So we have lots of old, cold and leaky houses in the UK. I’ve written about the issue before but the solution is not straightforward, cheap or easy to fix. To really get to know the issues, the hurdles, costs and the benefits of retrofitting an old property I figured I had to go through it myself. So what was it like?
Background
I bought the 2 bedroom terrace house and it was largely empty of furniture. I stripped the flooring so luckily had a bare shell to work with. I would say that this is pretty major work and yes it can be done on a room by room basis but it's much quicker and easier for the builders if all the walls can be accessed at the same time. I've done a fair bit of work before so did this work myself but I would say to get professionals in if you don’t have any experience of working on your home.
Whole house, Fabric First approach
Check out my previous blog post on your guide to insulation HERE and it’s clear that around 35-45 % of a home’s heat is usually lost through the walls so this was the priority to address.
WALLS
Many older houses can’t be externally insulated and this is also much more expensive, so in my opinion, the best option for the majority of homeowners is to insulated internally. The house in east Manchester I was renovating is small at only 850 ft sq, so I was loath to lose precious floorspace. However I would only need to insulated the outer walls as the party walls didn’t need any.
Choices
There are a few options for ways to go about wall insulation but I narrowed it down to either insulated plasterboard or a separate insulation, batten, plasterboard construction.
There is a problem in that insulated plasterboard doesn’t have 100mm thick insulation which is the width i’m after. The max is 72.5mm which is really only 60mm of insulation with 12.5mm of plasterboard stuck onto it.
Getting stuck in
I figured I would make my own 112mm insulated plasterboard. I used adhesive foam to glue the Celotex to the plasterboard and then adhesive foam to stick the whole lot to the walls. At the time I had read up on best practice but thought that I could still mechanically fix the plasterboard and the insulation to the brickwork. Anyway after a conversation with my plasterer who wouldn’t plaster onto these boards, I had a rethink. For a couple of hours, I thought I would have to rip all the insulation off the walls as well and there blood drained from my face until I had figured out I didn’t need to.
I just had to rip off the plasterboard, install battens to fix the insulation to the brickwork and then fix the plasterboard to the battens. His argument was its better to deal with an ice cube than try to deal with an iceberg later if the adhesion fails. He had a point so I blew a portion of my budget one re buying sheets of plasterboard. It also involves buying whop off 180mm concrete screws but it worked a treat. These concrete/brick screws are expensive but amazing, and saved an awful lot of hassle.
The Numbers
There is no doubt that installing insulated plasterboard would have saved me a lot of time. Cost wise, the separate solution is cheaper (£59.57 vs £63.44) but there is a lot more labour which will make it a more costly option. How much by is hard for me to estimate. I would think I could have installed all the insulated plasterboard in 3-4 days for the whole house whereas I think it took me around 3 times that with the battens. The extra time to put up the vapour barrier, battens and plasterboard means a lot of cutting drilling and screwing.
However the U values and the efficiency of doing it this way means there is a much more efficient house which was my ultimate aim, see chart below. Battening it out also takes up 137mm rather than 72.5mm so if you can’t sacrifice that much space then stick to insulated plasterboard. For me, losing an extra 6cms isn’t noticeable and the increase in performance is remarkable.
I also took off the existing plaster on all the rooms bar the 2nd bedroom which meant I lost a little less floorspace than I would have done by keeping is on. Keeping the plaster on is clearly the easier and cleaner option and its really only around 30mm thick in most places. Taking the plaster off is a pain and creates lots of dust, time and money to get rid of it and I was left with some fairly suspect walls I then had to patch up.
I would also say the battens outperform the insulated plasterboard even further than the figures below because there is a 25mm air gap between the insulation and the plasterboard which is all important with foil radiant reflectors. In taking off the plasterboard, some of the foil backing was torn off with it so I installed a vapour barrier foil.
The Science bit
So the lower the U-Value the better. Retrofit regulations for existing walls is 0.30W/m²K which is very nearly achieved with the 72.5mm insulated plasterboard. However the 0.19 for the 100mm insulation is very close to meeting new build specification of 0.18. The radiant barrier and 25mm air gap may mean it could even outperform new builds which is really exciting (for me at least).
Insulated Plasterboard 72.5mm | 100mm PIR - 25mm Batten - 12mm plasterboard | |
U-Value | 0.33 | 0.19 |
Total cost per 2.88m sheet | 58.44 | 59.57 |
If you can lose 14cm of your room then go for thicker insulation, it will pay for itself in the long run. If you are already having the inconvenience of a retrofit then the labour and extra cost of going with thicker insulation often isn’t that much different as a proportion of the work.
