self build waterproof basement formwork membrane concrete insulation

I always go to the futurebuild exhibition, which was called Eco Build until a couple of years ago. I'm always impressed by some of the speakers and I add bits here as time goes by.

I added this image after watching a presentation from the futurebuild 2020 show called "The Future Is Regenerative".


self build basement

futurebuild 2020

This image is a slide from a futurebuild 2020 presentation by the lead architect of the team that won the Sterling Prize in 2019 and many other prizes besides. This project, Goldsmith Street in Norwich, is a Passivhaus Superstar. it was interesting that this architect said it is not necessary to use Passivhaus Approved products. However, he said it was necessary that the builder was required to prove all his work was carried out well. Air tight had to mean air tight, no temporary sticky tape over the cracks.

sterling winner
  1. air tight
  2. 400mm of insulation and triple glazed windows
  3. winter sun maximised
  4. summer sun reduced
  5. heat recovery ventilation
  6. no cold bridges or energy leaks

This is a quote from one of the speakers:

capture free energy from the sun

Another speaker spoke about his team's design starting with a plot of the solar exposure before deciding how best to design a Passivhaus.

The utility room and other rooms not requiring much heat were on the North side while the main roof faced South. They included a Snug at the Western end that gets the evening sun.

Big windows faced South and stone tiles on 150mm thick concrete on 200mm of insulation provided a thermal mass store to soak up daytime sunshine.

Overhanging roofs and balconies provided summer shading.

solar angles
      capture free energy from the sun

capture free energy from the sun

Mechanical Heat Recovery Ventilation, when it works, is brilliant saving a lot of money for a small investment. But MHRV needs maintaining. One customer who is very pleased with his MHRV says he pays £25 a month by Direct Debit for all his heating, cooking and hot water for a 5 bedroom house with a flat incorporated for his son.

He questioned my doubts about MHRV. I said my concern was I had been persuaded that shutting a MHRV unit away in a corner of the loft where no one ever changes the filter can stop it working, meaning no energy saving and possibly toxic air if no fresh air gets in.

He told me that his MHRV unit is very accessible and as well as changing the filter 4 times a year, quite expensive but very simple, they take the filter out every fortnight and vacuum up the lint that collects in it, rather like cleaning a tumble dryer filter.

He said it is amazing how much lint collects in only two weeks. His MHRV saves him a lot of energy and makes his air lint and dust free throughout the house. It is as if the MHRV does half his vacuuming for him, so it makes sense to vacuum the filter frequently and change it before it clogs up with pollen and so on that vacuuming cannot remove.

  If you want to save energy and reduce CO2, you must avoid filling your home with clever kit that doesn't do too much, you must make sure your architect finds a sensible place for your MHRV unit and of course you need to insulate, reduce draughts and avoid over heating in summer.  

Insulating a home with a basement.

I have attended many exhibitions including workshops at Ecobuild in March 2019. I have also kept in touch with some clients to find out how their energy saving performed. Usually not as well as hoped.

The question is: What Works well?

Air Tightness Preventing draughts saves money.
Insulation The only question is how much is too much.
MHRV Mechanical Heat Recovery Ventilation requires frequent maintenance to remain effective. It is reported that thousands of units are no longer saving any money and people have become ill from toxic air.

Site your unit somewhere very accessible and you will be able to maintain the filters yourself.
Thermal Mass Thermal Mass softens the effect of cold weather and it softens the effect of hot weather. Thermal Mass can halve your heating equipment and do away with air conditioning. It saves kit as well as energy.

But ...

Photo Voltaics Photo Voltaics facing South generate most electricity at mid-day when we don't want electricity.

Whereas panels that face West don't generate as much but at least they generate electricity when we want it, which is when we make our tea after work.

When we can store all the energy they can produce we might save the world. We aren't there yet.

So, in the meantime, generate solar power when it saves you 18p a kW h instead of when you get paid next to nothing by the grid.
Wind turbine You need huge blades. 100m radius is good. They work in the North Sea, they will never work on a house.
Ground Source Heat Pump - shallow buried tube GSHP with coils of tubes buried in your garden don't work after the first Winter because the soil cannot warm up completely over the summer. The soil starts next Winter too cold to provide you heat another year.
Ground Source Heat Pump - deep borehole GSHP with a deep borehole will work but you will never get your investment back.
Ground Source Heat Pump - in water Works
Air Source Heat Pump ASHPs don't save energy. When it is coldest outside and you need the most heat your heat pump costs as much to run on electricity as the value of the heat you get from it. Gas would be cheaper.

Experts at Ecobuild said keep your money instead of spending it on kit because less kit saves earth's resources, and keep your money instead of spending it on energy because less energy is best at reducing global warming.

