Difference between revisions of "Insulation"

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'''Insulation''' reduces heat transfer, thus  
'''Insulation''' reduces heat transfer, thus  
* Reduces heat loss in winter, saving on heating costs and improving comfort
* Reduces heat loss in winter, saving on heating costs and improving comfort

Revision as of 09:41, 11 February 2008

olocarolrelr Insulation reduces heat transfer, thus

  • Reduces heat loss in winter, saving on heating costs and improving comfort
  • Reduces rate of heat gain in summer, saving on ac costs.
  • Prevents freezing of pipes
  • Reduces run cost of HW systems

Main DIY Applications

  • Wall cavity insulation (for either original wall cavities or a retrofitted cavity behind plasterboard)
  • Solid wall insulation (fitted to wall surfaces)
  • Loft insulation
  • Pipe insulation to prevent freezing or heat loss
  • HW tank insulation
  • Underfloor insulation

Types of Insulation

Trapped Air

Still air is a good insulator, and is the basis of more or less all insulation products currently used in housing. One way or another, each insulation product traps air, and it is the air that does the job.

Hence if 6" of insulation is compressed to 4", it will have the insulation value of 4" of insulation.


Cavity walls insulate much better than solid walls, and are an early example of domestic trapped air insulation. Walls with no cavity can have a trapped air cavity attached using battens and plasterboard.

Large cavities allow some air movement, hence foamy and woolly insulation products give better insulation than a cavity alone.

Battens and other barriers to air movement can be used to improve an empty cavity's insulation a little, but denser insulation products provide better insulation value, and are worth using.

Expanded Polystyrene

Low cost insulation available in slab form and (still?) small beads for loose fill.

Mainly used for:

  • Roof insulation
  • Wall insulation
  • Floor insulation

Also used for beanbags, and rarely for extra fridge & freezer insulation.

Polystyrene is flammable, and produces toxic smoke on burning. This problem is worse when painted with oil based paints.

Historically used for

  • Cavity wall insulation
    • Can saturate with water and cause damp problems
    • Beads pour out of any hole made in the wall
  • As insulating decorative ceiling tiles
    • Dangerous in a fire
      • Spread fire rapidly
      • Generate thick toxic smoke when burnt
    • Ugly
  • As a thin crack covering layer on walls

Polystyrene ceiling tiles are best removed for safety, as is polystyrene backed wallpaper.

Polystyrene in wall cavities is relatively well protected from fire, and is not considered a fire safety issue. However polystyrene cavity insulation in contact with PVC electrical cable fitted in cavities causes the cable to leach plasticiser and become unsafe.


Comes in roll form and also loose fill.

  • Lasts the life of the building no matter what life throws at it.
  • Waterproof
  • Insectproof
  • Verminproof
  • Fireproof
  • Springs back to shape if squashed
  • Lightweight
  • Loosefill can be blown about in a draughty loft
  • Produces prodigious loose glass fibres
  • Tiny spiky glass fibres cause splinters
  • Concerns about its safety are occasionally expressed on the basis that it releases miniature sharp spikey non-dissolving airborne fibres, somewhat like some forms of asbestos.
  • Dust mask should be used during handling
  • Gloves are also recommended to reduce splinters
  • Compressing 6" down to 4" gives you the insulation value of 4" of fibreglass.

Much used for loft insulation


A mineral fibre similar to glass fibre, but denser, so much less airborne fibre.

  • Popularly used for loft insulation
  • Comes in roll form and also loose fill.


  • Survives temperatures upto 400C
  • R value for 1" insulation: 5.3
  • Kingspan is the leading manufacturer

PVC Cladding

Insulating render mixes

Includes cement mixes containing polystyrene beads

  • Fireproof

Shredded Paper

Sometimes used as loose fill loft insulation

Waste paper is treated with fire retardant and chopped. It may also be shredded.


Cardboard is a very low cost insulation material. Its low cost helps ensure higher returns on investment by eliminating much of the investment cost. Fitting used cardboard results in zero extra manufacturing energy use.

Cardboard wall insulation is popular in the US, but seems to have had little takeup here in the UK.

Its flammability can be resolved by painting it with a mixture of borax & boric acid.

It is damp susceptible, and can support mould if damp. It should not be used in situations where damp may occur.

