Author: Es Tresidder

Five minute read.


The plan for our house is to retrofit it to meet the rigorous EnerPHit standard, the Passivhaus standard for existing properties. But before starting that it's important to have a good idea of how the home works (or doesn't work!) at the moment, so as to understand what will be needed to reach the levels of performance required by the EnerPHit standard.

Our house, pre-retrofit, from the front.

Our house is a small (about 84m2 treated floor area, a Passivhaus measure of useful floor area), 1.5 storey, three bedroom timber frame house built in 1975. Without doing any investigation of the fabric I know that we use about 1,100 litres of heating oil, costing about £600 per year and emitting over three tonnes of CO2 each year. Almost all of this oil is for heating the house - the oil boiler does do hot water but it is not very effective meaning we usually wash our hands with cold water, fill the kitchen sink from the kettle and the bath from the electric shower. That's three tonnes of CO2 for a house that we deliberately run colder than we would like (thermostat set at 18°C), that feels uncomfortable even when the heated to 20/21°C (Why do I feel Chilly?) and that suffers from damp and mould problems.


So why is the house so inefficient? The EPC says the walls and roof are insulated, and there's pretty new double glazing on all but one window. Let's do some investigations...

The EPC for our house (produced before we bought the house) assumes that the loft and walls are pretty well insulated. 4 out of 5 stars sounds pretty good, right?

First of all let's look in the loft. The EPC for that assumes that there is 200mm of insulation throughout. When you pop your head into the loft it indeed looks like there is relatively new, thick insulation on the flat (because the house is 1.5 storeys some of the roof insulation is sloping), go a metre or so in either direction from the loft hatch and the insulation changes and thins to about 15mm. I suspect someone has been paid to insulate the loft and has deliberately bodged it to deceive either an EPC assessor, the home owner, or both. The construction industry is crazy.

Thick insulation next to the loft hatch, not so thick beyond there...
Thick insulation next to the loft hatch, not so thick beyond there...

So we've got 15mm of insulation in the loft, what about the walls, which the EPC also says are insulated? Looking at the gables in the loft it looks like the same insulation as is in the loft continues down into the timber stud walls, and removing a few bits of plasterboard in key places confirms this - 100mm deep timber frame but with only ~15mm of insulation. Couple this derisory thickness with the fact that the insulation is fibrous, in many places has no wind protection and is in a very leaky house (more on this below) and you end up with a house that is performing a long way below the assumptions in the EPC.

Current loft at the west gable. 15mm of insulation above the ceiling and the same in the studwork walls (to the right here)

Thin insulation in the timber stud wall, also stopping short of the timber stud.

This is looking into the roofspace at the eaves. This space is well ventilated (as it should be), but the insulation visible is fibrous and very thin. The wind washing of this insulation will render it almost completely useless during windy weather (think fleece or wooly jumper on a windy day with no windproof layer on top).

What about under the floorboards? Well the good news is that the EPC was, for once, extremely accurate here; there is no insulation whatsoever, nor any draughtproofing, under the floorboards. Remove a section of floorboard and you can feel a strong breeze, this ventilation is critical to maintaining the timbers used in the floor, and we'll need to be careful with the design of retrofit measures here to not increase the moisture risk to these timbers. No insulation, and air able to enter or leave the house directly through gaps in the floorboards explains why, even with thick carpets, the floor feels cold most of the time.

No insulation or draught proofing under the floorboards makes for chilly feet. Thankfully no sign of damp so far in the places I've pulled up boards.

We also had an old friend Ben Wear (who you can find at do a pressure test to establish how airtight the existing building is. Not suprisingly it's super leaky. Depressurise the house and all the carpets lift (as air comes in from the underfloor space), and in some places the air just pours in. What's perhaps more surprising is that despite being leaky our house is not what I would call 'well ventilated'. Bedrooms are stuffy in the morning, some cupboards suffer from damp and mould and it is very difficult to dry clothes indoors, even in summer, unless the heating is on. All this despite our house being much more leaky than is sufficient for trickle vents+extractor fans to be deemed an acceptable method of ventilation by building regulations. Our pressure test result was somewhere around 15 m3/m2/hr at 50 pascals, three times the 5 m3/m2/hr above which natural ventilation is deemed acceptable. The video below shows considerable leakage from under the kitchen sink (where services come into and leave the house), from above a sliding door and through the window/door seals.





