By Paul Watts
The UK is committed to reducing it's carbon emissions by at least 60% by 2050 and are investigating ways to try to reach this target. Some far reaching changes will have to be introduced by the Government, some already have. The higher cost of energy combined with the EU driven Energy Performance Certificates (EPC's) have hugely increased interest in home owners looking for the most efficient way to make their buildings more energy efficient.
The EPC was intended to be a comprehensive energy report, which aims to encourage buyers and sellers to improve the energy efficiency of the property. EPCs are mandatory when a building is constructed, sold or rented out. The certificate provides an energy efficiency rating for the building rated A-G, very similar to that which can be seen when purchasing electrical goods.
Carbonfootprint.com tell us that:
'EPCs are produced by trained assessors using a standard methodology which takes into account the performance potential of the building and its services (including the fabric of the building and current installations – heating and lighting systems). By using standard assessment criteria the energy efficiency of one building can easily be compared with another building of the same type, so providing an insight into the buildings efficiency for potential buyers or tenants.'
An EPC is always accompanied by a recommendation report that which lists potential opportunities to improve the energy rating of the building along with example pay back periods.
From 1 October 2008 all buildings whenever sold, built or rented require an Energy Performance Certificate. Penalties of 12.5% of the rateable value of the building will apply to owners or landlord if unable to present an EPC on the request of a buyer/tenant.'
Well, so much for the theory but what does this mean in practice, and in particular for the 4 million pre-1919 solid wall constructed buildings?
Approximately a quarter of the UK dwellings are of a traditional, solid wall construction and of course require different methods as well as different materials if the buildings are to continue to work. Unfortunately, the cost restrictions on the EPCs to make them politically acceptable to the UK public means that the assessor has to make generalisations. For example no allowance is made for the insulation afforded to a building by a thatch roof, and a solid wall is always deemed to be a 13" brick wall. Thatch offers excellent thermal properties and solid walls might be many feet thick.
As a result there are going to be lots of older buildings that are wrongly assessed, in all probability the vast majority of buildings will be.
So we have thousands of Government appointed assessors using a flawed system to provide home owners with a flawed report on the energy efficiency of their homes, we then have other agencies giving flawed advice on how to improve the buildings. For example the Energy Saving Trust offers this specific advice on their website:
How external wall insulation works
This involves adding a decorative weather-proof insulating treatment to the outside of your wall. The thickness of the insulation needs to be between 50 and 100mm and is usually installed where there are severe heating problems or the exterior of the building requires some form of other repair work providing the opportunity of adding insulation.
Most people reading this would take the term 'weather-proof' to mean that the building needs to be sealed on the outside. This could well prove disastrous for a solid wall building. So what should be done to improve the thermal performance of the UK's old housing stock without creating problems?
Traditional buildings are sometimes described as cold, damp and draughty by their detractors. Indeed they can be, so these problems need to be addressed if the thermal performance is to be improved.
Dealing with draughts
Draughts are a common but sometimes overlooked problem with older buildings. Modern buildings have to conform to strict regulations concerning the number of air changes per hour. Specialist companies can offer a test by installing a fan in the doorway of the principal entrance the dwelling, sealing all flues and chimneys, and systematically going around the building to determine where the leaks may be and how best to seal them. It is not desirable to completely seal a traditional building as breathability is necessary but most older dwellings have scope to improve heat loss through gaps in the structure without causing it problems.
A less scientific way of checking for air leaks is to wait for a windy day and carefully go around room by room and feel where the draughts are coming in. It can then be decided on how best to deal with each issue.
Dealing with dampness
Inappropriate materials should be removed if possible and replaced with 'like for like'. If a building was built using very soft materials and breathable paints, then these should always be used in their maintenance. Even the wrong selection of natural hydraulic limes (NHL) can adversely effect a building.
Reducing the air changes in a building can increase the amount of moisture trapped in it leading to condensation. Attention should therefore be given to removing excess of moisture close to the source such as a mechanical extraction in the bathroom and kitchen. This is important as the creation of mould can create health issues and people can assume condensation is another form of damp and look to seal rather than allow to breathe.