  • Very low cost
  • Available free
  • Damp susceptible
  • Flammable but easily fireproofed


A relatively novel building product, low density papercrete has good insulation properties and is made mostly out of waste paper and cement, with a number of possible additions including expanded polystyrene and fire retardants.

It is not on general sale and requires either a specialist mixer to produce or ready chopped paper.

Sheep's Wool

Sheep's wool is sometimes used as a natural replacement for fibreglass and rockwool.

  • Natural product
  • Non-irritant, no protective clothes required.
  • Can absorb and release moisture. Unlike glass/mineral wool where moisture reduces insulation.
  • Is a carbon "sink" over 45% of the weight is carbon, low energy required to manufacture, just sheep.
  • Life 50+ years
  • biodegradable
  • Does not spread fire, but burns away in a fire.
  • Treated against insects.
  • Costs more than fibreglass & rockwool
  • Cheap if you or a nearby sheep farmer has wool they can't sell.


Straw has long been used as insulation, and is another low cost option.

  • Susceptible to damp & mould
  • Nest material for birds
  • May contain unhatched insect eggs
  • Flammable, which can be resolved by plastering over the straw to deny the admittance of air for combustion.
  • Low cost
  • Used to be available in slab form, which is occasionally seen in use.

Clay beads

LECA expanded clay beads are occasionally used as house insulation.

  • Non-flammabe

Vermiculite is a similar material.

Bubble wrap

Only rarely used in houses, wrapped round water tanks or used as an insulating window blind.

  • Degraded by UV light.
  • Flammable
  • Also used as greenhouse double glazing
  • May last ok in dark places eg lofts & cupboards.


Felt strip is used as pipe lagging, wound around the pipe(s)

  • Brown, hairy and untidy looking
  • Best used for pipes out of sight
  • For insulating single pipes, foam tube is much quicker to fit.
  • Good for insulating grouped pipes, where foam jackets would be difficult to fit.

Foamed Concrete


Aerogel is a very low density glass/air gel rated at 0.013 W/mK. Its high price restricts it to applications where high insulation value per size is necessary. Sold by Spacetherm.

Other Insulation Methods

As well as fitting sheet insulation material or loose fill, 2 other methods are also used to improve house insulation


Wood & PVC cladding are both applied to house exteriors, often gable end walls for some reason, to add a little thermal insulation.

Insulating render

Unsatisfactory Insulation Materials

  • Carpet
    • Too thin to give much insulation
    • Flammable
    • Reduces draughts
  • Polystyrene ceiling tiles & wallpaper
    • Too thin to give much benefit
    • Very flammable
    • Dents very easily
  • Sand
    • Traps air but is too thermally conductive
  • Bubblewrap
    • Degrades quickly from UV exposure

By Application


  • Rockwool
  • Fibreglass
  • shredded or chopped fire retardant treated paper
  • Sheep's wool (available in batts as Thermafleece)


  • Polystyrene
  • Straw
  • Polyisocyanurate where depth of insulation needs to be minimised

Cavity Wall Insulation

Fitted to existing wall cavities

  • Rockwool, blown in
  • Fibreglass, blown in
  • Polystyrene bead, poured or blown in

Wall Cavity Insulation

Fitted to retrofitted cavities

  • Polystyrene slab
  • Fibreglass
  • Rockwool batts
  • Cardboard

Solid Insulation for Walls

Fitted to the surface of solid walls, and rarely to cavity walls to increase insulation level further.

  • Proprietary hard surfaced insulating sheets are mostly used.
  • Polystyrene foam backed plasterboard sheets may also be used

Minimum cost options

  • Waste cardboard sheet
  • Shredded waste polystyrene
  • Papercrete
  • Straw


With 69,000 house fires in 2001, the performance of insulation in a fire affects loss of property and life. There are 3 main categories of fire performance:

  • Fireproof materials such as fibreglass and mineral wool act as a fire barrier if they remain in position.
  • Fire retarded materials will burn away when flames reach them, but will not spread the fire further. Thus these do not act as fire barriers.
  • Flammable materials such as untreated cardboard can ignite and spread fire. These products should generally be treated before use with a fire retardant, although there are examples where pattern of use provides another means to prevent spread of fire (eg plastered strawbale construction).

See Also

Borax Fire Retardant

Thermalcheck insulated plasterboard

Spray-on Roof Insulation


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