Around a third of an untreated home's heat loss is through the walls. Insulating these walls can help retain this heat, making your home more comfortable to live in and saving you money on your heating bills.

Most houses built before the 1930s have solid walls made of stone and/or brick. You can often tell if your house has solid walls from the brick pattern. If the bricks have a long-short-long pattern as in the left hand image below, it is likely to be of solid construction with no cavity. If you can only see the long side of the bricks as in the right hand image, it is likely of cavity wall construction.

Solid Wall

Cavity Wall

Thickness of walls can also be an indicator; solid brick construction are usually around 22cm thick, cavity wall 27-30cm, and solid stone can be up to 50cm thick.

If your house has solid walls, you have to apply insulation either to the internal or external wall surface.

 

External wall insulation (EWI)

 

External wall insulation involves applying insulation to the outside walls of your home, followed by a layer of protective render or cladding. If you want to avoid internal disruption, or are already planning some work on the exterior of the property (e.g. re-rendering), then EWI might be a good option.

Unlike internal wall insulation, it won’t affect the size of your rooms, but you might need planning permission as it could change the appearance of your home (check with your local authority before starting work). There are a number of different colours and finishes available, so you have significant control over the appearance of the end result. For economies of scale and to minimise the disruption, many people are joining up with neighbours to insulate several adjoining houses at the same time.

The Insulated Render & Cladding Association (INCA) hold a register of tested systems and accredited installers. 

 

Internal wall insulation (IWI)

If you are carrying out significant work internally in your house, such as re-plastering your walls or changing major fittings, it’s an ideal time to think about internal wall insulation. IWI typically involves fixing a stud frame (below left) to the walls, which are in-filled with insulation material. The advantage of this method is that rooms can be tackled one at a time. Another option is fitting rigid, ready-made insulation or plasterboard laminates up to 90mm thick directly onto the wall (below right). There is a wide range of options and finishes available depending on your budget and wall construction. 

 

Key issues to consider include:

• Space – IWI will slightly reduce the size of your rooms.
• Cost – A thinner insulation board that makes the same energy saving as a thicker one will be more expensive.
• Additional disruption – Skirting boards, window sills and electrical fittings will need removing and reattaching to the new wall surface. The new walls will need to be decorated.
• Interstitial condensation - Not to be ignored as this occurs where air passes from inside a building to the outside, cools quickly and condenses on the cold side of any insulation material. It is avoidable by using a barrier, separating the air inside the house from the insulation, or by having a breathable insulation material.

Key considerations for both types of Solid Wall Insulation:

• Damp - Ensure the building is checked over for damp problems, which may require remedial work before insulation work can begin.
• Breathability - Many buildings (particularly older ones) are built with materials that 'breathe' or allow the movement of air and moisture. Adding a non-breathable insulation layer to an older property may interfere with the transference of air and moisture through the material and if incorrectly specified or installed could cause damage.
• Thermal bridging - This occurs where there is a break in the insulation (e.g at wall junctions and the reveals around windows and doors). If these areas are neglected then heat loss will be higher and it may cause condensation.
• Advice - Consider what is best for your house and get expert advice on how your chosen product should be installed.

 

Want to do some more research?

Bristol City Council have created an online tool and detailed downloadable guide with everything you need to know about Solid Wall Insulation.

 

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For more information-

Advice - Centre for Sustainable Energy have information sheets on External Wall Insulation and Internal Wall Insulation

Advice - Energy Saving Trust

Advice - Bristol City Council's Warm Up Bristol Tool 

Trade Association - INCA - Insulated Render & Cladding Association