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  3. How to install under floor insulation

How to install under floor insulation

Installing your own underfloor insulation is a pretty simple DIY project, depending on the access under your place. It’s easy to do yourself, and you’ll be well on the way to a warmer, healthier home.

Instructions

A fully insulated home includes ceiling, wall and underfloor insulation. Installing your own underfloor insulation is a pretty simple DIY project, depending on the access under your place. It’s easy to do yourself, and you’ll be well on the way to a warmer, healthier home.

Getting started

Before you begin

  • Decide what kind of insulation you need. In this guide we’re using Mammoth underfloor insulation. The only safety gear you’ll need is a pair of goggles and a dust mask. This insulation is friction-fitted, so it’s easy to install. It’s also made from up to 70% recyclable materials.
  • Select the correct R-value before you calculate how many bales of insulation you’ll need. Coverage area per bale varies with different types and grades of insulation. Check in-store for more information.
  • If you’re using another brand of insulation, check what kind of safety gear you’ll need.

R-value

  • There are two different types of friction fit Mammoth underfloor insulation with different R-values. NOVAfloor, with an R-value of 1.4, is high density for exposed underfloor areas, and Multi, with an R-value of 1.9, is medium density for semi-enclosed underfloor areas.

Measure up

  • Measure the floor area you’ll be insulating.
  • Measure the distance between your joists.
  • Mammoth Insulation is friction fitted, so you’ll need the width of your insulation to be 5-35mm wider than the distance between your joists – this will help you decide what width insulation you’ll need to use.
  • If you’re unsure how much insulation to buy, take these measurements in-store and they’ll help you decide how much you need.

Getting it done

Preparation

  • If you have any old silver foil (Sisalation) covering your joists, now’s the time to cut it out and remove it. In some situations this may have been stapled under wiring so make sure you turn the power off first and take care when cutting around electrical wiring.
  • Give the area a clean, getting rid of any dust or cobwebs. Wear a dust mask and goggles.

Installation

  • Start from the back corner of the house and work your way to the front.
  • Get a pad of insulation that’s 5-35mm wider than the distance between your joists. Start from the side of the house, and begin by squeezing the long edge of the section against the inside of one of the joists.
  • Fit the section hard up against the floorboards and compress or fold the remainder of the section hard against the other joist. In some cases sections can be double folded. The fold can protrude below the bottom of the joist by up to 15mm.
  • Fit the next section by butting both ends together without gaps. It should sit firmly in place without any tucks or creases.
  • If you need to cut any pads to fit, simply hold it up in the gap and mark it to the length required. You can rip this type of insulation by hand, or use an insulation saw to cut it.
  • Electrical wires: Where possible Mammoth insulation should be fitted behind electrical wires. Warning tags should be placed at points where the insulation covers electrical wiring, or simply spray the insulation with glow spray paint over where the wires are located.
  • Waste pipes: Leave a 100mm clearance between the insulation and waste pipes – this means you’ve got room to access them later if need be.
  • Lights: For any lights under the floor leave a 200mm clearance between the insulation and light fitting.