During this winter’s cold spell, many householders encountered problems of condensation forming on the inside surface of roofing felts, which collected and dripped down onto the ceiling, causing dampness to rooms below. Many complained of ice forming from this condensation on the underside of the cold roofing felt. When this started to melt, it dripped down and caused puddles of dampness to form.
So where does this condensation come from? Well it is not from the outside environment, or from the cold- water storage tank, even many may be uncovered. Some of this vapour could have been generated by small expansion tank, venting the central heating system, often located in the attic space. But by far, most of this condensation is formed from warm vapour-laden air that drives under pressure from heated habitable rooms into the cold attic to condense on the coldest and least ventilated surfaces, such as roofing felt.
Posts Tagged ‘attic insulation’
Controlling vapour diffusion and dampness from condensation
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.
Attic Insulation
The recommended amount of insulation to be in your attic is 300mm or 12” of fibreglass. In many homeowners cases at the moment they may only have roughly between 4” and 6”. So by upgrading your attic insulation as a homeowner you will see a big difference. Getting back to the type if insulation you put in your attic, today we are talking about Fibreglass Insulation.