Photovoltaics generate the most facing South at mid-day, but that is when we don't need much electricity. There have been instances where solar and wind powered electricity combined was more than was being used and the wholesale price went negative. Energy had to be wasted.

One answer will be to charge up electric car batteries while they are parked up during the day, instead of buying petrol and instead of selling electricity cheaply to the grid.

Perhaps, one day, company-owned electric cars will be charged up from solar panels while they are parked outside the office (while the wholesale price of electricity is negative); the computer will sell electricity from the car batteries to the grid when the wholesale price is high enough and the computer will make sure the car has enough power to get the worker home and back to work in the morning.

In this imagined scenario the company will own the car, its batteries and the power it puts into them. And it will sell power as well as its usual business.

Until then the rest of us need a Tesla Powerwall and a Tesla car which both cost a lot of money.

Alternative Energies.

It is very easy, when extolling the virtues of alternative energy, to forget that the iron used to make the kit was mined in Australia and it took a huge amount of coal and water to turn it into steel as well as oil to transport it around the world. The same for the copper pipes, the enamel, the plastics, the aluminium and the copper wiring. We use a huge amount of energy and water to turn earth resources into manufacturing materials. Buying kit created pollution and increased global warming. Changing a component or throwing the whole thing away and replacing it creates even more.

There is growing doubt in the UK that we could ever save as much energy and CO2 with alternative energy generation as we spend creating, maintaining and replacing the kit. Neither is there much certainty alternative energies could ever, really, save us money.

We must use less energy, not spend, spend, spend on alternative energy. Recovering energy from cooking and body heat with MHRV and softening cold snaps and hot snaps with thermal mass are surely the no-brainers.

A new council estate in Norwich won the RIBA Stirling Award because of, in part, its thick insulation and Mechanical Heat Recovery Ventilation.

Time will tell if they still work in 5 years or if no one changed the filters.
If you search 'Goldsmith Street Norwich' hopefully you will find an update on these new council houses built with air-tight timber frames, excellent insulation, triple glazing and MHRV.

I'm not selling anything here. This page is my conclusion and recommendation after years of exhibitions and going back to customers and asking them how their energy efficiency choices had worked out.

Most customers had a warm basement, even without heating, but often the rest of the house did not work out as well as expected.

Insulating Concrete Formwork ICF

I built with ICF for about 8 years but there were two major reasons I stopped.
  1. It went out of shape and burst.

  2. Wonderful insulation but any thermal mass potential is lost because of the insulation inside between the heat in the room and the concrete core.
Modern Methods of Construction MMC.

There is a lot of talk about improving the quality of house building by building homes in factories and delivering them in panel form and erecting them on site.

I can see a lot of benefits but the sadness is that panels will be lightweight and have no thermal mass. These homes will need more heat on the coldest days and more cooling on the hottest days than my preferred choice using concrete and thermal mass.

Thermal Mass.

My own very simple definition and explanation of the benefits of solar gain and thermal mass.

Solar gain is sun's warmth coming in through glass and thermal mass is heavy masonry warmed by solar gain because it is the internal surface in your rooms not covered by insulation.

More South-facing and better glass will increase solar gain.

Heavy masonry construction with no insulation on the inside will increase thermal mass.

Thermal mass stores so much energy that if it turns hot some of that excess heat soaks into the masonry, so you don't need air conditioning; and if it turns cold the masonry releases some heat into the room so you don't need so much heating.

When it is hot you can cool your home by opening a window overnight. When it turns cold you can recycle heat from your lost body heat, from cooking and from hot water you used to wash with MHRV. Your thermal mass will release some heat into your rooms and what you still need from your central heating to top up to temperature will be much less than if you had none of these alternatives.

Thermal mass does not keep your home at a fixed temperature.
It stops your home getting so hot or so cold you cannot bear either.

If you put on a cardigan or strip off to just a T shirt instead of switching something on you will use a lot less energy and that means you needn't buy as much kit.

Less kit and less energy are both necessary to help reduce global warming. Both will save you money.

The EU Directive that bought us energy performance certificates, I think we were 8 years late introducing them, also requires new homes from 2020 to be Nearly Zero Energy Buildings with most of their energy from renewable sources. Definition of NZEB near the bottom of the page.

Clearly we are nowhere near meeting this next target.

The target after that is massively reducing leaked refrigerant from aircon, fridges and heat pump systems, such as ground source and air source. Apparently, leaked refrigerant from a heat pump system often completely negates all the greenhouse gases saved using less energy to get heat.

I had not even heard of this till March 2019, so I doubt we will meet it in the next year or two.

Ministers were told in February 2019 that, from 2025, new homes should not be connected to mains gas or use gas for cooking, heating or hot water if Britain is to meet its legally binding emissions target.

