Installing loft insulation is one of the cheapest and most effective ways to prevent heat escaping your home, since heat rises and would otherwise be lost through your loft.
Loft insulation can reduce your energy use and your bills, helping both the planet and your wallet.
Some types of insulation you can install yourself; for others, you'll need professional help.
We spoke to two Which? Trusted Traders - Dean Taylor from The Loft Boys and Liam Mellor of LCM Flat Roofing - who have 12 and 10 years experience respectively of installing insulation. Read on for their advice.
Different types of loft insulation have different purposes. The main types are
Blanket insulation, which insulates effectively, but can be too bulky to fit in small spaces or around obstructions, is the most common type.
Dean told us that it's all you should need if the temperature of your loft doesn't need to be regulated: if, for example, you're just going to use it as storage space.
Blanket insulation comes in rolls and is usually made of rock, glass or mineral fibre. According to Dean, it's easy to fit, especially between joists.
Blanket insulation isn't suitable for insulating the underside of your roof, though.
If that's what you want to do - let's say, you're intending to spend time in your loft or to store temperature-sensitive items there - you can buy insulating sheets made of natural or synthetic materials from home improvement retailers.
They can then be decorated by painting or covering with plasterboard.
While insulating the underside of your roof is usually very effective in terms of heat retention, Dean cautioned that it's the most expensive type of loft insulation. It also needs to be installed by a qualified professional - more on this later.
This is made from a variety of granular or lightweight materials such as cork granules, mineral wool or cellulose fibre. More sustainable types of loose-fill insulation can be used, such as recycled newspaper.
Loose-fill insulation fits easily between irregularly spaced joists or around obstructions, and is useful for topping up existing insulation in attics.
However, it can come loose in draughty lofts and safety equipment and protective clothing are necessary to install it safely.
This type of insulation is blown into the gaps between joists. You'll need a professional tradesperson to install blown-fibre insulation, who should be able to complete the job easily.
This can be more expensive than other times of insulation.
You can install some types of insulation yourself. We've got tips on on putting blanket insulation in your loft later in this article, for example.
But it's important to know when to call on the specialist skills of a trader.
For example, Dean told us that 'Installing a warm loft (where insulation is above the roof deck, the panel underneath the roofing material that's usually made of wood) is definitely not a DIY job. It involves specialised work on the roof and messing it up could have dire consequences for the stability of your whole home. A professional will spot problems such as damp or asbestos'.
As we mentioned before, insulating sheets are the most expensive type of loft insulation and need to be installed by a qualified professional. Loose-fill and blown-fibre will also require a skilled tradesperson with the necessary equipment to install it correctly.
If you enjoy DIY projects, you can install blanket insulation yourself. Dean provided us with a list of tools that you'll need, a checklist of preparations to ensure you stay safe, and a brief guide on how to actually do it.
There are three types of insulation for flat roofs (compared to only two for pitched roofs) and a professional will be able to help you determine which one is best for your property.
Warm deck or warm roof has insulation above the roof deck (the panel underneath the roofing material that's usually made of wood). It's recommended in damp and cold areas - which, sadly, includes the UK.
Cold deck or cold roof has insulation below the roof deck and the associated joists. Typically, you leave a gap for ventilation, as condensation could form, and lead to rot.
In both warm deck and cold deck options, the weather membrane (typically formed of roofing felt and bitumen) will be the topmost layer, protecting against rain.
Dean told us that: 'A flat roof should be insulated from above - which is definitely a job for a professional.'
Liam also explained that 'The best way to insulate a flat roof is with foil backed foam insulation board but more importantly installed as a warm roof deck (on top of the roof surface) not a cold roof deck (between the rafters) which isn't as thermally efficient.'
Alternatively, your flat roof might be an inverted roof. This puts insulation above the weather membrane, protecting it from heat and cold. It can even protect against wear and tear if there is access to the roof. The top-most layer is generally gravel or a similar material.
Most lofts already have some form of insulation. However, it's often poorly installed, is being squashed by loft boarding and stored items, or is below the recommended thickness of 270mm.
Dean suggests lifting up a loft board and inspecting what's there.
He said 'Be wary of cables and pipes, and ensure there's a gap for airflow above the insulation. Without this, condensation can build up. The air pockets within the insulation should be fully open with nice fluffy insulation.'
Liam added that: 'A common mistake is cutting the insulation to fit between rafters or joists. It's much better installed as an independent layer without breaks in the insulation. A warm deck roof design without air flow requires a vapour barrier to prevent condensation, but is much more energy efficient than the older cold deck roof design.'
Which? Trusted Traders recognises reputable traders who pass an strict assessment process. We check the trader's credit reports, customer satisfaction and business procedures as well as conducting an interview and assessment.