FLOORS
Covered in my previous blogpost HERE, the suspended flooring was the biggest pain to sort out. Lifting the floorboards and insulating between the joists is a time consuming and awkward job but its one that gets the best results. I also laid XPS board which has a high compression strength over the floor boards and the concrete floor which is a much easier process.
LOFT
The roof already had 100mm of insulation so I laid an extra 200mm which again is the easiest and least disruptive way to insulate your home, if a little dirty and dusty.
Running Costs
I’m lucky enough to have another 2 bedroom terrace very close by to benchmark with and this only has 50mm XPS insulation on the or walls at the rear kitchen and bathroom that tend to suffer from condensation. Its a little larger, at 950 vs 850 sq ft but how does it perform against this house?
Both houses have been rented out so I needed to select periods where they have been occupied at the same time. The only periods were in the weeks when guests stayed for the weekend rather than in the week matched so I took the weekly costs for 5 weeks pertaining to these weeks in October and November.
GAS USAGE (£)
Week | Uninsulated Terrace | Insulated Terrace |
07/10 - 14/10 | 14.89 | 5.11 |
14/10 - 21/10 | 6.59 | 3.78 |
28/10 - 04/11 | 9.85 | 7.82 |
4/11 - 11/11 | 7.89 | 7.08 |
18/11 - 25/11 | 15.80 | 8.23 |
GAS TOTAL | 55.02 | 32.02 |
ELECTRICITY USAGE (£)
Week | Uninsulated Terrace | Insulated Terrace |
07/10 - 14/10 | 10.33 | 6.21 |
14/10 - 21/10 | 8.87 | 7.07 |
28/10 - 04/11 | 15.16 | 5.83 |
4/11 - 11/11 | 10.17 | 6.41 |
18/11 - 25/11 | 11.19 | 5.18 |
ELECTRICITY TOTAL | 55.72 | 30.7 |
Both houses have secondary heating of an electric fire in the living room which accounts for the higher electricity bills in the uninsulated house. It has almost exactly the same appliances.
Total gas and electricity is £110.72 for the uninsulated vs £62.72 for the insulated house. This is an impressive 43.4% saving. It should be noted that the savings would be even more if I hadn’t insulated the Kitchen and bathroom in the "Uninsulated house".
Because I have history of energy use over the course of the year the table below is a very good reflection of real energy use
YEARLY SAVINGS
Uninsulated Terrace | Insulated Terrace | Saving | |
Annual Gas Use KwH | 6782 | 3845 | 2937 |
Annual Gas Use £ | 397 | 225 | 172 |
Annual Electricity use KwH | 1203 | 682 | 521 |
Annual Electricity Use £ | 287 | 163 | 124 |
Annual total | 684 | 388 | 296 |
Bear in mind that these energy figures are from a rental that is occupied only around 30% of the time. The average gas use for a mid terrace that is fully occupied would be around 11,000 Kwh and average use for electricity is around 2500 kWh. These figures are put into the table below.
AVERAGE HOME SAVINGS
Average Mid terrace | Retrofitted | Saving | |
Annual Gas Use KwH | 11000 | 6237 | 4763 |
Annual Gas Use £ | 645 | 365 | 279 |
Annual Electricity use KwH | 2500 | 1418 | 1083 |
Annual Electricity Use £ | 596 | 338 | 258 |
Annual total | 1240 | 703 | 537 |
Instalation Costs
Total costs of insulation is broken down below along with an estimated labour cost, although this will be much less accurate. Labour is costed at £200 per day.
Total Cost | |
Walls | |
PIR insulation | 808 |
Battens | 85 |
Screws | 136 |
Superfoil + tape | 140 |
Plasterboard | 220 |
Plaster skim (total outsourced) | 1200 |
Expanding Foam | 96 |
Materials Total | 2685 |
Estimated labour | 2000 |
TOTAL | 4685 |
Loft | |
200mm mineral wool | 199 |
Labour | 150 |
TOTAL | 349 |
Floor | |
Hemp insulation | 209 |
Breathable Membrane | 109 |
Airtight tapes | 93 |
20mm XPS boards | 404 |
Aluminium tape | 34 |
Estimated Labour | 900 |
TOTAL | 1749 |
Total insulation costs | 6783 |
Total insulation costs of £6783 and a saving of £537 per year would give a 12 year 8 month payback. From then on you would have a much warmer and cheaper home to run. Over the course of 20 years the difference would be a saving of £10,740 gross and £3957 nett if you are paying for your insulation based on current prices. If energy prices goes up then the savings could be even greater.