An expert at a workshop (Whole Life Carbon at the Futurebuild exhibition on March 7th 2019) described that in order to get data his team analysed a new home just completed by a mass national housebuilder. The SAP calculation approved by building control was a U Value of 0.16. But the actual U Value, mainly due to poor air tightness and cold bridging, was worse than 0.30.
Thermal Mass Explained

"From an energy perspective, it would be difficult to have too much, and generally the more thermal mass the better"
This guide was given free at the Futurebuild Exhibition and is available for free from Click on this image to download it in full.

It will help the person doing your SAP calculation include the benefit of thermal mass.
  • "Revisions to the Standard Assessment Procedure (SAP) for Part L1 of the Building Regulations and more challenging requirements for addressing overheating in new homes."
  • "Ongoing improvements in glazing and window technology, which makes passive solar design more effective (lower heat loss and improved solar gain)."
Part of your SAP calculation will include a figure for TMP. 100 is low, 250 is medium and 450 is high.

Some figures for you to come back and refer to:

Entirely timber frame (and presumably SIPs and ICF) about 70.
Traditional (brick cavity, beam and block, some load bearing and some stud partitions, timber upper floor and roof) about 200.
Entirely heavyweight construction 500 to 650 depending on size and other variables.

I added this next piece over Christmas 2020 from somewhere within tier 4. I expect to revise it a few times.

Do Building Regs require insulation throughout?

Building Regs would seem to, but actually we have to pass the SAP or SBEM calc test and there could be an exception.

Researching this during a conversation with a client, who paid me for my £125 service, I found the following: and this seems to tie up with a couple of clients who built their basements without insulation everywhere.

The guide above, Thermal Mass Explained, states on page 15 that thermal mass capacity is limited to the first 100mm. This seemed unfair to me, especially in light of the fact that the failure of ground source heat pumps prove heat passes through soil very slowly - so why shouldn't all the concrete and the soil beyond count toward basement thermal mass?

I looked for proof that very dense concrete is an insulator by virtue of the fact that heat passes through it slowly.
Without the success I hoped.
This publication,
has a link to a page with a link at the bottom to a
free spreadsheet produced by the same people.

Please investigate this for yourself if SAP calcs are a mystery to you.

The little revelation I found is that from an insulation perspective the soil beyond the concrete structure can count toward the insulation.

The soil beyond the basement cannot count toward thermal mass but it can count toward insulation.

The simple conclusion seems to be that basement floors don't necessarily have to be insulated because they always have at least 2m of soil beyond them.

That means I can change my sketch at the very top of the page by removing insulation underneath and that allows me to remove the footings for face brickwork as well.

self build waterproof basement formwork membrane concrete insulation top insulation revised with soil insulation

                   A slide from a presentation at Futurebuild.

UK energy consumption

It is a fact that our electricity suppliers can pay 3 times as much for wholesale electricity at 5.30pm as they paid 45 minutes earlier before we got home and switched everything on.

It is likely that we will soon have to pay 3 times more for early evening electricity compared to mid-afternoon electricity. So it must make sense to face our solar panels at where the sun is when we want electricity.

Setting the washing machine to an afternoon wash is fairly simple, but steps to use a lot less electricity at peak time - especially if we no longer heat with gas - will require careful thought.

You need not be heating your home at peak time at all. If it is warmed a little earlier, at a cheaper electricity rate, your energy might cost a lot less. Or, if you rely on thermal mass, your home might be slightly cool late-afternoon, waiting for cooking and bathing to top up your temperature.

Emissions will be less if we buy less kit and aren't heating up our living space during peak time because, to meet peak demand, the worst polluting power stations are only turned up at peak time.

On April 24th the Futurebuild people made a number of the presentations at their March exhibition available for free online. You might have to register here.
The information in this box is from the presentation: "The Value of Energy Positive Buildings".
The slide above is from the presentation: "Lark Rise Energy Project".

We should be asking ourselves what actually works?

First and foremost, good workmanship - which might require continuous, effective inspection to refuse to accept anything sub standard - works a lot better than rushed work and sub standard materials.

Note the quotation above about the mass built house designed to 0.16 but built to worse than 0.30 by a national house builder.

And the other note above the six-point sketch of the Sterling Prize-winning homes "necessary that the builder was required to prove all his work was carried out well"

If you are a self-builder you have the chance to demonstrate to the country that carbon, energy use and emissions can genuinely be greatly reduced. And that it need not be expensive to do so. But how?

Another gem of a simple idea from my happy MHRV customer.

He put his cavity wall insulation in himself. He has blockwork inside and outside that is 50mm of rockwool then 150mm of insulation board, such as Celotex, QuinnTherm or Recticel, then his cavity then his brick.

