Loft & Roof Insulation

Cross-layered mineral wool quilt is the most common material. Insulation rolls are laid between the joists and then a second layer is run at right angles across the top of them. This cross-layering covers the joists themselves and eliminates thermal bridging through the timber.

Suitable for complex roof structures where laying mineral fibre quilt flat may be challenging. In instances where lofts pose challenges for accessibility, such as having small hatches and limited space, the conventional loft insulation rolls may prove inadequate. In such scenarios, an alternative solution is blown-in insulation. This technique involves the use of specialised equipment to inject small pieces of insulating material throughout the loft, ensuring comprehensive coverage in every corner.

While standard rolls are typically manageable for do-it-yourself installation, blown-in insulation requires the expertise of a professional installer and may take several hours, contingent on the loft’s dimensions. It’s essential to consider, however, that if your loft functions as a storage area, blown-in insulation might not be the most practical choice. The thorough coverage makes it challenging to identify joists for board placement, and any pressure exerted by the boards can compromise the insulation’s effectiveness.

In a well-insulated loft, cooler air might lead to the ingress of cold draughts through the loft hatch. Combat this by upgrading to an insulated loft hatch and adding draught-excluding strips around the hatch edges.

For pitched roofs without loft access, installation of a loft access hatch is essential, provided it can be safely positioned for ladder access. It’s crucial to ensure adequate headroom for insulation installation and that the joists can support the extra weight. The loft hatch, measuring at least 600 mm x 450 mm, should include a frame and an insulated, draught-stripped hatch cover with a catch compressing the draught-stripping on all four sides when closed.

In a warm roof, the insulation layer sits above the structural decking. This keeps the deck at a temperature close to the interior of the building, which reduces the risk of condensation. A vapour control layer sits beneath the insulation and a waterproofing membrane sits on top. Warm roof construction is the most common type and is suitable for most building types.

When installing a new warm roof, particular attention should be paid to the junction with external walls to avoid thermal bridging. Extending the roof insulation profile over the wall, or combining with external wall insulation at that point, is best practice.

In an inverted roof, the insulation sits above both the structural deck and the waterproofing layer. The waterproofing is protected by the insulation above it, which can extend its lifespan. The insulation used in this type must be highly resistant to water absorption and dense enough to withstand imposed loads.

In a cold roof, insulation sits within or beneath the roof joists rather than above the deck. Ventilation is essential in this type of construction to prevent moisture build-up, achieved by leaving an air gap between the top of the insulation and the underside of the roof covering. Cold roofs carry a higher risk of thermal bridging at the joists and require careful design to avoid moisture problems.

The recommended depth for loft insulation is 270mm for mineral wool, which is the most commonly used material. If your loft already has insulation but it is shallower than this, topping it up is worthwhile as the additional cost is low and the thermal improvement is meaningful. Different materials may require different depths to achieve the same performance, so it is worth checking with your installer.

Standard loft insulation using mineral wool rolls is one of the few retrofit measures that is genuinely suitable for a competent DIYer. Rolls are widely available from builders’ merchants and DIY stores, and the installation process is straightforward in an accessible loft with a standard structure. Blown insulation, flat roof insulation, and room in roof insulation all require professional installation.

Loft insulation will not cause damp if installed correctly. However, insulating over an existing damp or condensation problem can trap moisture and make things worse. It is important to check the condition of your loft before installing and to ensure ventilation at the eaves is maintained after installation. If you have any concerns about damp, get it assessed before proceeding.

Yes, insulating the loft floor will make the roof space above colder, because heat from the rooms below is no longer warming it. This is not a problem in itself, but it does mean that any water tanks, pipes, or other elements in the loft space need to be insulated separately to protect them from freezing in winter.

Loft insulation typically lasts for around 40 years with no maintenance required. Once installed correctly it does not degrade significantly over time, making it one of the most durable and long-lasting retrofit measures available.