SuperHome Database

Derby, Kingsway, Thornhill Road

House Summary

Kate and Geoff Ball

House Type:
1950s detached house

Carbon saving:
81% - SuperHomes Assessed  

Reported saving on bills:

Total invested:
approx. £170k total project cost- including everything from design and certification to paint.

  • Derby sH new rear
  • Derby SH green roof
  • Derby final air test (airtesting fan)
  • EnerPHit plaque – Derby SHv1
  • kitchen diner – Derby SHv1
  • Living Room – Derby SH v2
  • ventilation air inlet valve Derby SH v1

Measures installed:

  • Cavity Wall Insulation
  • Condensing boiler
  • Draught-proofing
  • Eco materials
  • External Wall Insulation
  • Floor Insulation
  • Low Energy Appliances
  • Low Energy Lighting
  • Mechanical Ventilation Heat Recovery
  • Roof Insulation
  • Solar PV Panels
  • Triple Glazing
  • Water Saving Devices

Upcoming events

Early interest in Open Days encourages SuperHome owners to host more events. If you'd like to visit this property please contact the owner and let them know. SuperHomers are often happy to respond to questions about their refurbishment project by email between times. Please read ‘more on contacting this SuperHomer’ before you make contact.

What visitors are saying

"Kate and Geoff were incredibly hospitable and clearly now experts. The information was well presented and their story inspiring... Kate mentioned some small devices for the tap to reduce the speed of the water flow which I will have a look for. It was great to learn about the concept."

"Excellent to be welcomed into a home not yet fully finished. A great way to see a concept off the page in real 3D!"

"Once again, learnt some new things which will help in my refurbishment - a very helpful visit!"

“A most engaging and excellent presentation by Kate. Nice to see examples of materials - more choice than expected. It really is a super home."

“Very interesting and inspiring.”

“Kate was very enthusiastic, informed and helpful. Very helpful to hear the do's and don'ts from someone who has done it and to see what can be achieved.”

“Very friendly and informative presentation.”

"Excellent and informative - stimulating!"

"Very welcoming, prepared and informative, and the scones were brill!"

"Really informative and interesting presentation. Covering so many important points. The house is inspiring."

"Excellent- informative, lots of information, critical detail. Now need to research more!"

Personal story:

Geoff is a civil engineer with Severn Trent water; I (Kate) trained as a science teacher, but now home educate our four children. We’re both interested in the environment, science, and green and ethical issues generally. Geoff loves playing with spreadsheets and data, and is a total perfectionist; I like data too but really enjoy making and building things, and tend to get things done, even if they’re not quite exactly right. It’s proven to be a pretty good combination for getting through a big building project mostly cheerfully!
We moved to this house to be closer to Geoff’s work- the 12-mile bike ride each way was proving to be just too long with small kids to see in the evenings. With home educating (and childminding before the little two came along), being close to the city centre is perfect for getting to places like libraries, museums, swimming pools and parks using public transport and bikes with the children.
We were really lucky to find this house within a mile of the city centre, but with a big garden and lots of living space; we’re having a great time getting the house and garden sorted out so it’s perfect for us.


We knew this house would need some improvements when we bought it, and were interested in the Passivhaus standard. It fairly quickly became clear that more comprehensive works were needed on the house than we’d anticipated (the roof was an obvious problem, the drains less so!), so in spite of some feelings of guilt that we were about to trash what looked superficially like a perfectly good home, we decided the sensible thing to do was to go the whole hog and fully upgrade to as close to Passivhaus standard as possible with an East-West facing 1950s house, all in one go. Doing the project piecemeal would have meant far longer building works, and, due to the difficulties of joining bits together, we would have had to settle for far worse performance, probably at an overall higher cost.
We enjoy technical challenges, and have had a great time working with people who really know their stuff to design improvements that will make the house eco friendly and easy to live in.
While we know that the energy savings from one house are insignificant, we hope that by showing people what we’ve done that’s worked, and what definitely hasn’t worked, we’ll be able to help other people to improve the comfort of their homes at the same time as helping the environment.

Property background:

The house was well presented but in need of works when we moved in in 2010: The paintwork was neat, carpets clean and tidy, and the garden immaculate, but both the pitched and flat roofs were starting to leak, the boiler was over 25 years old and there was damp coming through a wall due to badly placed concrete outside.
Possibly most interestingly, there was a leaking sewer hatch under the dining room.
In winter, wind whistled through the unsealable rotten wooden windows, down the chimneys and up under the floor. It was impossible to get the house anywhere near warm. Something needed to be done.

