DKP Energy Efficiency
Energy Efficiency &
Low-Energy Building Design Consultancy
Frequently Asked Questions (FAQs)
What is a 'fabric-first' approach?
PassivHaus compared to Passive House, differences......?
- We offer a 'fabric-first' approach to house design. This means looking first at the
construction of the thermal fabric of the proposed dwelling; the floor, walls and roof. These elements are only constructed once, with little
chance that they will be upgraded. So they should be designed with maximum insulation levels to minimise heat loss throughout the designed
life of the building. Once the thermal envelope of the house has been determined, the fixed services (heating, lighting, hot water & ventilation)
can be specified. A 'fabric first' approach results in a lower space heating energy demand, so this low energy demand can be satisfied in the
most cost-effective way. This may be a smaller than normal gas or oil boiler, electric heaters, or biomass-fuelled room heaters. Savings from
a 'fabric-first' approach are savings year after year. With the current rate of fuel price inflation, gas and elecricity will cost twice as
much as it does in 2013 by 2022!, just nine years.
What is the Code for Sustainable Homes (CfSH)?
- 'PassivHaus' is high standard of dwelling devised in Germany in the early 1990s by
Professors Bo Adamson of Sweden and Wolfgang Feist of Germany and the first dwellings to be completed to the Passivhaus Standard were
constructed in Darmstadt in 1991. “A Passivhaus is a building, for which thermal comfort can be
achieved solely by post-heating or post-cooling of the fresh air mass,
which is required to achieve sufficient indoor air quality conditions –
without the need for additional recirculation of air.” This means
that a house can be built without a traditional central heating system, it is kept warm by the sun, human activities,
and electrical devices. A 'PassivHaus' is designed to be very air-tight, and so
uses a MVHR sytem to ensure high air-quality levels are maintained. There are specific maximum values for heating demands.
A PassivHaus is certified by Accredited
Designers. A Passive House is a dwelling designed and built to similar standards, but without the maximum heating demand imposed, or the
certification process. We can design your Passive House to the highest standards, helping you to save money on heating bills year after year.
Off mains-gas these savings can be over £1000 per year, every year.
What is MVHR (Mechanical Ventilation with Heat Recovery)?
- The Code for Sustainable Homes (CfSH) is the national standard for the
sustainable design and construction of new homes. It aims to reduce
carbon emissions and promote higher standards of sustainable design
above the current minimum standards set out by the
The CfSH provides 9 measures of sustainable design:
- water usage
- surface water runoff (flooding and flood prevention)
- health and well-being
It uses a 1 to 6 star system to rate the overall sustainability performance of a new home against these 9 categories.
If you are building a house that is to be assessed under the CfSH, you will be required to provide a CfSH preAssessment
to support your Planning Permission Applicaion, a CfSH Design Stage Asessment & Interim Certificate prior to commencement of works,
and Post Construction Stage Assesment when the dwelling is finished.
How tight is 'air-tight'?
- MVHR is the system that brings in constant fresh air to a house, while at the same time keping the
heat inside the house. It does this by exracting warm damp air from rooms such as kitchens, bathrooms, utility rooms, toilets, and en-suites.
This warm air is pulled through a heat-exchanger before it leaves the house. The other side of the heat-exchanger pulls in fresh air from the
outside. This clean fresh air is warmed up before it is distributed throughout the house. This continuous process ensures that the air-quality
inside the house is maintained, odours and moisture are removed, and fresh air is always available. Contrary to popular myths, you CAN open the
windows in a house fitted with MVHR. However, it means that you can keep the windows closed in the winter, keeping your house warm and quiet.
MVHR can be installed into an existing building, but it is easier to integrate it into a new building as it is being designed.
MVHR when properly installed ino an air-tight house can push up the SAP rating of a house design, and save the occupants money.
Timber-Framed construcion vs masonry construction, pros & cons?
- Living in an 'air-tight' is NOT living in a plastic bag!
Air-Tightness refers to uncontrolled ventilation; leaks in the building fabric, open vents, chimneys & flues. When you feel draughts in a
house, you can feel cold air being blown into your house as warm air is being sucked out elewhere. You have spent money on heating that warmed air,
and now you will spend more money heating this incoming cold air. Air-tightness, or air-permeability is tested with a 'door-blower' test. A lower test value is best,
down to around 3m³/m².h but if you want an even lower value, you should consider using MVHR (see above). Current Building Regulations allow an
air-tightness value up to 10m³/m².h but this would be a very draughty house! Where services such as water pipes, gas pipes etc puncture
the thermal envelope (walls, floor, roof) they must be sealed, and attention should be paid to window & door frames too.
