The amount of insulation your home has will affect how well it can stay warm in winter and cool in summer. In England, only 7% of the housing stock was built after 2012[1], so the majority of houses will need retrofitting to add insulation (or to top up existing insulation) to decarbonise our housing stock.
There are many different types of insulation, which have different performances and properties. A key thing to understand is whether an insulation material is breathable, which means that it is moisture permeable, or not. It is important to understand this when insulating existing buildings as if you are working with a building that was built with a breathable construction then if you use a non-breathable insulation you can trap moisture in the structure which can cause damp and mould, limit the performance of the insulation and damage the building fabric. Generally natural insulation materials, such as wood fibre, sheep’s wool and cork, are breathable and synthetic insulation materials such as polystyrene boards are not. Natural insulation materials usually have lower embodied carbon (carbon dioxide emissions created during the manufacturing and transport of materials) than synthetic insulation materials Natural insulation materials tend to have higher thermal conductivity than synthetic materials, which means you need a thicker layer of them to achieve the same performance. Both synthetic and natural building materials can come in roll and board form.
If you are improving the insulation and airtightness of a building you may also need to improve the ventilation, as a higher performance building will lose less air through uncontrolled infiltration. To make sure you have an adequate supply of fresh air you may need to consider background ventilation systems such as trickle ventilation or extract ventilation.
If you have any damp problems in your house it is important to understand the cause of these and rectify them if necessary before insulating, as incorrectly specified or installed insulation can exacerbate damp problems.
Roofs
- Loft insulation – the recommended minimum depth of mineral wool loft insulation is 270mm[2], and you can add more than this to achieve a better performance. If you have less loft insulation than this you can simply add more to bring it up to the recommended depth. If you use your loft for storage you can increase the insulation without losing storage space by using loft legs to increase the depth of the joists. If you have LED spotlights in the ceiling below you can use loft lids to cover the electrical fitting and allow you to safely insulate around and over the light fittings. Fit an insulated loft hatch and put draught sealing strips around the perimeter of the loft hatch. Remember to allow ventilation in the loft space above the insulation to prevent condensation and damp.
Walls
- Cavity wall insulation – if you have an uninsulated cavity wall then cavity wall insulation may be a good option for you. Cavity wall insulation needs to be installed by a professional who will drill small holes in the wall and blow in insulation, which is usually mineral wool, polystyrene beads or polyurethane foam. Use a registered installer who is a member of the NIA, the CIGA or the BBA. With cavity wall insulation the amount of insulation you can install is limited by the depth of the cavity, so to achieve a high performance you might need to think about additional external or internal insulation. Cavity wall insulation can be installed quickly and with no internal disruption.
- External wall insulation (EWI) – is a great option for insulating for certain types of properties. Adding EWI will change the appearance of your property so you are likely to need Planning Permission, and if you live in a conservation area or a listed building this is unlikely to be granted. When installing EWI, a layer of insulation is fixed to the external wall of the building and then covered with a weatherproofing layer. You can use a range of insulation types depending on the performance you are aiming to achieve, and you are not limited in terms of thickness as you are when insulating an existing cavity, so it is easier to achieve modern performance standards on an existing building by using EWI.
- The options for finishes are similarly varied allowing you to achieve the aesthetic you want, from render to timber cladding to brick slips and more. An advantage of EWI is that it wraps around the entire vertical surface of the building, helping to ensure continuity of insulation and avoid cold bridging at junctions between floors and roofs. Installing EWI does not cause disruption internally, but you may need to adapt details around windows, doors and roof junctions and moving external pipework to suit the thickness of the insulation.
- Internal wall insulation – insulating internally is a good option, particularly for buildings with solid walls that are listed or in conservation areas (please note that you will need Listed Building Consent to do work to a listed building). When installing Internal Wall Insulation (IWI) you can use a range of insulation types, and you can increase air tightness and control moisture movement using Vapour Control Layers (VCLs). Make sure to also insulate between floors to avoid cold bridges at floor junctions. When insulating internally you will lose some space inside and there will be internal disruption, however it can improve the thermal efficiency without affecting the appearance of the building, preserving the character of historic buildings and their settings.
Floors
- Suspended timber floor insulation – insulating between the joists is a great option to reduce heat loss and cold draughts through floors in buildings with suspended timber floors. It involves lifting the existing floor finish, installing a mesh, breather membrane or battens to support the insulation, and then laying insulation between the joists. It is important to make sure you have a minimum sub-floor void of 150mm and that this is well ventilated. The joists in old buildings are rarely straight so it is best to use a flexible insulation which can be fitted tightly between the timbers. Using a breathable construction will reduce the risk of moisture in the timber, and using a VSD membrane on top of the insulation will further decrease this risk. The floor finish can then be re-laid on top. When insulating suspended timber floors it is possible to install underfloor heating using a tray system for the pipework, particularly if you are installing a heat pump, as underfloor heating works well with this type of heating system.
- Solid floor insulation – insulating solid floors in existing buildings can be more challenging as to add insulation you either need to raise the floor level by adding insulation and a screed or dig out the existing floor and install a completely new floor, but it can be very effective at reducing heat loss from a building. There are options for breathable and non-breathable insulation for solid floors.
To understand the existing construction of your house, and its specific constraints and opportunities, it is sensible to seek advice from a professional who can carry out a survey and specify a suitable solution. Choosing the correct materials and construction will help to ensure you get the results you want and good value for money.
At Keystone Architecture and Design we are passionate about improving the sustainability of the built environment. We have the knowledge and skills to take a holistic approach to designing your new building or extension, ensuring you get a high-performance building with the spaces you need and the finish quality you want. If you are considering a high-performance new build, a Passive House project or retrofitting an existing property please contact us to see how we can help by email, phone or by using the contact form on our website.
07752 979244
[1] https://www.ons.gov.uk/peoplepopulationandcommunity/housing/articles/ageofthepropertyisthebiggestsinglefactorinenergyefficiencyofhomes/2021-11-01#:~:text=One%20in%20six%20homes%20in,and%20in%20Wales%2C%205%25.
[2] https://energysavingtrust.org.uk/advice/roof-and-loft-insulation/