Deep retrofit – the big prize?

Simple home energy efficiency improvements (such as new boilers, cavity wall insulation etc) can bring valuable comfort and health benefits to the occupants of inefficient homes – especially those in fuel poverty – as the last article revealed (see here). However, energy, carbon and bill savings tend to be modest, rarely topping 15% or 20% – and sometimes energy use actually increases!

If housing is to contribute its share of the 80% cuts in carbon emissions this country is committed to, in order to play is part in tackling climate change, retrofits will need to go deeper – a lot deeper. But will occupants benefit from the extra work? And is it affordable?

In the first part of this article we looked at the damage fuel poverty and cold homes do to occupants’ health, and found good evidence that when these twin evils were tackled, occupants could enjoy measurable improvements in their health. Encouragingly, some local health bodies are recognising this and investing in home retrofit to help improve people’s health.

So if, as researcher Jenny Love has suggested “Partial retrofit allows for energy use to increase” – which is what some studies suggest has happned — what must be done to cut it instead?

If we are to see more “deep” retrofit we will need to see a lot more solid wall insulation. There have been several thousand (at least ) solid wall retrofits carried out in recent years, mainly under the energy company obligations – CESP and then ECO – in big multi-property projects, mainly to social housing tower blocks, and some estates of older, solid-walled semis or terraces.

An assessment of three such projects, in the North on England, concluded that there had indeed been energy savings:

Monitoring of meter readings is showing savings levels “of around 30% post-EWI, with relatively short bursts of heating keeping properties warm for longer periods of time”. One resident commented: “The house has always been cold but the health problems I’ve had in recent years have made it even more of an issue. … Before the house was insulated I used to put £30 a week on my meter [and wear extra clothes in some rooms], since it was done two weeks ago I’ve put £12 on the meter and still have money left.”

What do we mean by ‘deep’?

Although the retrofits in the study quoted above did involve EWI plus other measures such as new boilers and loft insulation, they were mass programmes arranged as ‘bulk buys’ – and the level of design and detailing was haphazard, because of time and cost constraints. The works did not tackle floors, windows and doors, nor did they address ventilation – despite the fact that airtightness may have been increased by default thanks to the insulation. And thermal bridging was rife – many installations stopped short of both the ground, and the eaves for ease of installation, and reveals were generally left uninsulated as well.

Such an approach falls well short of the potential thermal performance of a deep retrofit. For example, calculations suggest repeating and linear thermal bridges like these may account for around a third of the heat loss from the entire building – but with good detailing, these losses can be cut by around a half. These kinds of programmes also appear to be associated at least in a minority of cases with new problems with dampness and condensation inside the home, an issue which will be looked at in Part 3.

But deep retrofit is not just a collection of measures, it is a holistic plan including strategies for insulation and airtightness of the fabric, and for ventilation and other buildong services – looking at the whole building (or estate) and deciding what needs to be done to transform the performance – in terms of both energy, and comfort.

This may involve new doors and windows; solid wall insulation or additional internal or external insulation on top of cavity insulation; extensive airtightness improvement (confirmed by airtest) plus ventilation upgrades; where possible, floor insulation or alternatively a ‘skirt’ of external insulation to insulate the ground – and services upgrades where appropriate.

Whatever the measures that are deployed, the principle of “deep retrofit” is that the occupants should be fully “wrapped up” in an insulating layer, and cold air should not be allowed to get behind the insulation or through into the living spaces, and undermine the comfort and efficiency.


Reroofing is a good moment for deep retrofit

Care is taken to avoid cold bridges – where the benefit of the insulation can be lost and at worst, cold spots that suffer condensation, might occur. Crucially, this level of detailed planning benefits no end from involving a designer or design team modelling junctions, comparing options, and evaluating any risks.

An early showcase for this approach in the UK was the Retrofit for the Future programme, where over 100 houses belonging to social landlords had transformational retrofits, aiming to reduce carbon emissions from the homes by 80% with a combination of fabric improvements, new and efficient services, and renewable technologies.