Key changes made:

We’ve super-insulated the whole building envelope and made it airtight; this has included taking up floors to install PIR insulation beneath, including down to the footings at all walls.
There’s now a modified cement coat over the outside of the brickwork giving an airtight seal, then 250mm graphite EPS external wall insulation.
The roof has had 400mm mineral wool insulation wrapped over it, above an airtight layer of OSB and membrane.
Rotten, leaky double glazed windows and doors were replaced with thermally broken with triple glazed units, braced out into and wrapped over with insulation to reduce thermal bridging.
High efficiency heat recovery ventilation has been installed throughout the house, and a small solar-compatible combi boiler has replaced the old inefficient inefficient, to provide hot water and top-up heat in winter.
These changes have made the house go from being cold, damp and draughty to warm, dry and comfortable, at the same time as reducing our energy bills dramatically.
The two bedrooms we gained almost as a side-effect of the renovations mean that we were able to invite two housemates to share with us- meaning we were actually slightly better off financially than before the retrofit, in spite of the extra mortgage we had to get to pay for all the improvements. Then we had two more children, which has meant that for the time being the house is a bit too noisy at erratic times for lodgers- but we plan to have another housemate or two when things are a bit more settled- we really enjoyed sharing the house.
We’re really pleased that the house has worked just as the Passivhaus planning package predicted; the comfort levels are fantastic, and it’s been so much fun we’re almost tempted to do it again!

Also see:

Our Passive House Case Study 

Our refurb in Self Build & Design Magazine

How we improved the airtightness of our house

Measures installed in detail:

• Cavities filled with blown mineral wool fibre
• ‘A’ rated Viessmann condensing combi, Honeywell controller and 100% new TRVs – though 5 radiators have been removed, 7 remain; a maximum of 3 have been required even in winter.
• Draught-proofing throughout – airtightness testing result 0.32 air changes per hour at 50Pa pressurisation and depressurization
• Eco materials: re-use of existing carpets etc. where possible, FSC certified timber throughout build, use of reclaimed parquet through ground floor
• External wall insulation,  retrofitted walls: Cavities insulated, cementitious airtight coat then 250mm graphite EPS external insulation with armoured render coating applied
• External wall insulation, new walls: timber stud frames filled with mineral wool, then airtight membrane and taped 18mm OSB, then 250mm graphite EPS
• Floor insulation: 180mm PIR insulation with 100mm PIR down stands to footings and 30mm PIR up stands to prevent slab contact with wall to reduce thermal bridging- total floor U value  0.140W/m2K
• Low energy appliances throughout
• All light bulbs low energy CFL
• Paul Novus MVHR installed for whole house ventilation – heat recovery above 90%
• Roof insulation: 400mm rockwool between OSB I beams, continuous with external wall insulation
• 3.96kWp Innotech recycled 220W photo voltaic panels on South and East roof
• Solartwin system to be installed with thermal store to feed into the solar compatible combi when top-up heat is required.
• Windows and doors: Passivhaus suitable Eco Passiv triple glazed units
• Water saving taps, toilets and showers

Benefits of work carried out:

The house is warm, dry and comfortable.
Cooking smells vanish from the kitchen, and clothes dry within a day in bad weather, wherever in the house they are hung.
The gas bills have plummeted by over £100 per month, and the solar feed in tariff is covering the rest of the fuel bills.
Our water use has dropped dramatically at the same time as comfort has improved with aerated showers from the new combi boiler replacing the old power showers, and very low-flush loos replacing the enormous 1950s models. The reclaimed parquet flooring is easy to clean, and the slightly altered layout together with a first-floor extension above the existing 1980s single storey extension have allowed us to share our house with two housemates.
Before having more children (which has meant that lodgers aren’t an option for a while), the reduction in bills and the rent from sharing the house more than covered the additional mortgage payments the refurbishment required- though it was of course lucky that we had the initial capital, space and layout to allow us to share the house. Now, the certainty being comfortably warm even when sorting out a poorly child in the middle of the night is really lovely to have!

Favourite feature:

Coming out of winter, the MVHR wins hands down. No more problems drying laundry; no more condensation running down windows and walls, causing damage and mould. It’s the most complicated and highest-maintenance thing we’ve done to the house, but without the MVHR running, we’d have to open the windows to ventilate throughout winter, defeating the point of super-insulation and airtightness. And it’s just as silent as advertised. Definitely a worthwhile investment.

Update for summer: With two hayfever sufferers in the house, the MVHR is still the top eco device- the pollen filters mean that on high pollen days, we can just shut all the windows and doors, boost the MVHR for a little bit, and have a lovely cool pollen-free house. Wonderful.

