10 Key Considerations When You’re Planning External Insulation
Keep your home warm and energy-efficient with this essential guide to insulating externally
External insulation is more expensive than other methods of insulating your home. You will also need to install a new external plaster system with a mesh underlay, which adds up to a high cost per square metre. Be sure to calculate an outline cost, including scaffolding, before you begin.
When talking about insulation, we often focus on the dew point. This is the point where the temperature makes hot air turn to condensation. With external insulation, your dew point is on the outside, where you can control it. This means that, as the condensation forms on the outer layer, it’s blown away by the wind.
This is ideal, as all other forms of insulation trap this moisture inside the property, causing a build-up that needs to be ventilated.
This type of insulation will form a new layer across the external surface of your home. Any existing wires for broadband, phones or your electricity supply will need to be diverted or removed. You may have to contact your service supplier to make this happen.
For the electricity supply, there are strict guidelines in place, so plan this in advance to ensure you don’t end up with wires across your new render.
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The existing look of your home may alter once the insulation is complete. You’ll be adding a layer of at least 100mm to the building, so proportions will change, particularly around the eaves and windows. These changes may alter your elevation, and some subtle features may be lost.
There are about 100 render colours to choose from. My advice would be to try to resist the urge to make a bold statement and err on the side of subtlety. Less is definitely more in this case: a colour needs to stand the test of time.
There are grants available for external insulation work, depending on the type of house and householder’s circumstances. Ensure you investigate your options before you begin, and make sure your contractor is set up to comply with the grant process, as it can be tedious.
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External insulation contractors are busiest in the autumn and winter, so their costs will go up according to supply and demand. You will get best value during the warmer months, even though you may not be able to enjoy the benefits until later in the year.
The render applied to the outside of a building is very sensitive to cold temperatures; it cannot be applied during frosty weather or prolonged wet periods. This may result in a delay and force you to have scaffolding outside your house for longer than you’d planned.
As external insulation adds more than 100mm to the outside of your home, your existing windowsills might be too short. You can extend them using pressed metal sills or, for a more attractive alternative, you could replace them with wider concrete ones.
If you’re going to all the expense of upgrading your insulation, you may need to consider whether it’s worth updating your windows. Old double-glazed ones are less effective at keeping heat inside and have a very low U-value. As such, you may lose much of the benefit of your new investment.
Are you considering investing in external insulation? Did you find this advice useful? Share your thoughts in the Comments.