Build Tight & Ventilate Right is the mantra of the Energy Savings Trust, so that's exactly what we offer. MVHR with airtight insulation.
Eliot Warrington, MD & Founder
Interior Wall Insulation (IWI)
Solid wall insulation for period properties

interior wall insulationWhether it's a period property, an old agricultural building or commercial premises, if it has solid brick, masonry or stone walls they'll be leaking heat like a sieve. Heritage building, conservation area or listed status normally means that exterior cladding is out of the question. So with no significant cavity between the inner and outer skin (i.e. more than 40mm), standard practice on pre-1930 buildings, there are only two options left; either fix everything else with the exception of the the walls and accept that at least 30% of your heat will be lost through them, or insulate the interior of the wall and accept that you'll lose around 90-100mm of internal floor space. While you may not want to lose any floor space, when you experience the comfort the insulation brings you'll soon get over it. The benefits of Interior Wall Insulation (IWI) are enormous and far outweigh any negatives.

Retrofitting Interior Wall Insulation to an occupied property is not a job not for the faint hearted, but sadly it's essential for the long term sustainability of the building. If 30% of your heating bill is 500 this year, five years ago it would have been 200 and in another five years it could be 1000 per year. This is effectively the cost of having un-insulated walls.solarcrest headquarters

Retrofit Challenges

The challenges for those fitting Interior Wall Insulation include the need to retain period features such as architraves or wood paneling, and the adjustment of skirting boards, electrics, plumbing, radiators and carpets to suit the new wall which is 4" thicker than it used to be. IWI is much easier if you're refurbishing or renovating the whole building.

IWI Options

Interior Wall Insulation options range from a very slim Space Therm blanket (ridiculously expensive), multi-layer foil with insulated wadding (fiddily and difficult to finish, particularly at the edges), hygroscopic hemp or wood fibre boards (limited thermal performance & potential for odours), expanded polystyrene or phenolic panels (ok if fitted correctly but prone to air gaps and condensation*), or spray-in foam insulation (fast, effective, airtight & no waste but only suitable for large areas).


Standard practice is normally to fix insulated PIR bards directly to the wall or into a frame. It works well on paper and, if fitted correctly, in practice too. The problem is some hasty builders have a habit of rushing and leaving gaps. Unless the PIR boards fit perfectly to fully insulate the entire wall, heat can escape through the gaps to warm the void space between the insulation and the cold exterior wall. Condensation then forms in what is normally an unventilated space, then damp, then mould, then odours then problems. It might look ok when the gaps are hidden with tape, but tape doesn't stop heat escaping. It's best to avoid the gaps and the void space behind the insulation.

Solarcrest system..

For masonry, steel and other rigid and/or non-breathable surfaces Solarcrest recommend high-density, closed cell BASF Walltite spray foam. Designed as a wall stabiliser, Walltite will add strength to crumbly or flaky walls at the same time providing an airtight and vapour-tight barrier. It's applied directly to the wall so there's no gap behind, meaning warm air can't meet a cold surface, and it expands on contact so there are no gaps between.

To achieve the target 0.3 U-value you'll need 25mm behind a timber or steel frame and 75mm between the uprights. After leaving a small air gap for services and a fitting a standard foil-backed plasterboard, our wall stabilising, air-sealing, condensation preventing insulation will cost around four inches.

For timber frame walls where the insulation needs to be both breathable and flexible Solarcrest recommend open-cell spray foam. The same product we recommend for the roof.

About Solarcrest

As BASF certified Foammasters Solarcrest are approved installers of both open and closed cell spray foam insulation. We only work with the best BBA certified products on the market that we know will stand the test of time. With an installer network that extends to most of the UK, our typical projects include both airtight roof and wall insulation with a balanced supply/extract heat recovery system to ventilate the airtight property.

Generally we only recommend spray foam as part of a wider refurbishment or redecoration project, where most if not all the property can be sprayed at once. Our install team will often fit the ventilation during the same visit, encapsulating the ducting where practical and saving weeks of laborious effort on site. Our Spray foam + MVHR combination is the fastest way to 'build tight - ventilate right'.

BASF foam mastersinterior wall insulationSee our airtight roof insulation
interior wall insulationSee our Heat Recovery Ventilation
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call us for a spray foam insulation quoteCall 01625 423020 to discuss your project