He explained that the rockwool follows the contours of his blockwork, ensures no air gap between the blockwork and his rigid board and ensures that joints in his rigid board are closed by rockwool.

These next 2 examples are going off at a bit of a tangent:

They are photos of insulation added to the outside of a property (that I am 're-arranging' in my spare time), all paid for by the Green Deal Scheme entirely free to the lady on benefits who lived there before I bought it.

The workforce may have only drilled their holes a bit too shallow but they did so all over all the external walls, and the gap, which is open at the top, allows all the heat to escape before it reaches the insulation layer that was supposed to keep it in. (The bits of spray foam were put there by me before I decided to replace a window frame).

You probably cannot trust anyone unless all their work is independently inspected and approved.

poor workmanship insulation green deal front poor workmanship insulation green deal back

ICF is bad (my many reasons not to use ICF are two pages further on). Timber frames and SIPs are poor because they don't store energy. Heat pumps are too expensive or don't work unless the heat source is a large body of water.

What worked best of all, and for less cost, was thermal mass with no cold bridging, excellent air tightness and recovering heat.

The best thermal mass is dense concrete. Cement in the UK is responsible for only 1.47% of our carbon emissions (compared to an average 6% worldwide). Yet concrete can massively reduce the 28% of our emissions that are due to domestic heating - and likely to rise as we install more air conditioning unless we do something about it.

What we need from the heating and cooling of our homes is the ability to lose body heat at a comfortable rate. We don't want to be too cold and lose heat too fast, neither do we want to be too hot and unable to cool down. And daytime and night-time might require different room temperatures.

Thermal Mass is the ability of a heavyweight material to store a lot of heat and release it slowly. The denser and the least conductive the better.

Cast insitu concrete, brickwork and stonework are all good.

Concrete blocks are less dense and so less good. Beam and block is less effective than concrete cast in place.

concrete   brick   stone
thermal mass concrete   thermal mass brick   thermal mass stone
Solid walls and floors could be plastered or tiled as well.  

The experts at the Futurebuild workshop discussed the high carbon cost of materials and equipment as well as energy. Apparently, specifying up to 8 times the equipment needed is not uncommon. Neither is it uncommon to completely replace a whole unit instead of replacing just the part that failed. This all wastes carbon emissions and precious water along the supply chain.

They went on to explain that sourcing all the building materials and all the materials your equipment is made from, as well as all the transportation; and the end of life costs in removing and replacing anything all add up toward your Whole Life Carbon. A concrete office block completely gutted and refitted when a new tenant moves in and then demolished after only 10 years to be replaced by an even bigger concrete tower, is a terrible waste of carbon.

One of the expert's teams had to quantify the carbon in a new public building. They found that a lot of the timber was Canadian but it had been sold and moved to Southern USA before being purchased and transported to Britain. The total carbon was more than twice Scottish timber that only travelled 300 miles or so. In comparison, how far would your concrete travel? The aggregate, 77% by weight, might be quarried where they batch the concrete. If so usually a maximum of only 20 miles. The cement: a 15th of your concrete might have come from Port Talbot and another 15th from Greece. Another 15th is the water that only travelled as far as the truck. Overall, concrete is greener than many suppose.

Some of the best results the experts at the workshop got anywhere were concrete used where its useful life would be expected to exceed 150 years - which could be your house. The carbon investment in a concrete house becomes insignificant annually if it will be in use unchanged for 150 years.

Another cause of carbon waste the experts were keen to make clear was the effect on Whole Life Carbon designing a building and its services to fully meet the demands for energy during the coldest and the hottest times.

Your MHRV supplier might well try to supply you with an average one air change per hour with ducting to every room. But will this be too much when everyone is out or asleep?   This sketch came up first page in Google: I think the experts would say this is over-engineering and over-selling.
Plus, the exhibitor at the HB&R Show cast doubt that MHRV would work after the first couple of years.
Looking carefully at every example he might be right. In every example this supplier has hidden the units deep in the loft where they are least likely to be maintained properly.

The experts said that in order for every building in the land to get enough mains energy for air conditioning during the hottest few hours a year and full-bore heating during the coldest few hours a year, the extra national grid infrastructure and extra building equipment and services and energy certain to cope are twice what is required on the other 363 days a year.

They impressed upon us that if our buildings can only cope with 95% the peak demand during the coldest and hottest few hours a year, then the total Whole Life Carbon for everything required (mains supply infrastructure, equipment and energy) is halved.

And the way to smooth out the need for peak energy is thermal mass.

One of the experts said that his Victorian, London home, refurbished to maximise thermal mass, air tightness, insulation outside and heat recovery ventilation maxed at 25oC throughout the heat wave last year. A new build could do even better.

ICF basement house   Case Study. Begun 2012, updated with good news 2014, updated again with very bad news 2017.

