Roofs are the most important element of a house to insulate as heat rises in our rooms and this warm air will cool rapidly when it touches cold roof or ceiling surfaces. It will cause convection and cause cold downward draughts, creating more heat loss and discomfort, especially where high ceilings occur that are poorly insulated. Roof can also emit more heat than walls per surface area, on cold nights with clear sky conditions. You can see the same thing happening on the roof of a car on the morning after a cold night, where condensation or even frost will form on the roof first, even when ambient temperatures are above freezing. Depending on whether a bungalow, two storey or multi-storey building, roofs will contribute differently to heat loss. Relative to a given floor area, a poorly insulated roof of a bungalow will have twice the heat loss of a similar two storey house and three times that of a three-storey house. Typically the average roof contributes 25% of the heat loss through all the external elements. Roofs however are usually easier and much cheaper to insulate than walls.
Posts Tagged ‘Duncan Stewart’
Practical measures for upgrading insulation – Roof Insulation
In my last blog, I focused on some basic principles of Building Science that apply to most of our existing homes. I highlighted the following physical issues that can impact on thermal comfort and indoor-air quality. I outlined principles that can reduce space heating energy demand, by upgrading the building fabric’s elements that enclose all the external envelope of the house, such as the roof, external walls, ground floors, windows and external doors
Sealing against draughts and wind infiltration:
This work should be carried out on the outside of the insulation layer, of external walls, roof and ground floor, especially at critical junctions, such as at roof eaves, attic trap doors, chimneys/fireplace, dormer roofs and attic conversions, caulking and taping joints between block work walls and window frames. Also, opening sashes of windows and doorframes not draught-sealed, gaps around pipes, cables and cavity block walls that are dry-lined on the inside.
Reducing heat loss through the building fabric
Roof/Attic: To be well insulated, roofs or attics should be fitted with about 400mm of mineral or glass wool insulation or other high performance, rigid insulation boards to thickness of say 250mm, that achieve similar performances in thermal transmittance (U-value – measured in watts per sq metre, per degree Kelvin). I hope to deal with this topic in a later blog.
Insulation to attic floors:
The insulation should be laid on a continuous, vapour resisting, airtight membrane that is sealed at all joints and junctions and to adjoining external walls. This is to prevent warm vapour laden-air in the habitable rooms of the house from driving through the permeable ceiling plaster, where it seeks to stabilise pressure with the colder, lower vapour pressure air above in attic space or outside the building. It is critical that this membrane should be fitted on the inside, warm surface of the insulation to prevent condensation and dampness forming within the insulation and where the temperature of the airtight membrane will always be maintained above the dew point. The trapdoor to the attic should also be draught sealed like an external door. More recent houses may have a foil-backed plasterboard ceiling. This helps, but in my opinion is not sufficient, as un sealed gaps occur at joints, allowing warm vapour-laden air to drive into the insulation and cold attic space.
Introduction of Carbon Tax to Ireland
Saturday 1st of May saw the introduction of Carbon Tax to Ireland. The Carbon Tax of 4.3% will add around €43 to filling a 1,000 litre home heating oil tank and around €41 to an average annual gas bill. In these tough economic times increasing home heating bills is the last thing that we need. The tax is going to hit already struggling homeowners with fuel poverty on the rise. We as a nation need to realise that the day of burning fossil fuels is coming to an end. The supply is slowly but surely running out. Coal and peat is to be taxed from September 2010 also.
Fossil Fuel and Climate Change
On top of all the money lost to Ireland and our local economies by importing fossil fuel, by the global scarcity of supply coming with rising prices of fuel but more so by Climate Change. It is clearly now really happening and is unequivocal. It is predominantly being created by CO2 emissions generated by us humans in the Developed World, from burning fossil fuel. It is causing huge hardship and hundreds of thousands of deaths each year to poor in the developing world. It is by far, the greatest challenge ever for human civilisation on this planet to have to face. We are now on a trajectory for a six degree rise in global surface temperature in this century, unless global Governments and all of us act now. Our greenhouse gas concentrations in the atmosphere have now reached 390ppm – that is 40% above Pre-Industrial time levels and is now at a level of concentration that has not occurred since about 20 million years ago. Over that huge length of time our CO2 stabilised at about 280ppm. We are scientifically in ‘unknown territory’! It puts all our children’s future in peril.
Bio-Mass Fuels
Other fuels include bio-gas (methane) from anaerobic digestion of food and slurry waste.
Liquid bio-fuels like bio-diesel from rapeseed oil or flexi-fuel like bio-ethanol from creamery waste whey or cellulosic wood based feedstock, producing second generation ethanol. Importing ethanol or bio-diesel is not a good solution. It is often made from corn which is very energy intensive and CO2 emitting. It can cause deforestation to rain-forests and food and water shortages in poor countries. It also means importing this fuel like our oil, gas and coal.
Wood-Chip as a source of biomass in Rural Ireland
The next fuel to consider if living in rural Ireland is wood-chip. If you are lucky enough to have thinning available from forestry or land to grow short-rotation, coppice- willow. After harvesting, the wood is first left stacked and covered to air-dry sufficiently. It’s typically dried for at least the six warmer months of the year. It is then chipped and stored. If it’s not dry enough it may ferment and heat up like compost, so needs to be turned. The damper it is, the less efficient and wasteful to burn with more gas emissions. It is therefore critical to reduce its moisture-content down to around 25degrees Celsius.
Heat Energy solutions for homes – sourced from Biomass
In my last blog I discussed the use of solar collector systems for generating renewable, zero-CO2 emissions, domestic hot water and space heating for Irish homes. I also showed some solutions for heat pumps. This time, I wish to explore the potential and options available from various biomass sources and their appropriate heating appliances and systems.
The first renewable fuel to consider is wood, which is the most common traditional fuel for heat from the early times of hunters and gatherers. -Typically used as dried wood branches and split logs. The drier the wood the more efficient in producing heat. If wood is damp, a huge portion of the combustion heat is absorbed by evaporation and wet wood is difficult to generate enough heat to dry before it can heat sufficiently to form a gas vapour from the wood fuel, so as to ignite in the presence of oxygen. Some species of wood burn better, are denser and contain a higher calorific value than others.
What is realistically achievable? Part Two – Targets…..
First: – Getting back to our ’big global challenges’ that need urgent response, these include:
1. Global warming,
A changing climate and deforestation:
- All of these are in need of urgent remedy and contributing to: – increasing surface temperature, rise in sea levels, – accelerating ice-melt, -more extreme, unpredictable and frequent weather events, – more intense floods, droughts, stressing water and food shortages, heat waves and species extinction.
