Before insulating a loft or a loft conversion it’s important to note the following to determine how and what you use to insulate a loft. It’ll help you to better understand what finish you might be looking to achieve, especially when you’re opting for a loft conversion. In any respect, any project in the loft should be first and foremost for increasing the energy efficiency of the house overall. If you’re looking to insulate a ceiling or for roof insulation, you need to know if you want a warm roof or a cold roof. A warm roof is a roof that has insulation in the loft walls and floor, meaning that the loft space is insulated. A cold roof is a roof that has insulation just on the floor of the loft, insulating the space below but leaving the loft space uninsulated. Choosing between a warm or cold roof is usually dependent on whether you’re planning to use the loft space or not.

Topic of contents:

1. Are you going to use your loft as further living space?

2. What materials do I need to insulate a loft?

3. What type of insulation should I use?

4. Insulating a loft conversion

Are you going to use your loft as further living space?

Converting loft space into a warm loft, whether there’s existing insulation or not, will require more insulation as the change in use will affect your project. If you’re looking to insulate a loft conversion so you can use the loft as extra living space then you don’t want to leave the insulation on display and there may be further considerations to make about acoustic and fire-rated insulation. Similarly, if there is existing floor insulation, you may want to look into upgrading or increasing the thickness of this as you might not know the thermal conductivity of the insulation or how long it has been there.

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You don’t want to increase the height of the floor too much as this will take away the headspace that the room offers. Especially for pitched roofs, adding too much floor height can result in less usable floor space as areas closer to the eaves don’t have enough head height to allow a person to stand up. It’s wise to consider thin floor insulation options as well as insulating the ceiling in the rooms below to add that all-important energy efficiency.

Acoustic insulation is a fantastic idea for when you insulate a loft as it can minimise the impact noise from footsteps through the loft and into bedrooms below. It will also stop airborne noise, including voices and conversations, from travelling between the loft and the rooms below.

Is your loft strictly storage only?

Many lofts in the UK are used for the storage of typical items like Christmas decorations, spare chairs and knick-knacks people don’t want to throw away. If you want to insulate your loft to increase the energy efficiency of your home but your loft is used for storage, it’s worth considering covering over the insulation. This is especially important if the insulation is mineral wool or glass wool roll or slab as being in and out of the loft could disturb the insulation fibres, which is an irritant for skin, throat and eyes.

Covering insulation is easily done with inexpensive and thin plywood or OSB board to finish off the setup and increase the usability and length of time you’re able to spend in the uninhabited loft space.

insulation-slab Thin-Insulation-Board strong-adhesive Plywood-OSB-Board

What materials do I need to insulate a loft?

You can use most types of insulation to insulate a loft, including insulation board, insulation roll and insulation slab. If you’re planning to leave your insulation exposed, then it’s recommended that natural insulation or insulation board be used as there are no glass or mineral wool fibres to itch people in the loft. Natural insulation roll is manufactured from recycled and sustainable materials too so it’s more eco-friendly, perfect for eco-homes and reducing carbon emissions.

loft-rollInsulating a loft using insulation board or insulation slab lends itself to easy and rapid installation as it can be friction-fit into timbers. In a pitched roof, you can measure timber joists to be spaced at 400mm or 600mm so if you cut insulation board to size, you can push the board into place before securing it with netting. You can achieve this with insulation slab in the pitch and with insulation roll in the floor too.

When you insulate a loft floor you’re also insulating the ceiling of the rooms below. You can fit any of the above-mentioned insulation materials into the loft floor, taking care to watch the height of the floor, before topping off the insulation with structural grade plywood or OSB board. To add a layer of acoustic insulation you can install an acoustic matting layer before the final floor finishings of carpet etc. to reduce impact noise from footsteps in the loft.

insulation-board Insulation-Roll insulation-slab natural-insulation

What type of insulation should I use to insulate a loft?

Different types of insulation offer different benefits and properties that appeal to individual projects. For example, in a loft conversion insulation project insulated plasterboard may be a quicker way to secure thermal insulation and dry line the room at the same time. In applications where the insulation needs to hit stringent and specified thermal targets, for example, a combination of a thin insulation board and a layer of multifoil insulation may be the ideal combination.

Type of InsulationMaterialAdvantages
Insulation roll and insulation slabGlass wool, mineral wool, recycled plastic, sheep’s woolCan be friction-fit between studs and joists
Slab holds shape in wall applications
Lightweight and inexpensive
Rigid insulation boardPIR, polystyrene, phenolic foam, EPS, XPS, woodfibreRelatively thin for good thermal values
Can be cut to shape around obstructions
Good for large, expansive areas
Multifoil InsulationPolymer bubble, aluminium, polyethylene foamReflective properties
Lightweight, relatively thin
Used on its own or to boost other insulation properties
Insulated PlasterboardGypsum board, PIR, polystyreneInsulates and dry lines
Very versatile
Water-resistant and fire-resistant variations

Insulating a loft conversion

Converting an unused loft into a used space will add more value to your home as well as increase the EPC certificate which is what prospective buyers use to gauge how energy efficient your home is. There are however certain targets that your home will have to meet to be signed off as a legal conversion by the council.

In England, Scotland and Wales you must meet a minimum required u-value of 0.18 W/m2K for a pitched roof refurbishment so it’s recommended that you choose products partly based on their thermal conductivity. If you’re using Celotex insulation board with a lambda value of 0.022 W/mK for example, you can opt to install a layer of multifoil insulation or finish off the job with insulated plasterboard to achieve the u-value that you need too.

Please note: U-values and the thermal performance of your loft conversion depend on the build-up and any current insulation materials in place. Please consult a professional architect or your local council if you’re unsure.


For free and impartial advice on products, installation and DIY projects please contact our helpline on 01752 692 206. If you’re unsure on the technical side of insulating a loft then we strongly recommend that you contact a local professional.

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