treeve
Major Contributor
[Thermal Insulation improvements under Government Schemes]
NOTE : Always seek responsible professional advice on this. The whole subject is NOT simply a matter of how much insulation that is applied to meet misapplied Government targets..
The major consideration is Condensation and the effects that it can have if left unchecked.
Not all roof spaces are convenenient or are constructed as being suitable for future additional insulation. Using the prescribed glass fibre rolls, it is ten inches thick. That fills spaces and prevents air flow within the roof space. Not all roofs are built using the standard gang-nail trusses, such as were made by Twinaplate. Many are what are known as a Cut Roof. Being formed of main trusses, purlins and floating (jack) rafters. Ceilings were attached to these main trusses by fixing to ceiling bearers. The whole construction was suitable for four inches of glass fibre, as it could be installed between the ceiling joists.
As insulation requirements rise and as expectations in human comfort rise in the face of cold seasons and occasional sudden drops, let alone the heating costs as they rise with rising fuel costs, so installation of insulation to roof spaces is more problemmatic.
I was involved in the early days of the standard requirements being applied. We followed the installation standards and produced drawings and specifications accordingly. The contract was made and the houses were built. The clients moved in. In three days we were contacted by them, as they were experiencing a series of flows of running water coming down from the roof construction. We arrived to see a series of buckets and bowls collecting water at an alarming rate. This was condensation at its worst. We took measurements and recorded temperatures. I went back to the office and sat down with a calculator and found that the dew point (the point in the construction where condensation occurred) was within the roof space just below the roof underfelting. I immediately contacted the Building Research
Station, having referred to many other scientific discourses and let them know my findings. They were astounded and checked it all through, admitting that the construction in the Building Regulations actually encouraged condensation. They had been working on gangnail constructed roof shapes. It was shortly after that that a vapour barrier became a requirement in new construction in Building Regulations.
Whatever is proposed to be placed in your roof space, ask for a dew point calculation. Ensure that a vapour barrier is placed UNDER the roof space, between the ceiling and any insulation material; the vapour barrier should be taped together to form a continuous barrier to any moisture rising from your living areas. It is not only direct water vapour and steam, such as from a bathroom shower or from the kitchen. The rooms should be well ventilated in any case, using wall vents, extract fans or simply window openings or ventilators. This also assists in reduction in concentration of Radon gas where present (a radon vent is another point entirely).
New work and notifiable works of alterations are a matter of The Building Regulations, but this is about non-notifiable intent to improve.
Airborne moisture needs to be prevented from reaching any cold surface in the roof construction, a steel beam for example or water pipe.
It is no good at all in merely having statutory ventilation cut in the eaves or fitted to the gables. Besides offering an entry point for insects and more moisture from the atmosphere, all this achieves is in reducing the temperature even more, in the roof space, resulting in even lower temperatures, reducing the overall thermal insulation, and increasing the temperature gradient and heightening the risk of condensation or in freezing the water tank (as insulated as that may be).
In other examples I have been called in over, it was after such an insulation using 6 inch glass fibre quilt. It was some years after the installation. For no apparent reason ceilings began to show patches of black mould growth. Inspection revealed that condensation had been occurring over an extended period, the fibrelass had reached saturation point and could no longer hold the moisture with its surface tension. It all had to be removed and re-built. There is no substitute for careful design and good workmanship.
Rule of Thumb/Approved Construction may not be suitable for the construction in your home.
I write this in response to two cases of which I was asked just lately. It is also a matter that condensation harbours mould growth, it is not simply a case of placing a bucket on the living room floor.
I have been retired from the [Architectural/Surveying/Engineering] Construction Industry, but I am increasingly alarmed at the extent of reliance on Rule of Thumb. Each building should be assessed on its own merits and should be the subject of a proper calculation set.
NOTE : Always seek responsible professional advice on this. The whole subject is NOT simply a matter of how much insulation that is applied to meet misapplied Government targets..
The major consideration is Condensation and the effects that it can have if left unchecked.
Not all roof spaces are convenenient or are constructed as being suitable for future additional insulation. Using the prescribed glass fibre rolls, it is ten inches thick. That fills spaces and prevents air flow within the roof space. Not all roofs are built using the standard gang-nail trusses, such as were made by Twinaplate. Many are what are known as a Cut Roof. Being formed of main trusses, purlins and floating (jack) rafters. Ceilings were attached to these main trusses by fixing to ceiling bearers. The whole construction was suitable for four inches of glass fibre, as it could be installed between the ceiling joists.
As insulation requirements rise and as expectations in human comfort rise in the face of cold seasons and occasional sudden drops, let alone the heating costs as they rise with rising fuel costs, so installation of insulation to roof spaces is more problemmatic.
I was involved in the early days of the standard requirements being applied. We followed the installation standards and produced drawings and specifications accordingly. The contract was made and the houses were built. The clients moved in. In three days we were contacted by them, as they were experiencing a series of flows of running water coming down from the roof construction. We arrived to see a series of buckets and bowls collecting water at an alarming rate. This was condensation at its worst. We took measurements and recorded temperatures. I went back to the office and sat down with a calculator and found that the dew point (the point in the construction where condensation occurred) was within the roof space just below the roof underfelting. I immediately contacted the Building Research
Station, having referred to many other scientific discourses and let them know my findings. They were astounded and checked it all through, admitting that the construction in the Building Regulations actually encouraged condensation. They had been working on gangnail constructed roof shapes. It was shortly after that that a vapour barrier became a requirement in new construction in Building Regulations.
Whatever is proposed to be placed in your roof space, ask for a dew point calculation. Ensure that a vapour barrier is placed UNDER the roof space, between the ceiling and any insulation material; the vapour barrier should be taped together to form a continuous barrier to any moisture rising from your living areas. It is not only direct water vapour and steam, such as from a bathroom shower or from the kitchen. The rooms should be well ventilated in any case, using wall vents, extract fans or simply window openings or ventilators. This also assists in reduction in concentration of Radon gas where present (a radon vent is another point entirely).
New work and notifiable works of alterations are a matter of The Building Regulations, but this is about non-notifiable intent to improve.
Airborne moisture needs to be prevented from reaching any cold surface in the roof construction, a steel beam for example or water pipe.
It is no good at all in merely having statutory ventilation cut in the eaves or fitted to the gables. Besides offering an entry point for insects and more moisture from the atmosphere, all this achieves is in reducing the temperature even more, in the roof space, resulting in even lower temperatures, reducing the overall thermal insulation, and increasing the temperature gradient and heightening the risk of condensation or in freezing the water tank (as insulated as that may be).
In other examples I have been called in over, it was after such an insulation using 6 inch glass fibre quilt. It was some years after the installation. For no apparent reason ceilings began to show patches of black mould growth. Inspection revealed that condensation had been occurring over an extended period, the fibrelass had reached saturation point and could no longer hold the moisture with its surface tension. It all had to be removed and re-built. There is no substitute for careful design and good workmanship.
Rule of Thumb/Approved Construction may not be suitable for the construction in your home.
I write this in response to two cases of which I was asked just lately. It is also a matter that condensation harbours mould growth, it is not simply a case of placing a bucket on the living room floor.
I have been retired from the [Architectural/Surveying/Engineering] Construction Industry, but I am increasingly alarmed at the extent of reliance on Rule of Thumb. Each building should be assessed on its own merits and should be the subject of a proper calculation set.
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