When the builders finally arrive on site and start to pull things apart so you can make the improvements you want, have you ever thought about what materials they use to rebuild the place?
We think nothing of the plasterboard and gypsum that arrive on site in vast quality, or of the acrylic paints and mastics that are used in almost every room. And what about the cement mortar that is used between bricks to ‘match existing?’ All these modern materials became mainstream when they were innovative back in the earlier part of the Twentieth Century. This was a time with a big interest in modernity and new products, new gadgets and new ways of life. People didn’t ask if it was harmful or going to cause problems into the future. The manufacturers were promoting them as cheap alternatives to the traditional and everyone wanted to be up to date. The problem is that there were no tests done to see how they worked with traditional materials on traditional buildings.
And the honest answer is they don’t. Traditional buildings, with solid wall construction need to breathe. What that means is that materials like stone, brick and timber can absorb a certain amount of moisture due to the weather conditions and then release it as vapour when the conditions improve. Clay tiles are the same, they absorb water to saturation point and this forms a barrier through which no more water can penetrate. This then evaporates naturally after the weather changes. Internally, moisture created by human use – cooking, bathing, simply breathing – also evaporates through the fabric of the building. Condensation doesn’t build up in traditional buildings (bathrooms and kitchens excepted) the same way it does in modern construction because the fabric of the building allows for it to dissipate.
Modern materials are based on formulations that are designed to be impermeable. They create barriers through which moisture cannot pass and any moisture that has entered the fabric of the building – or is created inside it – gets trapped. This is why building regulations require mechanical extraction in all bathroom and kitchen refurbishments. But they’ve completely overlooked the fact that buildings with a solid wall construction are not built to be air tight. If there is an insistence that traditional buildings are lined with gypsum plasterboard (which is cement based) because it is fire retardant, there is a complete lack of understanding that so is lime plaster. The fore runner has been around for centuries, it acts as a fire retardant barrier because lime is heated to 900-1000 degrees during manufacture. It changes the chemical compound and makes it both heat and water resistant (at the same time as preserving its porosity.) Lime plaster gives the same delay to a spreading fire as plasterboard, allowing for help to arrive.
The junction points between the old building fabric and the new additions are potential weak points, which is why I mentioned plasterboard being cement based. It allows no movement of vapour, so where plasterboard meets lime plaster the historic performance of the building materials is altered. This creates the possibility of damp. An area where the moisture is trapped will show itself with mildew or darkening and flaking paint work. It’ll eventually become wet to the touch and the materials will rot. In a building that has been regularly maintained and has survived for hundreds of years without damp, the only thing that has changed is the materials being used on it. Time and again heritage contractors point out the fact that modern materials are not compatible with historic fabric, but this detail seems to escape the mainstream contractor – and yet they work on many a building with solid wall construction.
It is tempting to simply go with the flow and let your contractor use the materials he always uses. But, he will not be paying the bill when you discover damp, in fact he will probably be a contributing factor to its appearance. Damp proof courses introduce modern barriers to traditional fabric and all that does is seal in the moisture and push it elsewhere – as you can see from this section of wall in my dining room. The ‘repair’ was done at some point in the past and the lime plaster above has blown, so the whole area now has to be raked out and redone – with lime plaster, to allow for the passage of vapour through the wall. I don’t live in a listed building, but any building with solid wall construction should be treated as if it is – for the health of the building.
A conservation led refurbishment takes the traditional fabric as the departure point for the project. It considers the historic materials used in the rest of the building and does not compromise their performance. It takes a holistic approach that allows for the building to breathe and it doesn’t introduce any materials that will inhibit this. And yes, that may sound very old fashioned but that is the point, the period when it was constructed was a long time ago and things were done differently then. That does not mean they were wrong or need to be modernised. Sympathetic repair restores the natural balance and integrity of the buildings performance and it’s important to remember that this improves a buildings thermal efficiency: areas of damp draw warm air to them because heat naturally likes to disperse.
Buildings with solid wall construction have gaps between their component parts, however small they may be – they weren’t designed with precision measurements let alone with an intention of being sealed off from the exterior atmosphere. This is why air source heat pumps aren’t a great fit with traditional buildings, they require thermal efficiency and yet again it’s an example of an innovation that wasn’t tested for its compatibility with the existing – and predominant – building stock. To really look after a building with solid wall construction, you need to respect the way it was built. It has already survived a lot longer than you’ve been in the planet and this makes it vulnerable to change. Trying to drag it into the modern world with repairs or alterations in unsympathetic materials will alter the way historic fabric functions and this may not be the best thing for your house. As it’s probably your most expensive asset perhaps now is the time to start considering what it needs – go ahead and do your alterations but do them in a way that considers the building itself.
Putting the Love In 