Roof Insulation

Roof insulation and energy efficiency are getting more and more attention in modern house building.

If you wish to build a new house, in any part of the world that has fairly stiff building regulations, you have to consider energy conservation from the outset.  The regulators have taken the choice away from homeowners and builders, as to whether to build energy efficiently or not.

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This has come about recently because of the energy crisis.  We are reminded of it every time we fuel up our cars.  Every time we have to pay our energy bills for heating or cooling our homes.

Houses have been built with various forms of energy efficient construction for a long time now, the technology has been around for a while, but whereas it used to be a matter choice, on the owner's part, whether to take on the extra up front cost in the construction process in the hope of it paying off in the long run, now it has been taken out of our hands. We have to do it.

Where I live in Northern Australia, I cannot submit a set of drawings for a new house without detailing how I plan to achieve efficient energy conservation. I have to give specific details of the materials used and their "R" values. The term R Value is used by industry to describe the insulating properties of materials.  Every wall floor or roof insulation product has an approved R value rating.

Roof insulation - Thermal foil underlay to reflective roof sheeting

In my part of the world, our regulations will state the minimum R values to be achieved by the roof, the walls, the floor and wall openings.  These will vary, depending on geographic location, the actual orientation of the house etc.  For instance, where I am we have different targets for East-West walls (receive more sun) than North - South walls.

• This photograph of a roof in the tropics may cause you to think that what I am talking about here, is going to be of no relevance to you in North America or Northern Europe.
• We are insulating to stop heat entering our buildings, and our costly air-conditioned air from leaving them.
• In Europe you want to stop cold air entering your home and your expensively produced warm air from leaving it.
• We must use the insulating R values of our materials to achieve our ends.
  • In the photo above the roof surface itself has an R value because of it's colour and reflectance.
  • The blue coated foil underlay has a higher reflectance R value.   Both sides of the foil have a mirror like aluminium coating, and it was found that the blue spray did not affect the R value of the product, so the blue colour is only there to protect the fixers from what would otherwise be a blinding glare.
  • The foil or sarking performs another important function, that of minimising and controlling condensation.
  • When warm and moist air (say the inside of your roof space) touches a colder surface (your roofing material at night) condensation forms.
  • The foil not only reduces condensation but carries any that does form down past the external walls of the building.
  • Apart from not wanting free moisture dripping inside you roof space, dampness or moisture almost totally destroys the insulating properties of fibreglass or rockwool type insulation batts.

Roof insulation - insulwool blanket bonded to foil sarking

• The spaces between the roof truss bottom chords or the ceiling battens will have up to 100mm thick rolls of insulwool, rockwool or other type of insulating batts installed
• The ceiling sheeting itself, say 10mm plasterboard, neatly fitted around the wall with no gaps into the roof space, will have an R value.
• The total of these R values, for the plasterboard, the ceiling batts, the thermafoil, and the roof sheeting, will be used to determine the total R value of the roof.
• To the right is a photo of a roof insulation fibreglass blanket that is bonded to the foil sarking.  This method is commonly used for industrial roofs or houses with high ceilings.

Improving the Roof Insulation of existing roof spaces.

A quick Google search will reveal many companies that specialise in placing roof insulation inside your roof space, to make your home more energy efficient.

• The most common way that I have done it is to buy roof insulation batts, made out of mineral fibre or fibreglass matting and go up into the roof space and fit them between the ceiling joists, resting on the ceiling battens.
  • This is a popular option for DIY-ers.
  • Inside an old roof space is always dirty and dusty, in addition the material that you will be working with will give off dust and maybe be itchy and cause skin irritations well.
  • Always wear a throw away protective suit (they are cheap), a fairly good quality dust mask and an old hat.
  • Try to get a good light up there, if there is not one already installed.
  • Stand, kneel or crawl only on the joists or truss bottom chords, beams or walls.
  • Never put weight on ceiling battens or ceiling sheeting.
  • The batts quite often come rectangles that one way will fir between 450mm joist centers and the other way will fit between 600 joist centers.  Otherwise they come in rolls of varying widths.
  • It is simply a mater of fitting them neatly between the ceiling joists.
• Many companies offer to spray a foam roof insulating system into your loft or roof.
• There are also loose fill type products that are blown into the roof by contractors, or there are DIY kits of similar materials available.  When using loose fill materials, seal up any holes in the ceiling first.
• There are also of course a few board type materials that can be sawn and fit between either the rafters or the ceiling joists, Styrofoam comes to mind.

A final thought for DIY-ers.  Roof spaces can get very hot at times.  A few years ago we were building an extension to a house, and the owner mentioned to me that he was going into the roof to run an electrical wire.

About half an hour or so later It occurred to me that I hadn't heard Monty moving around for a while.  To cut a long story short he had passed out through heat stroke. If we hadn't been there he could very well have died.

So, I do not EVER go up into a roof space without either having an offsider working with me, or at least someone in the house, that knows I am up there.

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