3 years on… Yep, still the MVHR. Turns out that if you fail to dust the bathroom valves for a couple of years you get a bit of a humming noise. Which goes away when you actually remove the dust. Oops.

Project update:

Shortlisted for the Local Area Building Control ‘Building Excellence Awards’ for the East Midlands.

EnerPHit certification confirmed last week- hooray! It’s likely we could- just- have scraped full Passivhaus by modelling every thermal bridge fully, but it would have been both expensive and very, very close. So we decided to spend money on the things which will actually help the house perform better instead: We feel we need a greengage tree more than full certification!

3 years since we finished all the important bits of the project- and everything is still working fantastically. We’ve completely failed to repaint the garage door, the splashback for the kitchen was removed to the garage during renovations and is still there (gives a nice backdrop to the bikes…) and we’ve still not sorted out shelves in the airing cupboard… But the MVHR has worked exactly as advertised and far better than we anticipated (though dusting the intake valves once in a while turns out to be a good idea), the triple glazing is still as good as new, there’s no mildew or damp anywhere at all, and everywhere is warm and comfortable. And quiet- at least, there’s no traffic noise- we make quite enough noise inside the house.
Sadly, even EnerPHit certification doesn’t make it any easier to get drawings off the walls or toys out of U bends – but it does mean that milk spills across carpets never result in yoghurt smelling rooms- I’m really rather impressed by that- and drying the unbelievable quantities of laundry that four children create is really easy. I’m just waiting for the Passivhaus Institute to invent something eco friendly which will tidy up the house for me!

Updated on 22/02/2016

Common questions and answers for this SuperHome

Could you give me a rough idea of how much your external insulation cost (per square metre)? Does that include scaffolding?+

Our external wall insulation cost about £28k in total, with a wall area of about 230m² which works out at about £120 per m² internal wall surface area. I got that figure from our PHPP, which is kind of the wrong surface area since it’s a bit too small and doesn’t include the below-DPC wall area except as a thermal bridge reduction. So the figure per m² should be somewhat lower for external metres of wall covered- I’d guess around £100-£110 per m² external wall covered. The house internal floor area is 173m2, if that helps for comparison!

The price was for two layers of cross bonded graphite EPS to 250mm total thickness above DPC, and 200mm single layer white EPS between DPC and foundation toe, with a cementitious parge coat over the walls, mechanical fixings with thermal bridge reducing rondelles above DPC, bitumen replacement adhesive and protection below DPC, armour mesh and render.

It doesn’t include scaffolding- we had the scaffolding up to re-roof and put up the extension anyway. Obviously doing the roofs, extension, trenching and everything else made the scaffolding fairly complex, but even so it was between £3k-£4k on a house which isn’t that tall, but does have a considerable perimeter.

What affected the price of your external wall insulation?+

The price for external wall insulation varies wildly, depending on the installer used (I would not go near Westville again with a bargepole!), the supplier and the material used.

The big suppliers for conventional insulation materials include Sto, Weber and Permarock. Permarock were far cheaper for fundamentally the same insulation compared to Sto – although the Permarock render finishes may possibly be less durable on tower blocks.

With the material used, as a guide, the thinner the material for the same overall U value, the more expensive it’s going to be. So broadly, white polystyrene is the cheapest, aerogel is very expensive and grey polystyrene, phenolic and mineral wool all coming somewhere in between. I’ve recently been sent samples of waste wood fibre external wall insulation batts, and also calcium silicate insulation, both of which are surprisingly light and obviously the waste wood is great environmentally, but I have no idea about cost. Mineral wool is surprisingly heavy in external wall insulation form, but is completely impossible to set fire to. EPS will burn, but is pretty impervious to moisture, so poor storage on site isn’t too much of an issue there.

How did you install external wall insulation around outside energy meters? (if you had them)+

We don’t have meters on the external wall in the white boxes, but even so sorting this one out was tricky. We moved the gas meter 5m onto part of the garage wall which wasn’t affected by the external insulation, then passed the gas pipe between the meter and the boiler through the insulation and a grommet. The water main rises through the utility floor, again through an airtight grommet and the insulation and up to the meter.

We were able to keep the electricity meter within the insulation and airtight layer like the water meter by making most of the garage into a utility room- moving it was going to be very expensive as various things meant that a total rewire would have been needed. An alternative was to make an airtight, insulated box over the meter, but that would have been very fiddly.

If you have recessed white boxes, if there’s space, it may be possible to change them for surface mounted boxes, mounted to the surface of the insulation. You may need an intermediate stage with the meters braced off the wall to get the insulation installed (we did, for the gas pipe): Then it should be reasonably easy to get the pipe or wire through a grommet into the house with a minimised hole in the insulation.