According to SE2, who analysed the results: “Even the poorest performing property in the analysis saw a reduction in CO2 emissions of almost 40%, with the vast bulk of properties retrofitted during the competition achieving savings between 50% and 80%.”

An important aspect of deep retrofit like that in Retrofit for the Future, is airtightness. Infiltration of cold air (and exfiltration of warm air) cost energy and comfort. Exfiltration allows warm, moist indoor air to penetrate and possibly condense on cold elements in the fabric. On top of that, air movement through the fabric actually impacts on the effective u-value of the insulating materials that are installed. (This is very well explained in Mark Siddall’s article in Green Building Summer 2009, also available on the AECB website here.)

However, if you are reducing infiltration, you do need to look at the ventilation. Although uncomfortable and unwelcome in cold weather, draughts are also a way to bring fresh air into a building – and if the rest of the building’s ventilation is inadequate, stopping draughts may be a problem.

This is sometimes taken as a “reason” not to improve airtightness “too much”. However, many unretrofitted properties need the ventilation improving anyway, whether or not they are being retrofitted. Windows, trickle vents and intermittent extract ventilation are not necessarily well-designed and well-installed, and are all notoriously under-used by many householders – and particularly, those in fuel poverty (see article here).

Thus in one of the Retrofit for the Future homes, monitoring before retrofit showed poor indoor air quality, with windows only opened infrequently. Even without a thermal retrofit, simply installing whole house ventilation would make a building like this healthier. But as the occupants in this case complained how cold their house was (indoor temperatures ranged between 14 and 18 only) there was little chance they would have welcomed more fresh air in winter, without additional measures to help them keep warm.

You could argue that if you aren’t making the house so airtight that a whole house ventilation system is necessary, you probably aren’t going to get the thermal results you are looking for. This is where well-designed controlled vantilation can be so valuable; it can increase the supply of fresh air while allowing for a decrease in discomfort and cold draughts. A range of whole house ventilation strategies is available, and the choice may be determined by occupant preference, the physical constraints of the building, and the preference of occupants and building owners.

Costs and benefits of deep retrofit

Deep retrofit is undoubtedly a lot more expensive to carry out than, say a boiler/cavity/loft combination – though you do save more fuel. On paper, shallow ‘low hanging fruit’ measures give the best financial returns; as you go deeper these returns appear to diminish.

However, these calculations are usually based on the assumption of equal temperature before and after retrofit. What happens to these economics when you look at the likelier reality of higher temperatures after than before? Something quite interesting, it turns out.

As part of its CarbonLite Retrofit training course, the AECB has analysed the modelled energy savings from a range of different retrofit ‘packages’, on a set of typical UK house types, and compared the performance with the estimated cost of the interventions.

What the modelling suggests is that in fact the retrofit “payback time” for what they call a “medium” retrofit is actually shorter than for a shallower set of measures. (see bold text).

Courtesy of AECB

Returns for shallow, medium and deep retrofit with comfort take. Graph courtesy of AECB

The AECB CarbonLite Retrofit team modelled the overall lifetime costs (capital costs based on a 20 year loan, plus paying for ongoing maintenance, plus energy costs) of two alternative retrofit strategies, each to a “medium” and “deep” level, for three representative UK house types – a bungalow, a semi, and a three-storey terrace. “Medium”, very roughly, entailed some solid wall insulation, high quality double glazing, airtightness of 3 and whole house mechanical extract ventilation (MEV); “deep” entailed up to 300mm solid wall insulation if external, triple glazed windows and extensive floor insulation, airtightness of 1.5, and mechanical ventilation with heat recovery (MVHR). By contrast “light” involved loft and cavity insulation and small improvements to airtightness with no ventilation changes.

On the graph above, depth of retrofit (in terms of % CO2 savings) is plotted for each basic house type and approach (internal or external), against the time to ‘break even’ – critically, this was calculated with the assumption that the house was heated only to 17 degrees beforehand, but that post retrofit comfort take increased the temperature to 20 degrees afterwards.

