BUYER’S GUIDE TO INSULATION

F O C U S O N Insulation

Materials and methods, from external, internal and cavity wall to floor and loft

WO R D S R E B E C C A F O S T E R

Bradley Van Der Straeten (b-vds.co.uk) designed a loft extension for a three-bedroom house in Stoke Newington, north London. Kingspan Optim-R 50mm vacuum insulation panels line the roof with Kingspan Thermataper fixed on top (kingspan.com). The project cost £110,000

Limit the heat lost from your home in the winter and reduce the risk of overheating in the summer with well-installed insulation made with the most effective material for your property.

UNDER THE ROOF

Because heat rises, it makes sense to insulate the attic to prevent warmth leaking through the roof. ‘The best-value retrofit insulation is in the loft,’ says Dr Sarah Price, technical director at Qoda Consulting (qodaconsulting.com). ‘An attic floor covered to at least 30cm depth gives the greatest energy saving per pound of spend.’

Laying rolls of mineral or sheep’s wool is something you could tackle yourself. Avoid covering air vents, grilles and bricks, and if there is no ventilation you may need to fit an airbrick or similar to prevent a rise in humidity. Any pipework and water tanks should be insulated too. Cellulose fibre can be used to fill the nooks and crannies between the joists and the blanket of insulation – this loose-fill material is blown into place. A semi-rigid batt, such as hemp slab, is also suitable for DIY installation. Rigid foam insulating board or hemp slab are ideal for insulating the sloping roof of an attic that has been converted into living space.

‘Budget from £1,200,’ says Nigel Donohue, CEO of the Insulation Assurance Authority (theiaa.co.uk). ‘The cost will depend on the size of your home, the existing insulation and any remedial work required.’

ABOVE AND BELOW This extension to a six-bedroom Victorian villa in Cambridge includes cavity wall and roof insulation. Its walls are filled with Rockwool Full Fill Cavity Batts. The roof is lined with Rockwool Hardrock Multi-Fix (DD) roofing boards to a depth of 235mm thick (rockwool.com). The entire project, by CDC Studio (cdcstudio.co.uk), cost around £4,000 per sqm

FILL THE GAP

Most masonry homes built after the 1920s are likely to have cavity walls with an inner layer of blockwork and an outer layer of brick separated by an airspace. This gap can be filled with cavity wall insulation (CWI).

Commonly, holes are drilled into the brickwork, giving access to the cavity, and the insulating material is blown or pumped in through the holes. Mineral wool, polystyrene beads – which are blown in through a long nozzle so even the corners are reached – and polyurethane foam are all CWI options. Mineral wool and hemp slabs or rigid polyisocyanurate (PIR) boards are suitable for timber-frame new home projects, with the boards available in several different thicknesses depending on the level of thermal performance required.

INSPECTION IS KEY

Before committing to retrofitting CWI, have an installer use a small camera on a long, flexible mount, called a borescope, to inspect the airspaces and assess their condition. Any debris or material in the cavity will need to be removed before installation. Plus, any damp, cracked render or damaged brickwork must be addressed so that the CWI performs as it should.

CWI products are priced per sqm, with expanding foam at the higher end of the price scale at around £30 per sqm. ‘Set aside between £1,200 and £2,400 for the entire property,’ says Nigel Donohue. Many installers include the cost of an initial survey in the final fee, but check before going ahead.

ADD A WARM JACKET

External wall insulation (EWI) is an option for homes with solid walls. Material choices include mineral wool that’s been compressed into a semi-rigid batt, or wood-fibre board, cork panel and various thermal render systems. Research the advantages of each and select the one that best complements your home and meets your budget and performance requirements.

‘Wood fibre is sustainable and breathable, but it normally offers a slightly lower performance for a comparable thickness and may be more expensive than other options,’ explains Camilla Govan, business development manager at Green Building Store (greenbuildingstore.co.uk).

Planning EWI installation in advance and getting an experienced professional to carry out the work is advisable. ‘By adding a depth of new material to its exterior surface, the wall will extend further forward, which can cause problems where it meets the roof,’ says Camilla. It’s also important to ensure all joins around pipework and cables, rainwater drainage and boiler outlets are airtight.

Budget between £10,000 and £16,000 for a wholehouse project, advises Nigel, though the total cost will also be dependent on the material chosen and the complexity of the installation.

The exterior of this four-bedroom house in Essex was upgraded to improve its thermal performance. A thermal render system from Weber (uk.weber) was applied to the brick walls and new double-glazed windows fitted. The exterior and interior remodelling was designed by Gregory Phillips Architects at a cost of around £5,000 per sqm (gregoryphillips.com)

Practice Mitchell + Corti extended and remodelled a four-bedroom Victorian house in Queen’s Park, north London, adding Pavatex Isolair wood-fibre board to the interior walls (pavatex. com). The insulation for the entire project cost from £16,000-£20,000. (mitchellandcorti.com)

AN INSIDE JOB

Homes with solid stone or brick walls are candidates for internal wall insulation (IWI). It’s also useful for properties where the exterior walls can’t be covered due to design or planning constraints. The insulating material is applied to the inner face of the exterior walls. Rigid foam board, wood-fibre board, semi-rigid batt and cork panel are some of the suitable options.