Alternatively, moving gas meters short distances (as in, through a wall) is permissible by an ordinary plumber – not sure about electricity meters, but if you can get one or both into the building and so the airtight layer that would make things a lot simpler.

Where did you find useful advice when doing your retrofit?+

The AECB.  If you’ve not joined the AECB yet I thoroughly recommend it- it’s about £40 per year for an individual, and their guidance and details are really, really helpful and prevented us from falling into about a zillion very expensive pit traps.

Also, the Grove Cottage report gave us a handy starting point. Andy Simmonds is the current chair of the AECB, and it’s his house.

How did you achieve such high levels of airtightness?+

The airtightness case study here should fill you in on the training and testing, and learning process involved. We followed Paul Jennings’ (ALDAS) advice, got training for the build team early on, and I was horribly obsessive about the airtight layer at every stage of the build. Builders with camera phones made this a lot easier, plus living on site and doing lots of the taping ourselves.

What is the breakdown of energy savings by type of measure installed ?+

The case study of our Passive House here answers this question in some detail towards the end. I think the AECB have (or are developing) a tool to work this one out- including £ per tonne of carbon saved too. We can’t really tell which bit does what by itself – the whole thing together is needed to eliminate draughts and convection currents, for example.

As a retrofit pioneer do you attract any stick from visitors who might not be able to afford these improvements?+

Tough one. We try to focus on the principles of energy saving, right from the basics- what is heat, how is it transferred, what is the difference between airtightness and ventilation, and then look at various methods of improving performance, right from using newspapers to block gaps in ill-fitting windows (which we did before the renovation!) to sealing floorboard gaps, insulating pipes, appropriate loft insulation fitting etc etc, up to the high-end expensive stuff we’ve done. I also asked a whole lot of insulation companies for samples, so I have a big box of brochures, samples, fixings etc suitable for all sorts of different projects- that seems to go down well often. We do feel that we have been really lucky to have the money  to be able to do this work, and it is hard to strike a balance between explaining what we’ve done, and sounding smug.

Do you know your home's CO2 emissions both before and after?+

I’m afraid I don’t know the actual CO2 before and after – and given that we have different occupancy, run the house at least 5 degrees warmer all winter, and have a much bigger volume than before, any theoretical CO2 figures are likely to be way off the mark anyway compared to our actual use.

The house ran very cold, no matter how much the 25-year-old boiler was on before the refurb – essentially it was impossible to maintain a comfortable and healthy temperature in winter. The house stays at about 22 degrees C all year now, with an occupancy of 6 rather than 4, about 40m2 additional total floor area and gas bills down from £128pcm in 2011 to £24pcm now – including heating and hot water but not cooking, which is with an induction hob and electric oven.

Electricity use has decreased by a couple of kWh/day on average (about 8kWh/day to about 6kWh/day) but we do now have solar panels with 3.96kWp capacity- the effective increase in use is, we think, due to changing from gas to electric hobs, increased occupancy (increased computer use, particularly when we had lodgers – now we have two more small children, who are too young to use computers much!) and, significantly, the MVHR.

We could, of course, run the house at about the 15 degree C mark to mimic pre-refurb conditions – I suspect we would use essentially no gas all year for heating in that case as the gain from body heat, cooking and bathing would maintain that kind of room temperature through winter – but it would be uncomfortable again!

How much of the money you invested was on energy related measures?+

With the £170k we spent, the house needed a new pitched roof, new flat roof, new sewers (which meant digging up sections of the floor anyway), new windows and doors, new boiler, etc etc- and we built two large extensions, totalling 40-50m2 total additional floor area.

The works also required total redecoration – and even having lifted and saved some of the carpets, lots of paint, flooring, plaster etc was required. So separating out which costs were strictly for energy related measures and which were incidental to other works is completely impossible!

For comparison, we think we could have saved up to £40k max by retrofitting and extending to building regs standards- which would not have given us anywhere near the comfort levels we now have or the bill reduction (including the solar FIT our utility bills are effectively now zero, down from over £200 pcm). In addition, comparable houses in the area sell for enough that the increase in house price should have more than covered the retrofit cost- we went from 3 bed to 5 bed, which in this area makes a huge difference to house price.

How did the reclaimed parquet flooring work out?+

Our parquet is reclaimed beech installed using Lecol adhesive onto a concrete base. I cleaned the blocks and installed it and co-opted family to help with sanding and finishing. It is a messy and very time consuming job (scraping bitumen off every block is not funny!) – but the result was a cheap floor that we like. Getting parquet laid is extremely expensive.

