The Ultimate Guide to Underfloor Insulation

The floors of your house can be a cause of significant heat loss, making up around 10% of the total heat lost in a house. To prevent this, and to ensure a thorough thermal envelope around your house, underfloor insulation can be installed, helping to reduce heat loss. 

In this guide, we’ll talk you through your options in terms of underfloor insulation, in both modern houses with concrete foundations, and traditional houses with suspended wooden floors. We’ll also take a look at the costs of getting underfloor insulation installed, and whether you can do it yourself. Creating a thorough thermal envelope of insulation around your house will keep you warm in the winter and cut your energy bills.

Underfloor Insulation for Suspended Wooden Floors

Suspended wooden flooring within houses has been used since the early 1700s. Prior methods of building houses used either bare foundations or solid bricks, which were susceptible to issues with dampness. Building a suspended wooden floor, with wooden joists suspended over a void, coupled with airbricks or vents in the external walls, ensured effective air movement within the underfloor area. While this solved the issue of dampness, it created a new issue, draughts within the floor of a house. Heat can be lost through uninsulated or poorly insulated suspended wooden floors, which can be resisted through the use of underfloor insulation products.

To insulate your suspended wooden floors you will need to install insulation products between the floor joists. Your choices for this will be either underfloor insulation boards or rolls of mineral wool fibre. If your suspended timber floor is above an unheated cellar or basement, then you can install insulation below the ground floor from there using a ladder. In most UK houses, however, there is simply a small void below your wooden floors. Installing underfloor insulation in a house with a small void below a suspended wooden floor will potentially involve removing all floorboards and any flooring items placed over it. 

This can be a costly and time-consuming process, particularly if you have tiling or carpeting over your floorboards. Combining redecoration and insulation can save you money, keeping your home warm and giving your suspended timber floors a new look. Sometimes, especially in homes with a small connected void, there will be an access point through which an insulation installer can fit into the crawl space. This will be a professional and difficult job, but can avoid taking up your floorboards.

If you are using solid insulation boards, these will need to be cut to snugly fit between floor joists. In order to secure them within the joists, you can attach small battens of wood to the insides of joints, which the rigid boards of insulation can rest over. Any gaps between boards and joists should be filled with insulation sealant. Building regulations require 70mm of foam board underfloor insulation.

To use underfloor insulation rolls, you will have to attach netting below your floorboards to hold them in place. Insulation rolls can be cut to size to fit snugly within the joists, with a vapour control layer installed over the joists. Sheeps’ wool insulation can offer breathability, with the vapour control layer resisting any penetrating dampness. Building regulations require 150mm of blanket underfloor insulation.

Removing floorboards is a complex process, but if it is done carefully then they can be reinstalled after the insulation is fitted. A quick alternative to underfloor insulation is draught-proofing the gaps between floorboards, which can help to limit the heat lost to draughts. This can be done with small pieces of treated timber, with sealants like papier mache, or with compressible foam rods. There are modern alternatives to traditional underfloor insulation, such as using small remote-controlled robots to spray insulation underneath wooden floors, though these would obviously be professional installations.

Underfloor Insulation in Concrete Floors

Concrete floors became popular in houses in the decade after the war, partly due to restrictions on imported timber. A concrete foundation is a large block of concrete, poured to the size of the house that will be built on it. While it is technically possible to install underfloor insulation below concrete foundations, this is an extremely costly process, involving breaking up and replacing concrete floors. Instead, a suitable option for most homeowners is to install insulation on top of a concrete floor.

Installing insulation over a solid concrete floor will first require you to remove whatever flooring is currently in use. Combining underfloor insulation with redecoration can be a great idea to save money. Once you have your concrete flooring bare, you should first install a damp-proof membrane above the floor. This is to avoid condensation and to keep your insulation dry and effective. You can then lay insulation boards across your floor, attaching them with adhesive and sealing the joins with waterproof tape.

To finish the floor you can use timber boards, preferably with a tongue and groove design. They can be glued together using epoxy timber screed. You must leave a 10mm gap around the edge of the floor, which is then filled with cork expansion strips. From there, fit skirting boards over the expansion strips, and finally add your choice of floor finishings, such as tiles, carpet, or lino.

Installing underfloor insulation can be a difficult process for a DIY amateur, as you will have to remove things like skirting and possibly doors, before measuring, cutting, and fitting a series of materials.

The Cost of Having Underfloor Insulation Installed

Underfloor insulation can be a costly process, with a semi-detached house costing between £1200 and £1725 to have it professionally installed. Installing underfloor insulation, either in a house with suspended wooden floors or a house with concrete foundations, is a complex procedure, that may be above the abilities of most amateurs. There are also costs associated with replacing flooring, or for any floorboards that are damaged while being removed from suspended floors. Completing the job yourself is likely to save you around £500, considering that installing underfloor insulation will take a professional around 3 days to complete.

Our Comprehensive Range of Underfloor Insulation

Building Materials Direct offers a wide range of underfloor insulation for sale, with delivery options across the UK. We have a range of underfloor insulation boards and rolls for sale, to increase the energy efficiency of your home. We have accessories for installing underfloor insulation, like damp-proof membranes, waterproof tape, and vapour control layers. If looking to install underfloor insulation yourself, we will offer every product you could need, all at competitive prices, with delivery across the UK.

Need Quality Insulation Delivered to You?

Browse Our Insulation Range