You’ve heard about Passivhaus and the superb comfort, excellent air quality, super-low energy costs and tiny COemissions all sound great. You’ve decided Passivhaus is what you want for your dream home, so when should you get a Passivhaus expert on board? (more…)

I wrote a short paper for the recent International Passivhaus conference about heating Passivhaus buildings using electricity preferentially when there is an abundance of wind. As grid electricity decarbonises matching variable supply from renewables with demand will become increasingly useful. In Scotland the main renewable power source in winter is currently (and likely to continue to be) wind power, so it made sense to match the heating just to that. It’s a short study (just two pages) that I’m hoping to extend in the future. You can read it here.


There was also a poster that went with it. You can see that here.



I’ve owned an electric car since July 2016 and I’m generally pretty enthusiastic about EVs. I’m excited by the idea that we might be able to make enormous reductions in transport energy use through switching from fossil fuels to electricity, and that we can simultaneously decarbonise electricity generation in order to have truly zero-carbon transport.



In the previous post I looked at the main factors other than internal air temperature that affect how thermally comfortable we feel in a room. Internal surface temperature played a big role, both because of its influence on radiant heat loss and because of the ability of cold surfaces to cause fast-moving air through down draughts.



I live in a 70’s house that has had double glazing installed but little else in the way of thermal improvements since then. Imagine the following situation. Yesterday was a mild winter’s day, temperatures around 10°C, and I was comfortably warm working at home. Today the weather’s changed, it’s been cold all night and now it’s hovering around zero and cloudy outside. Wearing the same clothes, and with the thermostat set at the same temperature, I feel chilly. After spending the morning cradling numerous cups of tea and still not warming up I finally turn the thermostat up a degree. Why, if the air temperature inside my house is the same on both days, do I feel colder today?


An extended version of this article appeared on UKclimbing in March 2017.


This summer we made a big move from Brussels to near Fort William on the west coast of Scotland. Moving away from the good transport links of a big city had us looking to buy our first family car to make the most of life in the highlands.


Electrifying transport is a big part of every strategy I’ve seen to move to a sustainable and zero CO2 economy, so I was keen to avoid internal combustion engine, (ICE) car if I could. Initially I thought an electric car in such a remote place would be a non-starter. Surely the range would be inadequate? What about the hills? But the more I looked into it the more I thought it could maybe work. I checked maps of charging points and realised that, in every possible direction from our new house there was a rapid charger at least every 60 miles, comfortably within the range of the cars in our budget. But even experienced owners of electric cars were dubious of the idea, the message seemed to be these cars were great for urban commuting or as a second car, but as your only car in the wilds of Scotland? Forget it.


Finally we decided to take the plunge and see what happened. Jonathan Porterfield of was an extremely helpful font of information and found us a pre-registered 30 kWh (that’s the battery capacity) Nissan LEAF Acenta with a dozen miles on the clock for £16k, £10k less than the retail price. It was even red, our son’s favourite colour.


The car’s stated range is 155 miles under the European testing method and considerably less under the US testing method (107 miles). Of course the range you actually get will depend very heavily on weather conditions, terrain and how you drive it, especially how fast you go (just as it does in an ICE car).


I’m going to focus on the practicalities rather than the costs except to note that a recent study from MIT concluded that electric cars had the cheapest lifetime costs of all cars; the very low running costs more than pay back the small additional purchase cost.


Here are some quick thoughts about how it’s been for the first 4 months of highland life. We’ve driven 4700 miles in it so far, a mix of short, medium and long journeys.