In 2012 I built a basement and all the house walls with ICF.

These clients initially thought they had achieved zero energy bills for their new home with U Values around 0.20 rather than 0.10.

You can see a video I made in 2014, two years later, explaining this basement and its heating here.

These clients thought that their fuel bills would be zero because
  1. Photo Voltaics on the roof,
  2. Ground Source Heat Pump bringing heat in,
  3. Heat Recovery Ventilation saving some heat before it is lost outside,
  4. Air Source Heat Pump in the basement heating their water cheaply by extracting even more heat from the still fairly warm air on its way out,
  5. 150mm of ICF insulation above ground,
  6. Roof trusses stuffed with insulation and
  7. Excess electricity sold to the grid.
When I made the video in December 2014 the weather had been very cold already. They calculated that in that first month they spent just £26 on buying energy. The rest came from their GSHP. On an annual basis, after selling excess electricity in Summer, they thought their bills would be about zero.

But when I returned again in April 2017 to catch up on old times, their bills were £1,000 a year for energy.

Something had gone wrong. Actually, two things in particular seemed to have gone wrong.
  1. The GSHP had got expensive. It no longer cost less than £26 a month to heat their house. It was costing 10 times that because the ground had become too cold.

  2. With no thermal mass because of the ICF insulation inside, they got too hot in Summer and installed air conditioning.

The guys selling ICF, timber frames and SIPs are all trying to sell you a building method that wastes the opportunity to store energy in thermal mass - in concrete.

True, it takes less energy to warm the air in a cold house of lightweight construction. But why should the house have got cold?

True, it takes less energy to cool the air in a warm house of lightweight construction. But why should the house have got too warm?

True, all these choices are more air tight than brick and block cavity walls. These days, the mass housebuilders cover over all the holes in the masonry and insulation with airtight plasterboard and skirting board. The cold still gets in.

BUT NOTE: the ICF description only says "making it possible". Not that it will.

And NOTE: the timber frame description puts made from renewable woodland first. Not saving energy.

AND: the SIPS description only compares SIPs to "older technologies".

My conclusion is that ICF, timber frames and SIPs all perform poorly compared to a cleverly designed new house built with maximum thermal mass.

My money is on the future being concrete. That might be reinforced and poured in situ, prefabricated or concrete block walls covered in brick or stone.

I Googled "benefit of ICF / timber frame / SIPs". These came up first:

ICF basement

timber frame basement

SIPs basement

Until March 2019 I was excited by solar powered panels on the roof. But it was telling that at Futurebuild many heat pump, solar panel and Tesla Powerwall suppliers didn't show this year.

The problem is that solar power in Britain is at its maximum when demand is at its minimum. Until we can store electricity solar doesn't have much value.

This BBC correspondent explains quite clearly why domestic wind turbines are sadly a waste of money as well.

Heat Pumps.

The ground source heat pump and the air source heat pump guys have been trying to let you believe that the efficiency in Summer is so good that even in Winter you save money. But put on the spot many can't tell you that you would save anything on the coldest days when you need the most energy.

They are also sneaky because the savings they claim are against electricity whereas most homes are heated by cheaper gas and oil, so the actual savings for most are far less.

But if, at exhibitions, you ask how much does it all cost, it seems to me that those talking in the realms of £7,000 are the ones who struggle the most to convince you that you will always save energy; while those talking about £20,000 are very confident you will save energy all the time, but they cannot promise any financial return on your investment.

However, saving money and saving energy aren't quite the same when it comes to renewables.

My customers who were, I think, disappointed with GSHPs seem to have saved money burying overlapping coils. Lots of pipe, not much soil to get heat from.

The expensive suppliers might tell you to have a straight pipe in a very deep borehole, say 150m deep, perhaps two boreholes.

GSHP basement GSHP basement

The expensive suppliers might be tapping into a far greater heat source than the cheaper guys.

I tend to think that the cheap guys use all the available heat in the ground quickly before the end of Winter; while the expensive guys have such a huge reservoir of energy deep enough to be warmed up by the centre of the earth that their installations succeed more often. But, compared to gas or a home designed to require less energy, the expensive guys will never break even on cost.

So why do people buy cheaper heat pumps?

Maybe because cheaper could be free over 7 years, because of RHI.

The Which? magazine has a guide. Note that RHI is aimed at those 'who are off the gas grid'. The reason why might be lower down this page.

Perhaps the Renewable Heat Incentive, RHI (Ofgem web site), will cover the whole cost of a small installation more easily than it will cover the whole cost of an expensive scheme; except that with a cheap scheme you probably still need some expensive, carbon-emission-rich energy from the grid and another heating system as well for the days a small heat pump cannot cope.

