The right way to insulate old buildings has been much debated over the years. Most period homes were built in the days before cavity walls and modern insulating materials and adding an extra layer can be a delicate balancing act – get it right, and you will be warm and comfortable, but get it wrong and your home could be damp from condensation, and you could even damage the building fabric.
Period homes are often through of as being draughty, and air leakage is responsible for as much as a third of a building’s heat loss. While reducing draughts by sealing up gaps and adding seamless insulation layers is key to making a house feel warmer, in order to prevent condensation it’s important that materials are breathable and ideally able to help control humidity in the atmosphere.
Insulation products made of natural materials work especially well with old buildings. ‘Natural fibres are truly breathable and can help buffer humidity levels, holding moisture in a less harmful way.’ Says Mark Lynn, managing director of Eden Renewable Innovations and a director of the Alliance for Sustainable Building Products. ‘This is particularly important in older homes, where ventilation and humidity levels may be problematic.’
Although natural products cost more than many mainstream options, they are renewable and can even help reduce the levels of indoor pollution. However, don’t overlook man-made insulation as there are some extremely effective, breathable products that are suitable for period homes. Often the best solution is to employ a mix of materials – consult an expert with experience of old properties.
Where to insulate:
LOFTS: If your loft is not currently insulated, then tackling it should be your first priority – it’s the easiest area to insulate and considering up to a quarter of an un-insulated home’s heat is lost through the roof, it’s an important one, too.
The most cost – effective solution is a ‘cold’ roof, where the insulation is laid on top of the ceilings of the rooms below. This is usually done by layering quilts or batts of insulation between and over the joists. Alternatively, loose-fill insulation, which fills all the gaps, can be used. It’s important to maintain ventilation paths at the edge of the roof to avoid condensation, which can rot the timbers.
If you want to convert the loft into a living space, you will need a ‘warm’ roof, where the roof itself is insulated. If reroofing is taking place, you could insulate above the rafters, although this will raise the roof height. The other option is to insulate between or below the rafters, or a combination of both. A variety of materials can be used, but its important to maintain an air gap beneath the tiles.
WALLS: It is estimated that 35 per cent of an uninsulated building’s heat can be lost through the alls, but this is disruptive to address. Homes build before 1920 had solid walls, as opposed to including a cavity that can be filled with insulation. Solid walls can be insulated either internally or externally – but both solutions involve covering the existing wall finish, which can mean the loss of period features.
For internal walls, rigid insulation boards can be applied, or a stud wall constructed and filled with soft insulation. Plaster is then applied over the top. This inevitably affects existing skirtying and cornicing. To Insulation external walls, a layer of insulation is applied and covered with lime render or other cladding. This can totally change the look of a house and affect elements such and overhangs, windowsills and door openings, so is not suitable for the beautiful facades of many period homes.
FLOORS: Around 10 per cent of a property’s heat is lost through the floors, of which there are two types: solid or suspended timber. Solid floors are in direct contact with the ground, so without lifting them it is difficult to add insulation, but topping them with breathable, natural carpets, such as wool or coir, will help. Avoid rubber-backed designs. If the original floor has preciously been replaced with concrete and includes a damp-proof membrane, then laying a floating wood floor on top can improve thermal performance. If there are damp problems with a concrete floor, consider replacing it with limecrete, made of breathable lime and aggregate.
Suspended floors are straightforward to insulate where there is access from below, such as a cellar. Quilt- type insulation can be fitted between the joists, supported with netting. Insulating from above involves lifting floorboards, so think twice if the floor is of historical value. If you do disturb the boards, lift a small number at a time. A variety of soft, insulating materials can be sed. Supported by nets of rigid materials can rest on timber battens.
Alongside insulating, it’s important to address gaps, as heat is easily lost through them. The Energy Saving Trust estimates that simply filling gaps can save up to £40 per room, per year on bills. Open chimneys are easy to block off with an inflatable Chimney Balloon or removable Chimney Sheep, while gaps between floorboards can be sealed with discreet strips, such as StopGap or DraughtEx.
Narrow gaps around windows and doors can create draughts as well as rattling noises. Avoid silicone sealants and instead use draught strips, which can be removed in the future if required. If you have single glazed windows that make a room feel cold, look at fitting secondary glazing.
BLANKETS AND FLEECES:
Soft batts or rolls of insulation are easy to fit between joists, studs and rafters. The cheapest option is glass or mineral wool, which has good thermal and sound insulating properties, but is irritating to skin. Sheep’s wool, such as Thermafleece, is a good alternative with advantages including being kind to skin and enhanced breathability and sound absorption. ‘Sheep’s wool is made from keratin, which can absorb and release more moisture and even remove indoor air pollutants,’ says Mark Lynn.
The other fleece option is hemp, a sustainable plant crop that is more breathable than mineral wool, can absorb up to 20 per cent of its weight in water and absorb noxious gas. If space is tight, look at Thermablok Aerogel, available in blankets and boards, which uses NASA-developed technology to eliminate cold bridging (which impacts on efficiency) while being breathable. It’s super thin – just a 10mm thickness can increase the insulation factor of a solid wall by up to 67 per cent.
RIGID BOARDS AND FOAMS:
There are a range of board options, the most common being ‘closed cell’ foam slabs, such as PIR (polyisocyanurate) PUR (polyurethane) and phenolic. Most are impervious to moisture. For a natural option, look at wood fibre board, which is made from timber waste, so is largely renewable and recyclable, has some humidity control and offers good acoustic performance. Boards need to be fitted together tightly, but avoid in awkward area’s as cutting around details without gaps is tricky.
SPRAY-ON AND LOOSE FILL:
Ideal for filling every nook and cranny, these insulations form a seamless layer. Cellulose, such as from Thermofloc, is a loose-fill option made form recycled newspaper. It can be poured in place or blown into voids and gaps. It’s eco-friendly, breathable and gives food acousitic and thermal properties, and is suitable for roofs, floors and walls. Also look at lysnene, a spray-on insulation with an ‘open cell’ composition that, on application, expands 100-fold in seconds to seal all gaps, service holes and hard to reach spaces
Period Living June 2018
Feature: Melanie Griffiths
Illustrations: Sarah Overs
Eden Renewable Innovations Ltd,
thermafleece, Natrahemp and SupaSoft (recycled plastic bottle) insulation
Soulands Gate, Dacre, Penrith, Cumbria CA11 0JF
Sales & General Enquiries: 01768 486285
Cellulose (recycled newspaper) insulation
Online retailers of Steico flec (wood fibre insulation) thermafleece, Natrahemp, Supasoft (recycled plastic bottle) Insulation and thermofloc
Recycled Plastic Bottle Insulation