What are ACDs (Accredited Construction Details)?
- Timber-frame has a bad reputation in the UK. This is partly deserved, some of the national builders
saw timber-frame as the way forward in the 1970s and 1980s. However they didn't have the skills or experience to fabricate and erect the frames
properly. These houses were damp, mouldy, creaky, and generally not well built. However, the timber-frame companies that currently offer frames
and kits are experts, their kits are top quality, and the designs can be tailored to owners needs. Timber-frame is quick to erect, a shell can be
water-tight in a few days, allowing follow-on trades on site sooner than with other construction methods. Timber-frame construction leads to houses
with low thermal-mass. This means that they heat up quicker when the central heating is turned on.
Masonry construction; block + block, or brick and block is THE traditional method of construction in the UK. It can provide a solid feel to a
house, and is easy to build. Last-minute changes can be accommodated, and most builders have experience of this method of construction.
However it can be time consuming, and careful site detailing is required to keep the air-permeability values down. Masonry can provide high thermal mass,
ironing out peaks and troughs in internal temperatures.
Both methods have their proponents, and associated issues.
LEDs compared to CFLs compared to Low Voltage Halogens. What are the
- Accredited Construction Details (ACDs) are sets of drawings and specificaions that when followed,
lead to reduced heat-loss through thermal bridges & uncontrolled ventilation leaks. There are sets of details available for Timber Frame &
Masonry Construction. They can be downloaded free of charge from the
ACDs give developers a set of junction details; walls meeting floor, walls meeting roof etc etc, that can improve the SAP rating of their
designs by approximately 15%. Each set of ACDs need to be signed off for each dwelling.
How do Heat Pumps work, and are they worth it?
- First, Halogens of ANY type are not 'low energy' by any means. They're about 90% inefficient,
ie they produce 90% heat and 10% light for each Watt of electricity they consume. Avoid them at all costs!
- CFLs are 'Compact Fluorescent Lamps', another type of fluorescent light, all based around the same properties. A glass bulb filled with
a gas that reacts to a electrical current causing it to illuminate. They use the same principles as the long fluorescent tubes we are used to
seeing. The early CFLs had a long warm up time, and so got a bad reputation. Modern CFLs have much quicker warm-up times, 80% light output
immediately, the final 20% within a few seconds. They are cheap to run, and are available in a wide variety of fittings.
- LEDs are 'Light Emitting Diodes'. They convert electricity into light with very litle heat output. They are about 90% efficient.
However some are marketed as direct 50W halogen replacements. They're NOT! A 5W LED can be equivalent to a 20W or 35W Halogen bulb.
However they are so much more efficient than Halogens, they should be the first choice for lighting in the house. They can be wired to provide colour
choice, dimmable, and many varieties of mood lighting. LEDs come in most fitments, as well as being available on flexible strips, tubes,
and as replacements for existing fittings. The most important metric to look for is the Lumens per Watt figure, the amount of light
output per Watt of electricity consumed.
- There are two basic types of Heat Pump; Air Source Heat Pump, and Ground Source Heat Pump.
They both work in the same way. An easy way to describe electrically-powered Heat Pumps is to compare them to a fridge in reverse.
A fridge takes heat energy from a space (the inside of the fridge) and moves it to the back of the outside. If you put your hand to
the back of a fridge, you can feel the heat coming off the black radiator pipe. An Air Source Heat Pump takes heat from the air outside
the house and moves it to a tank of warm water inside the house. The heat is transferred via a refrigerant gas, which is compressed to raise the
temperature to a useable level. A Ground Source Heat Pump takes heat from the ground via a long collector pipe. Both Air Source
Heat Pumps (ASHPs) and Ground Source Heat Pumps (GSHPs) have advantages and disadvantages. In order to get the most out of a Heat Pump,
and to run it at it's most economical settings, it needs to be sized accurately to the dwelling it is designed to heat. This
can be very complicated, and takes in many variables. The most important thing to remember is that they use electricity
(although gas powered ones are available) and so the Seasonal Coefficient of Performance (CoP) needs to be taken into account for the proposed
heating season. Heat Pumps work best at low temperatures, and so are suited to under floor heating (UFH). They cannot replace a conventional
'boiler + radiators' system without serious modifications to the entire system.