In this model, it is seen that heating a home which has had only a light retrofit, to 20 degrees eats into savings to the extent that one retrofit (the light retrofit of the bungalow) saves almost no fuel or carbon at all, and takes 90 years to pay back. (This echoes some of the findings from evaluation of the Warm Front, disucssed in the prvious article).

By contrast, the ‘medium’ retrofits all show more rapid paybacks than a shallower retrofit of the same house type. Deep retrofits become less cost effective (in purely energy terms) because of the cost of materials.

From the AECB forthcoming CarbonLite Retrofit Course – see More detail on the modelling will be available as part of the CarbonLite Retrofit course material later this year.

AECB’s modelling also suggested households that were already heating their homes to around 20 degrees, homes in exposed or cold locations, and building owners who had less expensive finance available, stood to get their money back more quickly – as of course would everyone if fuel prices rose faster than the current DECC projections used in the calculations. The more difficult the conditions, the better value deeper retrofit tends to be – as you would expect.

This is important news for people financing their own retrofits, as these findings indicate that for dwellings similar to these, if a more comprehensive job is undertaken, not only will they end up with a more all-round cosy and comfortable home if they spend more; up to a point at least, they’ll actually get their money back faster as well. The payback times can be long (often 20 years or more), but if owners don’t upgrade the fabric as much, yet still ‘take their comfort’, the payback is even longer!

Can we predict energy savings for individual households?

As the authors of the CarbonLite Retrofit research stress, these calculations are only indicative of trends. If accurate improvement in performance predictions from an individual building or set of buildings are required, this will need a bespoke calculation.

It is not simple however to arrive at a savings prediction for an individual building. It will require a detailed survey , and a calculation based on a detailed understanding of how occupants use the house currently, and how they will do so after retrofit, and on confident predictions of the ‘quality ‘ of the work to be carried out.

As Helen Brown of Encraft comments, for example: “If the airtightness is not known, how can you predict energy savings? You can’t”. Similarly, the thickness and U-values of walls will depend not only on the exact materials but also on their moisture content – as well as the detail of prevailing local temperature, wind and rain.

So predicting actual savings is probably unwise. Nonetheless, calculations can certainly help when comparing the impact of different possible measures and combinations of measures. These can be set against cost and convenience (or otherwise) to help to develop a bespoke plan.

It’s not (all) about the money, money

As Bob Prewett of Prewett Bisley Architects says, ‘you have to be guided by the building’. Prewett specialises in the highly sensitive retrofit of historic, sometimes listed older buildings, but many of the same considerations apply to a more ‘ordinary’ building.

Most of the partial, shallow retrofit programmes such as those run by the energy companies, can pretty much be conceived of as delivered by a van going round and treating one house after another.

Deep retrofit cannot work like that. A building definitely has its ‘moment’ for deep retrofit. Frst of all the owners need to be up for considerable disruption – but even then, deep retrofit only really makes sense when a building needs work already. The more that has to be renewed/replaced anyway, the less the ‘extra over’ of completing the job to a high standard of energy efficiency will be.

Bob Prewett likes to get ‘back to the bones ‘ in the elderly buildings he retrofits, removing any dodgy timbers, remediating all damp, and so forth. Not every building can be stripped right back like this (the home becomes unihabitable, for one thing) Ideally, you would be at the point in the maintenance cycle when at the very least, windows are being renewed, pointing repaired and, ideally, even re-roofing carried out – and with a bit of luck, significant internal renovations such as new floors (or at least, floor coverings).

In owner occupied properties the moment of most potential is commonly just after the dwelling is purchased – especially if the purchasers don’t need to move in immediately. If people are building an extension, they are also already committed to a lot of work and disruption — so again, this is a key moment.

In tenanted properties, these maintenance cycles still have to take place, but more comprehensive works tend to be co-ordinated across an estate, and so cannot so easily fit with the suitable moments in the occupants’ lives. Minimising internal disruption becomes all the more important – though for some landlords, it has proved worthwhile to decant tenants temporarily while internal works such as ventilation are installed.

