Upgrading an ‘F’
rated home to an ‘A’

Phase 1: ‘F’ to ‘C’

On completing Phase 1 of the retrofit, a full SAP calculation upgraded the ‘F’ EPC to a ‘C’ with a SAP Rating of 76, a 42point improvement. 

Preparatory Work included;

• Removal of the oil-fired central heating system (boiler, flue, radiators, pipework and bonded tank)
• Stripping out all plumbing, sanitary appliances, immersion heater, galvanised loft header-tank
• Removing all existing electrical wiring, sockets, switches, fuse board and light fittings
• Pulling up carpets, vinyl and and chipboard flooring
• Removing UPVC double glazed windows and doors

Phase 1 Retrofit Works included;

• Complete Rewiring
• 4.7KW of roof mounted PV’s
• 4no. storage radiators and a
• 12no. triple glazed windows installed
• 50mm PIR insulation boards and plaster-boarded to the inside of the external walls
• A standard Direct 250Litre, unvented and insulated immersion heater installed
• 5KW rated eco-design ready multi-fuel wood-burner.
• All plumbing and sanitary ware replaced
• All walls and ceilings over-boarded and  re-plastered
• Solid oak floor boards throughout https://www.diy.com
• Redecorating throughout https://www.brewers.co.uk

Phase 2: ‘C’ to ‘A’

Retrofit completed triggered an updated Full SAP re-calculation EPC achieving a 93 ‘A’, adding a further 23points.

Phase 2 retrofit works included;

• 50mm external wall insulation and silicone render system https://ewipro.com
• Five additional triple glazed windows and doors https://www.vincowindows.co.uk
• Composite front door https://www.vincowindows.co.uk
• Roof voids fully filled with quilt insulation, up to 1.5m in depth
• Between 230mm and 1.2metres of extruded polystyrene (EPS) to the underside of the suspended floor
• A Tesla Powerwall 13.7KWhr battery https://www.tesla.com/powerwall
• Passive stack vents installed to the bathroom, ensuite and kitchen
• Balcony over-looking the river

The Sound of EWI

External Wall Insulation (EWI) Reduces Noise Pollution.

An unexpexted consequence of installing external wall insulation (EWI) and silicone render to Number 23, was the calm and stillness that resulted inside the home.

The reduction in outside noises heard in each room, from the prevailing weather, passing cars and even bird song, have been transformational, creating a constant level of quietness and tranquillity throughout the home.

To measure the contrast in sound levels inside and outside Number 23, an iphone App @decibelmeter was used. Noise levels were measured on a gusty autumn day, outdoor sound levels varied between 98dB and 58dB, the APP recorded an average of 64dB, described as “conversation in office”. Inside the home, sound levels remained relatively constant at 38dB, spiking occasionally due to human activity, the App described these levels as “quiet rural location” and “library”.

It is apparent at Number 23 that the combination of expanded polystyrene boards and silicone render have provided discernible soundproofing.

EWI attributes that reduce sound transmission

As has been experienced at Number 23, EWI provides a reasonable level of resistance to airborne sound transmission, a process known as sound attenuation. This is the action of acoustic waves moving through the air and slowing over time. This reduction in the intensity of acoustic waves is known as attenuation.

Expanded polystyrene (EPS) while it has reasonable sound attenuation qualities, it is not the best material for noise control, nor for noise mitigation. Generally, the denser the material, the more effective it is at blocking sound. Denser materials have more mass, which make it more resistant to the vibrations of sound waves. The overall effectiveness of bespoke sound proofing materials, depends on a combination of density, elasticity, thickness, and the specific sound frequencies being addressed.

By contrast, polystyrene foam is lightweight and while relatively rigid, its closed-cell structure lacks the mass and density to effectively block sound transmission to the same degree as say a concrete block.

‘all noises are sounds but not all sounds are noises’ 

In considering a sound mitigation strategy with the aim of reducing noise in buildings, a useful adage to remember is;

The World Health Organization (WHO) defines noise above 65 decibels (dB) as noise pollution and noise exceeding 75 decibels (dB) is considered a nuisance, stating noise pollution is unwanted or unpleasant sound.

The EU Environment Agency in their report European Commission on Noise Pollution cites;

“..environmental noise contributes to 48,000 new cases of ischaemic heart disease a year, 12,000 premature deaths, 22 million people suffering chronic high annoyance and 6.5 million people suffer chronic sleep.”

US Environmental Protection Agency claim that noise pollution adversely affects the lives of millions of people, with direct links between noise and health. They reported adverse effects related to noise including stress related illnesses, high blood pressure, speech interference, hearing loss, sleep disruption, and lost productivity.

