• How to Insulate a Loft

    | by Holly Wood

    Keeping your home warm while reducing heating bills and energy consumption is a top priority for many homeowners. One of the most effective ways to achieve this is by insulating your loft.

    In this comprehensive guide, we will walk you through the process of installing cold loft insulation, a solution that proves especially practical in scenarios involving flat roof extensions and balconies where a warm roof may not be the ideal choice.

    Unlike a warm loft setup, where insulation is applied directly beneath the roof, a cold loft configuration sees insulation positioned right above the ceiling of the uppermost floor. This method prevents heat from your home from escaping into the loft area.

    So, whether you’re looking to upgrade your existing loft insulation or start from scratch, our guide will provide you with the knowledge and confidence to make informed decisions and ensure a warmer, more sustainable home.

    Why Insulate Your Loft?

    Before we delve into the details of how to install loft insulation, let’s briefly explore why insulating your loft is so crucial:

    1. Energy Efficiency: Loft insulation is a cost-effective way to make your home more energy-efficient. It helps trap heat in the main part of your house, reducing the need for continuous heating.
    2. Lower Heating Bills: By retaining heat, installing insulation in your loft can lead to substantial savings on your energy bills, as you won’t need to use as much energy to maintain a comfortable temperature.
    3. Enhanced Comfort: A well-insulated loft keeps your home cosy and comfortable during winter, ensuring a consistent and pleasant indoor temperature.
    4. Environmentally Friendly: Reducing energy consumption through insulation contributes to a smaller carbon footprint, making your home more eco-friendly.

    Now, let’s break down the process of installing loft insulation step by step.

    Safety Considerations

    Safety is paramount when working in your loft. Before you start insulating, make sure to:

    • Choose suitable protective clothing, including gloves and a dust mask.
    • Safely access the loft using a secure ladder or staircase.
    • Prepare the loft by clearing debris and creating a safe workspace.
    • Use walk boards to move around in the loft safely.
    • Ensure proper lighting in the loft.

    Additionally, when laying loft floor insulation, consider these safety measures:

    • Enlist a helper to assist you with materials and ensure your safety.
    • Keep insulation a minimum of 75mm away from hot flues, including enclosed chimneys, boiler pipes, or wood-burning stoves.
    • Exercise caution when working near power cables, and avoid walking on laid insulated loft floorboards.

    Assess Existing Insulation

    Before adding new insulation, determine how much existing loft floor insulation you already have:

    • Measure the depth of the existing insulation using a tape measure while in the loft.
    • Measure the spacing between your joists to determine the width of insulation rolls you can use.

    Knowing these details will help you calculate the amount of new insulation needed.

    Calculate New Insulation Requirements

    To determine the amount of new insulation needed, consider two factors:

    1. Required Thermal Resistance (R-Value): The higher the R-value, the better the insulation. A minimum R-value of 6.1 is recommended for loft floor insulation, but aiming for 7.0 is ideal.
    2. Insulation Roll Width: Choose a roll width based on your loft’s joist spacing (400mm or 600mm).

    To calculate the required R-value, start with your target R-value (e.g., 7) and deduct the R-value of the existing insulation. This will indicate how much additional R-value you need.

    For depth, the government recommends a minimum of 270mm for glass mineral wool insulation. Deduct the depth of existing insulation from this to determine the extra depth required.

    For roll width, choose narrow or wide rolls based on your joist spacing.

    Prepare for Installation

    Before laying insulation, prepare your loft by following these steps:

    • Remove any boards fixed to your ceiling joists with a screwdriver.
    • Check for insulation under the cold water tank. If the tank is elevated by at least 300mm, leave it in place; otherwise, remove it.
    • Clear space in the loft for a safe work area and create a flat storage area for insulation rolls.
    • Examine electrical or lighting cables to assess their slack and ensure they can be lifted on top of the new insulation if needed. Consult an electrician if unsure.
    • If you have recessed downlights in rooms below the loft, check if they are covered by insulation guards. Purchase and install guards if necessary.

    Choose Your Insulation Material

    You have two main options for loft floor insulation:

    1. Loft Floor Rolls: Loft insulation rolls are rolled out between the joists, making them easier to lay than insulated floorboards. Choose between loose or encapsulated rolls, depending on your needs.
    2. Insulated Loft Floor Boards: These boards combine polystyrene insulation with a chipboard top layer, providing a secure surface for storage. They are ideal for creating a top layer of insulation but still require loft rolls for the base layer.They offer a level and stable surface, ideal for creating additional storage space and ensuring convenient access. However, it’s important to note that they do not provide a structural flooring solution that would transform your loft into a habitable room.

    Calculate the Number of Insulation Packs

    To determine how much loft insulation is needed:

    • Measure the loft space length and width in meters.
    • Calculate the area in square meters.
    • Subtract 10% to account for the space between joists.
    • Divide the area by the coverage per pack to find the number of packs required.

    Laying Loft Floor Rolls

    If you choose loft floor rolls, follow these steps:

    • Start at one corner of the loft and work back towards the loft hatch, leaving a 25mm gap from the eaves for ventilation.
    • Unroll the insulation between the joists, ensuring a snug fit without compression.
    • Butt the joints of rolls closely together, without overlapping.
    • Cut insulation as needed to fit around obstacles.
    • Lay the top layer of rolls following the same process.

    Laying Insulated Loft Floor Insulation Boards

    If you opt for insulated rigid insulation boards (loft floor boards), here’s what to do:

    • Turn off the electrical supply to ensure safety.
    • Lay the boards at right angles to the ceiling joists, supporting each board across at least three joists.
    • Keep boards a minimum of 12mm away from hot water pipes.
    • Secure each board to the joists using 150mm wood screws and wood adhesive.
    • Trim boards to size using a panel saw.
    • Stagger the joints of the next row of boards for extra stability.
    • Switch the power back on after installation.

    Laying Insulation Around Cables

    If you need to work around electrical cables, follow these steps:

    • Turn off the electrical power supply.
    • Carefully lift the cables to sit on top of the insulation, ensuring not to stretch them.
    • Switch the power supply back on once the cables are safely positioned.

    Laying Insulation Around Recessed Downlights

    For proper insulation around recessed downlights, do the following:

    • Fit insulation guards around the downlights to prevent contact between insulation and lights.
    • Lay insulation over the guards for the base layer.
    • If using insulated loft floor boards, mark the position of the downlights on the chipboard surface and cut openings to fit the lights.

    Finish the Project

    • Tighten screws on insulated loft floor boards for a secure fit.
    • Fill holes in boards with insulation cut to size.
    • Switch the power back on if you haven’t already.


    In conclusion, insulating your loft is not merely an energy-efficient choice; it’s an investment in the comfort, sustainability, and cost-effectiveness of your home.

    The benefits are clear: reduced heating bills, a warmer living space, and a smaller carbon footprint.

    By following the steps and guidelines we’ve provided, you can ensure that your loft insulation project is carried out effectively and safely.

    As ever, we suggest you seek professional advice when tackling a new insulation project. Our blogs are purposed to be informative and taken as a general guideline.

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