The blog

Roger Hunt is an award winning writer and blogger specialising in sustainability, old houses, housebuilding and traditional and modern building materials. He is the co-author of Old House Handbook and the companion volume Old House Eco Handbook.

Cavity wall insulation

Cavity wall insulation

A question about cavity wall insulation may not be one that you’d expect to be asked when talking about old buildings. Generally, cavity walls are regarded as a modern form of construction but the subject has cropped up a couple of times in the Q&A sessions at the SPAB Old House Eco Courses that I lead with Marianne Suhr. Since I wrote the section on insulating cavities in Old House Eco Handbook, it usually falls to me to respond.

Cavity walls do occur in older buildings and they appear to date back to at least the mid-nineteenth century, although we may discover they predate this: National Energy Services is currently running a competition to find Britain’s oldest cavity wall dwelling.

The idea of introducing a cavity generally seems to be to do with preventing penetrating damp. With this in mind, I would always recommend seeking impartial expert advice before filling cavities, certainly early ones and especially in locations where wind driven rain is an issue. It goes without saying that any existing damp problems must be resolved prior to the installation of any type of insulation.

Before filling a cavity, it’s essential to ensure that it’s at least 50mm wide. In an older building this is often not the case. Indeed, the cavity may be inconsistent and may not even exist in some parts of the wall so a thorough investigation should be carried out to check what’s going on, possibly using CCTV. Whenever cavity wall insulation is planned, thermal imaging both before and after installation is advisable. This will help identify any areas that have not been fully filled as well as potential thermal bridges.

Installing the insulation involves drilling a series of holes, usually about 22mm diameter, at regular intervals across the external wall horizontally and vertically. If the wall is of brick, this should be done through the mortar joints, although inevitably the corners and edges of the bricks can be damaged. Where there’s a rendered finish, unsightly blemishes will inevitably be caused across the face of the wall. Through the holes the installer pumps in either loose-fill polystyrene bead, mineral wool or a foam insulant. In older buildings I wouldn’t advise foam because it lacks breathability and is irreversible as it adheres permanently to the structure. This also means that materials cannot be recycled in the future.

Once the installation is complete, all the holes must be filled to avoid moisture and wind penetration. A matching mortar should be specified with the contractor at the outset – in the case of old buildings this should generally be of lime.

Image: ©Roger Hunt

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SPAB Working Party

For the last 25 years conservation experts and volunteer heritage enthusiasts have come together to join the annual Working Party run by the Society for the Protection of Ancient Buildings (SPAB). I went along to join them and created a video about the Working Party at Sullington Manor Farm near Storrington, West Sussex. They were working…

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Lime, in the form of mortars, renders, plasters and paints, is a key component of old buildings and essential to their repair – or at least it should be. Today lime-based materials are also emerging into the mainstream and being used within low carbon construction systems, employed in everything from homes to superstores. All this…

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Impending development often means there is a chance to step back in time because archaeological investigation may be undertaken as part of the work. This is especially true in London where layers of history have been laid down by successive generations as the city has evolved. Visiting Barratt London’s Landmark Place site close to the…

SPAB Working Party

For the last 25 years conservation experts and volunteer heritage enthusiasts have come together to join the annual Working Party run by the Society for the Protection of Ancient Buildings (SPAB). I went along to join them and created a video about the Working Party at Sullington Manor Farm near Storrington, West Sussex. They were working…

Listed building allure

Listed building allure

Every year, many of the estimated 450,000 listed buildings in the UK change hands on the property market. In England and Wales these properties are designated Grade I, Grade II* or Grade II having being deemed to be of historical, cultural or architectural interest. All buildings built before 1700 Tweet

Environmental Pocketbook

Environmental Pocketbook

If you’re going to invest in just one book on sustainable, low carbon building I’d strongly suggest that you make it The Environmental Design Pocketbook. Now in its second edition, this useful volume by Sofie Pelsmakers should be essential reading for architects, designers, developers, planners, students, clients and anyone else involved in the construction and operation of buildings….

Fire in old buildings

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The devastating fire at the Grade I listed, 18th century National Trust mansion at Clandon Park, Surrey, once again highlights the need to do everything we can to protect old buildings. Whatever the size of the building, there are simple measures that can be taken to reduce the risk of fire, ensure early warning of a…

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The need for fresh air and light in buildings is something I’m often talking and writing about because it’s central to creating a good home, but the theme is nothing new. I was reminded of this when I recently visited the King Edward VII Estate, near Midhurst, West Sussex. Here, the former sanatorium is being…

Building lime knowledge

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Lime, in the form of mortars, renders, plasters and paints, is a key component of old buildings and essential to their repair – or at least it should be. Today lime-based materials are also emerging into the mainstream and being used within low carbon construction systems, employed in everything from homes to superstores. All this…

Drain problems

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A blocked drain is not a pleasant thing to wake up to. What’s worse is the realisation that it’s something that can generally be avoided by doing what I’m always talking about: maintenance. The drainage system is easily forgotten because much of it is hidden away underground but, as with any element of a building, it…

Building remembrance

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Visiting Blood Swept Lands and Seas of Red, the poppy installation at the Tower of London, reminded me that the built environment frequently plays an important part in both remembrance and memory. Each of the 888,246 ceramic poppies that flood the moat of the Tower depicts a death in the British forces in the First…

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This is the tale of my first major renovation project some years ago… On the table is the surveyor’s report; yellow Post-it notes stick from its pages in such profusion that they no longer have any relevance. Phrases like “needs attention”, “must be thoroughly overhauled” and “a fair amount of dampness” are highlighted by marker… Continue Reading