Harvard University have shown that noise pollution not only drives hearing loss, tinnitus, and hypersensitivity to sound, but can cause or exacerbate cardiovascular disease; type 2 diabetes; sleep disturbances; stress; mental health and cognition problems, including memory impairment and attention deficits; childhood learning delays.

Given the evidence available, it would be reasonable to conclude that reducing noise transmission into our homes and workplaces may lead to improvements in our health.

Air Pressure Test

‘build tight, ventilate right’

On completion the Air Pressure Test (APT) recorded 6.8m³/hr/m² @ 50 Pa.

This is a 3point improvement from the APT undertaken on 26/11/2015 which measured 9.8m³/hr/m². The reduced air leakage from the property can be attributed to a number of retrofit applications, the laying of new solid oak floor boards, the installation of the external wall insulation and silicone rendering system and additional triple glazed windows.

An Air Pressure Test (APT) calculates the air tightness of a building’s fabric, also known as its ‘air permeability’ or ‘leakage’ rate. This is a measure of the air that escapes the building via uncontrolled means. This does not include leakage from trickle vents, extract fans nor passive stack vents, these are sealed up during the testing process. Air Permeability is the measure of airtightness used in the UK Building Regulations Approved Document L.

Improving a buildings airtightness, reducing its air permeability assists in reducing heat loss. Air permeability, is usually quoted as cubic metres of airflow per square metre of total surface area at an induced pressure of 50Pascals, i.e. m³/hr/m² @ 50 Pa.

Understanding fabric performance is essential in avoiding unintended condensation issues resulting from reduced fabric air filtration following the application of an external wall insulation system.

Interstitial Condensation

Interstitial condensation in a building’s fabric occurs when warm, moist air penetrates into the fabric and meets a cold surface, there it cools, reducing its ability to carry water vapour and increasing the risk of condensation forming within the construction.

Installing the EWI system at Number 23 has reduced the risk of interstitial condensation from forming within the external fabric, effectively migrating the dew-point closer to the external surface of the external insulation. The risk of interstitial condensation occurring between interface layers within the external walls has been reduced.  At Number 23 the building defects associated with persistent interstitial condensation, degradation of materials, increased risk of mould formation and a reduction in air quality have been mitigated.

A Condensation Risk Analysis has evaluated the likelihood of interstitial condensation in the modified wall construction. These calculations demonstrate compliance with ‘UK Building Regulation Part C’. The analysis concluded that Number 23’s external wall detail, avoided critical surface moisture, with no danger of mould growth.

On the incidence of interstitial condensation, it concluded there was no risk of condensation forming at any interface in any month

Thermal Bridging

Thermal bridges (aka cold bridges) are thermally weak junctions with significantly higher heat transfer than surrounding materials.

These junctions form a thermal bridge between inner and outer surfaces e.g. window jamb, where paths of least resistance for heat transference, can result in up to 30% of total building heat loss. As a consequence, thermal bridges are at risk of internal surface condensation formation, potentially leading to mould growth, presenting a health risk.

Installing EWI at Number 23 has introduced an uninterrupted layer of insulation over potential thermal bridges.

Thermal bridging can be greatly reduced in existing buildings and almost completely removed in new buildings by installing an EWI the building. Therefore, overlaying the existing thermal bridges (such as those at external wall to party wall junctions) with insulation removes any significant thermal bridge, reduces heat loss and prevents condensation from forming.

Careful design detailing is required at junctions such as those at window and door reveals, roof eaves and verges and where the EWI system starts close to ground level.

Dampness In Walls

The most common causes of dampness in existing solid masonry external walls are, penetrating damp (often caused by deterioration of the existing mortar, blocked gutters or faulty rainwater goods), rising damp and condensation, particularly surface condensation.

For instance, missing or damaged render should be reinstated, faulty or missing flashings should be repaired or replaced and areas suffering from mortar deterioration should be re-pointed with a suitable mortar mix.

Dampness can have a negative effect on the physical properties of the materials used to construct a wall and best practice is to cure any damp problems before installing an EWI system onto an existing wall. This is not a problem for new build walls as they will not be subjected to the potential problems caused by long term exposure to the elements although the EWI system finish will need to be maintained to ensure the long term protection of the facade.

Solar Reflectivity

A constituent of the silicone top coat, Clay-White colour RAL 9003 used at Number 23 is Titanium Dioxide (TiO₂).

The presence of TiO2 increases solar reflectivity, which helps the home repel excess heat in summer. Another one if its characteristic  is that can withstand a significant degree of weathering, keeping whites brighter, longer, making it easier to maintain internal temperatures and keep cooling costs down.

TiO2 has light-scattering properties with a high refractive index, which mean that relatively low levels of the pigment are required to achieve a white, opaque coating. The range of light that is scattered depends on the particle size.