Choosing external wall insulation

To insulate a solid wall from the outside, a layer of insulation material is fixed to the walls with mechanical fixings and adhesive, then covered with protective layers of render or cladding. 

The finish can be smooth, textured or painted, tiled, panelled, pebble-dashed (for easy maintenance) or finished with brick slips to provide a real masonry brick finish. 

The finish will cover the whole of the outside of your property, including existing brickwork, and may change its appearance. So you must find out if you need planning permission:

To prevent condensation, recessed areas around windows must be insulated as well as the walls – with the depth of insulation depending on the width of the window frame.

All external pipework and other fittings will have to be removed and replaced, and it may be necessary to extend window sills and even the roof overhang to protrude beyond the new layer.  It is often possible to fit additional sills to avoid replacing any of the original structure.


Cladding or render?

Cladding comes in a variety of attractive colours and forms: timber panels or shingles, stone or clay tiles, aluminium panels or a brick finish.

Render can be either a thick sand and cement mix applied over a wire mesh – or a thinner, lighter cement over a strong fibre mesh. It is generally less expensive than cladding.


Finding an installer

External solid wall insulation should be fitted by a specialist installer trained by an approved system designer. Several insulation companies have developed complete external wall insulation systems that, if fitted properly by an approved installer, will achieve the required thermal performance, weather proofing and other requirements. You can find these system suppliers and their approved installers through one of the relevant trade associations:

Ask your installer if they are using Energy Saving Trust Recommended insulation, which is tested by independent experts and complies with relevant British Standards.  (Find out more about British Standards at the BSI website.)

The installer will need full access to your walls from the outside. 


What about damp?

Insulating the outside of your property, provided it is done properly, will give you a new weather proof layer that will protect you from penetrating damp for years to come, and should deal with any existing penetrating damp problems you may have had due to poor wall finish. The insulation will also increase the temperature of the internal surface of the wall, making it less likely that you will get condensation problems on your walls.

The main damp issue to be avoided with external wall insulation is rising damp. If you already have a problem with this, then it will have to be fixed before the insulation is fitted, otherwise you run the risk of trapping the damp inside the wall structure and so making the problem worse.

It is also important to make sure that the new external insulation layer and cladding do not bridge the damp proof layer in the wall. The insulation should start above this, otherwise water may be able to use the insulation to climb above the damp proof membrane, causing rising damp where it wasn't a problem before.

An approved installer fitting a recognised external insulation system will ensure that there are no problems with rising damp and that the external surface is fully weatherproof throughout, so you should not see any new damp issues and you may see some benefit if condensation has been a problem in the past.


Help for landlords

Until April 2015, the Landlord’s Energy Saving Allowance lets you claim up to £1,500 against tax for energy-saving improvements you have made to each house or flat you rent out. Find out more at the Directgov website.


Save money!

You’ll be charged a lower rate of VAT when you have energy-saving work done to your house, both for the materials and equipment, and for the labour. If the house is new, you pay no VAT at all. Find out more at the HMRC website.


Planning a home improvement project?