On the plus side however, many occupants will have lived though one or even repeated rounds of shorter-term, shallower repair and refurbishment – yet still be living somewhere cold, and possibly damp as well – so may see the logic of a one-off “deep” retrofit intended to be good for 20 or 30 years.

Occupants may also appreciate that the alternative to a deep, disruptive retrofit may be demolition and rebuilding – and possibly, them leaving the area for good. This is dramatically more disruptive – not only of individual lives, but also of entire communities.


So is it worth it?

Retrofit like this certainly offers a dramatic change in both indoor living conditions, and also in energy use and bills. According to Andy Simmonds, chief executive of the AECB and himself the occupant of a deep retrofit (to EnerPHit level), even without any comfort take, a holistic retrofit offers these comfort-giving improvements:

• No drafts from the wind or cold, because airtightness is improved to ~3 for a medium retrofit and ~1.5 for a deep.
• Fewer drafts from room air being chilled next to poor glazing in a medium retrofits (higher quality double glazing) and none at all in deep retrofits with triple glazing. Little or no condensation on windowpanes even in very cold weather.
• Even when the indoor temperatures are the same as before the retrofit it will feel warmer, because we are warmed or cooled by the radiant temperature of surfaces around us, as well as by the air temperature – and these surface temperatures will be higher because of the better fabric insulation.
• Air quality will be improved because an MVHR or MEV is exchanging the air more often – less condensation, and any smells are cleared more rapidly

On top of this, an increase in temperature is now more affordable: increases in temperature add a lot less to the energy bill per extra degree of warmth, and the bills in a warmer house after medium or deep retrofit will still be lower than they used to be in the old house, even though the house is warmer.

Twenty of the properties in the Retrofit for the Future programme were monitored for temperature and internal humidity after the retrofit. They tended to be maintained (by choice) between 19 degrees and 25 degrees, which is believed to be several degrees higher than the ‘before’ temperatures; residents in all of those with monitored temperatures have said that their homes offer a good level of comfort.

Air quality was good: Internal relative humidity data show average levels varying between 50% and 70% in all but one.

In one of the homes in the programme, the occupants saw their energy consumption cut by 85% and hope to see bills drop from £600 a year to £150.

The occupant, who has lived in the house for 21 years, said the changes had improved her quality of life and even helped with her asthma. She said: “It’s bright warm, no draughts… the air quality is amazing, it’s somehow fresher.”

Meanwhile in the owner-occupied sector, the owner of a 1950’s detached home that was renovated EnerPhit standard is quoted on the Passivhaus Trust website speaking similarly enthusiastically about comfort after deep retrofit:

“We thought that the advertised level of improved comfort of an EnerPHit home was probably exaggerated. However, since completing the works, we’ve been really surprised by the difference in quality of living EnerPHit provides. The comparison between living in an EnerPHit home and a building-regs level home is like the difference between living in a home with open fires and one with central heating.

“Not only is the house warmer, drier, cleaner and draught free, but the housekeeping chores needed to keep the house comfortable take a fraction of the time: We never have to wipe condensation off windows, laundry dries overnight on airers, smells vanish, and there is never any black mould anywhere.

Retrofit value for private customers

So although there is no doubt that retrofit is expensive, Russell Smith of Parity Projects is one who suspects this may not be the only reason few are carried out. “People don’t aspire to deep retrofit because they have never experienced it.” They simply don’t know it’s possible.

He adds: “Customers need a concrete idea of what they are buying – and obviously it needs to be appealing, but it could be comfort, carbon savings, prestige .. and their concerns won’t only be about cost. Lack of “hassle” is a big factor for almost everyone.”

For someone investing in their own home, this is an investment that they might set alongside other ‘discretionary spending’ such as a new kitchen or bathroom, or a new car – on all of which, Smith points out, some people at least are willing to spend thousands, if not tens of thousands, of pounds.

