Insulation

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 hot water 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 cylinder 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 its the air that does the job. So if 6" of insulation is compressed to 4", it has the insulation value of 4" of material.

Cavities

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 are now available that provide much better insulation value, and are worth using.

Expanded Polystyrene

now we know what polystyrene is shipped in

Low cost insulation available in

• slab form
• as small beads for loose fill & beanbags
• larger chunks for packaging

Mainly used for:

• Roof insulation
• Wall insulation
• Floor insulation

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

Sometimes used for cavity wall insulation

• Can saturate with water and cause damp problems
• Beads pour out of any hole made in the wall if not glued

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

Historic uses

Insulating decorative ceiling tiles

• Dangerous in a fire
• Spreads fire rapidly
• Generates thick toxic smoke when burnt
• Ugly

A thin crack covering layer on walls

• Dents very readily
• Grim news in a fire

These products, and polystyrene backed wallpaper, are best removed for safety.

Fibreglass

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 known carcinogenic 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

Rockwool

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.

Polyisocyanurate

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

Cellulose

• Loose fill
• Used in cavities
• Plant fibre
• Made from ground newspaper
• Low cost
• Better performance than fibreglass
• wikipedia

PVC Cladding

• Mainly used on gable wall ends
• Keeps rain off the wall
• Can make a messy wall look ok too, but not the world's favourite finish

Timber cladding

• Timber cladding is used as an interior and exterior finish
• Provides a degree of insulation
• Several timber designs available

Insulating render mixes

Cement mixes containing polystyrene beads, leca or vermiculite

• Fireproof
• Paint to prevent water ingress and freeze/thaw damage

Shredded Paper

• Sometimes used as loose fill loft insulation
• Waste paper is treated with fire retardant and chopped or shredded.
• Recycled
• Not damp tolerant

Cardboard

• Very low cost insulation material
• Rapid return on investment
• 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.
• Its damp susceptible, and can support mould if damp
• Should not be used in situations where damp may occur.
• Available free

Papercrete

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.

Its not on general sale and requires either ready chopped paper or a specialist mixer.

Sheep's Wool

Sometimes used instead of fibreglass or rockwool.

• Natural
• 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
• Life 50+ years
• Biodegradable
• Chars, but doesn't spread fire
• Treated against insects
• Costs more than fibreglass & rockwool
• Cheap if you or a nearby sheep farmer has wool they can't sell, unwashed wool is not allowed to be used.
• Insulation not comparable with PIR

Straw

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

• Susceptible to damp & mould, but less so than cardboard
• Nest material for birds
• Can 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, this is occasionally seen in use.

Clay beads

LECA expanded clay beads are occasionally used as house insulation.

• Non-flammable
• Unaffected by damp
• Used as loose fill, mainly under floors

Vermiculite

Similar to expanded clay beads

Bubble wrap

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

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

Felt

Felt strip is used as pipe lagging

• Its wound around the pipe(s) and secured with tape
• Brown, hairy and untidy looking
• Best used for pipes out of sight
• Good for insulating grouped pipes, where foam jackets don't fit.
• Foam tube is much quicker for insulating single pipes

Foamed Concrete

• Lightweight concrete blocks have insulation value
• Insulation is one of the reasons for their use in interior walls
• They don't survive outdoors unless rendered.

Aerogel

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

Bottles

Bottles were historically used as floor slab insulation. A layer of bottles was laid before pouring the concrete, resulting in a degree of insulation plus reduced concrete use. The bottle shape produces lots of miniature arches in the concrete, which are a near ideal shape for loadbearing.

Bottles can be used for outbuilding floors where the budget is extremely tight, but insulation not needed. For effective insulation there are now much better products.

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

Spray-on Roof Insulation

• Traps water, prone to causing rot
• Makes the roofcovering non-reusable

Free insulation options

• Waste cardboard sheet
• Shredded waste polystyrene
• Straw
• Bubblewrap for water tanks & cylinders
• Scrap clothing as pipe insulation

Applications

The more popular choices are given for each job

Loft

• Rockwool
• Fibreglass

Less often

• Shredded or chopped fire retardant treated paper
• Sheep's wool (available in batts as Thermafleece or rolls from www.BlackMountainInsulation.com)

Roof

• Polystyrene - cheap
• Polyisocyanurate - where depth of insulation needs to be minimised

Cavity Wall Insulation

Fitted to existing original wall cavities:

• Rockwool
• Fibreglass
• Polystyrene bead

Fitted to retrofitted cavities:

• Polystyrene slab
• Fibreglass
• Rockwool batts
• Polyisocyanurate

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.
• Polyisocyanurate
• Polystyrene foam backed plasterboard sheets may also be used

R & U Values

• R is a measure of resistance to heat flow, ie insulation
• U is a measure of heat conductance
• R value = 1/ U value

U is measured in watts per square metre per centigrade (W / m^2 C)

• The temperature figure is the temperature difference between the 2 sides of the insulation rather than ambient temperature
• W/m^2 k is more widely quoted, but has exactly the same value as above
• Beware of American R figures being quoted in completely different units

To determine a figure for multiple elements in series (which is how most walls are composed), just add up the R values of each element.

