Internal insulation or solid wall insulation – which is the right one for my property?
Are you thinking of insulating your solid walls, but you don’t know if interior or exterior insulation would be more suitable? We’ll look at some of the benefits and issues associated with each way to insulate a solid wall.
First, do you have a property with solid walls? If your property was built before the 1920s, chances are it has solid walls. You can tell by looking at the masonry, a property with cavity walls will have bricks laid out evenly and all laid lengthwise. Solid walls, on the other hand, will have alternating patterns, as some bricks will be placed on the wall so you can see the smaller ends from the outside.
Exterior wall insulation:
Exterior wall insulation consists of attaching a layer of insulation to the wall and then covering it with plaster or siding.
Some of the main benefits include:
- Improve the appearance of exterior walls (can also cover gaps or cracks on the wall, which can also reduce drafts)
- Provides sound insulation
- Reduces internal or interstitial condensation and humidity
- Airtightness can be better maintained
- Easier to manage thermal bridges such as exposed concrete frame or window sill
- Preserves the value of the thermal mass* of the walls by regulating the temperature inside.
*Thermal mass is the ability of a material to absorb and store thermal energy
Disadvantages:
- You may need planning permission, if the building is listed or in a conservation area you should check with your local planning authority.
- Downspouts and other protrusions, or service entry points, should be treated
- Waterproof course and window vents should not be covered
- It’s usually more expensive than interior wall insulation (£8,000-£13,000), especially if scaffolding is factored in (unless you’re coordinating it with other exterior work).
Unlike interior wall insulation, it won’t reduce your home’s footprint and can be installed without disturbing occupants.
Interior wall insulation
Interior wall insulation is done by installing insulation boards on the wall or constructing a stud wall filled with an insulating material such as mineral wool fiber.
Advantages :
- Does not alter the exterior appearance of the building
- Insulation can be installed piece by piece
- Cheaper than exterior insulation (£4000-£6000 for 2-3 walls, excluding kitchens and bathrooms).
Disadvantages:
- Loss of space in the room
- Inconvenient for residents, especially in bathrooms and kitchens which have units and appliances installed against the walls.
- Features such as baseboards, door frames, cornices, panels and picture rails can cause problems.
- It is necessary to move electrical outlets and switches
Here are some other important things to consider:
Air tightness:
An airtight property will have no unintended gaps, cracks or tears where air can enter and exit the building space and thus prevent heat loss. To achieve the airtightness of the building, you must ensure that the vapor barrier membranes are well sealed. It is important that unventilated air in the gaps behind plasterboard and insulation (including service spaces) does not mix with outside air or with cold ventilated areas such as those in the attic. These leaks could make the air behind the sheetrock very cold, leading to heat loss.
Breathability
Breathability refers to how well building materials are able to transmit moisture and breathable materials allow moisture to pass through walls without being trapped. A lack of breathability can lead to interstitial condensation which can lead to the deterioration of the building structure and the development of mold. Natural materials, including fiberboard, mats and mineral wool rolls, are better able to “breathe”, while polyurethane, polystyrene and phenolic foam panels do not “breathe”.
Smart membranes
Smart membranes are airtight membranes with variable vapor resistance. They can resist vapor penetration into structural members to combat interstitial condensation and are recommended for exterior and interior wall insulation. They consist of a sheet with different layers that allow or prevent moist air to pass through it depending on the relative humidity and temperatures on each side. For example, if a room has a high temperature and humidity and it is cold outside, this would prevent moisture from moving outside and could condense on cold surfaces. Alternatively, when it is cooler inside and there is less humidity, the humidity can gradually return to help dry out the interstitial space.
Thermal bridge:
Thermal bridges will occur whenever there is a break in the continuity of the insulation, for example at the junctions of solid exterior walls with interior walls. Thermal bridges lead to heat loss and the risk of condensation and mold growth. This can often be solved with thinner and/or better insulation.
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References:
https://www.spab.org.uk/advice/breathability-and-old-buildings
https://ewipro.com/2019/01/15/why-choose-a-breathable-external-wall-insulation-system/
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The use of service voids can improve airtightness and future insulation integrity as they allow new outlets and cables to be installed without having to penetrate layers of insulation or steam control.
Improving airtightness not only helps prevent heat loss, but also improves the durability of the building by preventing damage caused by the leakage of cold, moisture-laden air and condensation in the building. building envelope.
https://passivehouseplus.ie/magazine/guides/the-ph-guide-to-airtightness
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Caitlin Latimer is a project manager for the National Energy Foundation’s Better housing Better health project. Better Housing Better Health helps keep residents warm and comfortable in their homes and improves their home’s energy efficiency. In a preventative approach to health and well-being, the service offers residents a single point of contact for unbiased expert advice to help improve their home’s energy efficiency, save money and improve their comfort. The BHBH service covers Buckinghamshire, Oxfordshire, Hertfordshire and Bedfordshire. Visit www.bhbh.org.uk for more information.