Is polystyrene external wall insulation cost effective?

SuperHomer John Doggart finds polystyrene external wall insulation cost effective for increasing the comfort of his Victorian home in Camden.

External wall insulation will usually be an option for insulating the rear of an older house.  It may not always be a viable option for the front of a house. Desirable Victorian detailing and conservation area planning guidelines may prevent its use.

Fitting polystyrene external wall insulation

Fitting external wall insulation on the side and rear did not affect the look of the house as it was originally of rendered appearance. Now, behind the render, you’ll find 100mm of polystyrene insulation keeping the house warm inside in winter.

Insulating around pipes

The material was cut where necessary to take small pipes. Large pipes (eg. from gutters) have to be taken to the outside of the building and extended out so the insulation material goes behind them.

The polystyrene insulation blocks are fitted with pins with a flush plastic cap. These pins are driven through holes which have been pre-drilled through the insulation block and into the brickwork behind. Adhesive is also used in fixing this type of insulation.

When it comes to the corners an additional wire mesh is fixed on before it is plastered to offer extra protection. In this case the work took a week to do.

Choosing an installer

John chose an installer from the internet with a 15 year guarantee on the work. It is wise to make sure your installers are individually certified (not just the firm) before you proceed.

Planning Issues

There can be planning issues when you do external wall insulation as you may change the look of the property. Internal wall insulation was used at the front of John’s house so the Victorian details would not be obscured.

External wall insulation cost, grants and payback

The external wall insulation cost £9000 and there was a grant from Camden Council of £1500. This bought the total cost down to £7500. In the future the government ECO and Green Deal schemes should reduce the cost further. As it is, there is a 15 year payback time on this installation and the house is now very comfortable. John says “The interior temperature only drops 1- 1.5 degrees overnight, even in the coldest weather, so we’ve got a 5 star comfort house along with a highly cost effective payback.”

John’s home has undergone extensive eco renovation and includes external, internal and flat roof insulation. It is one of the homes in the SuperHomes network of older homes that have been renovated by their owners to reduce carbon emissions by at least 60%. Most SuperHomes host public open days in spring or September. For more, visit John’s SuperHome here.

Also See:
Should I be insulating a solid wall internally or externally?

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