‘Wood fibre is breathable and moisture buffering – it absorbs moisture when wet and evaporates water when it’s drier inside,’ says Dr Sarah Price. Insulating plaster, made from cork, clay and diatomaceous earth, is another eco-friendly choice.

As with other insulating methods, steps must be taken to avoid IWI thermal bridging, such as between the junctions with internal partitions and the floor, as well as to ensure breathability. ‘If warm air gets behind vapour-impermeable materials such as rigid PIR board or polyurethane foam, the moisture level may build up and cause mould to grow where you can’t see it,’ Sarah explains.

Inevitably, some interior space will be lost and the work can be disruptive so you may have to temporarily move out. Expect to pay from £4,000 to £7,000 for the entire house.

E PHOTOGRAPHY RICHARD CHIVERS, ANTHONY HARRISON, LUKE WELLER, OLLIE HAMMICK, FRENCH & TY

A COSY BASE

Heat escapes through gaps in floorboards, around skirting boards and pipework. How to fix the problem depends on whether you have a suspended floor or a solid one, and how much work you can put up with.

‘Are you prepared to dig down into the solid surface to add insulation, or lay it on top and raise the floor level?’ asks Camilla Govan. ‘Digging out a floor is expensive, whereas adding insulation on top is cheaper and less disruptive.’ Rigid foam board is easy to cut, shape and fit on top of a solid floor, as are multi-foil systems, comprising layers of foil and wadding.

Suspended timber floor choices include mineral wool semi-rigid batt, which is easy to cut to size, fibreglass blanket or loose-fill recycled cellulose. But if any of these options are not installed correctly, there’s a risk of the joist ends rotting at the junction with the external walls.

The cost of installation ranges from £500 up to £1,300, depending on the material chosen and the floor area to be covered. Insulating suspended floors costs around £105 per sqm, including supply and installation. Solid floors come in slightly lower, at around £80 per sqm. ABOVE To boost the thermal performance of this five-bedroom home in Notting Hill, London, Kingspan Thermafloor TF70 PIR 50mm rigid board insulation (kingspan.com) was installed on top of the floors at lower-ground floor level. On the top floor, 100mm Celotex GA400 rigid boards (insulation-uk.com) were installed between the roof rafters, with 65mm PL4000 insulated plasterboard beneath. The renovation, by Brosh Architects (brosharchitects.com), cost around £500,000

GLAZING UPGRADE

Replacing single-glazed windows and doors with double- or triple-glazed versions will reduce heat loss. Often, more heat is lost through gaps around the frames than the glass, which is why windows and doors should be professionally fitted within the insulation layer. If you can’t replace them, repair the frames, fit new seals or insulate the reveals to improve performance.

LEFT A 1980s three-bedroom house in Rotherhithe, south-east London, was refurbished by MW Architects (mwarchitects.co.uk) in order to improve the layout. Double-glazed Crittall W20 steel-framed windows and doors face the garden (crittall-windows.co.uk). Replacing all the windows and doors cost around £40,000. A similar project would cost £2,500 per sqm

CO O K W ITH CO N F I D E N C E

These kitchen appliances from Smeg look great and perform brilliantly

A quality oven and hob or cooker ensures a great result, no matter what meal you’re preparing. Smeg produces everything from built-in ovens to coffee machines, all with impeccable Italian styling.

The revolutionary Galileo collection includes the Dolce Stil Novo Omnichef SO6606APNR, which combines a traditional oven with steam and microwave functions that can be used either separately or all at once. This saves on space and offers great convenience, as the combined technology can cook a chicken to perfection in just 30 minutes.

With products to suit all needs, Smeg also offers the SO6302M2X, which combines an oven with a microwave, this time in classic stainless steel. The SpeedwaveXL range cooks with microwaves in a gradual, consistent way, and the Stirrer technology evenly distributes the microwaves, so there’s no need for a turntable.

To create a real focal point in the heart of your kitchen, the Portofino CPF120IGMPT range cooker includes an induction hob, three gas burners and an electric teppanyaki plate for grilling. Beneath the hob are two multifunction ovens with steam technology and pyrolytic cleaning.

A flexible and energy-efficient hob, the HOBD682D1 induction model has a powerful but quiet integrated extractor, ideal for an open-plan kitchen. The 80cm hob includes a MultiZone feature that operates as two independent cooking areas or can combine into one.

All Smeg appliances are robustly built and tested to ensure great quality. You can explore the full range online, or visit one of the showrooms in London or Abingdon, Oxfordshire.

TOP Side-by-side style from the Dolce Stil Novo Omnichef SO6606APNR, £3,399, and Combi SF4604PMCNR, £2,659 ABOVE The Portofino features handy storage compartments under each of its two ovens. Portofino CPF120IGMPT, £7,559

● For more information, visit s m e g u k . co m