£20,000, I'm not saying that is what yours needs to cost, might only be partially offset by the RHI yet more likely to provide all your energy cheaply and with substantially reduced-carbon-emissions. But only cheaply if you ignore the huge investment and only lower greenhouse gas emissions if no refrigerant gets lost during servicing.

£4,000 and the RHI might cover the heat pump cost completely, but you might not get much free heat that way and you could still be buying expensive energy from the grid as well.

It seems to me, that ASHPs too small for the job and GSHPs without access to enough soil struggle in cold weather - especially if your home got cold when the temperature dropped suddenly outside and you want a lot of heat fast.

Whereas a larger heat pump heating a house that is well insulated and protected from a sudden drop in temperature outside might cope adequately at all times - but if your home is well insulated and well protected with thermal mass do you even need a heat pump?

Another technology that caught my attention (in 2018) is Seasonal Thermal Energy Storage. STES.

Icax says on its website: "It is a characteristic of earth that heat only moves very slowly through it - as slowly as one metre a month."

Icax tells us what we hear all the time, that it is very expensive to store electricity. But, they say, it can be virtually free to store heat. What they seem to promote are two systems both with coils alongside each other buried in the ground.
  1. By Summer, solar energy is used to warm up the ground.

  2. By Winter, that same ground has the excess heat taken from it much more efficiently by GSHP because the soil is warm to begin with.
When I put this to heat pump suppliers at an exhibition, they doubted you could have enough surplus energy in summer, from solar panels, to put enough heat into the ground to provide for a whole Winter. Are Icax right? I don't know. There is an academic exploring a similar idea. A chartered engineer and chartered geologist, she is a research fellow whose blog describes her excitement at the idea. Two of her blog pages here: testing and monitoring.

Should we be storing heat in the soil beneath our basements?

We would need the heat to be very deep beneath our basements so that it didn't come out into our habitable space too early when we didn't want it to.

If you have already dug 3.5m down the only safe way to go further might be with piles or a borehole. If you hit water then any energy you tried to store would be washed away instead.

I'm not sure storing energy underground could be viable.

About 20 years ago, the Building Research Establishment, BRE, produced a paper about the U value of a basement without insulation.

The U Value of an average domestic basement, just because it is buried, is about 0.16 before you add any insulation.

The point, therefore, is that a basement neither needs much insulation nor much heating.

Unfortunately, you cannot include a figure for 'cave' in your SAP calculation, but you can include a figure for thermal mass.
ICF basement U Values ICF basement U Values ICF basement U Values

Finally, my recommendation.

I would
  • Maximise thermal mass: all the floors, all the walls and the flat roof all built with waterproof, always completely crack free, reinforced, waterproof concrete.

                        - Some soft furnishings will be needed to reduce echo.

  • Excellent air tightness. Windows, doors and service entries as well as the concrete structure. Letterbox outside, not a hole in a door.

  • Mechanical Heat Recovery Ventilation easily and frequently serviced by the occupier.

  • Continuous insulation under the basement, all over the walls and over the roof outside the thermal mass preventing any cold bridging.

                        - Just the above, I am led to understand, is likely to exceed Passivhaus Standard, depending on your windows.

  • I might still cover the roof in solar panels but only to charge up my electric car.

insulation revised with soil insulation Fabric First Approach.

Continuous insulation outside the thermal mass walls and floors. Shown here in yellow. Minimum 2 metres of soil between the basement floor slab and the outside air.

A Chinese manufacturer, Himin, can make a roof entirely of solar panels. You needn't have a roof with panels fixed to it. Just one roof of panels. Other manufacturers make photo voltaic roof tiles.

I am making the assumption that solar panels might not be completely weatherproof so my waterproof roof is the flat roof above the bedrooms.

At most times, a rise in temperature from solar gain, cooking, heating, washing and body heat is stored in the concrete until released during the night resulting in less heating required first thing in the morning.

You might only need a 1 KW plug-in electric heater on a timer and timed to use the cheapest electricity to make a difference to the whole house before you wake up.

Can a concrete house be zero carbon over its lifetime? Without generating energy on site from wind or solar probably not. But concrete can have the lowest carbon cost needing less equipment, less equipment changes and less energy than any other structural fabric.

The benefit of the concrete house is its air-tightness and thermal mass. Once up to temperature, you hardly need anything to keep it there because of cooking, washing and your own body heat.

You still have to choose your domestic hot water provision. The cheapest might be electric hot water heated partially by solar energy and brought up to temperature on demand by electricity. London is going to forbid immersion heaters soon. Storing hot water is wasteful because stored hot water soon goes cold.

The environmental benefit of concrete is not in how much renewable energy you get from an investment of tens of thousands of pounds, but how much less energy you use during its incredibly long life time than building any other way.