For those of us who aren’t in the market for a new kitchen or similar outlay, there seems to be a very strong case for subsidised borrowing for deep retrofit. The AECB analysis showed that with interest rates at just one per cent, instead of the 3.5 assumed in their headline calculations, payback times decreased dramatically, and even the deepest retrofits ‘leapfrogged’ the shallow approaches in some cases. Even if the owner did not expect to stay in a property long enough to “get their money back”, the marginal costs could be modest enough to bring the very attractive improvements in comfort within many more people’s reach.

What if its not you paying the bills – but your tenants?

For a social landlord, the decision to invest in a deeper retrofit is based on slightly different criteria. Even though they are not responsible for tenants’ energy bills, there is still an element of financial interest for them. Tenants in fuel poverty can be bad financial news for landlords, as they are more likely to default on their rent. (see bold text). A deeper retrofit will provide a deeper, and more lasting, protection to the landlord’s income stream.

A jobseeker in one of the universal credit pilot areas interviewed on BBC Radio 4 explained that he receives £140 per week, half of which is for his rent which, under universal cCredit, he is responsible for paying – as are many of the low-waged tenants in the social and private rented sector, who are also in fuel poverty.

“I would like to think I’m responsible, but still, it’s difficult to manage on £70 a week,” he said. “If you’ve got another £70 a week that’s seemingly floating and you’re stuck for electric or something like that, the temptation is so great, just to buy some more electric.”

Landlords also spend a great deal of money o repairs and maintenance – which may be exacerbated when tenants in fuel poverty fail to ventilate their homes properly. A deep retrofit which protects both internal and possibly external surfaces from condensation and the weather may well save money in the long run (at least one landlord investing in deep retrofit — Portsmouth City Council — plans to monitor exactly that question).

Tenants certainly want their homes improved: “In recent surveys, tenants have placed the management of condensation and damp high on their list of priorities, above such things as replacement kitchens and bathrooms,” according to a report from a council housing forum in Gloucestershire. And as one landlord at least has admitted formally, unhappy tenants do cost them money – as understandably, they complain, and thus take up a lot of officer time.

In the large post-war development being retrofitted to EnerPHit by Portsmouth City Council, Wilmcote House,  a “vocal” tenants group have driven the case for improvement in their homes. The city felt the homes were so poor that they considered demolition. Once that was on the cards, it effectively meant the full cost of demolition and rebuild, more or less, was available to carry out a deep retrofit instead.

At Wilmcote House, it was felt that retrofit to Enerphit would enable all the main problems with the flats to be tackled, for example:
• Tenants can’t afford to heat them: the electric heating was expensive, up to £25 per week and people were demanding their expensive heating was replaced – the retrofit would significantly cut space heating costs.
• Many tenants had poor health which they linked to damp in the homes, and there were also problems with mould, in cupboards for example. Heat recovery ventilation and warm surfaces should address this.
• The buildings had an ‘unloved’ appearance – external cladding and new windows and balcony sunspaces would offer a renewed appearance and sense of pride

Landlords talk about ‘futureproofing’ their estates against ongoing increases in energy costs (or indeed, ongoing falls in income)

Exeter City Council, which is building all its new properties to Passivhaus and carrying out retrofits to EnerPHit, points out that if they don’t go deep, “people won’t be properly out of fuel poverty – or not for long.”

Social landlords tend to take a wider view of their remit and genuinely want to improve the health, and the lives, of their tenants. As Emma Osmudsen of Exeter City put it: “This is an investment for future health and comfort, and the building physics shows it will work best over the long term. We are focused on addressing need, and our tenants are the people in greatest need.”

If building owners who don’t even pay the building energy bills are finding it worthwhile to
invest in deep retrofit, it is certainly plausible to suggest that owner occupiers – at least those anticipating a reasonably long interest in a building – might find it a worthwhile investment too – given that they actually get to live with the results. But this is unlikely to happen at scale unless people’s understanding of what is possible widens dramatically – and unless that understanding remains favourable, and isn’t derailed by worrying reports from bad installations. Financial incentives would certainly help things develop faster.

For this to be a success, people will also need to find the construction teams who can design and install the retrofit well enough to deliver on the promises. There will be more consideration of what makes a safe, quality retrofit in Part 3.