Important pointers for installing insulation

August 22, 2015

Insulation keeps a house cool in summer and warm in winter; and the investment will eventually pay its way in saved energy. Here are some important pointers for installing roof insulation.

  • As you put more insulation into your roof space, you will have to heave yourself from the ladder through the ceiling hatch. Securing a stout rope to the rafter directly above the hatch and grab the rope firmly to give yourself a hand and to make this part of the job easier. Add a couple of knots to the rope for a good grip.
  • Dust is the enemy of reflective foil insulation. Once the shiny surface is obscured it loses its effectiveness. Clean it to restore its insulating properties, or replace it.
  • Before laying insulation, look for holes around wires, pipes and air ducts through which air could flow beneath the insulation. Plug these holes with an injection of fireproof sealant or expanding foam.
  • Aluminum foil laminate is an important component in domestic insulation systems as it helps to deflect heat away from the house. Tack this material to the underside of your rafters. If your foil laminate has only one shiny side, make sure the shiny side faces towards the sky.
  • If your insulated roof space is unvented, keep a space between the fibreglass batts or blankets and the eaves with proprietary plastic ventilator trays fitted between the joists. Without ventilation, warm moist air rising from the house will condense in the roof space and settle as moisture causing mold and mildew.
  • A well-insulated roof can cause the warm air in a house to collect in upstairs rooms. Keep them from overheating with adequate ventilation and adjustable heating.
  • Use a broom to push fibreglass batts under the eaves where headroom is limited. Wear protective gear and don't tear the insulation or place it over soffit vents.
  • It's the air trapped in the tiny spaces within the insulating material that provides the insulation. Compress your insulation too much and it will be much less effective.
  • Keep insulation at least 25 centimetres(10 inches) clear of flues, chimneys (particularly metal chimneys from open fires) and heat-producing electrical fixtures, such as recessed lights, fans and transformers.
  • Tack a board or a sheet-metal shield between the joists on each side of a fixture or fit a purpose-made shield to contain loose fill material.

For extra help installing roof vents, here is a handy how to guide.

Important pointers for installing insulation

What you will need

  • Respirator or dust mask
  • Goggles
  • Gloves
  • Tape measure
  • Insulation batts
  • Walking plank (600 mm × 2.4 m, or 2 ft x 8 ft, piece of plywood)
  • Straightedge
  • Utility knife
  • Soffit vents
  • Drill
  • Jigsaw, sabre or keyhole saw
  • Screwdriver
  • Stainless-steel self-tapping screws
  • Scrap lumber

1. Measure and cut

  • Turn off the power supply and check your roof space for wiring faults and vermin.
  • Measure the distance between the joists to determine the width of the batts to buy.
  • Cut your batts to length with your utility knife, holding them steady between your straightedge and some scrap lumber.

2. Install batts

  • Press the batts between the joists, taking care not to compress them.
  • Leave a 25 centimetre (10 inch) space around flues, chimneys and heat-producing electrical fixtures.

3. Position your vents

  • Position your vent so air flows into the roof space, up the underside of the roof and out the ridge vent.
  • Place the vent on the soffit (the area of your roof that is directly under your eaves).
  • Trace around the vent, then measure 2.5 centimetres (1 inch) in and draw that outline.
  • Drill out the four corner holes.

4. Cut the vent hole

  • Using your jigsaw, sabre or keyhole saw, cut along the outline.

5. Install your vents

  • Place your vent in the opening you just made and, if necessary, screw it into place.
  • Some vents snap in place and do not require fastening.

Keep these important pointers in mind (and follow the handy how to) to install insulation that's likely to last — and save you some money.

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