The least contentious of areas to insulate, an efficient product should be chosen to offer an effective means of keeping the heat in the rooms below. Many different options are available but the environment is always thankful if a natural product is used. Two UK produced products should be considered top contenders:-
A recycled newspaper loose lay made by Warmcell offers a cost effective and easily applied insulation. Make sure that the eaves cannot have the fibres drop down and prevent the loft getting the correct level of ventilation, this is usually done by putting timber noggins between the joists to retain the product. A minimum of 220mm of thickness is required to provide a good insulation. Care must be taken to try to cover all timber joists as they can transmit cold through 'cold bridging'. Simply cut the bag open and spread it evenly across the loft.
Another well known UK product is sheepswool insulation. Provided as a batt or now in a roll, sheepswool is a very popular product. It offers effective insulation that does not fail if the loft should develop a leak and soak the sheepswool. It has even been shown to remove the carcinogen formaldehyde from the atmosphere. This needs to be carefully cut to size to prevent gaps between the joints and is more expensive than the cellulose fibre.
Another way to insulate the roof space is to insulate under the slates/tiles on the apex. It would not be advisable to take the short term choice of spray foam insulation beneath the tiles. This is not natural, can cause condensation issues and will require a complete renewal of the slates/tiles as none can be salvaged when the time comes. Modern foam based boards can be employed but worth considering are the woodfibre boards available. These can be supplied in tongue & groove in order to help with reducing air changes and are very good at reducing the overheating effect of a hot sun (decrement) and therefore reduces the need for air conditioning. These work best on top of joists rather than in between and work equally well on a flat roof.
External wall insulation
Undoubtedly, the best way to add insulation to a solid wall is to apply it to the outside of the building. This must be breathable and be rendered with lime plasters and decorated with breathable paints. Tradical produce a hemp/lime plaster that can be applied with a trowel. Pavatex offer a wood fibre board Unger Diffutherm that can be used. This is not going to be a cheap option but it can be an excellent option in some cases. The board should be at least 100mm thick plus the plasters, this can present problems with roof overhang, window sills etc. that all need to be considered. Some walls may have too much character to realistically have a board fitted to them. The boards only have a small amount of flex and must not have a void between them and the wall, so the wall needs to be levelled with lime mortar before the board can be fitted.
Of course there may well be aesthetic considerations that would also preclude the use of external insulation but it has very definite benefits.
• It is much easier to avoid cold spots and condensation
• easier to reduce air changes
• no internal space or character lost
• the walls retain their thermal mass & heat storage capacity
Internal wall insulation
Distinctly second best in terms of performance and upheaval, internal insulation still offers warmer buildings and lower carbon use and lower energy costs. As long as the building breathes to the outside, it may be possible to use non-breathing insulation on the inside without major issues but it is often best to allow the walls to breathe inside as well as outside.
Some prefer the application of a drywall stud work as this stops the damp showing in the first instance but it can simply be masking problems that will start to rot the stud work soon after being fitted due to the build up of moisture. This leads to other issues such as fungi, timber decay and health issues. If this method is employed, it is best to allow moisture to escape to a void above the false wall, do not try and trap it.
A certain amount of character can be retained if hemp plasters or reed boards are used directly onto the walls as these can follow contours whereas stud work is straight and flat.
Any insulation applied to an internal wall needs to be carefully thought through as cold spots can be created where there were none and the 'dew point' will be moved into the wall rather than the surface. The dew point is the point at which water vapour is cold enough to turn into droplets of water, if this is out of sight within the wall this is referred to as interstitial condensation and needs to be avoided.
One product on the market specifically designed to deal with this problem is Pavadentro, a wood fibre board that has a built in vapour check to reduce the amount of vapour that passes from the room to the cold wall. The vapour can be slowed and held in the insulation until it can be harmlessly released into the room again.
The most thermally efficient form of floor insulation is the modern foam type boards such as Xtratherm or Kingspan, as always with traditional buildings, this is not the whole story. When re-laying a floor the Building Regulations say that you must bring the floor up to a minimum u-value and lay a damp proof membrane.
Of course, sealing the floor can push extra moisture into the lower part of the walls creating damp issues. This is why a lot of people are now fitting limecrete floors with breathable insulation, these need to be excavated more than for modern insulation so care should be taken not to undermine the stability of the building. Thought also should be given to the floor covering with porous flagstones being the best option.
Adding insulation to your home can make it more comfortable, cheaper to keep warm and reduce your carbon footprint and can be a very good move but before starting work be sure as you can that you have chosen the materials well.
By using the wrong materials you could be causing health problems for yourself and structural damage to the building. Don't rely solely on the advice from an energy consultant who may or may not understand the needs of a traditional building.
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