We had limited headroom in our house, and so we dug out our old concrete floors in order to insulate without reducing the headroom to below building regs. This is, of course, an expensive option- but with dodgy sewers under our floors it made sense for us.

While wood is certainly a better insulator than tile, it’s definitely not as good as carpet- with or without underlay, or as good as a floating timber floor installed onto an insulation layer. Our cork floored shower room floor feels warmer than the parquet even though the cork is far thinner than the parquet tiles.

If you are not looking to insulate to Passivhaus/EnerPHit standards then using a layer of polyurethane insulation as thick as you can manage considering ceilings and doorframes, or even aerogel or vacuum panels (depending on your budget) under a floating wood floor could make a big difference to how warm your floor feels- you can buy inexpensive sheets of polyurethane insulation from builders’ merchants (or online) in any 10mm-multiple depth you like.

I don’t know if building inspectors would consider the insulating value of wood flooring, but hardwood is pretty dense so isn’t a great insulator.

The most noticeable thermal bridge in our house is the ridge beam, which is, of course, timber (engineered pine rather than hardwood so it should be a better insulator than parquet blocks). Snow melts off our ridge before it melts from anywhere else in the house- including the windows!

For airtightness with a cavity wall, how did using an external parge coat and cavity wall closers help?+

We used an external parge coat for airtightness, but regarded the existing internal wet plaster as a kind of helpful secondary mostly-airtight layer- since there was nothing else we could seal the floor slab to!

The first stage of sorting out the roof was to strip back tiles and the lower part of the felt to see exactly what was there at the roof-wall junction. It turned out that, rather oddly, the ceiling binders and roof timbers were sitting on top of a row of bricks which had been mortared onto the cavity. So the builders scraped back the loose mortar and used a polymer modified cement to seal the bricks a little more convincingly to the top of the cavity. This is effectively all inside our airtight layer, but may well make a significant contribution to reducing air movement.

Our other area where cavity closures were needed was the old flat roof (which is now the floor inside the new extension). Here, there was no cavity closure at all- we could see the insulation inside the cavity. the top was levelled with the polymer modified cement then OSB3 strips stuck on with Orcon F glue and Tescon tape between the joists. This took quite a bit of fiddly taping and was very sticky! Again, this is all inside the airtight layer- the OSB and Intello extension wall airtightness joins to the parged brick ground floor wall outside the closed cavity.

For the old pitched roof, the existing rafters were very small (the old ridge beam is 1x4in, which would explain why the roof had sagged and was leaking), but sufficient to attach OSB3 and Intello membrane to. In fact, this probably strengthened the whole thing! Both these layers were taped and sealed to the external parge, and now lie underneath the new (much larger) ridge beam and the wood I beam thingies which hold the 400mm rockwool insulation, more OSB3, breather membrane and tiles (and solar panels).

If we were to do this again now, we would use one of the more airtight fibre board options as it would work out cheaper and much less fiddly than working with- effectively- two airtight layers over the roof and the new extension, which has a timber frame and the same airtightness method.

Our final airtightness reading was 0.3 air changes per hour, so we may have been a bit obsessive- but as I’m sure you’re finding, it’s very hard to judge how airtight something is going to be until after you’ve tested, and it’s really not worth getting wrong!

If it’s possible, try to avoid having to tape around joists or other irregular (or simply not fully sealable) objects- when the tapes are under any tension at all, they tend to shift and unseal themselves over a couple of days as the acrylic glue slips- so the more complicated taping there is, the higher the odds of getting points of failure.

How did you retrofit mechanical ventilation with heat recovery?+

Our MVHR unit is in the loft mounted on the North gable wall , so the ducts to the outside have as short an internal run as possible.

The internal ducts run through the attic space to the upstairs room, terminating in ceiling mounted (extract) and very high wall mounted (inlet) valves.

To get downstairs the ducts drop through the airing cupboard and run in a false ceiling in the downstairs cloakroom then out through (rather obvious and large) boxing again to ceiling or high wall mounted valves.

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Assessment types

SuperHomes Assessed

A home that has been visited and assessed by us and confirmed as reaching the SuperHome standard, which demonstrates a 60% carbon saving.

Homeowner Reported

Information has been provided by the homeowner about their home and energy use prior to the installation of measures and following their installation which demonstrates a carbon saving. This information has not been verified.

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The homeowner has provided information on their home including what measures have been installed which has enables an assessor working on our behalf to assess their carbon savings. This home has not been visited to verify the measures installed.


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