The house value will also go up due to the home being better insulated. According to a times article this will add up to 14% on the property price. I bought the house for £135,000 and had it valued after I had finished the work and it was valued at £160,000. Admittedly much of this was due to the rest of the renovation which included a new kitchen and bathroom with all renovations including the retrofit totalling a bit under £20,000.
Summary
Challenges of Retrofitting an Old Terrace House
1. Significant Disruption:
Retrofitting is major work, and while it can be done room by room, it’s far easier and quicker for builders if the entire property is accessible at once. Living in the property during the retrofit adds complexity.
2. Loss of Space:
Internal wall insulation can eat into room dimensions. For small properties like your 850 sq ft terrace, losing 14cm per wall can feel like a substantial tradeoff.
3. Labour-Intensive:
Choosing more efficient solutions, such as the batten-insulation-plasterboard method, can significantly increase labour time (e.g., 10 days vs. 3-4 days for insulated plasterboard).
4. Dust and Waste:
Stripping plaster off walls creates a lot of dust and disposal headaches. It’s messier but allows for slightly less floorspace loss.
5. Complex Decision-Making:
Deciding between methods (e.g., insulated plasterboard vs. battens) and understanding U-values and thermal performance can be daunting for non-professionals.
6. Unexpected Hurdles:
Retrofitting can come with surprises that cost time and money. Peeling back the layers of an old house inevitably reveals previous dodgy workmanship or poor build quality that will need recifying.
Benefits of Retrofitting
1. Energy Efficiency:
By achieving U-values as low as 0.19 W/m²K, the thermal performance can rival or even outperform new builds. This leads to significant energy savings and reduced heating bills.
2. Increased house price
You’re likely to recover at least a good proportion of the renovation costs and will often add more value than the insulation costs.
3. Comfort:
A well-insulated home eliminates draughts and maintains a more stable indoor temperature, improving overall comfort.
4. Environmental Impact:
Retrofitting cuts energy consumption, reducing your carbon footprint and contributing to sustainability goals.
5. Long-Term Savings:
Though retrofitting can be expensive upfront, the improved energy efficiency pays off through reduced utility costs.
6. Increased Property Value:
Retrofitting can make older homes more attractive to buyers, especially with rising awareness of energy efficiency.
7. Customisation:
As a hands-on homeowner, you can have the flexibility to tailor the project to your preferences, from insulation thickness to construction methods.
Conclusion
To answer the question how easy is it to retrofit an old house? The answer is “Not easy” and if you’re employing others to do the work then it’s not that cheap either. However the savings are significant and if you can get subsidised insulation through the ECO/GBIS scheme or remortgage and incorporate the work into your mortgage payments then it starts to make a lot of sense. In fact, If you qualify for this insulation then its a no brainer. Even if you don’t, it’s still worth having the work done.
For the many who don't qualify for free insulation and don't have the immediate funds to do this then, if you can, re mortgaging the house to release the funds to insulate would be the most sensible option. For a 2 bed terrace, Adding £6,500 onto your mortgage at 6% would add £390 per year or £32.50 per month while it saves £537 per year or £44.75 per month. You can see why there is a big push to insulate Britain!
It’s especially worth it if you are already doing work to your home or suffering from a damp, humid and cold house that is unhealthy to live in. I’ve dealt with a couple of clients who have suffered from the debilitating effects of inhaling mould spores so the cost of not dealing with these issues can be far greater than financial ones.
This isn’t a sales pitch, I have no affiliation with any insulation installer but have been reading up on this subject for years and have always tried to take a balanced view. My take on heat pumps is one area that I have written about previously HERE and can see the pros and cons of these technologies. The benefits are growing year on year and, for me at least, part of the issue is that previously I had been suspicious of the salesmen and women who have called touting for business. Of course they would say that the benefits outweigh the costs because their livelihoods depend on it.
The evidence i’ve seen, and the data I’ve collected, strongly suggest that we all should be insulating our homes better. A warmer, more efficient home is better for the environment, will emit less carbon dioxide and be a healthier, happier place to live while also saving you money.
Want to know more?
Click on the link below to find out how to save energy and learn if you are eligible for a government grant.
Interested in seeing or even staying in the 2 houses in Manchester I've renovated? Take a look at the links below
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