Heavy lofting: a brief overview of loft insulation

Loft insulation is a great way to have the roof of a house clean of bird faeces.

This is because pigeons and sea-gulls love household heat loss, which is why poorly insulated homes have colonies of birds living on their roofs. Whilst this look will make a house the perfect filming location for the next Alfred Hitchcock remake, it means that huge amounts of energy are wasted on heating.

Continue reading for a simple guide on how to insulate a loft and subsequently reduce annual household energy bills and carbon dioxide emissions.

Pouf over your head: what is loft insulation?

A quarter of all household heat loss takes place at the roof.

Loft insulation essentially uses an insulating material to create a thermal barrier between the home’s interior and the outside world, significantly reducing this loss. It is effectively wrapping the loft up in a blanket.

There are two types of loft insulation. The blanket can either sit between the joists in the loft – the horizontal beams running along the floor of the roof space – or between the rafters – the slanted beams running along the roof itself. 

In the case of insulating between the joists, the material prevents significant heat transfer from the home interior to the roof space. Insulating between the rafters will allow heat to transfer into the loft space itself, but will be trapped inside underneath the roof.

Of course, the insulation also works to keep the home’s interior cool in the summer, acting as a barrier between the hot exterior and the cool interior.

The result is an enormous reduction in carbon dioxide emissions.

Energy Savings Trust estimates that loft insulation in a mid-terraced house cuts 550 kg of annual CO2 emissions. The estimate for detached house is 990 kg. In monetary terms, this translates to between £135 and £240 in annual household energy bills.

With a lifetime of around 40 years and building regulations becoming increasingly stringent concerning energy efficiency, loft insulation will stop a property’s value going down. Who’d have thought that a blanket would be such a valuable asset?

We don’t need no loft insulation

Sadly, a blanket is not a valuable asset for those in flat-roofed and thatched homes.

National building regulations mean that flat roofs must have external board insulation, but retrofitting can be dear. It may often be the case that the only affordable way of doing so is to wait until the roof needs replacing.

Meanwhile, thatched roofs provide natural insulation for the lofts beneath them.

Woodstuffs: rafters and joists

The upside of insulating between joists is that self-installation of the kind is very easy. The only requirement from a practical point of view is that the joists are evenly-spaced. The downside is that the roof area itself remains without uninsulated. This is problematic if there is a room in the space.

On the other hand, insulating between the rafters treats the loft as another part of the home interior. However, this requires more expensive materials along with some specialist installation. The majority of people who are not expert DIYers will need a professional installer to do the job.

Versus pros: self-installed loft insulation

Self-installation is surely the best option for the standard household.

If the roof area is empty, easily accessible and has equally-spaced joists, then there is little in the way to prevent self-installed loft insulation from being an effective measure.

Prior to self-installation, however, any existing moisture issues must be addressed.

The reason being that loft insulation, particularly between joists, will only exacerbate the problem (see ‘health and safety risks’). An easy way of spotting moisture issues is if the loft hatch door fits more snugly in the Winter than it does in the Summer.

The most common form of self-install loft insulation is blanket wool.

Rolls cost between £1.50 and £12 per square metre. They are usually made of sheep wool, mineral fibre or recycled materials. All said materials are effective and moderately environmentally friendly.

Estimates put the average total cost of self-installation at between £100 and £250.

It is best to select a roll whose thickness equals the height of the joists, usually around 100 mm. As for the width of the blanket, cutting where necessary is fine and has no effect on performance.

Since government advice insists the loft insulation be at least 270 mm thick, multiple layers of the material will need to be rolled out.

The most thermally effective way of installing several layers is to roll each layer at right-angles to one another. And don’t squash the blanket down. Doing so will hamper the material’s ability to insulate.

Additionally, loose-fill insulation is a very cheap way of topping up insulation. A 12 kg bag of the stuff can cost around £13.

Loose-fill insulation is usually made from recycled materials such as cork and newspaper. In fact, any waste material of the sort can easily be made from scratch for precisely £0.

It must be emphasised, though, that loose-fill alone is not sufficient loft insulation.

Self-installed loft insulation is dead simple and may be tempting, but it is not always suitable.

No time to DIY: fit and forget loft insulation

The most likely reason to need professionally-installed loft insulation is if there is a room or storage area in the loft space.

To do so, installers fit a specific size of boards between the rafters. This type of insulation is called sheet insulation and it too is fairly environmentally friendly, usually a cork or wood product. 

Even insulation between joists can require professional installation services if the hatch is too small for an adult fit through. Installers can use specialist equipment to blow granules of cellulose fibre of mineral wool into the roof space to the specified thickness of 270 mm.  

In terms of selecting a good loft installer, this insulation measure is so elementary that there is little room for areas of concern (we’re happy for once??!).

As a result, there have been few complaints of faulty and unsuitable loft insulation and the only regulation of the industry exists in the form of government guidelines of minimum thickness. 

Predictably, the cost of professional installation is greater than that of self-installation, standard costs sitting between £285 for a mid-terraced house and £395 for a detached house.

However, Green Homes Grant Scheme (a government-run scheme providing households with subsidised energy saving measures) will include loft insulation, the updates of which will be posted here.

Low-income households can already qualify for free loft insulation via the government’s ECO scheme.

As with all insulation, dampness is the most common problem, so an alertness to the issue signals a trustworthy installer.

Water, water, everywhere: problems with dampness

Dampness is the result of moisture in the air being unable to escape the home. Clearly, insulating a loft reduces the number of ways moisture can escape.

Besides the health risks of dampness (see ‘damp duty’ in our article on cavity wall insulation), it is particularly unwelcome in the loft as it can lead to rotten timber. This is dangerous and repair costs will be astoundingly greater than those of primary prevention.

Insulating between joists only exacerbates the problem as it makes the loft even colder than before installation. The colder the loft, the more severe the level of condensation when some moisture does inevitably creep through.

The way to prevent moisture accumulating in the loft is to ensure both it and the home interior are well ventilated. Good installers will advise on how best to keep the loft ventilated.

In addition, extractor fans in kitchens and bathrooms are fantastically useful appliances to reduce moisture levels inside. Modern ones even draw very little power.

Alternatively, households can install whole home ventilation systems (for more details, see ‘importance of ventilation’ in our cavity wall insulation article).

Health and safety concerns

Other than dampness, there are a number of health and safety risks concerning loft insulation.

Firstly, households storing cold water tanks in the loft must insulate the tank as well if opting for insulation between joists. This is because the insulation will result in a colder loft, risking the water freezing in Winter, which in turn can cause pipes to burst. 

If self-installing loft insulation, other insulating materials in which to wrap cold water tanks are in plentiful supply. Otherwise, good installers will either advise on best practice or insulate the tank themselves.

Secondly, some insulating materials can cause irritation to the skin. Be sure to wear protective clothing during self-installation.

Clubbing together

As a self-install product, loft insulation lends itself well to club buying.

Loft insulation is cheapest by the square metre when bought as a large roll of the material. That said, households are unlikely to source the precise amount they require for their loft when buying in bulk.

In such case, clubbing together with neighbours who also wish to install loft insulation makes use of excess material, lowering the total cost per household. Join a local carbon club with Don’t do a Dodo to get started.

Right now, you can find national club offers on the following loft insulation:

Knauf Earthwool loft insulation roll 44

This roll made by Knauf is the household name of self-install loft insulation. The material is known to be very safe and environmentally friendly and comes in a wide range of lengths and thicknesses.

What would the dodo do?

The dodo would waste countless pennies and carbon kilos through its reluctance to insulate its prehistoric house. If you can afford it, don’t do that.

Sam