these two options will give you the better EPC.
Some things are likely to be beneficial either way, such as loft insulation, but otherwise, hold on to your money until we get some proper governmental guidance.

I would wait. They keep changing the algorithm. The EPC test is also not accurate enough. I replaced my gas boilers in 2020 with boiler ready plus viessman gas boilers with weather sensors and we are still a D. Even if we were allowed to install double glazing (listed building) we would only get 4 points which would still be a D. The newer EPC are quite different to the older types and say any work done has to be in the order they suggest to get the extra points they list. They are pushing insulation. So if I remember correctly insulation is given as the first thing on the list.
We had the EPC done while we were installing in built draught proofing to sash windows so new parting beads and new staff beads with the brushes installed. The sashes have to be removed and routed so brushes can be inserted at the tops and bottoms. The windows are 3.6 metres high and the EPC inspector said it would be worth 1 point but when we were finished after the EPC was done he said it would not make a difference.
Given my experience and the fact we are not able to check or validate the results I would wait as long as possible. When the EPC inspector did 2 EPCs for me on 2 flats which both had installed the most up-to-date boilers I queried the results because I thought the score was low. He sent me a screen print of the choices he ticked for the boiler and I pointed out that he had omitted to tick another box which recognized the fact that it had a weather sensor to which he said he had never ticked that box before and didn't know what it was for. I also noticed there didn't seem to be a box which recognized the installation of a smart room thermostat. After he ticked the box I gained 1 point on one flat but the other flat didn't increase in value. He said it's because the score is based on hidden scores that we can't see and the one flat didn't tip over enough to allow an increase in 1 point.

Reply to the comment left by Jessie Jones at 15/07/2023 - 09:50There was a post, on a previous discussion about this, from an EPC inspector. He pointed out that currently the EPC is about cost where as the Low carbon initiative is not. In fact they are working against each other. He gave the example of a property with only electric would, when the rules change in Dec 2023, be down graded 13 EPC points. His advice was for electric only homes to get their EPC done before the Dec deadline, at least that way your covered for 10 years. That of course assumes the Gov won't insist that all properties have to redo their EPC under the new rules, something I fear the GOV, of either flavour, might well do.

Lawrie, the comments above seem to cover most of your options.

The government's dither and delay does nobody any favours, with Richi Sunak demonstrating no interest in providing a structured long term plan for residential housing to, as our lest favourite chancellor said, "fix the roof while the sun is shining". In fact, quite the reverse, it was RS who pulled the shutters down early on the disastrous Green Homes Grant.

For two years, iHowz have pushed the government to publish their plans following the EPC/MEES consultation almost 3 years ago. To date all they have provided is meaningless statements.

Over the peak of the energy crisis, the government were subsidising bills to the tune of £4bn/month while only limited additional funding was made available to the local authority LADS and energy provider ECO schemes.

The cheapest energy will always be that which you do not use. As has been suggested, if you don't have a recent EPC then it is worth asking an assessor to review and advise what will be most cost-effective to achieve a rating of C.

Review your insulation / draft proofing to see if there are cost-effective measures that are achievable - don't forget, you can claim exemptions on recommendations if planning or lease restrictions apply. This is often the case for listed properties or those in conservation areas.
Higher cost works such as window upgrades will depend on your payback period or estimated value added. Don't forget to keep pictures and receipts for any hidden works, such as insulation, as many assessors will not accept your assurances that works have been carried out.

The lack of clear guidance on the proposed new EPC/MEES standards make it difficult to take a long-term / low carbon approach as the current EPC methodology is cost based - not carbon - so some measure, such as electric heating can result in a lower rating than GCH.
That said, given that it seems unlikely that this government will move forward on EPCs until next spring (earliest) and implementation could be spring 2025, so you probably wouldn't be at too much risk by swapping an old boiler with the latest combi with heating controler and TRVs on radiators.
That should get you to C on current cost threshold and (fingers crossed) existing EPCs would be valid for at least 5 years from new standards.

Finally, don't forget to highlight at the post works assessment any works (with documented evidence) and any exemptions which apply to previous recommendations.