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General Information
Insulating the loft is one of the best things you can do to reduce
heating costs which does not cost vast sums of money. Around 25%
of heat is lost through the ceilings of a house (even more if you
have a bungalow) and can pay for itself in under a year. Originally
our house had 150mm of fairly old insulation over most of the roof
area. Over the last three years this has been increased to around
350mm using 'Space Blankets' in all areas that are not floored
(around half the total loft area). Space Blankets are simply fibre
matting encased in a plastic bag with a foil layer to reflect heat.
These blankets are available in various lengths with thickness
of between 100mm and 300mm. Apart from reducing heat loss loft
insulation helps achieve a more even heat distribution throughout
a room and has the added benefit rooms tend to stay cooler in summer.
I am not a great fan of the loose fill insulation that is available
since it can blow about in high winds and tends to find any holes
in the ceiling. Depending on what you started with the payback time
of doing this could be as quick as one year.
Process
Insulation works best if it is laid in two layers - one layer between
the rafters and a second layer across the rafters with a total
thickness of around 350mm. Don't push the insulation right up to
the edge of the roof otherwise you will stop the roof breathing
causing problems with condensation, a gap of 25mm to 50mm is sufficient.
Electrical cables should be routed over the insulation, the reason
for this is that cables can run warm in use and insulating them
will increase any heating effect. Be extremely careful when dealing
with cables since it is quite common to come across poorly insulated
connections in the loft especially around light fittings as I have
found out the hard way. Pipes can safely be left under the insulation.
Hot areas (such as down lights) need a safety gap around them of
at least 75mm to reduce the danger of overheating and fire. It
is possible to buy proper protective screens from major DIY outlets
but they are relatively expensive. If the loft has flooring it
should have at least 200mm of insulation under the flooring
laid between the rafters. Don't insulate under water tanks otherwise
there will be an increased risk of them freezing up.
It is worth making sure all pipes in the loft (especially
those not covered by the insulation) are also properly insulated
and that tanks are wrapped in insulating jackets since the loft
temperature will be lower after insulation with the consequent
risk of freezing
Odd Tips
Make sure that all pipes and cables entering the loft from rooms below are properly sealed so that warm air cannot leak into the loft. Ensure that ceiling mounted light fittings are properly sealed against draughts. Don't forget to insulate the loft trapdoor and seal it against draughts. If the loft has windows or skylights make sure they fit properly and are sealed against draughts, a curtain can work wonders with single glazed windows and skylights.
Precautions
Mineral wool insulation can irritate the skin and throat and should
be installed with care. Wear a suitable dust mask and protective
gloves to avoid irritation.
Be extremely careful when dealing with electrical cables.
Do not try to work standing on the joists, use a piece of board
reaching across three joists that is stable to kneel safely
upon.
Light the work area properly, if there is no lighting installed
in the loft, run an extension lead up into the void and hang a
suitable light from a beam.
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