I am convinced that once built and lived in, my proposed home would require the least energy to keep it warm and cool compared to any other scheme, unless that scheme cost several times as much.

You might not like any of my thinking. Fair enough. I'm not selling it, I'm only sharing it.

Phil Sacre
2018, 2019, 2020 and 2021.

A little coup for me recently (2018).

A client mentioned that a good friend of his is a Professor of Environmental Engineering.

I asked whether this page reflected the professor's conclusions. I was told he "very much supports" my points.

Then, shortly after, I received this paragraph, presumably aimed at the client but with my web page in mind.

"Putting the concrete on the room side of the insulation (ie ground-insulation-concrete-room) it will retain heat (like a storage heater) and reduce the rate (speed) at which the overall room cools down and heats up. It will make no difference (over a season) how much heat you use to heat the basement (if its kept at a reasonably constant temperature). It will take longer to heat if you allow the basement to cool down so if you wanted to use the basement infrequently for short periods (eg as a spare bedroom) and then leave it empty (and cool) then it may not be the best solution (although that could be overcome by adding more insulation internally)."

It seems to be saying three things.
  1. Concrete inside, insulation outside: will help keep the accommodation constantly comfortable;
  2. It would cost no more to keep your basement at a comfortable temperature, if insulated as I suggest.
  3. But if you wanted a particular space to get cool and only warm it occasionally, you might choose insulation inside (whether timber frame, SIPs, ICF, concrete or masonry), so that it cooled fairly quickly and could be warmed temporarily with less energy.

* Additional thought at Christmas 2020, from tier 4.

A client, his structural engineer and I are in deep discussion about whether insulation should be inside or outside.

The architect simply said 125mm of insulation is required, which I find too simplistic.

The structural engineer thinks the insulation would be more difficult to fit perfectly well outside in the difficult ground expected, and he has a valid point.

The professor, above, states "It will make no difference (over a season) how much heat you use", which I found difficult to comprehend but I think I have - if only the pure scenario of a totally buried basement with no windows and no house above either is what is being considered.

I think, after a lot of reflection, that I still favour external insulation because it overcomes cold bridging issues at floor levels doing away with the need for insulation over upper floors and beneath ceilings to prevent cold bridges. And if you have solar gain then the thermal mass makes better use of it.

* 21st September 2018. I just returned from the London Homebuilding & Renovating Show 2018.


One of the speakers was Tim Pullen. He consults, sells his book and writes for the HB&R magazine. His talk included "how to choose the right heating system"

I photographed a few of his slides and I will try to share with you some of his more interesting observations.

He warned that neither electric or LPG would figure in his choices because they are too expensive. That made me think about how GSHP and ASHP people talk about their systems giving you 3 or 4 times the energy back for the ELECTRICITY you put in to run them. And before you could boil an egg Mr Pullen made a similar point. Heat from gas is cheapest by far. Can heat from alternative energies compete with gas on price?

HB&R Tim Pullen 1.jpg

This slide tells us that a 200m² house insulated to meet only Building Regulations needs 11,000 kWh p.a.

Oil, cheaper than electricity would have cost, when this slide was produced, £750 to heat the space and £1,150 to heat Domestic Hot Water.

However, the same house to Passivhaus requires only 3,000 kWh p.a.

The purpose of these slides was, as you can see, to compel us to design a lower energy requirement into our proposed project before we choose a relevant heating system.

HB&R Tim Pullen 2.jpg

Here he compared different energies. Presumably mains electricity on a standard tariff would be in the region of £2066. And if GS or AS heat pumps were a third the cost they would be about £680 - which he says they are. But getting your investment back on GSHP or ASHP is only viable, it seems, compared to standard rate electricity. They aren't much cheaper than gas, or even oil.

HB&R Tim Pullen 3.jpg

I cannot remember exactly what Mr Pullen said about this slide. But, I believe he said that the RHI is no longer paid for solar.

HB&R Tim Pullen 4.jpg

Next I went to this stand

HB&R usethesun.jpg

It caught my eye because a poster said that a PV panel that heats water as well as generate electricity is more efficient. This man fully agreed. If a PV panel is cooled during hot weather it will generate more electricity. Even if the heat energy collected is wasted it makes more money.

So, I asked him, what should an ordinary couple in an average house with a roof facing East and West buy?

Without any hesitation he said this air source heat pump because the RHI and the cost of energy saved equal or slightly exceed the credit payments and after 7 years you stop paying for your credit, you stop receiving the RHI and you still get cheaper heat.

But if you go back 2 slides, I have gas so I would only save £100 or 12% or so a year.

They displayed a Tesla Powerwall 2 at £7,000. Their poster explained how solar power could charge it up, so could economy 7 mains electricity, and both would save compared to standard tariff electricity. You could charge your electric car from the Powerwall with economy 7 electricity downloaded the night before, and so on.