  • I thought the range/efficiency would get really hammered by all the hills around here. It doesn’t. I’m sure there is a difference in efficiency, but it’s small enough that I don’t notice it compared to flat driving. Of course it uses loads more energy going up hill than on the flat, but much of that extra energy is won back by the regenerative braking recharging the batteries on the way back down.
  • Because of the hills and the remoteness I thought the highlands would be a really difficult place to make life with an electric car work. So far I’d say the opposite. Because the hills don’t make much difference to your efficiency (see above) and because speeds are generally much lower than elsewhere in the country, the range is actually better here than elsewhere.
  • Although I don’t have a lot of experience driving nice cars (this is the second car I’ve owned but I’ve driven quite a few smart hire cars) I’d say this is by far the nicest I’ve driven. It accelerates really quickly, it’s extremely quiet, corners really well, has a really useful speed limiter for everyday driving and cruise control for the motorways.
  • Because of the regenerative braking you hardly have to use the brakes at all, you just take your foot off the accelerator and that’s enough to slow you for corners etc. I pretty much only use the brake pedal (which is part regenerative, part friction) for stopping at lights/junctions/roundabouts. This is pleasant to drive and I’m hoping it, along with a vastly simpler transmission compared to an ICE car, will translate into very low maintenance costs.
  • We’ve found that we get around the advertised EU range of 155 miles for pootling around into town to do the shopping (30 and 40mph max speeds), but for more general use around the highlands we typically get between 120 and 130 miles on a charge. For the energy geeks amongst you 120 miles of range from a 30kWh battery equates to 15kWh per 100km, which is what Mackay used as his assumption for electric cars in ‘Without Hot Air’. For faster driving on motorways and dual carriageways we seem to get about 90 miles of range on a full charge.
  • For any journey up to ~100 miles round trip I’d say it’s more convenient than an ICE car. For most people journeys longer than that are rare (they certainly are for us). So on a day to day basis you just charge it overnight and never have to worry about stopping to charge. This is a big improvement on an ICE car even before you start thinking about the cost savings.
  • Anything up to a 200 mile journey I’d say it’s as convenient, for me, as an ICE car. Sure, for that distance you have to stop once or twice, for 20 or 30 minutes each time, but I’d want to do that anyway to give my body and mind a break from driving.
  • For longer distances it’s certainly less convenient than an ICE car, but in reasonable weather it’s not that bad (see below). For these journeys hiring an ICE car is an option, or getting the train. In fact Nissan offer 2 weeks of ICE car use per year if you buy a LEAF, although that doesn’t really work for us as it is from the dealer you bought from and our’s was in Darlington!
  • For long journeys the fact that rapid charging is free (if you’re an Ecotricity customer) goes a long way to making up for the extra inconvenience of more frequent stopping…


Having said that the experience has on the whole been very good, we have had two minor epics. The first in the very early days, leaving the house for a trip to the beach at Arisaig with only 65% charge (before we had the home charger installed) thinking it would probably be OK and if it wasn’t I could nip to Mallaig where there is a fast charger. It wasn’t enough and when we got to Mallaig the charger wasn’t working (this is the only time I’ve had a charger not work, so in general they are very reliable). I found a friendly man at the harbour who let me plug in to his wall socket for two hours before I drove very slowly home. Now we’ve got a home charger and never leave for a long journey without a fully charged battery.


The second was driving to Derbyshire (400 miles from here) to see family in stormy weather with gale-force southerly winds. The range was considerably reduced and we had to stop 7 or 8 times to charge. Grim grim grim. On the way back the weather was calmer and the whole journey was really nice, we stopped 5 times, the last one just a 10 minute top up. I reckon it took about an hour longer than it would have done in an ICE car, although more than that if you normally share driving and don’t actually stop for breaks. I think in future if the weather forecast was as bad as it was I would either change my plans or split such a long journey halfway.


I thought having an electric car would be one of those things, like rarely flying and heating my house to only 19 degrees, that I do because I’m concerned about climate change, but that I’d rather not do. On the contrary I’d say for our lifestyle it’s a nicer, more convenient car to have. The experience so far has been really positive and it gives me hope that electric cars can very rapidly take over from ICE cars in the years to come, especially as cars with double the range of ours for a similar price are on the horizon in the next 2 or 3 years.