21st Nov 2022 -

When looking to improve the energy efficiency of your house, there are few more cost-effective methods than installing insulation. Offering both thermal and acoustic support, house insulation can stop heat from escaping your house, keeping you warm whilst reducing your heating bills. Insulating your house will both help the environment and benefit you financially.

In this guide from Building Materials Nationwide, we’ll look at various areas of your house that could benefit from additional insulation. We’ll then look at the average cost for installing these insulation types. After that, we’ll cover ways to insulate specific types of houses, such as houses with solid outside walls, or houses with a flat roof.

The Types of House Insulation Available

loft insulation

In a typical house, a considerable amount of heat is lost through the walls, roof, and floors. At a rough estimate, 25% of heat loss in a house is through the roof, 35% is through walls and gaps around windows, and 10% is through the floor. Insulating these areas can help to limit this heat loss.

Loft and roof insulation is often easy to install within a house, with several insulation types that you will be able to install yourself. You can install blanket insulation within the joists of your loft, with insulation slabs and rolls made from mineral wool or sheep’s wool, produced by brands like Rockwool and Knauf. They can be cut to size and fitted within your loft. Another option is loose-fill insulation, which is poured between joists to give an even coating.

This is a cost-effective way of providing thermal insulation, though it is not suitable for use within draughty lofts, which can blow the insulation around. Insulation boards can be used under a pitched roof, either nailed under the roof joists or fitted between them (If fitted between roof joists they must be installed so they do not directly touch the roof). Insulation boards offer great thermal insulation and allow you to easily make use of your loft space. A professional option is blown-fibre insulation, which coats your loft and roof with a sprayed foam substance.

A construction worker wearing a full white PPC overall with gloves and a black mask installing spray foam insulation within the interior of a wooden wall frame structure.

The outside walls of a house can be insulated to reduce heat loss and should be prioritised over internal walls. If your house has cavity walls, where there are two brick walls with a space between them, then cavity wall insulation can be easily installed through a method called filling. Filling involves drilling a series of small holes in the mortar of your exterior wall, through which one of several insulation types is pumped. The common choices are mineral wools, polystyrene beads, and polyurethane-injected foam. While all of these offer thermal insulation, polystyrene beads and polyurethane-injected foam are more suited to difficult walls or stone walls.

Cavity wall insulation is designed to last for as long as a house lasts, providing decades of thermal support. There are some situations where your house may not be suitable for cavity wall insulation, so if you are in an area with high levels of wind-driven rain or your walls are in bad condition, it may be worth getting a surveyor to make an assessment of your walls before pursuing injected insulation.

Ground floor insulation can be used to reduce heat loss in a house. While acoustic insulation can provide benefits within the higher floors in a building, particularly if shared by multiple occupants, in terms of thermal insulation you should focus on the ground floor. Traditional homes had floors made from wooden floorboards suspended on timber joists. While it is important to allow some airflow under your ground floor to avoid a buildup of dampness, mineral wool insulation slabs can be laid between the joists, supported by netting. In more modern homes flooring is often solid concrete, which does lead to reduced heat loss.

If you want to insulate a solid concrete floor, you can fit a layer of rigid foam insulation on top, which can then be covered by chipboard and your flooring choice of carpet, laminate, or tiles. Unlike loft insulation and cavity wall insulation, ground floor insulation can be an invasive process to install, involving removing flooring to access either the timber joists or the concrete floor below.

The Average Cost of Insulating a House

The cost of insulating an average-sized loft with entry-level blanket insulation would be about £100 for materials, with an extra £200 to £300 for professional installation, depending on size. Installing the recommended 270mm of blanket insulation in an uninsulated loft can save hundreds of pounds per year in energy bills. While basic loft insulation can be installed yourself with some DIY experience, sprayed foam insulation will require a professional, costing between £300 and £450 for materials and labour depending on the size of your loft. There may be increased costs for loft insulation if you have a water tank in your loft, or if you have electrical wiring, as these will require separate insulation or moving.

The cost of cavity wall insulation via filling will vary from about £345 in a one-floor flat, up to around £600 for a detached house. In the case of the one-floor flat, you could be looking at energy bill savings of £95 a year, and in the detached house, it could be up to £310 a year.

The costs of installing floor insulation can vary, costing between £500 and £1300 depending on the type of floor, and the work needed to access it. Once installed, you can expect energy bill savings of between £35 and £85 a year depending on house size.

Under certain circumstances, you may be eligible to apply for a grant covering the costs of cavity wall and loft insulation. The Energy Company Obligations scheme mandates that energy companies with over 150,000 customers must provide up to £1000 towards loft and cavity wall insulation, to help make homes more energy-efficient. To qualify you must own your own home (with a few exceptions), and be receiving one of a list of benefits, such as universal credit, pension credit, or carer’s allowance. To find out if you may qualify for one of these grants, speak to your energy provider.

The Best Ways to Insulate a House Without Cavity Walls

Some houses, particularly houses built before 1920, are often fitted with a single solid outside wall. There are two main ways to insulate internally in a house with solid walls, either attaching rigid insulation boards to the wall, or building a stud wall against the wall, fitted with insulation materials like mineral wool rolls, and covered with insulated plasterboard, reducing heat loss. This can be a complicated process to fit, reducing floorspace and requiring things like door frames and fittings to be removed and reattached upon completion.

You can also insulate a house with no cavity externally, by fixing a layer of thermal insulation cladding to the outside of your house. This will avoid reducing floor space while offering other benefits like protection from extreme weather. They can be painted in a variety of finishes, or finished with brick slips to give the impression of a brick wall. Installing external wall insulation cladding may require planning permission.

Insulation Board vs Insulation Roll

How to Insulate a House With Steel Framing

Steel frame houses are prone to high levels of heat loss, but are not suitable for cavity wall insulation, as a well-ventilated cavity is vital to prevent moisture from corroding the steel frame. A form of insulation suitable for the walls of a steel-framed house is a cavity rail system, in which rails are fitted to the frames of your house, which can support external insulation cladding options. The reason for the rail is to leave a gap of 15mm between the insulation and the brickwork, allowing ventilation and preventing moisture buildup. Like the external panels of a solid brick house, the insulation applied through a cavity rail system can be disguised with brick slips. You may require planning permission to install a cavity rail system on steel houses.

How to Insulate a House With a Flat Roof

There are two types of flat roofs, warm roofs and cold roofs. Warm flat roofs are the most common type of flat roof in the UK, consisting of a timber deck, followed by a vapour barrier, your insulation boards, and a waterproofing layer. In a cold flat roof, insulation is installed between wooden joists, with a raised timber deck and a waterproofing layer above it. To insulate a warm flat roof, a rigid insulation board with a thickness of around 100mm should be laid on top of the vapour barrier, with a waterproofing system laid on top of that. For a cold flat roof, parts of the roof may need to be taken down to add or replace insulation. Insulating a flat roof is a job for professionals, requiring experience and specialist equipment.

Our Excellent Range of Insulation

At Building Materials Nationwide we have a comprehensive range of house insulating materials in stock. If you are looking for high-quality loft insulation, such as boardsslabs, and loose-fill, we offer a range of excellent choices. We offer internal wall and external wall insulation, as well as a range of insulated plasterboards. We also stock a range of acoustic insulation, providing sound dampening within a home. We sell all types of insulation for a house, with delivery options across the UK. If your house is uninsulated or has poor insulation, you don’t need to feel cold forever.

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