But the easier sell would seem to be the ASHP paid for by RHI. He didn't really seem interested in reducing fossil fuel.

(This is still what I wrote in 2018).

My recent copy of "The Economist" has an article saying that at mid-day during our Summers coal and nuclear power stations need to switch off, which puts up their costs, because solar panels on houses produce much of the very low level of power needed at those times.

So, it now seems more reasonable to me that electricity from the grid costs 18p but we can only sell it to the grid for 4p. When we want to sell electricity the grid doesn't need it as much as when we want to it buy from the grid in Winter at night. Simple supply and demand.

Indeed, if we have many more solar panels, then perhaps at very sunny moments panels will try to sell more to the grid than the nation is using at that moment. What happens then? Does stuff explode? Perhaps the grid will have to refuse to buy solar electricity and we will have to do something else with our excess power.

This brings me to the unanswered points in my graphic at the top of the page.

We should generate as much solar power as we can. But we should not be selling it. We should be storing it until we need it ourselves.

The next big emergency has to be air pollution and the particles from petrol engines and diesel engines but, I read, twice as much again from log burning and coal burning, which we choose for the theatre of a real fire in our living rooms. Fine particles from these three sources are now being blamed for causing stunted lung growth in our children and dementia in our elderly.

Twice as many damaging particulates are produced by fires as from traffic though, of course, in most areas fires aren't as concentrated as cars in cities, particularly at school gates dropping off and picking up the very children the particulates are harming most.

I have spent today looking into charging electric cars from solar.

I found a useful starter guide on Youtube by the Red Dwarf and Scrapheap Challenge star: Robert Llewellyn, here.

With all the kit: electric car, Tesla Powerwall 2 and solar panel photovoltaics - and the grid, you charge the car first with solar electricity, next with Tesla stored electricity, third with economy 7 electricity at night and, only if you must do you use standard tariff electricity. He says he hasn't used any standard tariff electricity despite having two electric cars to charge.

Economy 7 costs about 8p a unit whereas standard tariff might be 18p.

If the Tesla Powerwall wasn't fully charged by solar you can, or soon will, charge it with economy 7.

    I think that puts it all fairly simply.

    In the video, RL said that over previous weeks he had charged the car with 320 miles directly from his solar panels. My petrol car would cost £50 for that much petrol. He has also charged the car from the Tesla Powerwall that was itself charged from his solar panels. All that saved petrol has effectively gone into his pocket to repay his investment. Financially, it looks like you could save money over the lifetime of the kit.

    Air pollution and carbon emission-wise, with no petrol and no log burner he is saving our planet and our children while many of the rest of us are causing them both harm.

    It might be that over 10 years some of us would save money having a Tesla Powerwall and charging it at night with economy 7 electricity even if we did not have any solar panels. That would benefit the power generators because you would use your battery power during standard tariff periods, daytime, and the generators would have a more even demand over 24 hours. All your grid electricity could be 7p a unit cheaper. Your car could cost 10p a mile less to power.

    I found talk that in future we might be paid to use the battery storage we own. We might be paid to sell stored electricity to the grid, at the times the grid is trying to avoid firing up another power station, more than the electricity cost us the night before on economy 7.

    Everyone is different. As far as I can tell, back of an envelope savings might be:

  1. Not owning an electric car. Charging your Tesla Powerwall 2 half each with your own solar and economy 7 but only using 10kWh a day and not the 13.5kWh capacity of the batteries: Save £400 a year toward your investment of £10,000 or so.

  2. Driving 300 miles a week in your electric car (50 kWh) and charging it 50:50 with free solar power and economy 7: Save £1,700 a year on petrol and another £100 or more on domestic electricity.
The film says batteries came down in price 40% last year. If they do that again and electric cars don't cost too much more than petrol, it seems that the full kit described here will soon be economically viable as well as excellent for the health of our planet and children.

Do you know how the Gilets Jaunes protests started in France? I heard on the BBC that a health visitor working in a rural area was incenced that President Macron put up the cost of petrol to subsidise the cost of electric cars.

She complained that only the rich could afford an electric car so her struggling to provide a service to the needy living miles apart in the countryside was put at risk because she, scraping a living, was having to subsidise the lifestyle of the most wealthy living in cities.

From DIRECTIVE 2010/31/EU

Article 9
Nearly zero-energy buildings

1. Member States shall ensure that:
(a) by 31 December 2020, all new buildings are nearly zero-energy buildings;

2. 'nearly zero-energy building' means a building that has a very high energy performance, as determined in accordance with Annex I. The nearly zero or very low amount of energy required should be covered to a very significant extent by energy from renewable sources, including energy from renewable sources produced on-site or nearby;

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