Insulation Values

Masonry

• Brick: R = 0.03 per 25mm

• Single brick (4") R = 0.12
• Concrete 0.015 per 25mm
• Limestone R = 0.017 per 25mm

• Lime plaster R = .05 per 25mm

• Unventilated Cavity R = 0.18
• Outside air bounday layer = .03

• Inside air boundary layer = .12

• Aerated cement block

Wood

• Softwood typically 0.25 per 25mm
• Timber cladding typ 0.44 for 25mm

Insulation materials

• Marmox R= 0.75 per 25mm
• Kingspan R = 1.08 per 25mm

• Celotex R= 1.31 per 25mm
• Thermafleece (treated sheep's wool) R = 0.65 per 25mm

• Expanded polystyrene slab 0.63 - 0.88 (loose fill value is lower)
• Fibreglass loosefill R = 0.45 per 25mm
• Fibreglass batt 0.55-0.76 per 25mm
• Straw bale 0.26 per 25mm
• Vermiculite loose fill 0.4 per 25mm
• Pearlite 0.48 per 25mm
• Rockwool loosefill 0.44-0.65 per 25mm
• Rockwool batts 0.52-0.68 per 25mm
• Cellulose 0.52-0.67 per 25mm (for both dry & wet sprayed)
• Polyurethane panel 0.97 - 1.2 per 25mm
• Foil faced polyisocyanurate panel 0.97 - 1.2 per 25mm
• Aerogel 1.76 per 25mm
• Vacuum 5.28 per 25mm
• Cardboard 0.52 per 25mm
• Wood chips and similar products R=0.18 per 25mm

Note that some insulation types have R values that deteriorate a bit over time due to compaction or loss of their insulating gas component.

Windows

• Window, single glazed: 0.18
• Window, double glazed: 0.35
  • can be improved to over 0.5 with noble gas fill & glass coatings
• Window, triple glazed: 0.52

Cold Bridging

A common issue with insulation is cold bridging. This is where there are gaps in the insulation where existing building materials prevent fitting of insulation. Some examples are:

• insulation sheet fitted into timber frame, leaving the frame itself uninsulated
• Cavity wall insulation unable to insulate around windows, due to lintel above, and existing masonry on all sides
• Plasterboarded over battens with insulation fitted between them

Cold bridging also has the potential to cause a damp problem. Where previously either no condensation occurred, or it occurred over a large area and evaporated fairly quickly without incident, after insulation condensation can concentrate onto relatively small cold bridges and cause mould or fabric damage.

Wind and insulation values

Any gaps that admit wind allow heat loss to simply bypass the insulation in that area. Thus good insulation requires plugging any gaps. Depending on the situation this can be done with loosefill insulation, injected expanding foam, pressed in foam strip, or for opening doors and windows, brush strip or foam strip.

Testing insulation values

Some insulating materials don't have a known insulation value, they've not been tested. If you want to use oak shavings for example, you can if you wish set up an experiment to determine their insulation value.

A stack of the following may be used, in this order:

• heat source (eg spotlight)
• metal plate to spread heat out evenly
• an insulation material of known value (R1)
• insulation material under test (R2)
• metal plate to spread heat out evenly

Thermometers or thermocouples are added at each boundary, and thick high insulation value panels are added around the 4 sides of the stack.

The stack is left with the heat source on for hours to stabilise, then the temperatures are read at each boundary. The temps that need reading are:

• top metal plate
• bottom metal plate
• the interface between the 2 insulation layers

The insulation value of the unknown layer is determined from the ratio of thermal resistance (insulation) values. Where the resistances are R1 and R2:

middle interface temp - bottom plate temp = (top plate temp - bottom plate temp) x R2/(R1+R2)

Most accurate results are obtained when the insulation values of the 2 layers are in the same ballpark, and top plate temp is high. For accuracy, avoid using results where the middle interface temp is close to top or bottom plate temp, or results derived from a stack with only a low top plate temp.

Self testing is sufficient for applications where BR approval is not required. To obtain BCO approval requires the test results and building insulation design to be signed off by an engineer.

Fire

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

• Fireproof materials such as fibreglass and mineral wool act as a fire barrier if they remain in position.
• Fire retardant 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 method of use provides another means to prevent spread of fire (eg plastered strawbale construction).

See Also

• Heat loss
• Borax Fire Retardant
• Thermalcheck insulated plasterboard
• Spray-on Roof Insulation
• Papercrete
• Insulating a pool
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