21 February 2010
How We Are Reducing Our Family Environmental Impact – Insulating the Loft
One of the major users of energy in a house is for heating the building. Space and water heating in homes gives off about 20% of the UK's carbon dioxide emissions, which is about 5 tonnes CO2 per home every year.
However, one of the key issues for old houses, and in our case very old house, is that they have not been built with the benefit of modern technology that has invested much time, effort and legislation to make housing more heat efficient and so retain much of the heat within the building rather than to radiate it out into North Yorkshire - it's a godforsaken task to heat up Northern England.
So as a start, you need to keep as much heat in as possible.
So my theory has been simple work down from the roof to the ground floor slowly but surely insulating the house. We will work from the top downwards, as hot air rises so you want to capture it as it tries to escape upwards first rather than worrying about the ground levels at the outset.
The first thing, we felt, was to get insulation laid in the roof between the joists. This had been done using old fashioned roof insulation over 10 years ago, insulating to 100mm in depth. But we decided to insulate again with a cross layer of 200mm recycled glass mineral wool blankets. For the first attempt at this, we bought recycled mineral wool - each pack of this Knauf Insulation Space Blanket contains 2.4 wine bottles (it was a 200mm thick roll of 1.48m2) and has a R value of 4.50m2K/W. Government advice is to get insulation to about 300mm.
I liked this because it comes in a roll and encased in fire retardant polyethylene film, so does not need all that cutting and special equipment that normal loft insulation needs, and even more important it’s currently subsidised by e.on under some Government scheme to mitigate climate change so it was half price at Homebase, costing just £5.74 per roll.
It has got a metallic coating which Knauf Insulation claims reflects heat and so keeps more heat in – I think this sounds a bit spurious!
That means that the 35 rolls that I bought cost £143.50; this should mean that we recoup the energy savings within 2 - 3 years (assuming that we will save 10% of our fuel bills and that we had covered the whole roof void with the same insulation, i.e. multiply cost by 3/2; 25% of heat loss in total is through the loft and we already had 100mm in place, so I reckon 10% would be a good estimate for additional savings).
It was pretty easy to lay it and took me about 5 hours over the other weekend to buy the kit and lay it over two-thirds of the roof void.
Typically, however, when I got into the roof, I discovered that the heating engineers (or plumbers as I would have known them) never completed the lagging of the pipes nor the insulation of the water tanks, which was okay as they never relaid the insulation so the heat from the house kept the area around the tank warm – so muggins here had to finish that off as well.
Now feeling a bit good about myself, I bought something last week that’s a bit less simple to lay but definitely a greener alternative.
There are two main alternatives: one from newspapers (Warmcel) and the other from British sheep’s wool and recycled polyester (Thermafleece). These both have the same levels of insulation capability as mineral wool, but I chose Warmcel and bought 15 bags of this from £165.27, costing £11.02 per bag inclusive of transport to us. The Thermafleece is roughly double Warmcel again for the same price per m2 for the same depth, i.e. four times as expensive roughly as the recycled mineral wool insulation and so tripling the payback period.
So going back to my payback calculations – Warmcel has a payback of 4 – 6 years, which I am happy about, but Thermafleece has a payback of 8 – 12 years, which is too long for me. Basically, I think for the cost-reward, it’s probably best to go with either the Space Blanket or (to give you a greener feeling about life) go with the Warmcel. I cannot see the point with going for Thermafleece unless you feel romantically attached to lining your house in a woolly jumper.
But you do need to put the insulation down yourself as it's pretty simple, and if you get a builder to do the work, you will blow any meaningful chance at getting a payback.
To buy these greener insulation materials, try these to web sites:
